public class ShowCurrentTimeTag extends SimpleTagSupport {    @Override    public void doTag() throws JspException, IOException {        // TODO Auto-generated method stub        Date now=new Date();        DateFormat dFormat=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");        String str=dFormat.format(now);        PageContext pc=(PageContext) getJspContext();        pc.getOut().write(str);    }}

在WEB-INF目录下，建立一个扩展名为tld（Tag Libary Definition）的xml文件。
注：tld如果在WEB-INF或者在jar包的META-INF目录下，都能自动找到。

<!--myTag.tld--><?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">    <tlib-version>1.0</tlib-version>    <short-name>myTag</short-name>    <uri>http://www.cai.com/myTag</uri>    <tag>        <description>show current time</description>        <name>showTime</name>        <tag-class>com.cai.tag.ShowCurrentTimeTag</tag-class>        <!-- 开始和结束标签之间的内容类型 -->        <body-content>empty</body-content>    </tag></taglib>

如果tld不在WEB-INF或jar的META-INF目录下，修改web.xml，对tld和url进行一个映射

<!--web.xml--><?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">  <jsp-config>      <taglib>          <taglib-uri>http://www.cai.com/myTag</taglib-uri>          <taglib-location>/tld/myTag.tld</taglib-location>      </taglib>  </jsp-config></web-app>

在JSP中使用tag

<%@ page language="java" contentType="text/html; charset=UTF-8"    pageEncoding="UTF-8"%><%@taglib prefix="myTag" uri="http://www.cai.com/myTag"  %><!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>    <myTag:showTime/></body></html>

这里写图片描述

带属性的标签

需要为tag元素添加attribute元素
1. name：设置属性名，即变量名
2. required：设置属性是否为必须属性
3. fragment：该属性是否zhichiJSP脚本，表达式等动态内容，子元素的值是true或false

//Person.javapublic class Person extends SimpleTagSupport {    private String userName;    private String password;    public String getUserName() {        return userName;    }    public void setUserName(String userName) {        this.userName = userName;    }    public String getPassword() {        return password;    }    public void setPassword(String password) {        this.password = password;    }    @Override    public void doTag() throws JspException, IOException {        Writer out=getJspContext().getOut();        out.write("用户名："+userName+"<br />");        out.write("密码："+password);    }}

<!--myTag.tld--><tag>    <description>show current time</description>    <name>ShowInfo</name>    <tag-class>com.cai.tag.Person</tag-class>    <!-- 开始和结束标签之间的内容类型 -->    <body-content>empty</body-content>    <attribute>        <name>userName</name>        <required>true</required>        <fragment>true</fragment>    </attribute>    <attribute>        <name>password</name>        <required>true</required>        <fragment>true</fragment>    </attribute></tag>

<myTag:ShowInfo password="fdsfsdf" userName="gsdgsdg"/>

这里写图片描述

带标签体的标签

//IteratorTag.javapublic class IteratorTag extends SimpleTagSupport {    private String collection;    private String item;    public String getCollection() {        return collection;    }    public void setCollection(String collection) {        this.collection = collection;    }    public String getItem() {        return item;    }    public void setItem(String item) {        this.item = item;    }    @Override    public void doTag() throws JspException, IOException {        //从page scope中获取属性名为collection的集合        Collection itemList=(Collection) getJspContext().getAttribute(collection);        //遍历集合        for(Object s:itemList) {            //将集合的元素设置到page范围            getJspContext().setAttribute(item, s);            //输出标签体            getJspBody().invoke(null);        }    }}

<!--myTag.xml--><tag>    <name>iterator</name>    <tag-class>com.cai.tag.IteratorTag</tag-class>    <!-- 开始和结束标签之间的内容类型 -->    <body-content>scriptless</body-content>    <attribute>        <name>collection</name>        <required>true</required>        <fragment>true</fragment>    </attribute>    <attribute>        <name>item</name>        <required>true</required>        <fragment>true</fragment>    </attribute></tag>

<!--Demo3.jsp--><body>    <h2>带标签体的标签-迭代器标签</h2>    <%        List<String> a=new ArrayList<String>();        a.add("one");        a.add("two");        a.add("three");        pageContext.setAttribute("a", a);    %>    <table border="1" bgcolor="#aaaadd" width="300">        <myTag:iterator item="item" collection="a">            <tr>                <td>${pageScope.item}</td>            </tr>        </myTag:iterator>    </table></body>

这里写图片描述

以页面片段为属性的标签

//FragmentTag.javapublic class FragmentTag extends SimpleTagSupport {    private JspFragment fragment;    public JspFragment getFragment() {        return fragment;    }    public void setFragment(JspFragment fragment) {        this.fragment = fragment;    }    @Override    public void doTag() throws JspException, IOException {        JspWriter out=getJspContext().getOut();        out.println("<div style='padding:10px;border:1px solid black;'>");        out.println("<h3>下面是动态传入的JSP片段</h3>");        fragment.invoke(null);        out.println("</div>");    }}

<!--myTag.xml--><tag>    <name>fragment</name>    <tag-class>com.cai.tag.FragmentTag</tag-class>    <!-- 开始和结束标签之间的内容类型 -->    <body-content>empty</body-content>    <attribute>        <name>fragment</name>        <required>true</required>        <fragment>true</fragment>    </attribute></tag>

<!--Demo4.jsp--><body><h2>下面显示的是自定义标签的内容</h2><myTag:fragment>    <jsp:attribute name="fragment">        <myTag:showTime/>    </jsp:attribute></myTag:fragment><br/><myTag:fragment>    <jsp:attribute name="fragment">        ${pageContext.request.remoteAddr}    </jsp:attribute></myTag:fragment></body>

这里写图片描述

动态属性的标签

用于处理属性个数和属性名个数不确定的情况
1. 还需实现DynamicAttributes接口
2. 配置标签时通过dynamic-attributes指定标签支持动态属性

public class DynaAttributeTag extends SimpleTagSupport implements DynamicAttributes {    //保存每个属性名的集合    private ArrayList<String> keys=new ArrayList<String>();    //保存每个属性值的集合    private ArrayList<Object> values=new ArrayList<Object>();    @Override    public void doTag() throws JspException, IOException {        JspWriter out=getJspContext().getOut();        out.println("<ol>");        for(int i=0;i<keys.size();i++) {            String key=keys.get(i);            Object value=values.get(i);            out.println("<li>"+key+"="+value+"</li>");        }        out.println("</ol>");    }    @Override    public void setDynamicAttribute(String arg0, String arg1, Object arg2) throws JspException {        //添加属性名        keys.add(arg1);        //添加属性值        values.add(arg2);    }}

<tag>       <name>dynaAttr</name>    <tag-class>com.cai.tag.DynaAttributeTag</tag-class>    <!-- 开始和结束标签之间的内容类型 -->    <body-content>empty</body-content>    <dynamic-attributes>true</dynamic-attributes></tag>

<body><myTag:dynaAttr name="aaaaaa"  password="fdsfsdf"/></body>

这里写图片描述

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标签

开发自定义标签类

带属性的标签

带标签体的标签

以页面片段为属性的标签

动态属性的标签