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    1   /*
    2    * $Id: EmptyTag.java 471754 2006-11-06 14:55:09Z husted $
    3    *
    4    * Licensed to the Apache Software Foundation (ASF) under one
    5    * or more contributor license agreements.  See the NOTICE file
    6    * distributed with this work for additional information
    7    * regarding copyright ownership.  The ASF licenses this file
    8    * to you under the Apache License, Version 2.0 (the
    9    * "License"); you may not use this file except in compliance
    10   * with the License.  You may obtain a copy of the License at
    11   *
    12   *  http://www.apache.org/licenses/LICENSE-2.0
    13   *
    14   * Unless required by applicable law or agreed to in writing,
    15   * software distributed under the License is distributed on an
    16   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    17   * KIND, either express or implied.  See the License for the
    18   * specific language governing permissions and limitations
    19   * under the License.
    20   */
    21  package org.apache.struts.taglib.logic;
    22
    23  import org.apache.struts.taglib.TagUtils;
    24
    25  import javax.servlet.jsp.JspException;
    26
    27  import java.lang.reflect.Array;
    28
    29  import java.util.Collection;
    30  import java.util.Map;
    31
    32  /**
    33   * Evalute the nested body content of this tag if the specified value is empty
    34   * for this request.
    35   *
    36   * @version $Rev: 471754 $ $Date: 2004-10-16 12:38:42 -0400 (Sat, 16 Oct 2004)
    37   *          $
    38   * @since Struts 1.1
    39   */
    40  public class EmptyTag extends ConditionalTagBase {
    41      // ------------------------------------------------------ Protected Methods
    42
    43      /**
    44       * Evaluate the condition that is being tested by this particular tag, and
    45       * return <code>true</code> if the nested body content of this tag should
    46       * be evaluated, or <code>false</code> if it should be skipped. This
    47       * method must be implemented by concrete subclasses.
    48       *
    49       * @throws JspException if a JSP exception occurs
    50       */
    51      protected boolean condition()
    52          throws JspException {
    53          return (condition(true));
    54      }
    55
    56      /**
    57       * Evaluate the condition that is being tested by this particular tag, and
    58       * return <code>true</code> if the nested body content of this tag should
    59       * be evaluated, or <code>false</code> if it should be skipped. This
    60       * method must be implemented by concrete subclasses.
    61       *
    62       * @param desired Desired outcome for a true result
    63       * @throws JspException if a JSP exception occurs
    64       */
    65      protected boolean condition(boolean desired)
    66          throws JspException {
    67          if (this.name == null) {
    68              JspException e =
    69                  new JspException(messages.getMessage("empty.noNameAttribute"));
    70
    71              TagUtils.getInstance().saveException(pageContext, e);
    72              throw e;
    73          }
    74
    75          Object value = null;
    76
    77          if (this.property == null) {
    78              value = TagUtils.getInstance().lookup(pageContext, name, scope);
    79          } else {
    80              value =
    81                  TagUtils.getInstance().lookup(pageContext, name, property, scope);
    82          }
    83
    84          boolean empty = true;
    85
    86          if (value == null) {
    87              empty = true;
    88          } else if (value instanceof String) {
    89              String strValue = (String) value;
    90
    91              empty = (strValue.length() < 1);
    92          } else if (value instanceof Collection) {
    93              Collection collValue = (Collection) value;
    94
    95              empty = collValue.isEmpty();
    96          } else if (value instanceof Map) {
    97              Map mapValue = (Map) value;
    98
    99              empty = mapValue.isEmpty();
    100         } else if (value.getClass().isArray()) {
    101             empty = Array.getLength(value) == 0;
    102         } else {
    103             empty = false;
    104         }
    105
    106         return (empty == desired);
    107     }
    108 }