自定义标签步骤

• 定义处理类
• 编写tld文件
• 页面引用

自定义标签常量

示例

TagSupport：输出内容到页面

import java.io.IOException;
import java.io.PrintWriter;

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

public class WriterTag extends TagSupport {

    private static final long serialVersionUID = 1L;

    @Override
    public int doStartTag() throws JspException {
        try {
            JspWriter jspOut = pageContext.getOut();
            jspOut.print("JSP页面内置的out就是JspWriter      JspWriter缓冲了再输出    print参数各种类型<br/>");
            jspOut.write("JSP页面内置的out就是JspWriter   JspWriter缓冲了再输出    write参数String/char/int<br/><br/>");

//       jspOut.flush();//刷新缓冲区保证先输出

            PrintWriter servletOut = pageContext.getResponse().getWriter();
            servletOut.print("Servlet里常用的out   PrintWriter没有使用缓冲区所以先输出  print参数各种类型<br/>");
            servletOut.write("Servlet里常用的out   PrintWriter没有使用缓冲区所以先输出  write参数String/char/int<br/><br/>");
        } catch (IOException e) {
            e.printStackTrace();
        }
        return SKIP_BODY;
    }
}

TagSupport：转换日期

import java.text.SimpleDateFormat;
import java.util.Date;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.TagSupport;

public class DateFormat extends TagSupport {

    private static final long serialVersionUID = 1L;

    private String pattern;
    private String var;
    private Date date;    //可选 默认当前时间
    private String scope;  //可选 默认page作用域

    @Override
    public int doStartTag() throws JspException {
        if (date == null) {date = new Date();}

        SimpleDateFormat  sdf = new SimpleDateFormat(pattern);
        if (scope == null || "".equals(scope) || "page".equals(scope)) {
            pageContext.setAttribute(var, sdf.format(date),PageContext.PAGE_SCOPE);
        }else if ("request".equals(scope)) {
            pageContext.setAttribute(var, sdf.format(date),PageContext.REQUEST_SCOPE);
        }else if ("session".equals(scope)) {
            pageContext.setAttribute(var, sdf.format(date),PageContext.SESSION_SCOPE);
        }else if ("application".equals(scope)) {
            pageContext.setAttribute(var, sdf.format(date),PageContext.APPLICATION_SCOPE);
        }
        return SKIP_BODY;
    }

    //属性名随意 但是方法名必须与标签属性的名字有关系 保证能找到对应的方法
    public String getScope() {
        return scope;
    }
    public void setScope(String scope) {
        this.scope = scope;
    }
    public String getVar() {
        return var;
    }
    public void setVar(String var) {
        this.var = var;
    }
    public Date getDate() {
        return date;
    }
    public void setDate(Date date) {
        this.date = date;
    }
    public String getPattern() {
        return pattern;
    }
    public void setPattern(String pattern) {
        this.pattern = pattern;
    }
}

SimpleTagSupport

import java.io.IOException;
import java.util.Iterator;
import java.util.List;

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

public class SimpleTagIterator extends SimpleTagSupport {
    private List<?> items;
    private String var;
    private Iterator<?> iterator;
    @Override
    public void doTag() throws JspException, IOException {
        iterator = items.iterator();
        while (iterator.hasNext()) {
            getJspContext().setAttribute(var, iterator.next());
            getJspBody().invoke(null);
        }
    }

    public List<?> getItems() {
        return items;
    }
    public void setItems(List<?> items) {
        this.items = items;
    }
    public String getVar() {
        return var;
    }
    public void setVar(String var) {
        this.var = var;
    }
}

编写mytags.tld

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
        "http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
<taglib>
    <tlib-version>1.0</tlib-version>
    <jsp-version>1.2</jsp-version>
    <short-name>baozi</short-name>
    <tag>
        <name>writer</name>
        <tag-class>org.baozi.tag.WriterTag</tag-class>
        <body-content>empty</body-content>
    </tag>


    <tag>
        <name>format</name>
        <tag-class>org.baozi.tag.DateFormat</tag-class>
        <body-content>empty</body-content>
        <attribute>
            <name>pattern</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>var</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>date</name>
            <required>false</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>scope</name>
            <required>false</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>


    <tag>
        <name>iter</name>
        <tag-class>org.baozi.tag.IteratorTag</tag-class>
        <body-content>JSP</body-content>
        <attribute>
            <name>items</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>var</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>


    <tag>
        <name>simpleiter</name>
        <tag-class>org.baozi.tag.SimpleTagIterator</tag-class>
        <body-content>scriptless</body-content>
        <attribute>
            <name>items</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>var</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>
</taglib>

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
         xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
   http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

    <!-- 
    可以使用这种配置 将tag的tld配置文件映射到一个uri中
    jsp页面:uri="mytags"
    
    <jsp-config>
        <taglib>
            <taglib-uri>mytags</taglib-uri>
            <taglib-location>/WEB-INF/mytags.tld</taglib-location>
        </taglib>
    </jsp-config>
     -->

    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>

页面中引用

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="baozi" uri="/WEB-INF/mytags.tld" %>
<%
        String path = request.getContextPath();
        String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
        %>
        <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
    <base href="<%=basePath%>">
    <title>My JSP 'index.jsp' starting page</title>
</head>

<body>
    <%
    List<String> list = new ArrayList<String>();
    list.add("AA");
    list.add("BB");
    list.add("CC");
    pageContext.setAttribute("list", list);
    %>
    <baozi:simpleiter items="${list}" var="test">
        ${test}-
    </baozi:simpleiter>
</body>
</html>