[Java] JSP笔记 - 自定义标签

Posted 2020-08-03 爱音乐的孩子是小白

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自定义标签的创建步骤：

自定义标签的四大功能：

自定义标签的类结构：

在 1.0 中呢，可以将 <body-content> 的值设置为 JSP， 2.0中则不允许在自定义标签体中出现jsp代码。

接下来呢，我直接贴一些Demo代码：

tagdatetag.tld (标签声明 XML，将之方于 WEB-INF 目录中)

<?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>A tag library exercising SimpleTag handlers.</description>
    <tlib-version>1.0</tlib-version>
    <short-name>SimpleTagLibrary</short-name>
    <!-- 标签URI，用于在jsp中指定uri -->
    <uri>/date-tag</uri>
    
    <tag>
        <description>Outputs Date String</description>
        <name>simple</name>
        <tag-class>com.demo.TagDate</tag-class>
        <body-content>empty</body-content>
        <attribute>
            <name>format</name>
            <required>false</required> <!-- 属性是否是必须的 -->
            <rtexprvalue>true</rtexprvalue> <!-- 让属性在运行时可以写入 -->
        </attribute>
    </tag>
    
    <tag>
        <description>Outputs Date String</description>
        <name>simple2</name>
        <tag-class>com.demo.TagDate2</tag-class>
        <body-content>empty</body-content>
        <attribute>
            <name>format</name>
            <required>false</required> <!-- 属性是否是必须的 -->
            <rtexprvalue>true</rtexprvalue> <!-- 让属性在运行时可以写入 -->
        </attribute>
    </tag>
    
    <tag>
        <name>displayOrSkipBody</name>
        <tag-class>com.demo.DisplayOrSkipBody</tag-class>
        <body-content>scriptless</body-content>
    </tag> 
    
    <tag>
        <name>skipPageOrEvalPage</name>
        <tag-class>com.demo.SkipPageOrEvalPage</tag-class>
        <body-content>empty</body-content>
    </tag>
    
    <tag>
        <name>interationTagDemo</name>
        <tag-class>com.demo.InterationTagDemo</tag-class>
        <body-content>scriptless</body-content>
        <attribute>
            <name>name</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>items</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>
    
    <tag>
        <name>modifyBodyContent</name>
        <tag-class>com.demo.ModifyBodyContent</tag-class>
        <body-content>scriptless</body-content>
    </tag>
    
    <tag>
        <name>if</name>
        <tag-class>com.demo.IfTag</tag-class>
        <body-content>scriptless</body-content>
        <attribute>
            <name>test</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>
    
    <!-- 标签组 -->
    <tag>
        <name>choose</name>
        <tag-class>com.demo.ChooseTag</tag-class>
        <body-content>scriptless</body-content>
    </tag>
    
    <tag>
        <name>when</name>
        <tag-class>com.demo.WhenTag</tag-class>
        <body-content>scriptless</body-content>
        <attribute>
            <name>test</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>
    
    <tag>
        <name>other</name>
        <tag-class>com.demo.OtherWiseTag</tag-class>
        <body-content>scriptless</body-content>
    </tag>
    
</taglib>

index.jsp (使用方法）

<%@ page language="java" contentType="text/html; charset=UTF-8" %>
<%@ taglib prefix="date" uri="/date-tag" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

<%pageContext.setAttribute("name", request.getParameter("name")); %>
<%pageContext.setAttribute("score", request.getParameter("score")); %>

Hello. 今天是
<date:simple format="yyyy年MM月dd日 HH:mm:ss" /><br>
<date:simple/><br>
<date:simple2/><br>
<date:simple2 format="yyyy/MM/dd HH:mm:ss" /><br>

<date:displayOrSkipBody>
    <h2>中国最大的免费在线培训平台</h2>
</date:displayOrSkipBody>


<!-- 条件判断标签 -->
<date:if test="${name==\'imooc\'}">
慕课网是中国最大的IT技能免费学习平台<br>
</date:if>
<date:if test="${name!=\'imooc\'}">
小伙伴们快点加入慕课网一起学习吧。www.imooc.com<br>
</date:if>

<%
    pageContext.setAttribute("nbastar", new String[]{"jordan", "kobe", "t-mac"});
%>
<!-- 循环遍列数组 -->
<date:interationTagDemo items="${nbastar}" name="name">${name}<br></date:interationTagDemo>

<!-- 修改标签体中的内容 -->
<date:modifyBodyContent>虽然我出现在这里，但是我不会显示</date:modifyBodyContent>

<!-- 标签组 -->
<date:choose>
    <date:when test="${score>90}">非常优秀<br></date:when>
    <date:other>加油吧少年<br></date:other>
</date:choose>

<br>
<a href="index2.jsp">链接到index2.jsp</a><br>
<a href="index.jsp?score=98">非常优秀</a><br>
<a href="index.jsp?name=imooc">Name为imooc</a><br>
</body>
</html>

部分实现代码：

package com.demo;

import java.io.IOException;

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

public class ChooseTag extends SimpleTagSupport {
    private boolean flag;

    public boolean isFlag() {
        return flag;
    }

    public void setFlag(boolean flag) {
        this.flag = flag;
    }
    
    @Override
    public void doTag() throws JspException, IOException {
        getJspBody().invoke(null); // 输出标签体的内容
    }
}

package com.demo;

import java.io.IOException;

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

public class WhenTag extends SimpleTagSupport {
    private boolean test;
    
    public void setTest(boolean test) {
        this.test = test;
    }
    
    @Override
    public void doTag() throws JspException, IOException {
        if (test) {
            getJspBody().invoke(null);
            ChooseTag choose = (ChooseTag) getParent();
            choose.setFlag(true); // 设置父标签的标识为true
        }
    }
}

package com.demo;

import java.io.IOException;

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

public class OtherWiseTag extends SimpleTagSupport {
    
    @Override
    public void doTag() throws JspException, IOException {
        ChooseTag choose = (ChooseTag) getParent();
        if (!choose.isFlag()) // 如果父标签的标识为true，表示WhenTag已被执行。那么这里就再执行了
            getJspBody().invoke(null);
    }
}

package com.demo;

import java.io.IOException;
import java.text.SimpleDateFormat;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;

/** 自定义 Jsp 标签  */
public class TagDate extends TagSupport {
    private static final long serialVersionUID = 1L;
    
    private String format;

    public TagDate() {}

    public String getFormat() {
        return format;
    }

    public void setFormat(String format) {
        this.format = format;
    }

    @Override
    public int doStartTag() throws JspException {
        if (format == null || format.length() == 0)
            format = "yyyy-MM-dd HH:mm:ss";
        SimpleDateFormat sdf = new SimpleDateFormat(format);
        try {
            pageContext.getOut().print(sdf.format(System.currentTimeMillis()));
        } catch (IOException e) {
            e.printStackTrace();
        }
        return super.doStartTag();
    }
}

package com.demo;

import java.io.IOException;
import java.text.SimpleDateFormat;

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

/** 自定义 Jsp 标签  */
public class TagDate2 extends SimpleTagSupport {
    private String format;
    
    public String getFormat() {
        return format;
    }

    public void setFormat(String format) {
        this.format = format;
    }
    
    @Override
    public void doTag() throws JspException, IOException {
        if (format == null || format.length() == 0)
            format = "yyyy-MM-dd HH:mm:ss";
        SimpleDateFormat sdf = new SimpleDateFormat(format);
        try {
            getJspContext().getOut().print(sdf.format(System.currentTimeMillis()));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }    
}

package com.demo;

import java.io.IOException;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.SkipPageException;
import javax.servlet.jsp.tagext.SimpleTagSupport;

/**
 * @author Administrator
 *
 */
public class SkipPageOrEvalPage extends SimpleTagSupport {

    @Override
    public void doTag() throws JspException, IOException {
        PageContext context = (PageContext) getJspContext();
        HttpServletRequest req = (HttpServletRequest) context.getRequest();
        String referer = req.getHeader("Referer");
        // 如果来源(referer)为空，则代表是在浏览器中直接输入地址访问的。不继续执行
        if (referer == null || referer.length() == 0) 
            throw new SkipPageException();
    }
}

完整源码下载：

链接: http://pan.baidu.com/s/1nu851u5 密码: 456e

【感谢】

慕课网， Eleven_Lee JAVA开发工程师

http://www.imooc.com/learn/480

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