j-customtags-6-4.html

这是用java编写自定义标签的一些源码和笔记

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<code>doAfterBody()</code> 通过在没有可迭代的项时返回 <code>SKIP_BODY</code> 实现了迭代。如果还有项，那么它就返回 <code>EVAL_BODY_AGAIN</code>。只要 <code>doAfterBody()</code> 返回 <code>EVAL_BODY_AGAIN</code>，容器就会继续对正文进行判断，如下所示：

 

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<code style="font-family: Courier New, Courier, monospace; font-size: 12">
  

 public int doAfterBody() throws JspException {

 

     /** Process body */

     ...

 

     /** Write the processed  buffer to the previous out */

     ...    

 

     if (iter.hasNext() == false) {

         return SKIP_BODY;

     } else {

 

         map = (Map) iter.next();

         return EVAL_BODY_AGAIN;

     }

 }

 

 </code>
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<p>
  

 

 
<code>doAfterBody()</code> 方法用 <code>getBodyContent()</code> 抓取正文，然后用正文内容的 <code>getString()</code> 方法得到字符串形式的内容。

 下一步它清除正文内容缓冲区，用 <code>StringTokenizer</code> 查找以 <code>${</code> 开始的字符串。

 它还创建一个名为 <code>buffer</code> 的 <code>StringBuffer</code>。 


 当它迭代 tokenizer 中的字符串时，将它们附加到缓冲区中。</p>
<p>

 如果 tokenizer 中的字符串以 <code>${</code>, <code>doAfterBody()</code> 开始，那么它就从字符串中提取键，并用这个键在 map 中查找值。它调用值对象的 <code>toString()</code> 方法将 map 中的值转换为字符串，并将结果附加到缓冲区中。下面的清单展示了这个过程是如何进行的。

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<code style="font-family: Courier New, Courier, monospace; font-size: 12">
  

 /** Process body */

 

 /* Get and clear the body */

 BodyContent body = this.getBodyContent();

 String content = body.getString();

 body.clearBody();

 

 /* Process the body with a String tokenizer */

 StringTokenizer token = new StringTokenizer(content);

 /* Create an output buffer of the processed body */

 StringBuffer buffer = new StringBuffer(content.length() * 2);

 

 /* Iterate over the strings from the tokenizer 

    and put them into the output buffer. */

 while (token.hasMoreTokens()) {

     String tok = token.nextToken();

     

     /* See if the String contains the special substring "${" */

     if (tok.startsWith("${")) {

     

         /* Parse the key out of the string */

         String key = tok.substring(2, tok.length() - 1);

 

         /* Use the key to look up the object in the map */

         Object value = (String) map.get(key);

         String svalue = tok;

         

         /* If the value is not null, 

            get the value's string representation */

         if (value != null) {

             svalue = value.toString();

         }

         

         /* Add the string representation of the value 

            to the output buffer */

         buffer.append(svalue + " ");

     } else {

         buffer.append(tok + " ");

     }

 }

 

 </code>
</pre>
<p>
  

 

 
<code>doAfterBody()</code> 方法在构建了输出缓冲区后，就将它输出到前面的 <code>out</code> 中，如下所示：

 

 </p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
  

     try {

         this.getPreviousOut().print(buffer.toString());

     } catch (IOException e) {

         throw new JspException(e);

     }

 

 </code>
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<p>
  

 

 这样，每一次迭代都处理正文并将它输出到前面的 <code>out</code> 中。如果前面的 <code>out</code> 是根 <code>JspWriter</code>，那么它就会写到浏览器中。

 


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