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// * with the License.  You may obtain a copy of the License at                                                              *
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// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
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package org.apache.juneau.microservice;

import static org.apache.juneau.internal.FileUtils.*;
import static org.apache.juneau.internal.IOUtils.*;
import static org.apache.juneau.internal.StringUtils.*;
import static org.apache.juneau.internal.CollectionUtils.*;

import java.io.*;
import java.net.*;
import java.text.*;
import java.util.*;
import java.util.jar.*;
import java.util.logging.*;

import org.apache.juneau.*;
import org.apache.juneau.config.*;
import org.apache.juneau.config.event.*;
import org.apache.juneau.config.vars.*;
import org.apache.juneau.internal.*;
import org.apache.juneau.microservice.console.*;
import org.apache.juneau.microservice.resources.*;
import org.apache.juneau.svl.*;
import org.apache.juneau.svl.vars.*;
import org.apache.juneau.svl.vars.ManifestFileVar;
import org.apache.juneau.utils.*;

/**
 * Parent class for all microservices.
 * 
 * <p>
 * A microservice defines a simple API for starting and stopping simple Java services contained in executable jars.
 * 
 * <p>
 * The general command for invoking these services is...
 * <p class='bcode'>
 *    java -jar mymicroservice.jar [mymicroservice.cfg]
 * </p>
 * 
 * <p>
 * Your microservice class must be specified as the <jk>Main-Class</jk> entry in the manifest file of your microservice 
 * jar file.
 * 
 * <h5 class='topic'>Microservice Configuration</h5>
 * 
 * This class defines the following method for accessing configuration for your microservice:
 * <ul class='spaced-list'>
 *    <li>
 *       {@link #getArgs()} - The command-line arguments passed to the jar file.
 *    <li>
 *       {@link #getConfig()} - An external INI-style configuration file.
 *    <li>
 *       {@link #getManifest()} - The manifest file for the main jar file.
 * </ul>
 * 
 * <h5 class='topic'>Entry point Method</h5>
 * 
 * Subclasses must implement a static void main method as the entry point for the microservice.
 * Typically, this method will simply consist of the following...
 * <p class='bcode'>
 *    <jk>public static void</jk> main(String[] args) <jk>throws</jk> Exception {
 *       <jk>new</jk> MyMicroservice(args).start();
 *    }
 * </p>
 * 
 * <h5 class='topic'>Lifecycle Methods</h5>
 * 
 * Subclasses must implement the following lifecycle methods:
 * <ul class='spaced-list'>
 *    <li>
 *       {@link #start()} - Gets executed during startup.
 *    <li>
 *       {@link #stop()} - Gets executed when 'exit' is typed in the console or an external shutdown signal is received.
 *    <li>
 *       {@link #kill()} - Can be used to forcibly shut down the service.  Doesn't get called during normal operation.
 * </ul>
 * 
 * <h5 class='topic'>Lifecycle Listener Methods</h5>
 * 
 * Subclasses can optionally implement the following event listener methods:
 * <ul class='spaced-list'>
 *    <li>
 *       {@link #onStart()} - Gets executed before {@link #start()}.
 *    <li>
 *       {@link #onStop()} - Gets executed before {@link #stop()}.
 *    <li>
 *       {@link #onConfigChange(List)} - Gets executed after a config file has been modified.
 * </ul>
 * 
 * <h5 class='topic'>Other Methods</h5>
 * 
 * Subclasses can optionally override the following methods to provide customized behavior:
 * <ul class='spaced-list'>
 *    <li>
 *       {@link #createVarResolver()} - Creates the {@link VarResolver} used to resolve variables in the config file 
 *       returned by {@link #getConfig()}.
 * </ul>
 */
public abstract class Microservice implements ConfigEventListener {

   private static volatile Microservice INSTANCE;

   private final MessageBundle mb = MessageBundle.create(Microservice.class, "Messages");
   private final Scanner consoleReader;
   private final PrintWriter consoleWriter;

   private Logger logger;
   private Args args;
   private Config cf;
   private ManifestFile mf;
   private VarResolver vr;
   private Map<String,ConsoleCommand> consoleCommands;
   private boolean consoleEnabled = true;
   
   private String cfPath;

   /**
    * Returns the Microservice instance.  
    * <p>
    * This method only works if there's only one Microservice instance in a JVM.  
    * Otherwise, it's just overwritten by the last call to {@link #Microservice(String...)}.
    * 
    * @return The Microservice instance, or <jk>null</jk> if there isn't one.
    */
   public static Microservice getInstance() {
      synchronized(Microservice.class) {
         return INSTANCE;
      }
   }
   
   /**
    * Constructor.
    * 
    * @param args Command line arguments.
    * @throws Exception
    */
   protected Microservice(String...args) throws Exception {
      setInstance(this);
      Console c = System.console();
      consoleReader = new Scanner(c == null ? new InputStreamReader(System.in) : c.reader());
      consoleWriter = c == null ? new PrintWriter(System.out, true) : c.writer();
      setArgs(new Args(args));
      setManifest(this.getClass());
   }
   
   private static void setInstance(Microservice m) {
      synchronized(Microservice.class) {
         INSTANCE = m;
      }
   }


   /**
    * Specifies the path of the config file for this microservice.
    * 
    * <p>
    * If you do not specify the config file location, we attempt to resolve it through the following methods:
    * <ol>
    *    <li>The first argument in the command line arguments passed in through the constructor.
    *    <li>The value of the <code>Main-Config</code> entry in the manifest file.
    *    <li>A config file in the same location and with the same name as the executable jar file.
    *       (e.g. <js>"java -jar myjar.jar"</js> will look for <js>"myjar.cfg"</js>).
    * </ol>
    * 
    * <p>
    * If this path does not exist, a {@link FileNotFoundException} will be thrown from the {@link #start()} command.
    * 
    * @param cfPath The absolute or relative path of the config file.
    * @param create Create the file if it doesn't exist.
    * @return This object (for method chaining).
    * @throws IOException If config file does not exist at the specified location or could not be read or created.
    */
   public Microservice setConfig(String cfPath, boolean create) throws IOException {
      File f = new File(cfPath);
      if (! f.exists()) {
         if (! create)
            throw new FileNotFoundException("Could not locate config at '"+f.getAbsolutePath()+"'.");
         if (! f.createNewFile())
            throw new FileNotFoundException("Could not create config at '"+f.getAbsolutePath()+"'.");
      }
      this.cfPath = cfPath;
      return this;
   }

   /**
    * Specifies the config for this microservice.
    * 
    * <p>
    * Note that if you use this method instead of {@link #setConfig(String,boolean)}, the config file will not use
    * the variable resolver constructed from {@link #createVarResolver()}.
    * 
    * @param cf The config file for this application, or <jk>null</jk> if no config file is needed.
    */
   public void setConfig(Config cf) {
      this.cf = cf;
   }

   /**
    * Specifies the manifest file of the jar file this microservice is contained within.
    * 
    * <p>
    * If you do not specify the manifest file, we attempt to resolve it through the following methods:
    * <ol>
    *    <li>Looking on the file system for a file at <js>"META-INF/MANIFEST.MF"</js>.
    *       This is primarily to allow for running microservices from within eclipse workspaces where the manifest file
    *       is located in the project root.
    *    <li>Using the class loader for this class to find the file at the URL <js>"META-INF/MANIFEST.MF"</js>.
    * </ol>
    * 
    * @param mf The manifest file of this microservice.
    * @return This object (for method chaining).
    */
   public Microservice setManifest(ManifestFile mf) {
      this.mf = mf;
      ManifestFileVar.init(this.mf);
      return this;
   }

   /**
    * Shortcut for calling <code>setManifest(<jk>new</jk> ManifestFile(mf))</code>.
    * 
    * @param mf The manifest file of this microservice.
    * @return This object (for method chaining).
    */
   public Microservice setManifest(Manifest mf) {
      return setManifest(new ManifestFile(mf));
   }

   /**
    * Convenience method for specifying the manifest contents directly.
    * 
    * @param contents The lines in the manifest file.
    * @return This object (for method chaining).
    * @throws IOException
    */
   public Microservice setManifestContents(String...contents) throws IOException {
      String s = StringUtils.join(contents, "\n") + "\n";
      return setManifest(new ManifestFile(new Manifest(new ByteArrayInputStream(s.getBytes("UTF-8")))));
   }

   /**
    * Same as {@link #setManifest(Manifest)} except specified through a {@link File} object.
    * 
    * @param f The manifest file of this microservice.
    * @return This object (for method chaining).
    * @throws IOException If a problem occurred while trying to read the manifest file.
    */
   public Microservice setManifest(File f) throws IOException {
      return setManifest(new ManifestFile(f));
   }

   /**
    * Same as {@link #setManifest(Manifest)} except finds and loads the manifest file of the jar file that the  
    * specified class is contained within.
    * 
    * @param c The class whose jar file contains the manifest to use for this microservice.
    * @return This object (for method chaining).
    * @throws IOException If a problem occurred while trying to read the manifest file.
    */
   public Microservice setManifest(Class<?> c) throws IOException {
      return setManifest(new ManifestFile(c));
   }

   /**
    * Creates the {@link VarResolver} used to resolve variables in the config file returned by {@link #getConfig()}.
    * 
    * <p>
    * The default implementation resolves the following variables:
    * <ul class='doctree'>
    *    <li class='jc'>{@link org.apache.juneau.svl.vars.SystemPropertiesVar} - <code>$S{key[,default]}</code>
    *    <li class='jc'>{@link org.apache.juneau.svl.vars.EnvVariablesVar} - <code>$E{key[,default]}</code>
    *    <li class='jc'>{@link org.apache.juneau.svl.vars.ArgsVar} - <code>$A{key[,default]}</code>
    *    <li class='jc'>{@link org.apache.juneau.svl.vars.ManifestFileVar} - <code>$MF{key[,default]}</code>
    *    <li class='jc'>{@link org.apache.juneau.svl.vars.IfVar} - <code>$IF{arg,then[,else]}</code>
    *    <li class='jc'>{@link org.apache.juneau.svl.vars.SwitchVar} - <code>$SW{arg,pattern1:then1[,pattern2:then2...]}</code>
    *    <li class='jc'>{@link org.apache.juneau.svl.vars.CoalesceVar} - <code>$CO{arg1[,arg2...]}</code>
    *    <li class='jc'>{@link org.apache.juneau.svl.vars.PatternMatchVar} - <code>$PM{arg,pattern}</code> 
    *    <li class='jc'>{@link org.apache.juneau.svl.vars.NotEmptyVar} - <code>$NE{arg}</code>
    *    <li class='jc'>{@link org.apache.juneau.svl.vars.UpperCaseVar} - <code>$UC{arg}</code>
    *    <li class='jc'>{@link org.apache.juneau.svl.vars.LowerCaseVar} - <code>$LC{arg}</code>
    *    <li class='jc'>{@link org.apache.juneau.config.vars.ConfigVar} - <code>$C{key[,default]}</code>
    * </ul>
    * 
    * <p>
    * Subclasses can override this method to provide their own variables.
    * 
    * <h5 class='section'>Example:</h5>
    * <p class='bcode'>
    *    <jd>/**
    *     * Augment default var resolver with a custom $B{...} variable that simply wraps strings inside square brackets.
    *     * /</jd>
    *    <ja>@Override</ja> <jc>// Microservice</jc>
    *    <jk>protected</jk> StringVarResolver createVarResolver() {
    *       <jk>return super</jk>.createVarResolver()
    *          .addVar(<js>"B"</js>,
    *             <jk>new</jk> StringVarWithDefault() {
    *                <ja>@Override</ja> <jc>// StringVar</jc>
    *                <jk>public</jk> String resolve(String varVal) {
    *                   <jk>return</jk> <js>'['</js> + varVal + <js>']'</js>;
    *                }
    *             }
    *          );
    *    }
    * </p>
    * <p class='bcode'>
    *    <cc># Example config file</cc>
    *    <cs>[MySection]</cs>
    *    <ck>myEntry</ck> = $B{foo}
    * </p>
    * <p class='bcode'>
    *    <jc>// Example java code</jc>
    *    String myentry = getConfig().getString(<js>"MySection/myEntry"</js>); <jc>// == "[foo]"</js>
    * </p>
    * 
    * @return A new {@link VarResolver}.
    */
   protected VarResolverBuilder createVarResolver() {
      VarResolverBuilder b = new VarResolverBuilder()
         .defaultVars()
         .vars(ConfigVar.class, SwitchVar.class, IfVar.class);
      if (cf != null)
         b.contextObject(ConfigVar.SESSION_config, cf);
      return b;
   }

   /**
    * Returns the command-line arguments passed into the application.
    * 
    * <p>
    * This method can be called from the class constructor.
    * 
    * <p>
    * See {@link Args} for details on using this method.
    * 
    * @return The command-line arguments passed into the application.
    */
   public Args getArgs() {
      return args;
   }

   /**
    * Sets the arguments for this microservice.
    * 
    * @param args The arguments for this microservice.
    * @return This object (for method chaining).
    */
   public Microservice setArgs(Args args) {
      this.args = args;
      ArgsVar.init(args);
      return this;
   }

   /**
    * Returns the external INI-style configuration file that can be used to configure your microservice.
    * 
    * <p>
    * The config location is determined in the following order:
    * <ol class='spaced-list'>
    *    <li>
    *       The first argument passed to the microservice jar.
    *    <li>
    *       The <code>Main-Config</code> entry in the microservice jar manifest file.
    *    <li>
    *       The name of the microservice jar with a <js>".cfg"</js> suffix (e.g. 
    *       <js>"mymicroservice.jar"</js>-&gt;<js>"mymicroservice.cfg"</js>).
    * </ol>
    * 
    * <p>
    * If all methods for locating the config fail, then this method returns <jk>null</jk>.
    * 
    * <p>
    * Subclasses can set their own config file by calling the {@link #setConfig(Config)} method.
    * 
    * <p>
    * String variables defined by {@link #createVarResolver()} are automatically resolved when using this method.
    * 
    * <p>
    * This method can be called from the class constructor.
    * 
    * <h5 class='section'>Example:</h5>
    * <p class='bcode'>
    *    <cc>#--------------------------</cc>
    *    <cc># My section</cc>
    *    <cc>#--------------------------</cc>
    *    <cs>[MySection]</cs>
    * 
    *    <cc># An integer</cc>
    *    <ck>anInt</ck> = 1
    * 
    *    <cc># A boolean</cc>
    *    <ck>aBoolean</ck> = true
    * 
    *    <cc># An int array</cc>
    *    <ck>anIntArray</ck> = 1,2,3
    * 
    *    <cc># A POJO that can be converted from a String</cc>
    *    <ck>aURL</ck> = http://foo
    * 
    *    <cc># A POJO that can be converted from JSON</cc>
    *    <ck>aBean</ck> = {foo:'bar',baz:123}
    * 
    *    <cc># A system property</cc>
    *    <ck>locale</ck> = $S{java.locale, en_US}
    * 
    *    <cc># An environment variable</cc>
    *    <ck>path</ck> = $E{PATH, unknown}
    * 
    *    <cc># A manifest file entry</cc>
    *    <ck>mainClass</ck> = $MF{Main-Class}
    * 
    *    <cc># Another value in this config file</cc>
    *    <ck>sameAsAnInt</ck> = $C{MySection/anInt}
    * 
    *    <cc># A command-line argument in the form "myarg=foo"</cc>
    *    <ck>myArg</ck> = $A{myarg}
    * 
    *    <cc># The first command-line argument</cc>
    *    <ck>firstArg</ck> = $A{0}
    * 
    *    <cc># Look for system property, or env var if that doesn't exist, or command-line arg if that doesn't exist.</cc>
    *    <ck>nested</ck> = $S{mySystemProperty,$E{MY_ENV_VAR,$A{0}}}
    * 
    *    <cc># A POJO with embedded variables</cc>
    *    <ck>aBean2</ck> = {foo:'$A{0}',baz:$C{MySection/anInt}}
    * </p>
    * 
    * <p class='bcode'>
    *    <jc>// Java code for accessing config entries above.</jc>
    *    Config cf = getConfig();
    * 
    *    <jk>int</jk> anInt = cf.getInt(<js>"MySection/anInt"</js>);
    *    <jk>boolean</jk> aBoolean = cf.getBoolean(<js>"MySection/aBoolean"</js>);
    *    <jk>int</jk>[] anIntArray = cf.getObject(<jk>int</jk>[].<jk>class</jk>, <js>"MySection/anIntArray"</js>);
    *    URL aURL = cf.getObject(URL.<jk>class</jk>, <js>"MySection/aURL"</js>);
    *    MyBean aBean = cf.getObject(MyBean.<jk>class</jk>, <js>"MySection/aBean"</js>);
    *    Locale locale = cf.getObject(Locale.<jk>class</jk>, <js>"MySection/locale"</js>);
    *    String path = cf.getString(<js>"MySection/path"</js>);
    *    String mainClass = cf.getString(<js>"MySection/mainClass"</js>);
    *    <jk>int</jk> sameAsAnInt = cf.getInt(<js>"MySection/sameAsAnInt"</js>);
    *    String myArg = cf.getString(<js>"MySection/myArg"</js>);
    *    String firstArg = cf.getString(<js>"MySection/firstArg"</js>);
    * </p>
    * 
    * @return The config file for this application, or <jk>null</jk> if no config file is configured.
    */
   public Config getConfig() {
      return cf;
   }

   /**
    * Returns the main jar manifest file contents as a simple {@link ObjectMap}.
    * 
    * <p>
    * This map consists of the contents of {@link Manifest#getMainAttributes()} with the keys and entries converted to 
    * simple strings.
    * <p>
    * This method can be called from the class constructor.
    * 
    * <h5 class='section'>Example:</h5>
    * <p class='bcode'>
    *    <jc>// Get Main-Class from manifest file.</jc>
    *    String mainClass = Microservice.<jsm>getManifest</jsm>().getString(<js>"Main-Class"</js>, <js>"unknown"</js>);
    * 
    *    <jc>// Get Rest-Resources from manifest file.</jc>
    *    String[] restResources = Microservice.<jsm>getManifest</jsm>().getStringArray(<js>"Rest-Resources"</js>);
    * </p>
    * 
    * @return The manifest file from the main jar, or <jk>null</jk> if the manifest file could not be retrieved.
    */
   public ManifestFile getManifest() {
      return mf;
   }

   /**
    * Returns the variable resolver for resolving variables in strings and files.
    * <p>
    * See the {@link #createVarResolver()} method for the list of available resolution variables.
    * 
    * @return The VarResolver used by this Microservice, or <jk>null</jk> if it was never created.
    */
   public VarResolver getVarResolver() {
      return vr;
   }

   /**
    * Returns the logger for this microservice.
    * 
    * @return The logger for this microservice.
    */
   public Logger getLogger() {
      return logger;
   }
   
   //--------------------------------------------------------------------------------
   // Abstract lifecycle methods.
   //--------------------------------------------------------------------------------

   /**
    * Start this application.
    * 
    * <p>
    * Default implementation simply calls {@link #onStart()}.
    * 
    * <p>
    * Overridden methods MUST call this method FIRST so that the {@link #onStart()} method is called.
    * 
    * @return This object (for method chaining).
    * @throws Exception
    */
   @SuppressWarnings("resource")
   public Microservice start() throws Exception {

      // --------------------------------------------------------------------------------
      // Try to get the manifest file if it wasn't already set.
      // --------------------------------------------------------------------------------
      if (mf == null) {
         Manifest m = new Manifest();

         // If running within an eclipse workspace, need to get it from the file system.
         File f = new File("META-INF/MANIFEST.MF");
         if (f.exists()) {
            try (FileInputStream fis = new FileInputStream(f)) {
               m.read(fis);
            } catch (IOException e) {
               throw new IOException("Problem detected in MANIFEST.MF.  Contents below:\n " + read(f), e);
            }
         } else {
            // Otherwise, read from manifest file in the jar file containing the main class.
            URLClassLoader cl = (URLClassLoader)getClass().getClassLoader();
            URL url = cl.findResource("META-INF/MANIFEST.MF");
            if (url != null) {
               try {
                  m.read(url.openStream());
               } catch (IOException e) {
                  throw new IOException("Problem detected in MANIFEST.MF.  Contents below:\n " + read(url.openStream()), e);
               }
            }
         }
         mf = new ManifestFile(m);
      }

      // --------------------------------------------------------------------------------
      // Resolve the config file if the path was specified.
      // --------------------------------------------------------------------------------
      ConfigBuilder cfb = Config.create();
      if (cfPath != null)
         cf = cfb.name(cfPath).varResolver(createVarResolver().defaultVars().build()).build();

      
      // --------------------------------------------------------------------------------
      // Find config file.
      // Can either be passed in as first parameter, or we discover it using
      // the 'sun.java.command' system property.
      // --------------------------------------------------------------------------------
      if (cf == null) {
         if (args.hasArg(0))
            cfPath = args.getArg(0);
         else if (mf.containsKey("Main-Config"))
            cfPath = mf.getString("Main-Config");
         else {
            String cmd = System.getProperty("sun.java.command", "not_found").split("\\s+")[0];
            if (cmd.endsWith(".jar"))
               cfPath = cmd.replace(".jar", ".cfg");
         }

         if (cfPath == null) {
            cf = cfb.build();
         } else {
            cf = cfb.name(cfPath).varResolver(createVarResolver().build()).build();
         }
      }

      vr = createVarResolver().build();
      
      if (cfPath != null)
         System.setProperty("juneau.configFile", cfPath);
      
      // --------------------------------------------------------------------------------
      // Set system properties.
      // --------------------------------------------------------------------------------
      Set<String> spKeys = cf.getKeys("SystemProperties");
      if (spKeys != null)
         for (String key : spKeys)
            System.setProperty(key, cf.getString("SystemProperties/"+key));

      // --------------------------------------------------------------------------------
      // Initialize logging.
      // --------------------------------------------------------------------------------
      try {
         initLogging();
      } catch (Exception e) {
         // If logging can be initialized, just print a stack trace and continue.
         e.printStackTrace();
      }

      // --------------------------------------------------------------------------------
      // Add a config file change listener.
      // --------------------------------------------------------------------------------
      cf.addListener(this);

      consoleEnabled = cf.getBoolean("Console/enabled", true);

      if (cfPath == null) {
         err(mb, "RunningClassWithoutConfig", getClass().getSimpleName());
      } else {
         out(mb, "RunningClassWithConfig", getClass().getSimpleName(), cfPath);
      }
            
      Runtime.getRuntime().addShutdownHook(
         new Thread() {
            @Override /* Thread */
            public void run() {
               Microservice.this.stop();
            }
         }
      );
      onStart();
      return this;
   }

   /**
    * Start the console for this application.
    * 
    * <p>
    * Note that this is typically started after all initialization has occurred so that the console output isn't polluted.
    * 
    * @return This object (for method chaining).
    * @throws Exception
    */
   protected Microservice startConsole() throws Exception {
      consoleCommands = new LinkedHashMap<>();
      for (ConsoleCommand cc : createConsoleCommands())
         consoleCommands.put(cc.getName(), cc);
      consoleCommands = unmodifiableMap(consoleCommands);
      
      final Map<String,ConsoleCommand> commands = consoleCommands;
      final MessageBundle mb2 = mb;
      if (! consoleCommands.isEmpty()) {
         new Thread() {
            @Override /* Thread */
            @SuppressWarnings("resource")  // Must not close System.in!
            public void run() {
               Scanner in = getConsoleReader();
               PrintWriter out = getConsoleWriter();
               
               out.println(mb2.getString("ListOfAvailableCommands"));
               for (ConsoleCommand cc : commands.values()) 
                  out.append("\t").append(cc.getName()).append(" -- ").append(cc.getInfo()).println();
               out.println();
               
               while (true) {
                  String line = null;
                  out.append("> ").flush();
                  line = in.nextLine();
                  Args args = new Args(line);
                  if (! args.isEmpty()) {
                     ConsoleCommand cc = commands.get(args.getArg(0));
                     if (cc == null) {
                        out.println(mb2.getString("UnknownCommand"));
                     } else {
                        try {
                           if (cc.execute(in, out, args))
                              break;
                        } catch (Exception e) {
                           e.printStackTrace();
                        }
                     }
                  }
               }
            }
         }.start();
      }
      return this;
   }
   
   /**
    * Initialize the logging for this microservice.
    * 
    * <p>
    * Subclasses can override this method to provide customized logging.
    * 
    * <p>
    * The default implementation uses the <cs>Logging</cs> section in the config file to set up logging:
    * <p class='bcode'>
    *    <cc>#================================================================================
    *    # Logger settings
    *    # See FileHandler Java class for details.
    *    #================================================================================</cc>
    *    <cs>[Logging]</cs>
    * 
    *    <cc># The directory where to create the log file.
    *    # Default is ".".</cc>
    *    <ck>logDir</ck> = logs
    * 
    *    <cc># The name of the log file to create for the main logger.
    *    # The logDir and logFile make up the pattern that's passed to the FileHandler
    *    # constructor.
    *    # If value is not specified, then logging to a file will not be set up.</cc>
    *    <ck>logFile</ck> = microservice.%g.log
    * 
    *    <cc># Whether to append to the existing log file or create a new one.
    *    # Default is false.</cc>
    *    <ck>append</ck> =
    * 
    *    <cc># The SimpleDateFormat format to use for dates.
    *    # Default is "yyyy.MM.dd hh:mm:ss".</cc>
    *    <ck>dateFormat</ck> =
    * 
    *    <cc># The log message format.
    *    # The value can contain any of the following variables:
    *    #  {date} - The date, formatted per dateFormat.
    *    #  {class} - The class name.
    *    #  {method} - The method name.
    *    #  {logger} - The logger name.
    *    #  {level} - The log level name.
    *    #  {msg} - The log message.
    *    #  {threadid} - The thread ID.
    *    #  {exception} - The localized exception message.
    *    # Default is "[{date} {level}] {msg}%n".</cc>
    *    <ck>format</ck> =
    * 
    *    <cc># The maximum log file size.
    *    # Suffixes available for numbers.
    *    # See Config.getInt(String,int) for details.
    *    # Default is 1M.</cc>
    *    <ck>limit</ck> = 10M
    * 
    *    <cc># Max number of log files.
    *    # Default is 1.</cc>
    *    <ck>count</ck> = 5
    * 
    *    <cc># Default log levels.
    *    # Keys are logger names.
    *    # Values are serialized Level POJOs.</cc>
    *    <ck>levels</ck> = { org.apache.juneau:'INFO' }
    * 
    *    <cc># Only print unique stack traces once and then refer to them by a simple 8 character hash identifier.
    *    # Useful for preventing log files from filling up with duplicate stack traces.
    *    # Default is false.</cc>
    *    <ck>useStackTraceHashes</ck> = true
    * 
    *    <cc># The default level for the console logger.
    *    # Default is WARNING.</cc>
    *    <ck>consoleLevel</ck> = WARNING
    * </p>
    * 
    * @throws Exception
    */
   protected void initLogging() throws Exception {
      Config cf = getConfig();
      logger = Logger.getLogger("");
      String logFile = cf.getString("Logging/logFile");
      if (! isEmpty(logFile)) {
         LogManager.getLogManager().reset();
         String logDir = cf.getString("Logging/logDir", ".");
         mkdirs(new File(logDir), false);
         boolean append = cf.getBoolean("Logging/append");
         int limit = cf.getInt("Logging/limit", 1024*1024);
         int count = cf.getInt("Logging/count", 1);
         FileHandler fh = new FileHandler(logDir + '/' + logFile, limit, count, append);

         boolean useStackTraceHashes = cf.getBoolean("Logging/useStackTraceHashes");
         String format = cf.getString("Logging/format", "[{date} {level}] {msg}%n");
         String dateFormat = cf.getString("Logging/dateFormat", "yyyy.MM.dd hh:mm:ss");
         fh.setFormatter(new LogEntryFormatter(format, dateFormat, useStackTraceHashes));
         fh.setLevel(cf.getObjectWithDefault("Logging/fileLevel", Level.INFO, Level.class));
         logger.addHandler(fh);

         ConsoleHandler ch = new ConsoleHandler();
         ch.setLevel(cf.getObjectWithDefault("Logging/consoleLevel", Level.WARNING, Level.class));
         ch.setFormatter(new LogEntryFormatter(format, dateFormat, false));
         logger.addHandler(ch);
      }
      ObjectMap loggerLevels = cf.getObject("Logging/levels", ObjectMap.class);
      if (loggerLevels != null)
         for (String l : loggerLevels.keySet())
            Logger.getLogger(l).setLevel(loggerLevels.get(l, Level.class));
   }

   /**
    * Joins the application with the current thread.
    * 
    * <p>
    * Default implementation is a no-op.
    * 
    * @return This object (for method chaining).
    * @throws Exception
    */
   public Microservice join() throws Exception {
      return this;
   }

   /**
    * Stop this application.
    * 
    * <p>
    * Default implementation simply calls {@link #onStop()}.
    * 
    * <p>
    * Overridden methods MUST call this method LAST so that the {@link #onStop()} method is called.
    * 
    * @return This object (for method chaining).
    */
   public Microservice stop() {
      onStop();
      return this;
   }

   /**
    * Kill the JVM by calling <code>System.exit(2);</code>.
    */
   public void kill() {
      // This triggers the shutdown hook.
      System.exit(2);
   }


   //--------------------------------------------------------------------------------
   // Lifecycle listener methods.
   // Subclasses can override these methods to run code on certain events.
   //--------------------------------------------------------------------------------

   /**
    * Called at the beginning of the {@link #start()} call.
    * 
    * <p>
    * Subclasses can override this method to hook into the lifecycle of this application.
    */
   protected void onStart() {}

   /**
    * Called at the end of the {@link #stop()} call.
    * 
    * <p>
    * Subclasses can override this method to hook into the lifecycle of this application.
    */
   protected void onStop() {}

   /**
    * Called if one or more changes occur in the config file.
    * 
    * <p>
    * Subclasses can override this method to listen for config file changes.
    * 
    * @param events The list of changes in the config file.
    */
   @Override /* ConfigEventListener */
   public void onConfigChange(List<ConfigEvent> events) {}

   
   //--------------------------------------------------------------------------------
   // Other methods.
   //--------------------------------------------------------------------------------
   
   /**
    * Returns the console commands associated with this microservice.
    * 
    * @return The console commands associated with this microservice as an unmodifiable map.
    */
   public final Map<String,ConsoleCommand> getConsoleCommands() {
      return consoleCommands;
   }
   
   /**
    * Constructs the list of available console commands.
    * 
    * <p>
    * By default, uses the <js>"Console/commands"</js> list in the config file.
    * Subclasses can override this method and modify or augment this list to provide their own console commands.
    * 
    * <p>
    * The order of the commands returned by this method is the order they will be listed 
    * 
    * @return A mutable list of console command instances.
    * @throws Exception
    */
   public List<ConsoleCommand> createConsoleCommands() throws Exception {
      ArrayList<ConsoleCommand> l = new ArrayList<>();
      for (String s : cf.getStringArray("Console/commands"))
         l.add((ConsoleCommand)Class.forName(s).newInstance());
      return l;
   }
   
   /**
    * Returns the console reader.
    * 
    * <p>
    * Subclasses can override this method to provide their own console input.
    * 
    * @return The console reader.  Never <jk>null</jk>.
    */
   public Scanner getConsoleReader() {
      return consoleReader;
   }
   
   /**
    * Returns the console writer.
    * 
    * <p>
    * Subclasses can override this method to provide their own console output.
    * 
    * @return The console writer.  Never <jk>null</jk>.
    */
   public PrintWriter getConsoleWriter() {
      return consoleWriter;
   }
   
   /**
    * Prints a localized message to the console writer.
    * 
    * <p>
    * Ignored if <js>"Console/enabled"</js> is <jk>false</jk>.
    * 
    * @param mb The message bundle containing the message.
    * @param messageKey The message key.
    * @param args Optional {@link MessageFormat}-style arguments.
    */
   protected void out(MessageBundle mb, String messageKey, Object...args) {
      if (consoleEnabled)
         getConsoleWriter().println(mb.getString(messageKey, args));
   }

   /**
    * Prints a localized message to STDERR.
    * 
    * <p>
    * Ignored if <js>"Console/enabled"</js> is <jk>false</jk>.
    * 
    * @param mb The message bundle containing the message.
    * @param messageKey The message key.
    * @param args Optional {@link MessageFormat}-style arguments.
    */
   protected void err(MessageBundle mb, String messageKey, Object...args) {
      if (consoleEnabled)
         System.err.println(mb.getString(messageKey, args));  // NOT DEBUG
   }
}