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.commons.el;
018
019import java.lang.reflect.Array;
020import java.util.Collection;
021import java.util.Map;
022
023import javax.servlet.jsp.el.ELException;
024
025/**
026 *
027 * <p>The implementation of the empty operator
028 * 
029 * @author Nathan Abramson - Art Technology Group
030 * @version $Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author: bayard $
031 **/
032
033public class EmptyOperator
034  extends UnaryOperator
035{
036  //-------------------------------------
037  // Singleton
038  //-------------------------------------
039
040  public static final EmptyOperator SINGLETON =
041    new EmptyOperator ();
042
043  //-------------------------------------
044  /**
045   *
046   * Constructor
047   **/
048  public EmptyOperator ()
049  {
050  }
051
052  //-------------------------------------
053  // Expression methods
054  //-------------------------------------
055  /**
056   *
057   * Returns the symbol representing the operator
058   **/
059  public String getOperatorSymbol ()
060  {
061    return "empty";
062  }
063
064  //-------------------------------------
065  /**
066   *
067   * Applies the operator to the given value
068   **/
069  public Object apply (Object pValue)
070    throws ELException
071  {
072    // See if the value is null
073    if (pValue == null) {
074      return PrimitiveObjects.getBoolean (true);
075    }
076
077    // See if the value is a zero-length String
078    else if ("".equals (pValue)) {
079      return PrimitiveObjects.getBoolean (true);
080    }
081
082    // See if the value is a zero-length array
083    else if (pValue.getClass ().isArray () &&
084             Array.getLength (pValue) == 0) {
085      return PrimitiveObjects.getBoolean (true);
086    }
087
088    // See if the value is an empty Map
089    else if (pValue instanceof Map &&
090             ((Map) pValue).isEmpty ()) {
091      return PrimitiveObjects.getBoolean (true);
092    }
093
094    // See if the value is an empty Collection
095    else if (pValue instanceof Collection &&
096             ((Collection) pValue).isEmpty ()) {
097      return PrimitiveObjects.getBoolean (true);
098    }
099
100    // Otherwise, not empty
101    else {
102      return PrimitiveObjects.getBoolean (false);
103    }
104  }
105
106  //-------------------------------------
107}