CacheTag


1   /*
2    * Copyright 1999,2004 The Apache Software Foundation.
3    * 
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    * 
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    * 
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */ 
16  
17  package org.apache.taglibs.cache;
18  
19  import javax.servlet.jsp.*;
20  import javax.servlet.jsp.tagext.*;
21  import org.apache.taglibs.standard.lang.support.ExpressionEvaluatorManager;
22  
23  /**
24   * <p>Caches a fragment of a JSP page.</p>
25   *
26   * @author Shawn Bayern
27   */
28  
29  public class CacheTag extends BodyTagSupport {
30  
31      //*********************************************************************
32      // Private state
33  
34      private String   nameExpr;                // tag attribute
35      private String   keyExpr;             // tag attribute
36  
37      private int scope;                  // parsed tag attribute
38      private String   name, key;               // parsed tag attribute
39  
40      private LRUCache cache;             // cache
41      private String   cached;              // value from cache
42  
43      //*********************************************************************
44      // Tag logic
45  
46      public int doStartTag() throws JspException {
47        evaluateExpressions();
48        cache = CacheUtil.getCache(scope, name, pageContext);
49        cached = cache.get(key);
50        if (cached != null)
51          return SKIP_BODY;
52        else
53          return EVAL_BODY_BUFFERED;
54      }
55  
56      public int doEndTag() throws JspException {
57        try {
58      String   s = cached;
59          if (s == null) {
60            if (bodyContent == null || bodyContent.getString() == null)
61          s = "";
62            else
63              s = bodyContent.getString().trim();
64            cache.put(key, s);
65          }
66          pageContext.getOut().write(s);
67        } catch (java.io.IOException   ex) {
68          throw new JspException(ex);
69        }
70        return EVAL_PAGE;
71      }
72  
73      //*********************************************************************
74      // Attribute accessors
75  
76      public void setScope(String   scope) {
77        if (scope.equalsIgnoreCase("page"))
78      this.scope = PageContext.PAGE_SCOPE;
79        else if (scope.equalsIgnoreCase("request"))
80          this.scope = PageContext.REQUEST_SCOPE;
81        else if (scope.equalsIgnoreCase("session"))
82          this.scope = PageContext.SESSION_SCOPE;
83        else if (scope.equalsIgnoreCase("application"))
84          this.scope = PageContext.APPLICATION_SCOPE;
85        else
86          throw new IllegalArgumentException  ("invalid scope");
87      }
88  
89      public void setName(String   nameExpr) {
90        this.nameExpr = nameExpr;
91      }
92  
93      public void setKey(String   keyExpr) {
94        this.keyExpr = keyExpr;
95      }
96  
97  
98      //*********************************************************************
99      // Constructor and initialization
100 
101     public CacheTag() {
102       super();
103       init();
104     }
105 
106     private void init() {
107       scope = PageContext.APPLICATION_SCOPE;
108       name = nameExpr = "";
109       key = keyExpr = "";
110     }
111     
112 
113     //*********************************************************************
114     // Private utility methods
115 
116     private void evaluateExpressions() throws JspException {
117       name = (String  ) ExpressionEvaluatorManager.evaluate(
118         "name",
119         nameExpr,
120         String  .class,
121         this,
122         pageContext);
123       key = (String  ) ExpressionEvaluatorManager.evaluate(
124         "key",
125         keyExpr,
126         String  .class,
127         this,
128         pageContext);
129     }
130 
131 }
132
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