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    */
017    
018     
019    package javax.servlet.jsp.tagext;
020    
021    /**
022     * Optional class provided by the tag library author to describe additional
023     * translation-time information not described in the TLD.
024     * The TagExtraInfo class is mentioned in the Tag Library Descriptor file (TLD).
025     *
026     * <p>
027     * This class can be used:
028     * <ul>
029     * <li> to indicate that the tag defines scripting variables
030     * <li> to perform translation-time validation of the tag attributes.
031     * </ul>
032     *
033     * <p>
034     * It is the responsibility of the JSP translator that the initial value
035     * to be returned by calls to getTagInfo() corresponds to a TagInfo
036     * object for the tag being translated. If an explicit call to
037     * setTagInfo() is done, then the object passed will be returned in
038     * subsequent calls to getTagInfo().
039     * 
040     * <p>
041     * The only way to affect the value returned by getTagInfo()
042     * is through a setTagInfo() call, and thus, TagExtraInfo.setTagInfo() is
043     * to be called by the JSP translator, with a TagInfo object that
044     * corresponds to the tag being translated. The call should happen before
045     * any invocation on validate() and before any invocation on
046     * getVariableInfo().
047     *
048     * <p>
049     * <tt>NOTE:</tt> It is a (translation time) error for a tag definition
050     * in a TLD with one or more variable subelements to have an associated
051     * TagExtraInfo implementation that returns a VariableInfo array with
052     * one or more elements from a call to getVariableInfo().
053     */
054    
055    public abstract class TagExtraInfo {
056    
057        /**
058         * Sole constructor. (For invocation by subclass constructors, 
059         * typically implicit.)
060         */
061        public TagExtraInfo() {
062        }
063        
064        /**
065         * information on scripting variables defined by the tag associated with
066         * this TagExtraInfo instance.
067         * Request-time attributes are indicated as such in the TagData parameter.
068         *
069         * @param data The TagData instance.
070         * @return An array of VariableInfo data, or null or a zero length array
071         *         if no scripting variables are to be defined.
072         */
073        public VariableInfo[] getVariableInfo(TagData data) {
074            return ZERO_VARIABLE_INFO;
075        }
076    
077        /**
078         * Translation-time validation of the attributes. 
079         * Request-time attributes are indicated as such in the TagData parameter.
080         * Note that the preferred way to do validation is with the validate()
081         * method, since it can return more detailed information.
082         *
083         * @param data The TagData instance.
084         * @return Whether this tag instance is valid.
085         * @see TagExtraInfo#validate
086         */
087    
088        public boolean isValid(TagData data) {
089            return true;
090        }
091    
092        /**
093         * Translation-time validation of the attributes.
094         * Request-time attributes are indicated as such in the TagData parameter.
095         * Because of the higher quality validation messages possible, 
096         * this is the preferred way to do validation (although isValid() 
097         * still works).  
098         * 
099         * <p>JSP 2.0 and higher containers call validate() instead of isValid().
100         * The default implementation of this method is to call isValid().  If 
101         * isValid() returns false, a generic ValidationMessage[] is returned
102         * indicating isValid() returned false.</p>
103         *
104         * @param data The TagData instance.
105         * @return A null object, or zero length array if no errors, an 
106         *     array of ValidationMessages otherwise.
107         * @since 2.0
108         */
109        public ValidationMessage[] validate( TagData data ) {
110            ValidationMessage[] result = null;
111    
112            if( !isValid( data ) ) {
113                result = new ValidationMessage[] {
114                    new ValidationMessage( data.getId(), "isValid() == false" ) };
115            }
116    
117            return result;
118        }
119    
120        /**
121         * Set the TagInfo for this class.
122         *
123         * @param tagInfo The TagInfo this instance is extending
124         */
125        public final void setTagInfo(TagInfo tagInfo) {
126            this.tagInfo = tagInfo;
127        }
128    
129        /**
130         * Get the TagInfo for this class.
131         *
132         * @return the taginfo instance this instance is extending
133         */
134        public final TagInfo getTagInfo() {
135            return tagInfo;
136        }
137        
138        // private data
139        private TagInfo tagInfo;
140    
141        // zero length VariableInfo array
142        private static final VariableInfo[] ZERO_VARIABLE_INFO = { };
143    }
144