1.
实现 forEach 标签: 两个属性: items(集合类型, Collection), var(String 类型)
doTag:
遍历 items 对应的集合
把正在遍历的对象放入到 pageContext 中, 键: var, 值: 正在遍历的对象.
把标签体的内容直接输出到页面上.
（1）首先建立一个customer类：
package com.lanqiao.javatest; public class Customer { private Integer id; private String name; private int age; public Customer() { super(); // TODO Auto-generated constructor stub } public Customer(Integer id, String name, int age) { super(); this.id = id; this.name = name; this.age = age; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override public String toString() { return "Customer [id=" + id + ", name=" + name + ", age=" + age + "]"; } }
（2）ForEachTag类，继承于父类： SimpleTagSupport
package com.atguigu.javaweb; import java.io.IOException; import java.util.Collection; import javax.servlet.jsp.JspException; import javax.servlet.jsp.tagext.SimpleTagSupport; public class ForEachTag extends SimpleTagSupport{ private Collection<?> items; public void setItems(Collection<?> items) { this.items = items; } private String var; public void setVar(String var) { this.var = var; } @Override public void doTag() throws JspException, IOException { // * 遍历 items 对应的集合 if(items != null){ for(Object obj: items){ // * 把正在遍历的对象放入到 pageContext 中, 键: var, 值: 正在遍历的对象. getJspContext().setAttribute(var, obj); //把标签体的内容直接输出到页面上. getJspBody().invoke(null); } } } }
（3）在lib下建立一个mytag.tld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"> <description>MyTag 1.2 core library</description> <display-name>MyTag core</display-name> <tlib-version>1.2</tlib-version> <short-name>lxn</short-name> <uri>http://lxn.com/myTag/core</uri> <tag> <name>forEach</name> <tag-class>com.lanqiao.javatest.ForEachTag</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>
（4）建立一个test.jsp页面：
<%@page import="java.util.HashMap"%> <%@page import="java.util.Map"%> <%@page import="com.atguigu.javaweb.Customer"%> <%@page import="java.util.ArrayList"%> <%@page import="java.util.List"%> <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <%@ taglib prefix="lxn" uri="http://lxn.com/myTag/core" %>
<!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> <br><br> <% List<Customer> customers = new ArrayList<Customer>(); customers.add(new Customer(1, "AAA")); customers.add(new Customer(2, "BBB")); customers.add(new Customer(3, "CCC")); customers.add(new Customer(4, "DDD")); customers.add(new Customer(5, "EEE")); request.setAttribute("customers", customers);
%> <lxn:forEach items="${requestScope.custoemrs }" var="cust"> -- ${cust.id } -- ${cust.name } <br> </lxn:forEach> <br><br> </body> </html>
2.使用标签处理器类，其中有一些方法：
package com.atguigu.javaweb; import java.io.IOException; import java.io.OutputStreamWriter; import java.io.PrintWriter; import java.io.StringWriter; import javax.servlet.jsp.JspException; import javax.servlet.jsp.tagext.JspFragment; import javax.servlet.jsp.tagext.SimpleTagSupport; //标签处理器类 public class TestJspFragment extends SimpleTagSupport { @Override public void doTag() throws JspException, IOException {
//JspFragment，是标签体，getJspBody()是获取标签体 JspFragment bodyContent = getJspBody();
//JspFragment.invoke(Witer): Writer 即为标签体内容输出的字符流, 若为 null, 则 //输出到 getJspContext().getOut(), 即输出到页面上. //1. 利用 StringWriter 得到标签体的内容. StringWriter sw = new StringWriter(); bodyContent.invoke(sw); //2. 把标签体的内容都变为大写 String content = sw.toString().toUpperCase(); //3. 获取 JSP 页面的 out 隐含对象, 输出到页面上 getJspContext().getOut().print(content); } }