JSP 传统标签extends TagSupport

1.控制JSP页面某一部分内容是否执行

public int doStartTag()

返回EVAL_BODY_INCLUDE，执行

返回SKIP_BODY，不执行

2.控制整个JSP页面是否执行

public int doEndTag()

返回EVAL_PAGE，执行

返回SKIP_PAGE，不执行

3.控制JSP页面内容重复执行

 1 package cn.itcast.web.tag;
 2 
 3 import javax.servlet.jsp.JspException;
 4 import javax.servlet.jsp.tagext.IterationTag;
 5 import javax.servlet.jsp.tagext.Tag;
 6 import javax.servlet.jsp.tagext.TagSupport;
 7 
 8 //控制标签体重复执行
 9 public class TagDemo3 extends TagSupport {
10 
11     int x = 5;
12 
13     @Override
14     public int doStartTag() throws JspException {
15         return Tag.EVAL_BODY_INCLUDE;
16     }
17 
18     @Override
19     public int doAfterBody() throws JspException {
20         x--;
21         if (x > 0) {
22             return IterationTag.EVAL_BODY_AGAIN;
23         } else {
24             return IterationTag.SKIP_BODY;
25         }
26     }
27 
28 }

4.修改JSP页面内容输出

 1 package cn.itcast.web.tag;
 2 
 3 import java.io.IOException;
 4 
 5 import javax.servlet.jsp.JspException;
 6 import javax.servlet.jsp.tagext.BodyTagSupport;
 7 import javax.servlet.jsp.tagext.Tag;
 8 
 9 public class TagDemo4 extends BodyTagSupport {
10 
11     @Override
12     public int doEndTag() throws JspException {
13         // TODO Auto-generated method stub
14 
15         String content = this.getBodyContent().getString();
16 
17         String result = content.toUpperCase();
18 
19         try {
20             this.pageContext.getOut().write(result);
21         } catch (IOException e) {
22             // TODO Auto-generated catch block
23             e.printStackTrace();
24         }
25 
26         return Tag.EVAL_PAGE;
27     }
28 
29     @Override
30     public int doStartTag() throws JspException {
31         // TODO Auto-generated method stub
32         return BodyTagSupport.EVAL_BODY_BUFFERED;
33     }
34 
35 }