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

 package cn.itcast.web.tag;

 import javax.servlet.jsp.JspException;
 import javax.servlet.jsp.tagext.IterationTag;
 import javax.servlet.jsp.tagext.Tag;
 import javax.servlet.jsp.tagext.TagSupport;

 //控制标签体重复执行
 public class TagDemo3 extends TagSupport {

     int x = 5;

     @Override
     public int doStartTag() throws JspException {
         return Tag.EVAL_BODY_INCLUDE;
     }

     @Override
     public int doAfterBody() throws JspException {
         x--;
         if (x > 0) {
             return IterationTag.EVAL_BODY_AGAIN;
         } else {
             return IterationTag.SKIP_BODY;
         }
     }

 }

4.修改JSP页面内容输出

 package cn.itcast.web.tag;

 import java.io.IOException;

 import javax.servlet.jsp.JspException;
 import javax.servlet.jsp.tagext.BodyTagSupport;
 import javax.servlet.jsp.tagext.Tag;

 public class TagDemo4 extends BodyTagSupport {

     @Override
     public int doEndTag() throws JspException {
         // TODO Auto-generated method stub

         String content = this.getBodyContent().getString();

         String result = content.toUpperCase();

         try {
             this.pageContext.getOut().write(result);
         } catch (IOException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }

         return Tag.EVAL_PAGE;
     }

     @Override
     public int doStartTag() throws JspException {
         // TODO Auto-generated method stub
         return BodyTagSupport.EVAL_BODY_BUFFERED;
     }

 }