jsp自定义标签

为什么要学习

当我们遇到查询分页、下拉列表回填、复选框回填…，重复代码过多，代码冗余代码的可读性较差，不便于阅读修改等问题，我们就可以使用自定义标签解决这些问题。

标签语言特点

<开始标签 属性=“属性值”>标签体
空标签
< br/>< hr/>
<开始标签>
<开始标签/>

标签的类型

ui标签           专门用来展示内容--->select
控制标签        	做流程控制用的--->if/foreach
数据标签        	c:set将某一数据赋值给某变量

自定义标签的开发及使用步骤

先写一个.tld文件

注意：tld文件必须保存到WEB-INF目录或其子目录

<tag>
    <name>set</name>//标签名
    <tag-class>com.zhangsiwen.jsp.day02.SetTag</tag-class>//助手类
    <body-content>JSP</body-content>
    <attribute>
        <name>var</name>//属性名
        <required>true</required>//是否必填
        <rtexprvalue>false</rtexprvalue>//是否支持表达式
    </attribute>
     <attribute>
        <name>value</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>

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

 <%@taglib prefix="z" uri="/zhangsiwen" %>

在写一个标签助手类，继承BodyTagSupport

标签属性必须与助手类的属性对应、且要提供对应get/set方法

package com.zhangsiwen.jsp.day02;

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 {
		pageContext.setAttribute(var, value);
		return SKIP_BODY;
	}
}

标签生命周期图

SKIP_BODY 跳过主体
SKIP_PAGE 跳过页面的后续部分
EVAL_BODY_INCLUDE 计算标签主体内容并输出
EVAL_BODY_AGAIN 再计算主体一次
EVAL_PAGE 计算页面的后续部分

if/set/out标签的案例

tld文件内容

<?xml version="1.0" encoding="UTF-8" ?>

<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
    version="2.0">
    
  <description>JSTL 1.1 core library</description>
  <display-name>JSTL core</display-name>
  <tlib-version>1.1</tlib-version>
  <short-name>c</short-name>
  <uri>/zhangsiwen</uri>

	<tag>
    <name>set</name>
    <tag-class>com.zhangsiwen.jsp.day02.SetTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <name>var</name>
        <required>true</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
     <attribute>
        <name>value</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
  
  <tag>
    <name>out</name>
    <tag-class>com.zhangsiwen.jsp.day02.OutTag</tag-class>
    <body-content>JSP</body-content>
     <attribute>
        <name>value</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
 
 <tag>
    <name>if</name>
    <tag-class>com.zhangsiwen.jsp.day02.IfTag</tag-class>
    <body-content>JSP</body-content>
     <attribute>
        <name>test</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>

</taglib>

if标签助手类

package com.zhangsiwen.jsp.day02;

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

public class IfTag extends BodyTagSupport {
	
	private static final long serialVersionUID = 7889433543629128352L;
	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;
	}
}

set标签助手类

package com.zhangsiwen.jsp.day02;

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 {
		pageContext.setAttribute(var, value);
		return SKIP_BODY;
	}
}

out标签助手类

package com.zhangsiwen.jsp.day02;

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 {
		JspWriter out = pageContext.getOut();
		try {
			out.print(value);
		} catch (IOException e) {
			e.printStackTrace();
		}
		return SKIP_BODY;
	}
}

引用标签库

 <%@taglib prefix="z" uri="/zhangsiwen" %>

jsp文件内容

<z:set var="sex" value="gay"></z:set>
<z:out value="${sex }"></z:out>
<z:if test="true">gay</z:if>
<z:if test="false">伪娘</z:if>

运行结果