JSTL自定义标签

两种实现方法

（1）创建一个标签处理器类实现sampleTag接口
public class HelloSimpleTag implements SimpleTag

HelloSimpleTag.java

package cn.stud.wlc.tag;

import java.io.IOException;

import javax.servlet.jsp.JspContext;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.JspFragment;
import javax.servlet.jsp.tagext.JspTag;
import javax.servlet.jsp.tagext.SimpleTag;

public class HelloSimpleTag implements SimpleTag {

//设置属性
private String value;
private String count;
private PageContext pagecontext;

//set方法是必须的 这些属性在tld文件里描述

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

    public void setCount(String count) {
        this.count = count;
    }

    public void doTag() throws JspException, IOException {
        // TODO Auto-generated method stub  
        //执行 标签体逻辑 实际应该编写到该方法中
        //可以后去PageContext的八个成员变量
        System.out.println("value:"+value+"count:"+count);
        pagecontext.getOut().print("hello word");

    }

    public JspTag getParent() {
        System.out.println("getParent");
        return null;
    }

    public void setJspBody(JspFragment arg0) {
        // TODO Auto-generated method stub
        System.out.println("setJspBody");
    }

    public void setJspContext(JspContext arg0) {
        // TODO Auto-generated method stub 
        //jsp页面的PageContext对象传进来
        //jsp引擎调用
        this.pagecontext = (PageContext) arg0;
        System.out.println("setJspContext");
    }

    public void setParent(JspTag arg0) {
        // TODO Auto-generated method stub
        System.out.println("setParent");
    }

}


（2）继承simpleTagSupport

package cn.stud.wlc.tag;

import java.io.IOException;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class MaxTag extends SimpleTagSupport {
private String num1;
private String num2;

public void setNum1(String num1) {
this.num1 = num1;
}

public void setNum2(String num2) {
this.num2 = num2;
}

//dotag之后的方法就不用挨个写了

public void doTag() throws JspException, IOException {
int a=0;
int b=0;

PageContext pageContext = (PageContext) getJspContext();
JspWriter out =pageContext.getOut();
try {
a=Integer.parseInt(num1);
b=Integer.parseInt(num2);
out.print(a>b?a:b);

} catch (Exception e) {
out.print("输入格式不正确");
}
}

}

在WEB-INF  lib下建立myTag.tld（标签库描述文件）的xml文件
<?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">

    <!-- 描述TLD文件 -->
    <description>there are custom tags of tag</description>

    <tlib-version>1.0</tlib-version>

    <!--建议在jsp页面中使用的标签前缀 -->
    <short-name>wlc</short-name>

    <!-- tld文件的ID -->
    <uri>http://www.wlc.com/myTag/core</uri>

    <!-- 描述自定义的HelloSimpleTag标签 -->
    <tag>

        <description>view ip of client</description>
        <!-- 标签的名 -->
        <name>Hello</name>
        <!-- 标签所在的全类名 -->
        <tag-class>cn.stud.wlc.tag.HelloSimpleTag</tag-class>
        <!-- 标签体的类型 -->
        <body-content>empty</body-content>
        <!-- 描述当前标签的属性值 -->
        <attribute>
            <name>value</name>
            <required>true</required>
            <!-- runtime expresSion value运行时表达式的值当前属性是否可以接受运行时表达式的值 -->
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>count</name>
            <required>false</required>
            <!-- runtime expresSion value运行时表达式的值当前属性是否可以接受运行时表达式的值 -->
            <rtexprvalue>false</rtexprvalue>
        </attribute>
    </tag>

</taglib>


在jsp中调用

<!-- 导入标签库文件(自定义) -->
<%@taglib uri="http://www.wlc.com/myTag/core" prefix="wlc" %>

  具体的使用

<wlc:Hello value="name" count ="10"/>

ctrl+shift+o去除多余的import