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// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
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package org.apache.juneau;

import static org.apache.juneau.internal.ClassUtils.*;
import static org.apache.juneau.internal.StringUtils.*;

import java.io.*;
import java.lang.reflect.*;
import java.util.*;

import org.apache.juneau.internal.*;
import org.apache.juneau.json.*;
import org.apache.juneau.parser.*;
import org.apache.juneau.serializer.*;
import org.apache.juneau.transform.*;
import org.apache.juneau.utils.*;

/**
 * Java implementation of a JSON object.
 *
 * <p>
 * An extension of {@link LinkedHashMap}, so all methods available in that class are also available to this class.
 * <p>
 * Note that the use of this class is optional.
 * The serializers will accept any objects that implement the {@link java.util.Map} interface.
 * But this class provides some useful additional functionality when working with JSON models constructed from Java
 * Collections Framework objects.
 * For example, a constructor is provided for converting a JSON object string directly into a {@link Map}.
 * It also contains accessor methods for to avoid common typecasting when accessing elements in a list.
 *
 * <h5 class='section'>Example:</h5>
 * <p class='bcode w800'>
 *    <jc>// Construct an empty Map</jc>
 *    Map m = <jk>new</jk> ObjectMap();
 *
 *    <jc>// Construct a Map from JSON</jc>
 *    String json = <js>"{a:'A',b:{c:'C',d:123}}"</js>;
 *    m = <jk>new</jk> ObjectMap(json);
 *
 *    <jc>// Construct a Map using the append method</jc>
 *    m = <jk>new</jk> ObjectMap().append(<js>"foo"</js>,<js>"x"</js>).append(<js>"bar"</js>,123)
 *       .append(<js>"baz"</js>,<jk>true</jk>);
 *
 *    <jc>// Construct a Map from XML generated by XmlSerializer</jc>
 *    String xml = <js>"&lt;object&gt;&lt;a type='string'&gt;A&lt;/a&gt;&lt;b type='object'&gt;&lt;c type='string'&gt;C&lt;/c&gt;&lt;d type='number'&gt;123&lt;/d&gt;&lt;/b&gt;&lt;/object&gt;"</js>;
 *    m = <jk>new</jk> ObjectMap(xml, DataFormat.<jsf>XML</jsf>);
 *    m = (Map)XmlParser.<jsf>DEFAULT</jsf>.parse(xml); <jc>// Equivalent</jc>
 *    m = (Map)XmlParser.<jsf>DEFAULT</jsf>.parse(Object.<jk>class</jk>, xml); <jc>// Equivalent</jc>
 *    m = XmlParser.<jsf>DEFAULT</jsf>.parse(Map.<jk>class</jk>, xml); <jc>// Equivalent</jc>
 *    m = XmlParser.<jsf>DEFAULT</jsf>.parse(ObjectMap.<jk>class</jk>, xml); <jc>// Equivalent</jc>
 *
 *    <jc>// Construct a Map from a URL GET parameter string generated by UrlEncodingParser</jc>
 *    String urlParams = <js>"?a='A'&amp;b={c:'C',d:123}"</js>;
 *    m = <jk>new</jk> ObjectMap(urlParams, DataFormat.<jsf>URLPARAM</jsf>);
 *    m = (Map)UrlEncodingParser.<jsf>DEFAULT</jsf>.parse(Object.<jk>class</jk>, xml); <jc>// Equivalent</jc>
 *    m = UrlEncodingParser.<jsf>DEFAULT</jsf>.parse(Map.<jk>class</jk>, xml); <jc>// Equivalent</jc>
 *    m = UrlEncodingParser.<jsf>DEFAULT</jsf>.parse(ObjectMap.<jk>class</jk>, xml); <jc>// Equivalent</jc>
 *
 *    <jc>// Construct JSON from ObjectMap</jc>
 *    m = <jk>new</jk> ObjectMap(<js>"{foo:'bar'},{baz:[123,true]}"</js>);
 *    json = m.toString();  <jc>// Produces "{foo:'bar'},{baz:[123,true]}"</jc>
 *    json = m.toString(JsonSerializer.<jsf>DEFAULT_CONDENSED</jsf>);  <jc>// Equivalent</jc>
 *    json = JsonSerializer.<jsf>DEFAULT_CONDENSED</jsf>.serialize(m);  <jc>// Equivalent</jc>
 *
 *    <jc>// Get a map entry as an Integer</jc>
 *    m = <jk>new</jk> ObjectMap(<js>"{foo:123}"</js>);
 *    Integer i = m.getInt(<js>"foo"</js>);
 *    i = m.get(Integer.<jk>class</jk>, <js>"foo"</js>);  <jc>// Equivalent</jc>
 *
 *    <jc>// Get a map entry as a Float</jc>
 *    m = <jk>new</jk> ObjectMap(<js>"{foo:123}"</js>);
 *    Float f = m.getFloat(<js>"foo"</js>);
 *    f = m.get(Float.<jk>class</jk>, <js>"foo"</js>);  <jc>// Equivalent</jc>
 *
 *    <jc>// Same as above, except converted to a String</jc>
 *    m = <jk>new</jk> ObjectMap(<js>"{foo:123}"</js>);
 *    String s = m.getString(<js>"foo"</js>); <jc>// Returns "123"</jc>
 *    s = m.get(String.<jk>class</jk>, <js>"foo"</js>);  <jc>// Equivalent</jc>
 *
 *    <jc>// Get one of the entries in the list as a bean (converted to a bean if it isn't already one)</jc>
 *    m = <jk>new</jk> ObjectMap(<js>"{person:{name:'John Smith',age:45}}"</js>);
 *    Person p = m.get(Person.<jk>class</jk>, <js>"person"</js>);
 *
 *    <jc>// Add an inner map</jc>
 *    ObjectMap m1 = <jk>new</jk> ObjectMap(<js>"{a:1}"</js>);
 *    ObjectMap m2 = <jk>new</jk> ObjectMap(<js>"{b:2}"</js>).setInner(m1);
 *    <jk>int</jk> a = m2.getInt(<js>"a"</js>);  <jc>// a == 1 </jc>
 * </p>
 *
 * <p>
 * This class is not thread safe.
 */
public class ObjectMap extends LinkedHashMap<String,Object> {
   private static final long serialVersionUID = 1L;

   private transient BeanSession session;
   private Map<String,Object> inner;
   private transient PojoRest pojoRest;

   /**
    * An empty read-only ObjectMap.
    */
   public static final ObjectMap EMPTY_MAP = new ObjectMap() {

      private static final long serialVersionUID = 1L;

      @Override /* Map */
      public Set<Map.Entry<String,Object>> entrySet() {
         return Collections.EMPTY_MAP.entrySet();
      }

      @Override /* Map */
      public Set<String> keySet() {
         return Collections.EMPTY_MAP.keySet();
      }

      @Override /* Map */
      public Object put(String key, Object value) {
         throw new UnsupportedOperationException();
      }

      @Override /* Map */
      public Object remove(Object key) {
         throw new UnsupportedOperationException();
      }

      @Override /* Map */
      public Collection<Object> values() {
         return Collections.emptyMap().values();
      }
   };

   /**
    * Construct an ObjectMap directly from a string using the specified parser.
    *
    * @param s The string being parsed.
    * @param p The parser to use to parse the input.
    * @throws ParseException If the input contains a syntax error or is malformed.
    */
   public ObjectMap(CharSequence s, Parser p) throws ParseException {
      this(p == null ? null : p.createBeanSession());
      if (p == null)
         p = JsonParser.DEFAULT;
      if (! StringUtils.isEmpty(s))
         p.parseIntoMap(s, this, bs().string(), bs().object());
   }

   /**
    * Shortcut for <code><jk>new</jk> ObjectMap(string,JsonParser.<jsf>DEFAULT</jsf>);</code>
    *
    * @param s The JSON text to parse.
    * @throws ParseException If the input contains a syntax error or is malformed.
    */
   public ObjectMap(CharSequence s) throws ParseException {
      this(s, null);
   }

   /**
    * Construct an ObjectMap directly from a reader using the specified parser.
    *
    * @param r The reader to read from.  The reader will be wrapped in a {@link BufferedReader} if it isn't already.
    * @param p The parser to use to parse the input.
    * @throws ParseException If the input contains a syntax error or is malformed.
    * @throws IOException If a problem occurred trying to read from the reader.
    */
   public ObjectMap(Reader r, Parser p) throws ParseException, IOException {
      this(p == null ? null : p.createBeanSession());
      parseReader(r, p);
   }

   /**
    * Shortcut for <code><jk>new</jk> ObjectMap(reader, JsonParser.<jsf>DEFAULT</jsf>)</code>.
    *
    * @param r The reader to read from.  The reader will be wrapped in a {@link BufferedReader} if it isn't already.
    * @throws ParseException If the input contains a syntax error or is malformed.
    * @throws IOException If a problem occurred trying to read from the reader.
    */
   public ObjectMap(Reader r) throws ParseException, IOException {
      parseReader(r, JsonParser.DEFAULT);
   }

   private void parseReader(Reader r, Parser p) throws ParseException {
      if (p == null)
         p = JsonParser.DEFAULT;
      p.parseIntoMap(r, this, bs().string(), bs().object());
   }

   /**
    * Construct an empty JSON object (an empty {@link LinkedHashMap}).
    */
   public ObjectMap() {
   }

   /**
    * Construct an empty JSON object (an empty {@link LinkedHashMap}) with the specified bean context.
    *
    * @param session The bean session to use for creating beans.
    */
   public ObjectMap(BeanSession session) {
      this.session = session;
   }

   /**
    * Construct a JSON object and fill it with the contents from the specified {@link Map}.
    *
    * @param m The map whose entries will be copied into this map.
    */
   public ObjectMap(Map<?,?> m) {
      this();
      for (Map.Entry<?,?> e : m.entrySet())
         put(e.getKey().toString(), e.getValue());
   }

   /**
    * Set an inner map in this map to allow for chained get calls.
    *
    * <p>
    * If {@link #get(Object)} returns <jk>null</jk>, then {@link #get(Object)} will be called on the inner map.
    *
    * <p>
    * In addition to providing the ability to chain maps, this method also provides the ability to wrap an existing map
    * inside another map so that you can add entries to the outer map without affecting the values on the inner map.
    *
    * <p class='bcode w800'>
    *    ObjectMap m1 = <jk>new</jk> ObjectMap(<js>"{foo:1}"</js>);
    *    ObjectMap m2 = <jk>new</jk> ObjectMap().setInner(m1);
    *    m2.put(<js>"foo"</js>, 2);                      <jc>// Overwrite the entry</jc>
    *    <jk>int</jk> foo1 = m1.getInt(<js>"foo"</js>);           <jc>// foo1 == 1 </jc>
    *    <jk>int</jk> foo2 = m2.getInt(<js>"foo"</js>);           <jc>// foo2 == 2 </jc>
    * </p>
    *
    * @param inner
    *    The inner map.
    *    Can be <jk>null</jk> to remove the inner map from an existing map.
    * @return This object (for method chaining).
    */
   public ObjectMap setInner(Map<String,Object> inner) {
      this.inner = inner;
      return this;
   }

   /**
    * Searches for the specified key in this map ignoring case.
    *
    * @param key
    *    The key to search for.
    *    For performance reasons, it's preferable that the key be all lowercase.
    * @return The key, or <jk>null</jk> if map does not contain this key.
    */
   public String findKeyIgnoreCase(String key) {
      for (String k : keySet())
         if (key.equalsIgnoreCase(k))
            return k;
      return null;
   }

   /**
    * Override the default bean session used for converting POJOs.
    *
    * <p>
    * Default is {@link BeanContext#DEFAULT}, which is sufficient in most cases.
    *
    * <p>
    * Useful if you're serializing/parsing beans with transforms defined.
    *
    * @param session The new bean session.
    * @return This object (for method chaining).
    */
   public ObjectMap setBeanSession(BeanSession session) {
      this.session = session;
      return this;
   }

   /**
    * Returns the {@link BeanSession} currently associated with this map.
    *
    * @return The {@link BeanSession} currently associated with this map.
    */
   public BeanSession getBeanSession() {
      return session;
   }

   /**
    * Convenience method for adding an entry to this map.
    *
    * <p>
    * Equivalent to calling {@code put(key, value)}, but returns this map so that the method can be chained.
    *
    * @param key The key.
    * @param value The value.
    * @return This object (for method chaining).
    */
   public ObjectMap append(String key, Object value) {
      put(key, value);
      return this;
   }

   /**
    * Conditionally appends a value to this map.
    *
    * @param overwrite Overwrite the previous value if there was one.
    * @param skipNullValue Skip adding the value if the value is <jk>null</jk>.
    * @param skipEmptyValue Skip adding the value if the value is an empty string.
    * @param key The key.
    * @param value The value.
    * @return This object (for method chaining).
    */
   public ObjectMap appendIf(boolean overwrite, boolean skipNullValue, boolean skipEmptyValue, String key, Object value) {
      if (value == null && skipNullValue)
         return this;
      if (skipEmptyValue && ObjectUtils.isEmpty(value))
         return this;
      Object current = get(key);
      if (current == null || overwrite)
         put(key, value);
      return this;
   }

   /**
    * Conditionally appends a value to this map.
    *
    * @param flag The boolean value that must be <jk>true</jk> in order to add this entry..
    * @param key The key.
    * @param value The value.
    * @return This object (for method chaining).
    */
   public ObjectMap appendIf(boolean flag, String key, Object value) {
      if (flag)
         put(key, value);
      return this;
   }

   /**
    * Convenience method for adding an entry to this map.
    *
    * <p>
    * A no-op if the value is <jk>null</jk> or an empty string/map/collection.
    *
    * @param key The key.
    * @param value The value.
    * @return This object (for method chaining).
    */
   public ObjectMap appendSkipEmpty(String key, Object value) {
      return appendIf(true, true, true, key, value);
   }

   /**
    * Convenience method for adding an entry to this map.
    *
    * <p>
    * A no-op if the value is <jk>false</jk>.
    *
    * @param key The key.
    * @param value The value.
    * @return This object (for method chaining).
    */
   public ObjectMap appendSkipFalse(String key, boolean value) {
      if (value)
         append(key, value);
      return this;
   }

   /**
    * Convenience method for adding an entry to this map.
    *
    * <p>
    * A no-op if the value is <code>-1</code>.
    *
    * @param key The key.
    * @param value The value.
    * @return This object (for method chaining).
    */
   public ObjectMap appendSkipMinusOne(String key, Number value) {
      if (value != null && value.intValue() != -1)
         append(key, value);
      return this;
   }

   /**
    * Convenience method for adding an entry to this map.
    *
    * <p>
    * Equivalent to calling {@code put(key, value)}, but returns this map so that the method can be chained.
    *
    * <p>
    * <jk>null</jk> values are skipped.
    *
    * @param key The key.
    * @param value The value.
    * @return This object (for method chaining).
    */
   public ObjectMap appendSkipNull(String key, Object value) {
      if (value != null)
         append(key, value);
      return this;
   }

   /**
    * Convenience method for adding a contents of another map to this map.
    *
    * <p>
    * Equivalent to calling {@code putAll(m)}, but returns this map so that the method can be chained.
    *
    * @param m The map whose contents should be added to this map.
    * @return This object (for method chaining).
    */
   public ObjectMap appendAll(Map<String,Object> m) {
      if (m != null)
         putAll(m);
      return this;
   }

   @Override /* Map */
   public Object get(Object key) {
      Object o = super.get(key);
      if (o == null && inner != null)
         o = inner.get(key);
      return o;
   }

   /**
    * Same as {@link Map#get(Object) get()}, but casts or converts the value to the specified class type.
    *
    * <p>
    * This is the preferred get method for simple types.
    *
    * <h5 class='section'>Examples:</h5>
    * <p class='bcode w800'>
    *    ObjectMap m = <jk>new</jk> ObjectMap(<js>"..."</js>);
    *
    *    <jc>// Value converted to a string.</jc>
    *    String s = m.get(<js>"key1"</js>, String.<jk>class</jk>);
    *
    *    <jc>// Value converted to a bean.</jc>
    *    MyBean b = m.get(<js>"key2"</js>, MyBean.<jk>class</jk>);
    *
    *    <jc>// Value converted to a bean array.</jc>
    *    MyBean[] ba = m.get(<js>"key3"</js>, MyBean[].<jk>class</jk>);
    *
    *    <jc>// Value converted to a linked-list of objects.</jc>
    *    List l = m.get(<js>"key4"</js>, LinkedList.<jk>class</jk>);
    *
    *    <jc>// Value converted to a map of object keys/values.</jc>
    *    Map m2 = m.get(<js>"key5"</js>, TreeMap.<jk>class</jk>);
    * </p>
    *
    * <p>
    * See {@link BeanSession#convertToType(Object, ClassMeta)} for the list of valid data conversions.
    *
    * @param key The key.
    * @param <T> The class type returned.
    * @param type The class type returned.
    * @return The value, or <jk>null</jk> if the entry doesn't exist.
    */
   public <T> T get(String key, Class<T> type) {
      return getWithDefault(key, (T)null, type);
   }

   /**
    * Same as {@link #get(String,Class)}, but allows for complex data types consisting of collections or maps.
    *
    * <p>
    * The type can be a simple type (e.g. beans, strings, numbers) or parameterized type (collections/maps).
    *
    * <h5 class='section'>Examples:</h5>
    * <p class='bcode w800'>
    *    ObjectMap m = <jk>new</jk> ObjectMap(<js>"..."</js>);
    *
    *    <jc>// Value converted to a linked-list of strings.</jc>
    *    List&lt;String&gt; l1 = m.get(<js>"key1"</js>, LinkedList.<jk>class</jk>, String.<jk>class</jk>);
    *
    *    <jc>// Value converted to a linked-list of beans.</jc>
    *    List&lt;MyBean&gt; l2 = m.get(<js>"key2"</js>, LinkedList.<jk>class</jk>, MyBean.<jk>class</jk>);
    *
    *    <jc>// Value converted to a linked-list of linked-lists of strings.</jc>
    *    List&lt;List&lt;String&gt;&gt; l3 = m.get(<js>"key3"</js>, LinkedList.<jk>class</jk>, LinkedList.<jk>class</jk>, String.<jk>class</jk>);
    *
    *    <jc>// Value converted to a map of string keys/values.</jc>
    *    Map&lt;String,String&gt; m1 = m.get(<js>"key4"</js>, TreeMap.<jk>class</jk>, String.<jk>class</jk>, String.<jk>class</jk>);
    *
    *    <jc>// Value converted to a map containing string keys and values of lists containing beans.</jc>
    *    Map&lt;String,List&lt;MyBean&gt;&gt; m2 = m.get(<js>"key5"</js>, TreeMap.<jk>class</jk>, String.<jk>class</jk>, List.<jk>class</jk>, MyBean.<jk>class</jk>);
    * </p>
    *
    * <p>
    * <code>Collection</code> classes are assumed to be followed by zero or one objects indicating the element type.
    *
    * <p>
    * <code>Map</code> classes are assumed to be followed by zero or two meta objects indicating the key and value types.
    *
    * <p>
    * The array can be arbitrarily long to indicate arbitrarily complex data structures.
    *
    * <p>
    * See {@link BeanSession#convertToType(Object, ClassMeta)} for the list of valid data conversions.
    *
    * <h5 class='section'>Notes:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Use the {@link #get(String, Class)} method instead if you don't need a parameterized map/collection.
    * </ul>
    *
    * @param key The key.
    * @param <T> The class type returned.
    * @param type The class type returned.
    * @param args The class type parameters.
    * @return The value, or <jk>null</jk> if the entry doesn't exist.
    */
   public <T> T get(String key, Type type, Type...args) {
      return getWithDefault(key, null, type, args);
   }

   /**
    * Same as {@link Map#get(Object) get()}, but returns the default value if the key could not be found.
    *
    * @param key The key.
    * @param def The default value if the entry doesn't exist.
    * @return The value, or the default value if the entry doesn't exist.
    */
   public Object getWithDefault(String key, Object def) {
      Object o = get(key);
      return (o == null ? def : o);
   }

   /**
    * Same as {@link #get(String,Class)} but returns a default value if the value does not exist.
    *
    * @param key The key.
    * @param def The default value.  Can be <jk>null</jk>.
    * @param <T> The class type returned.
    * @param type The class type returned.
    * @return The value, or <jk>null</jk> if the entry doesn't exist.
    */
   public <T> T getWithDefault(String key, T def, Class<T> type) {
      return getWithDefault(key, def, type, new Type[0]);
   }

   /**
    * Same as {@link #get(String,Type,Type...)} but returns a default value if the value does not exist.
    *
    * @param key The key.
    * @param def The default value.  Can be <jk>null</jk>.
    * @param <T> The class type returned.
    * @param type The class type returned.
    * @param args The class type parameters.
    * @return The value, or <jk>null</jk> if the entry doesn't exist.
    */
   public <T> T getWithDefault(String key, T def, Type type, Type...args) {
      Object o = get(key);
      if (o == null)
         return def;
      T t = bs().convertToType(o, type, args);
      return t == null ? def : t;
   }


   /**
    * Same as {@link Map#get(Object) get()}, but converts the raw value to the specified class type using the specified
    * POJO swap.
    *
    * @param key The key.
    * @param pojoSwap The swap class used to convert the raw type to a transformed type.
    * @param <T> The transformed class type.
    * @return The value, or <jk>null</jk> if the entry doesn't exist.
    * @throws ParseException Thrown by the POJO swap if a problem occurred trying to parse the value.
    */
   @SuppressWarnings({ "rawtypes", "unchecked" })
   public <T> T getSwapped(String key, PojoSwap<T,?> pojoSwap) throws ParseException {
      try {
         Object o = super.get(key);
         if (o == null)
            return null;
         PojoSwap swap = pojoSwap;
         return (T)swap.unswap(bs(), o, null);
      } catch (ParseException e) {
         throw e;
      } catch (Exception e) {
         throw new ParseException(e);
      }
   }

   /**
    * Returns the value for the first key in the list that has an entry in this map.
    *
    * @param keys The keys to look up in order.
    * @return The value of the first entry whose key exists, or <jk>null</jk> if none of the keys exist in this map.
    */
   public Object find(String...keys) {
      for (String key : keys)
         if (containsKey(key))
            return get(key);
      return null;
   }

   /**
    * Returns the value for the first key in the list that has an entry in this map.
    *
    * <p>
    * Casts or converts the value to the specified class type.
    *
    * <p>
    * See {@link BeanSession#convertToType(Object, ClassMeta)} for the list of valid data conversions.
    *
    * @param type The class type to convert the value to.
    * @param <T> The class type to convert the value to.
    * @param keys The keys to look up in order.
    * @return The value of the first entry whose key exists, or <jk>null</jk> if none of the keys exist in this map.
    */
   public <T> T find(Class<T> type, String...keys) {
      for (String key : keys)
         if (containsKey(key))
            return get(key, type);
      return null;
   }

   /**
    * Same as {@link #get(String,Class) get(String,Class)}, but the key is a slash-delimited path used to traverse
    * entries in this POJO.
    *
    * <p>
    * For example, the following code is equivalent:
    * </p>
    * <p class='bcode w800'>
    *    ObjectMap m = getObjectMap();
    *
    *    <jc>// Long way</jc>
    *    <jk>long</jk> l = m.getObjectMap(<js>"foo"</js>).getObjectList(<js>"bar"</js>).getObjectMap(<js>"0"</js>)
    *       .getLong(<js>"baz"</js>);
    *
    *    <jc>// Using this method</jc>
    *    <jk>long</jk> l = m.getAt(<js>"foo/bar/0/baz"</js>, <jk>long</jk>.<jk>class</jk>);
    * </p>
    *
    * <p>
    * This method uses the {@link PojoRest} class to perform the lookup, so the map can contain any of the various
    * class types that the {@link PojoRest} class supports (e.g. beans, collections, arrays).
    *
    * @param path The path to the entry.
    * @param type The class type.
    *
    * @param <T> The class type.
    * @return The value, or <jk>null</jk> if the entry doesn't exist.
    */
   public <T> T getAt(String path, Class<T> type) {
      return getPojoRest().get(path, type);
   }

   /**
    * Same as {@link #getAt(String,Class)}, but allows for conversion to complex maps and collections.
    *
    * <p>
    * This method uses the {@link PojoRest} class to perform the lookup, so the map can contain any of the various
    * class types that the {@link PojoRest} class supports (e.g. beans, collections, arrays).
    *
    * @param path The path to the entry.
    * @param type The class type.
    * @param args The class parameter types.
    *
    * @param <T> The class type.
    * @return The value, or <jk>null</jk> if the entry doesn't exist.
    */
   public <T> T getAt(String path, Type type, Type...args) {
      return getPojoRest().get(path, type, args);
   }

   /**
    * Same as <code>put(String,Object)</code>, but the key is a slash-delimited path used to traverse entries in this
    * POJO.
    *
    * <p>
    * For example, the following code is equivalent:
    * </p>
    * <p class='bcode w800'>
    *    ObjectMap m = getObjectMap();
    *
    *    <jc>// Long way</jc>
    *    m.getObjectMap(<js>"foo"</js>).getObjectList(<js>"bar"</js>).getObjectMap(<js>"0"</js>)
    *       .put(<js>"baz"</js>, 123);
    *
    *    <jc>// Using this method</jc>
    *    m.putAt(<js>"foo/bar/0/baz"</js>, 123);
    * </p>
    *
    * <p>
    * This method uses the {@link PojoRest} class to perform the lookup, so the map can contain any of the various
    * class types that the {@link PojoRest} class supports (e.g. beans, collections, arrays).
    *
    * @param path The path to the entry.
    * @param o The new value.
    * @return The previous value, or <jk>null</jk> if the entry doesn't exist.
    */
   public Object putAt(String path, Object o) {
      return getPojoRest().put(path, o);
   }

   /**
    * Similar to {@link #putAt(String,Object) putAt(String,Object)}, but used to append to collections and arrays.
    *
    * <p>
    * For example, the following code is equivalent:
    * </p>
    * <p class='bcode w800'>
    *    ObjectMap m = getObjectMap();
    *
    *    <jc>// Long way</jc>
    *    m.getObjectMap(<js>"foo"</js>).getObjectList(<js>"bar"</js>).append(123);
    *
    *    <jc>// Using this method</jc>
    *    m.postAt(<js>"foo/bar"</js>, 123);
    * </p>
    *
    * <p>
    * This method uses the {@link PojoRest} class to perform the lookup, so the map can contain any of the various
    * class types that the {@link PojoRest} class supports (e.g. beans, collections, arrays).
    *
    * @param path The path to the entry.
    * @param o The new value.
    * @return The previous value, or <jk>null</jk> if the entry doesn't exist.
    */
   public Object postAt(String path, Object o) {
      return getPojoRest().post(path, o);
   }

   /**
    * Similar to {@link #remove(Object) remove(Object)}, but the key is a slash-delimited path used to traverse entries
    * in this POJO.
    *
    * <p>
    * For example, the following code is equivalent:
    * </p>
    * <p class='bcode w800'>
    *    ObjectMap m = getObjectMap();
    *
    *    <jc>// Long way</jc>
    *    m.getObjectMap(<js>"foo"</js>).getObjectList(<js>"bar"</js>).getObjectMap(0).remove(<js>"baz"</js>);
    *
    *    <jc>// Using this method</jc>
    *    m.deleteAt(<js>"foo/bar/0/baz"</js>);
    * </p>
    *
    * <p>
    * This method uses the {@link PojoRest} class to perform the lookup, so the map can contain any of the various
    * class types that the {@link PojoRest} class supports (e.g. beans, collections, arrays).
    *
    * @param path The path to the entry.
    * @return The previous value, or <jk>null</jk> if the entry doesn't exist.
    */
   public Object deleteAt(String path) {
      return getPojoRest().delete(path);
   }

   /**
    * Convenience method for inserting JSON directly into an attribute on this object.
    *
    * <p>
    * The JSON text can be an object (i.e. <js>"{...}"</js>) or an array (i.e. <js>"[...]"</js>).
    *
    * @param key The key.
    * @param json The JSON text that will be parsed into an Object and then inserted into this map.
    * @throws ParseException If the input contains a syntax error or is malformed.
    */
   public void putJson(String key, String json) throws ParseException {
      this.put(key, JsonParser.DEFAULT.parse(json, Object.class));
   }

   /**
    * Returns the specified entry value converted to a {@link String}.
    *
    * <p>
    * Shortcut for <code>get(key, String.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @return The converted value, or <jk>null</jk> if the map contains no mapping for this key.
    */
   public String getString(String key) {
      return get(key, String.class);
   }

   /**
    * Returns the specified entry value converted to a {@link String}.
    *
    * <p>
    * Shortcut for <code>get(key, String[].<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @return The converted value, or <jk>null</jk> if the map contains no mapping for this key.
    */
   public String[] getStringArray(String key) {
      return getStringArray(key, null);
   }

   /**
    * Same as {@link #getStringArray(String)} but returns a default value if the value cannot be found.
    *
    * @param key The map key.
    * @param def The default value if value is not found.
    * @return The value converted to a string array.
    */
   public String[] getStringArray(String key, String[] def) {
      Object s = get(key, Object.class);
      if (s == null)
         return def;
      String[] r = null;
      if (s instanceof Collection)
         r = ArrayUtils.toStringArray((Collection<?>)s);
      else if (s instanceof String[])
         r = (String[])s;
      else if (s instanceof Object[])
         r = ArrayUtils.toStringArray(Arrays.asList((Object[])s));
      else
         r = split(asString(s));
      return (r.length == 0 ? def : r);
   }

   /**
    * Returns the specified entry value converted to a {@link String}.
    *
    * <p>
    * Shortcut for <code>getWithDefault(key, defVal, String.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @param defVal The default value if the map doesn't contain the specified mapping.
    * @return The converted value, or the default value if the map contains no mapping for this key.
    */
   public String getString(String key, String defVal) {
      return getWithDefault(key, defVal, String.class);
   }

   /**
    * Returns the specified entry value converted to an {@link Integer}.
    *
    * <p>
    * Shortcut for <code>get(key, Integer.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @return The converted value, or <jk>null</jk> if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public Integer getInt(String key) {
      return get(key, Integer.class);
   }

   /**
    * Returns the specified entry value converted to an {@link Integer}.
    *
    * <p>
    * Shortcut for <code>getWithDefault(key, defVal, Integer.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @param defVal The default value if the map doesn't contain the specified mapping.
    * @return The converted value, or the default value if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public Integer getInt(String key, Integer defVal) {
      return getWithDefault(key, defVal, Integer.class);
   }

   /**
    * Returns the specified entry value converted to a {@link Long}.
    *
    * <p>
    * Shortcut for <code>get(key, Long.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @return The converted value, or <jk>null</jk> if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public Long getLong(String key) {
      return get(key, Long.class);
   }

   /**
    * Returns the specified entry value converted to a {@link Long}.
    *
    * <p>
    * Shortcut for <code>getWithDefault(key, defVal, Long.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @param defVal The default value if the map doesn't contain the specified mapping.
    * @return The converted value, or the default value if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public Long getLong(String key, Long defVal) {
      return getWithDefault(key, defVal, Long.class);
   }

   /**
    * Returns the specified entry value converted to a {@link Boolean}.
    *
    * <p>
    * Shortcut for <code>get(key, Boolean.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @return The converted value, or <jk>null</jk> if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public Boolean getBoolean(String key) {
      return get(key, Boolean.class);
   }

   /**
    * Returns the specified entry value converted to a {@link Boolean}.
    *
    * <p>
    * Shortcut for <code>getWithDefault(key, defVal, Boolean.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @param defVal The default value if the map doesn't contain the specified mapping.
    * @return The converted value, or the default value if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public Boolean getBoolean(String key, Boolean defVal) {
      return getWithDefault(key, defVal, Boolean.class);
   }

   /**
    * Returns the specified entry value converted to a {@link Map}.
    *
    * <p>
    * Shortcut for <code>get(key, Map.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @return The converted value, or <jk>null</jk> if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public Map<?,?> getMap(String key) {
      return get(key, Map.class);
   }

   /**
    * Returns the specified entry value converted to a {@link Map}.
    *
    * <p>
    * Shortcut for <code>getWithDefault(key, defVal, Map.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @param defVal The default value if the map doesn't contain the specified mapping.
    * @return The converted value, or the default value if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public Map<?,?> getMap(String key, Map<?,?> defVal) {
      return getWithDefault(key, defVal, Map.class);
   }

   /**
    * Same as {@link #getMap(String, Map)} except converts the keys and values to the specified types.
    *
    * @param key The key.
    * @param keyType The key type class.
    * @param valType The value type class.
    * @param def The default value if the map doesn't contain the specified mapping.
    * @return The converted value, or the default value if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public <K,V> Map<K,V> getMap(String key, Class<K> keyType, Class<V> valType, Map<K,V> def) {
      Object o = get(key);
      if (o == null)
         return def;
      return bs().convertToType(o, Map.class, keyType, valType);
   }

   /**
    * Returns the specified entry value converted to a {@link List}.
    *
    * <p>
    * Shortcut for <code>get(key, List.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @return The converted value, or <jk>null</jk> if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public List<?> getList(String key) {
      return get(key, List.class);
   }

   /**
    * Returns the specified entry value converted to a {@link List}.
    *
    * <p>
    * Shortcut for <code>getWithDefault(key, defVal, List.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @param defVal The default value if the map doesn't contain the specified mapping.
    * @return The converted value, or the default value if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public List<?> getList(String key, List<?> defVal) {
      return getWithDefault(key, defVal, List.class);
   }

   /**
    * Same as {@link #getList(String, List)} except converts the elements to the specified types.
    *
    * @param key The key.
    * @param elementType The element type class.
    * @param def The default value if the map doesn't contain the specified mapping.
    * @return The converted value, or the default value if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public <E> List<E> getList(String key, Class<E> elementType, List<E> def) {
      Object o = get(key);
      if (o == null)
         return def;
      return bs().convertToType(o, List.class, elementType);
   }

   /**
    * Returns the specified entry value converted to a {@link Map}.
    *
    * <p>
    * Shortcut for <code>get(key, ObjectMap.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @return The converted value, or <jk>null</jk> if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public ObjectMap getObjectMap(String key) {
      return get(key, ObjectMap.class);
   }

   /**
    * Returns the specified entry value converted to a {@link ObjectMap}.
    *
    * <p>
    * Shortcut for <code>getWithDefault(key, defVal, ObjectMap.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @param defVal The default value if the map doesn't contain the specified mapping.
    * @return The converted value, or the default value if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public ObjectMap getObjectMap(String key, ObjectMap defVal) {
      return getWithDefault(key, defVal, ObjectMap.class);
   }

   /**
    * Same as {@link #getObjectMap(String)} but creates a new empty {@link ObjectMap} if it doesn't already exist.
    *
    * @param key The key.
    * @param createIfNotExists If mapping doesn't already exist, create one with an empty {@link ObjectMap}.
    * @return The converted value, or an empty value if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public ObjectMap getObjectMap(String key, boolean createIfNotExists) {
      ObjectMap m = getWithDefault(key, null, ObjectMap.class);
      if (m == null && createIfNotExists) {
         m = new ObjectMap();
         put(key, m);
      }
      return m;
   }

   /**
    * Returns the specified entry value converted to a {@link ObjectList}.
    *
    * <p>
    * Shortcut for <code>get(key, ObjectList.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @return The converted value, or <jk>null</jk> if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public ObjectList getObjectList(String key) {
      return get(key, ObjectList.class);
   }

   /**
    * Returns the specified entry value converted to a {@link ObjectList}.
    *
    * <p>
    * Shortcut for <code>getWithDefault(key, defVal, ObjectList.<jk>class</jk>)</code>.
    *
    * @param key The key.
    * @param defVal The default value if the map doesn't contain the specified mapping.
    * @return The converted value, or the default value if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public ObjectList getObjectList(String key, ObjectList defVal) {
      return getWithDefault(key, defVal, ObjectList.class);
   }

   /**
    * Same as {@link #getObjectList(String)} but creates a new empty {@link ObjectList} if it doesn't already exist.
    *
    * @param key The key.
    * @param createIfNotExists If mapping doesn't already exist, create one with an empty {@link ObjectList}.
    * @return The converted value, or an empty value if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public ObjectList getObjectList(String key, boolean createIfNotExists) {
      ObjectList m = getWithDefault(key, null, ObjectList.class);
      if (m == null && createIfNotExists) {
         m = new ObjectList();
         put(key, m);
      }
      return m;
   }

   /**
    * Returns the first entry that exists converted to a {@link String}.
    *
    * <p>
    * Shortcut for <code>find(String.<jk>class</jk>, keys)</code>.
    *
    * @param keys The list of keys to look for.
    * @return
    *    The converted value of the first key in the list that has an entry in this map, or <jk>null</jk> if the map
    *    contains no mapping for any of the keys.
    */
   public String findString(String... keys) {
      return find(String.class, keys);
   }

   /**
    * Returns the first entry that exists converted to an {@link Integer}.
    *
    * <p>
    * Shortcut for <code>find(Integer.<jk>class</jk>, keys)</code>.
    *
    * @param keys The list of keys to look for.
    * @return
    *    The converted value of the first key in the list that has an entry in this map, or <jk>null</jk> if the map
    *    contains no mapping for any of the keys.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public Integer findInt(String... keys) {
      return find(Integer.class, keys);
   }

   /**
    * Returns the first entry that exists converted to a {@link Long}.
    *
    * <p>
    * Shortcut for <code>find(Long.<jk>class</jk>, keys)</code>.
    *
    * @param keys The list of keys to look for.
    * @return
    *    The converted value of the first key in the list that has an entry in this map, or <jk>null</jk> if the map
    *    contains no mapping for any of the keys.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public Long findLong(String... keys) {
      return find(Long.class, keys);
   }

   /**
    * Returns the first entry that exists converted to a {@link Boolean}.
    *
    * <p>
    * Shortcut for <code>find(Boolean.<jk>class</jk>, keys)</code>.
    *
    * @param keys The list of keys to look for.
    * @return
    *    The converted value of the first key in the list that has an entry in this map, or <jk>null</jk> if the map
    *    contains no mapping for any of the keys.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public Boolean findBoolean(String... keys) {
      return find(Boolean.class, keys);
   }

   /**
    * Returns the first entry that exists converted to a {@link Map}.
    *
    * <p>
    * Shortcut for <code>find(Map.<jk>class</jk>, keys)</code>.
    *
    * @param keys The list of keys to look for.
    * @return
    *    The converted value of the first key in the list that has an entry in this map, or <jk>null</jk> if the map
    *    contains no mapping for any of the keys.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public Map<?,?> findMap(String... keys) {
      return find(Map.class, keys);
   }

   /**
    * Returns the first entry that exists converted to a {@link List}.
    *
    * <p>
    * Shortcut for <code>find(List.<jk>class</jk>, keys)</code>.
    *
    * @param keys The list of keys to look for.
    * @return
    *    The converted value of the first key in the list that has an entry in this map, or <jk>null</jk> if the map
    *    contains no mapping for any of the keys.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public List<?> findList(String... keys) {
      return find(List.class, keys);
   }

   /**
    * Returns the first entry that exists converted to a {@link ObjectMap}.
    *
    * <p>
    * Shortcut for <code>find(ObjectMap.<jk>class</jk>, keys)</code>.
    *
    * @param keys The list of keys to look for.
    * @return
    *    The converted value of the first key in the list that has an entry in this map, or <jk>null</jk> if the map
    *    contains no mapping for any of the keys.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public ObjectMap findObjectMap(String... keys) {
      return find(ObjectMap.class, keys);
   }

   /**
    * Returns the first entry that exists converted to a {@link ObjectList}.
    *
    * <p>
    * Shortcut for <code>find(ObjectList.<jk>class</jk>, keys)</code>.
    *
    * @param keys The list of keys to look for.
    * @return
    *    The converted value of the first key in the list that has an entry in this map, or <jk>null</jk> if the map
    *    contains no mapping for any of the keys.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public ObjectList findObjectList(String... keys) {
      return find(ObjectList.class, keys);
   }

   /**
    * Returns the first key in the map.
    *
    * @return The first key in the map, or <jk>null</jk> if the map is empty.
    */
   public String getFirstKey() {
      return isEmpty() ? null : keySet().iterator().next();
   }

   /**
    * Returns the class type of the object at the specified index.
    *
    * @param key The key into this map.
    * @return
    *    The data type of the object at the specified key, or <jk>null</jk> if the value is null or does not exist.
    */
   public ClassMeta<?> getClassMeta(String key) {
      return bs().getClassMetaForObject(get(key));
   }

   /**
    * Equivalent to calling <code>get(class,key,def)</code> followed by <code>remove(key);</code>
    * @param key The key.
    * @param defVal The default value if the map doesn't contain the specified mapping.
    * @param type The class type.
    *
    * @param <T> The class type.
    * @return The converted value, or the default value if the map contains no mapping for this key.
    * @throws InvalidDataConversionException If value cannot be converted.
    */
   public <T> T removeWithDefault(String key, T defVal, Class<T> type) {
      T t = getWithDefault(key, defVal, type);
      remove(key);
      return t;
   }


   /**
    * Convenience method for removing several keys at once.
    *
    * @param keys The list of keys to remove.
    */
   public void removeAll(Collection<String> keys) {
      for (String k : keys)
         remove(k);
   }

   /**
    * Convenience method for removing several keys at once.
    *
    * @param keys The list of keys to remove.
    */
   public void removeAll(String... keys) {
      for (String k : keys)
         remove(k);
   }

   /**
    * The opposite of {@link #removeAll(String...)}.
    *
    * <p>
    * Discards all keys from this map that aren't in the specified list.
    *
    * @param keys The keys to keep.
    * @return This map.
    */
   public ObjectMap keepAll(String...keys) {
      for (Iterator<String> i = keySet().iterator(); i.hasNext();) {
         boolean remove = true;
         String key = i.next();
         for (String k : keys) {
            if (k.equals(key)) {
               remove = false;
               break;
            }
         }
         if (remove)
            i.remove();
      }
      return this;
   }

   @Override /* Map */
   public boolean containsKey(Object key) {
      if (super.containsKey(key))
         return true;
      if (inner != null)
         return inner.containsKey(key);
      return false;
   }

   /**
    * Returns <jk>true</jk> if the map contains the specified entry and the value is not null nor an empty string.
    *
    * <p>
    * Always returns <jk>false</jk> if the value is not a {@link CharSequence}.
    *
    * @param key The key.
    * @return <jk>true</jk> if the map contains the specified entry and the value is not null nor an empty string.
    */
   public boolean containsKeyNotEmpty(String key) {
      Object val = get(key);
      if (val == null)
         return false;
      if (val instanceof CharSequence)
         return ! StringUtils.isEmpty(val);
      return false;
   }

   /**
    * Returns <jk>true</jk> if this map contains the specified key, ignoring the inner map if it exists.
    *
    * @param key The key to look up.
    * @return <jk>true</jk> if this map contains the specified key.
    */
   public boolean containsOuterKey(Object key) {
      return super.containsKey(key);
   }

   /**
    * Returns a copy of this <code>ObjectMap</code> with only the specified keys.
    *
    * @param keys The keys of the entries to copy.
    * @return A new map with just the keys and values from this map.
    */
   public ObjectMap include(String...keys) {
      ObjectMap m2 = new ObjectMap();
      for (Map.Entry<String,Object> e : this.entrySet())
         for (String k : keys)
            if (k.equals(e.getKey()))
               m2.put(k, e.getValue());
      return m2;
   }

   /**
    * Returns a copy of this <code>ObjectMap</code> without the specified keys.
    *
    * @param keys The keys of the entries not to copy.
    * @return A new map without the keys and values from this map.
    */
   public ObjectMap exclude(String...keys) {
      ObjectMap m2 = new ObjectMap();
      for (Map.Entry<String,Object> e : this.entrySet()) {
         boolean exclude = false;
         for (String k : keys)
            if (k.equals(e.getKey()))
               exclude = true;
         if (! exclude)
            m2.put(e.getKey(), e.getValue());
      }
      return m2;
   }

   /**
    * Sets a value in this map if the entry does not exist or the value is <jk>null</jk>.
    *
    * @param key The map key.
    * @param val The value to set if the current value does not exist or is <jk>null</jk>.
    * @return This object (for method chaining).
    */
   public ObjectMap putIfNull(String key, Object val) {
      Object o = get(key);
      if (o == null)
         put(key, val);
      return this;
   }

   /**
    * Sets a value in this map if the entry does not exist or the value is <jk>null</jk> or an empty string.
    *
    * @param key The map key.
    * @param val The value to set if the current value does not exist or is <jk>null</jk> or an empty string.
    * @return This object (for method chaining).
    */
   public ObjectMap putIfEmpty(String key, Object val) {
      Object o = get(key);
      if (o == null || o.toString().isEmpty())
         put(key, val);
      return this;
   }

   /**
    * Adds a mapping if the specified key doesn't exist.
    *
    * @param key The map key.
    * @param val The value to set if the current value does not exist or is <jk>null</jk> or an empty string.
    * @return This object (for method chaining).
    */
   public ObjectMap putIfNotExists(String key, Object val) {
      if (! containsKey(key))
         put(key, val);
      return this;
   }

   /**
    * Converts this map into an object of the specified type.
    *
    * <p>
    * If this map contains a <js>"_type"</js> entry, it must be the same as or a subclass of the <code>type</code>.
    *
    * @param <T> The class type to convert this map object to.
    * @param type The class type to convert this map object to.
    * @return The new object.
    * @throws ClassCastException
    *    If the <js>"_type"</js> entry is present and not assignable from <code>type</code>
    */
   @SuppressWarnings("unchecked")
   public <T> T cast(Class<T> type) {
      BeanSession bs = bs();
      ClassMeta<?> c2 = bs.getClassMeta(type);
      String typePropertyName = bs.getBeanTypePropertyName(c2);
      ClassMeta<?> c1 = bs.getBeanRegistry().getClassMeta((String)get(typePropertyName));
      ClassMeta<?> c = c1 == null ? c2 : narrowClassMeta(c1, c2);
      if (c.isObject())
         return (T)this;
      return (T)cast2(c);
   }

   /**
    * Same as {@link #cast(Class)}, except allows you to specify a {@link ClassMeta} parameter.
    *
    * @param <T> The class type to convert this map object to.
    * @param cm The class type to convert this map object to.
    * @return The new object.
    * @throws ClassCastException
    *    If the <js>"_type"</js> entry is present and not assignable from <code>type</code>
    */
   @SuppressWarnings({"unchecked"})
   public <T> T cast(ClassMeta<T> cm) {
      BeanSession bs = bs();
      ClassMeta<?> c1 = bs.getBeanRegistry().getClassMeta((String)get(bs.getBeanTypePropertyName(cm)));
      ClassMeta<?> c = narrowClassMeta(c1, cm);
      return (T)cast2(c);
   }

   /*
    * Combines the class specified by a "_type" attribute with the ClassMeta
    * passed in through the cast(ClassMeta) method.
    * The rule is that child classes supersede parent classes, and c2 supersedes c1
    * if one isn't the parent of another.
    */
   private ClassMeta<?> narrowClassMeta(ClassMeta<?> c1, ClassMeta<?> c2) {
      if (c1 == null)
         return c2;
      ClassMeta<?> c = getNarrowedClassMeta(c1, c2);
      if (c1.isMap()) {
         ClassMeta<?> k = getNarrowedClassMeta(c1.getKeyType(), c2.getKeyType());
         ClassMeta<?> v = getNarrowedClassMeta(c1.getValueType(), c2.getValueType());
         return bs().getClassMeta(c.getInnerClass(), k, v);
      }
      if (c1.isCollection()) {
         ClassMeta<?> e = getNarrowedClassMeta(c1.getElementType(), c2.getElementType());
         return bs().getClassMeta(c.getInnerClass(), e);
      }
      return c;
   }

   /*
    * If c1 is a child of c2 or the same as c2, returns c1.
    * Otherwise, returns c2.
    */
   private static ClassMeta<?> getNarrowedClassMeta(ClassMeta<?> c1, ClassMeta<?> c2) {
      if (c2 == null || isParentClass(c2.getInnerClass(), c1.getInnerClass()))
         return c1;
      return c2;
   }

   /*
    * Converts this map to the specified class type.
    */
   @SuppressWarnings({"unchecked","rawtypes"})
   private <T> T cast2(ClassMeta<T> cm) {

      BeanSession bs = bs();
      try {
         Object value = get("value");

         if (cm.isMap()) {
            Map m2 = (cm.canCreateNewInstance() ? (Map)cm.newInstance() : new ObjectMap(bs));
            ClassMeta<?> kType = cm.getKeyType(), vType = cm.getValueType();
            for (Map.Entry<String,Object> e : entrySet()) {
               Object k = e.getKey();
               Object v = e.getValue();
               if (! k.equals(bs.getBeanTypePropertyName(cm))) {

                  // Attempt to recursively cast child maps.
                  if (v instanceof ObjectMap)
                     v = ((ObjectMap)v).cast(vType);

                  k = (kType.isString() ? k : bs.convertToType(k, kType));
                  v = (vType.isObject() ? v : bs.convertToType(v, vType));

                  m2.put(k, v);
               }
            }
            return (T)m2;

         } else if (cm.isBean()) {
            BeanMap<? extends T> bm = bs.newBeanMap(cm.getInnerClass());

            // Iterate through all the entries in the map and set the individual field values.
            for (Map.Entry<String,Object> e : entrySet()) {
               String k = e.getKey();
               Object v = e.getValue();
               if (! k.equals(bs.getBeanTypePropertyName(cm))) {

                  // Attempt to recursively cast child maps.
                  if (v instanceof ObjectMap)
                     v = ((ObjectMap)v).cast(bm.getProperty(k).getMeta().getClassMeta());

                  bm.put(k, v);
               }
            }

            return bm.getBean();

         } else if (cm.isCollectionOrArray()) {
            List items = (List)get("items");
            return bs.convertToType(items, cm);

         } else if (value != null) {
            return bs.convertToType(value, cm);
         }

      } catch (Exception e) {
         throw new BeanRuntimeException(e, cm.innerClass,
            "Error occurred attempting to cast to an object of type ''{0}''", cm.innerClass.getName());
      }

      throw new BeanRuntimeException(cm.innerClass,
         "Cannot convert to class type ''{0}''.  Only beans and maps can be converted using this method.",
         cm.innerClass.getName());
   }

   private PojoRest getPojoRest() {
      if (pojoRest == null)
         pojoRest = new PojoRest(this);
      return pojoRest;
   }

   /**
    * Serialize this object into a string using the specified serializer.
    *
    * @param serializer The serializer to use to convert this object to a string.
    * @return This object serialized as a string.
    * @throws SerializeException If a problem occurred trying to convert the output.
    */
   public String toString(WriterSerializer serializer) throws SerializeException {
      return serializer.serialize(this);
   }

   /**
    * Serialize this object into a JSON string using the {@link JsonSerializer#DEFAULT} serializer.
    */
   @Override /* Object */
   public String toString() {
      try {
         return this.toString(SimpleJsonSerializer.DEFAULT);
      } catch (SerializeException e) {
         return e.getLocalizedMessage();
      }
   }

   /**
    * Convenience method for serializing this map to the specified <code>Writer</code> using the
    * {@link JsonSerializer#DEFAULT} serializer.
    *
    * @param w The writer to serialize this object to.
    * @return This object (for method chaining).
    * @throws IOException If a problem occurred trying to write to the writer.
    * @throws SerializeException If a problem occurred trying to convert the output.
    */
   public ObjectMap serializeTo(Writer w) throws IOException, SerializeException {
      JsonSerializer.DEFAULT.serialize(this);
      return this;
   }

   /**
    * Returns <jk>true</jk> if this map is unmodifiable.
    *
    * @return <jk>true</jk> if this map is unmodifiable.
    */
   public boolean isUnmodifiable() {
      return false;
   }

   /**
    * Returns a modifiable copy of this map if it's unmodifiable.
    *
    * @return A modifiable copy of this map if it's unmodifiable, or this map if it is already modifiable.
    */
   public ObjectMap modifiable() {
      if (isUnmodifiable())
         return new ObjectMap(this);
      return this;
   }

   /**
    * Returns an unmodifiable copy of this map if it's modifiable.
    *
    * @return An unmodifiable copy of this map if it's modifiable, or this map if it is already unmodifiable.
    */
   public ObjectMap unmodifiable() {
      if (this instanceof UnmodifiableObjectMap)
         return this;
      return new UnmodifiableObjectMap(this);
   }

   @Override /* Map */
   public Set<String> keySet() {
      if (inner == null)
         return super.keySet();
      LinkedHashSet<String> s = new LinkedHashSet<>();
      s.addAll(inner.keySet());
      s.addAll(super.keySet());
      return s;
   }

   @Override /* Map */
   public Set<Map.Entry<String,Object>> entrySet() {
      if (inner == null)
         return super.entrySet();

      final Set<String> keySet = keySet();
      final Iterator<String> keys = keySet.iterator();

      return new AbstractSet<Map.Entry<String,Object>>() {

         @Override /* Iterable */
         public Iterator<Map.Entry<String,Object>> iterator() {

            return new Iterator<Map.Entry<String,Object>>() {

               @Override /* Iterator */
               public boolean hasNext() {
                  return keys.hasNext();
               }

               @Override /* Iterator */
               public Map.Entry<String,Object> next() {
                  return new Map.Entry<String,Object>() {
                     String key = keys.next();

                     @Override /* Map.Entry */
                     public String getKey() {
                        return key;
                     }

                     @Override /* Map.Entry */
                     public Object getValue() {
                        return get(key);
                     }

                     @Override /* Map.Entry */
                     public Object setValue(Object object) {
                        return put(key, object);
                     }
                  };
               }

               @Override /* Iterator */
               public void remove() {
                  throw new UnsupportedOperationException();
               }
            };
         }

         @Override /* Set */
         public int size() {
            return keySet.size();
         }
      };
   }

   private static final class UnmodifiableObjectMap extends ObjectMap {
      private static final long serialVersionUID = 1L;

      UnmodifiableObjectMap(ObjectMap contents) {
         super();
         if (contents != null) {
            for (Map.Entry<String,Object> e : contents.entrySet()) {
               super.put(e.getKey(), e.getValue());
            }
         }
      }

      @Override
      public final Object put(String key, Object val) {
         throw new UnsupportedOperationException("ObjectMap is read-only.");
      }

      @Override
      public final Object remove(Object key) {
         throw new UnsupportedOperationException("ObjectMap is read-only.");
      }

      @Override
      public final boolean isUnmodifiable() {
         return true;
      }
   }

   private BeanSession bs() {
      if (session == null)
         session = BeanContext.DEFAULT.createBeanSession();
      return session;
   }
}