001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.juneau.commons.svl;
018
019/**
020 * Interface for the resolution of vars with a default value if the <c>resolve()</c> method returns <jk>null</jk>.
021 *
022 * <p>
023 * For example, to resolve the system property <js>"myProperty"</js> but resolve to <js>"not found"</js> if the
024 * property doesn't exist: <js>"$S{myProperty,not found}"</js>
025 *
026 * <p>
027 * Subclasses must implement the following method:
028 * <ul class='javatree'>
029 *    <li class='jm'>{@link #resolve(VarResolverSession, String)}
030 * </ul>
031 *
032 * <h5 class='section'>See Also:</h5><ul>
033 *    <li class='link'><a class="doclink" href="https://juneau.apache.org/docs/topics/MarshallSimpleVariableLanguage">Marshall Simple Variable Language</a>
034 * </ul>
035 */
036public abstract class DefaultingVar extends SimpleVar {
037
038   /**
039    * Constructor.
040    *
041    * @param name The name of this variable.  Must not be <jk>null</jk>.
042    */
043   protected DefaultingVar(String name) {
044      super(name);
045   }
046
047   @Override /* Overridden from Var */
048   public String doResolve(VarResolverSession session, String s) throws Exception {
049      var i = s.indexOf(',');
050      if (i == -1)
051         return resolve(session, s.trim());
052      var s1 = s.substring(0, i);
053      var s2 = s.length() == i ? null : s.substring(i + 1);
054      var v = resolve(session, s1);
055      if (v == null)
056         v = s2;
057      return v;
058   }
059}