jsp自定义标签

一，为什么要学习jsp自定义标签？

         在JAVA项目开发中，JSP自定义标签，可以使前端的展现简洁与方便

二，自定义标签的开发及使用步骤

      1.创建一个标签助手类(继承BodyTagSupport)

      2.创建标签库描述文件(tld)，添加自定义标签的配置

      3.在JSP通过taglib指令导入标签库，并通过指定后缀访问自定义标签

      4.架包

      5.在jsp页面头部通过taglib标签导入tld文件

三，jsp自定义生命周期图

五，代码

1.set标签

<tag>
    <name>set</name>
    <tag-class>com.leiliang.jsp.SetTag</tag-class>
    <body-content>JSP</body-content>
  	<attribute>
  		<name>var</name>
  		<required>true</required>
  		<rtexprvalue>false</rtexprvalue>
  	</attribute>
  	<attribute>
  		<name>value</name>
  		<required>false</required>
  		<rtexprvalue>true</rtexprvalue>
  	</attribute>
  </tag>

2.setTag助手类

package com.leiliang.jsp

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

public class SetTag extends BodyTagSupport{
	private static final long serialVersionUID = 1L;
	private String var;
	private Object value;
	public String getVar() {
		return var;
	}
	public void setVar(String var) {
		this.var = var;
	}
	public Object getValue() {
		return value;
	}
	public void setValue(Object value) {
		this.value = value;
	}
	
	@Override
	public int doStartTag() throws JspException {
		// TODO Auto-generated method stub
		pageContext.setAttribute(var, value);
		return SKIP_BODY;
	}
}

引用显示(set无输出)

<t:set var="sex" value="男"></t:set>

3.out标签

 <tag>
    <name>out</name>
    <tag-class>com.leiliang.jsp.OutTag</tag-class>
    <body-content>JSP</body-content>
  	<attribute>
  		<name>value</name>
  		<required>true</required>
  		<rtexprvalue>true</rtexprvalue>
  	</attribute>
  </tag>
<tag-class>com.leiliang.jsp.OutTag</tag-class>

4.tTag助手类

package com.leiliang.jsp;

import java.io.IOException;

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

public class OutTag extends BodyTagSupport{
	
	private static final long serialVersionUID = 1L;
	private Object value;
	
	public Object getValue() {
		return value;
	}

	public void setValue(Object value) {
		this.value = value;
	}

	@Override
	public int doStartTag() throws JspException {
		// TODO Auto-generated method stub
		JspWriter out = pageContext.getOut();
		try {
			out.print(value);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return super.doStartTag();
	}
	
}

引用显示(只做输出)

//取的之前的set值，用的是el表达式赋值
<t:out value="${sex }"></t:out>

5.if标签

<tag>
    <name>if</name>
    <tag-class>com.leiliang.jsp.IfTag</tag-class>
    <body-content>JSP</body-content>
  	<attribute>
  		<name>test</name>
  		<required>true</required>
  		<rtexprvalue>true</rtexprvalue>
  	</attribute>
  </tag>

IfTag助手类

package com.leiliang.jsp;

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

public class IfTag extends BodyTagSupport{
	
	private static final long serialVersionUID = 1L;
	private boolean test;

	public boolean isTest() {
		return test;
	}

	public void setTest(boolean test) {
		this.test = test;
	}

	@Override
	public int doStartTag() throws JspException {
		// TODO Auto-generated method stub
		
		return test ? EVAL_BODY_INCLUDE : SKIP_BODY;
	}
}

引用显示(进行判断)

	<t:if test="true">男</t:if>
	<t:if test="false">女</t:if>