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;
    }

}