JSP自定义标签

在JSP网页编程中，我们通常不满足于jstl或其他的框架，我们也可以自己写属于自己专用的标签。

在这里介绍一下表格中展示JavaBean的自定义标签的使用

第一步：写一个父标签，用来显示获取数据

　　新建一个ShowBeanTag.java

package com.wuyu.tags;
import java.io.IOException;
import java.lang.reflect.Field;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.TagSupport;

public class ShowBeanTag extends TagSupport {
	private static final long serialVersionUID = 1L;
	private String test;
	private Object object;
	@Override
	public int doStartTag() throws JspException {
		try {
			JspWriter out = this.pageContext.getOut();
			out.println("<table>");
		} catch (SecurityException e) {
			e.printStackTrace();
		} catch(IOException e){
			e.printStackTrace();
		}	catch (IllegalArgumentException e) {
			e.printStackTrace();
		}
		return EVAL_BODY_INCLUDE;
	}

	@Override
	public int doEndTag() throws JspException {
		// TODO Auto-generated method stub
		JspWriter out = this.pageContext.getOut();
		try {
			out.println("</table>");
		} catch (IOException e) {
			e.printStackTrace();
		}
		return SKIP_BODY;
	}
	public String getTest() {
		return test;
	}

	public void setTest(String test) {
		this.test = test;
	}

	public Object getObject() {
		return object;
	}

	public void setObject(Object object) {
		this.object = object;
	}
}

　　第二步：编写DisplayColumnTag.java，子标签的类

package com.wuyu.tags;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

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

public class DisplayColumnTag extends TagSupport {
	/**
	 *
	 */
	private static final long serialVersionUID = 1L;
	private String property;
	private String showValue;
	@Override
	public int doStartTag() throws JspException {
		try {
			JspWriter out = this.pageContext.getOut();
			JspTag parent = getParent();
			ShowBeanTag sbt = (ShowBeanTag)parent;
			Object obj = sbt.getObject();
			property =  property.substring(0, 1).toUpperCase() + property.substring(1);
			Method getMethod = obj.getClass().getMethod("get" + property, new Class[] {});
			out.println("<tr>");
			if(showValue != null){
				out.println("<td>"+ showValue +"</td>");
			}else{
				out.println("<td>"+ property +"</td>");
			}
			out.println("<td>"+ getMethod.invoke(obj, new Object[]{}) +"</td>");
			out.println("</tr>");
		}catch(IOException e){
			e.printStackTrace();
		}catch(NoSuchMethodException e){
			e.printStackTrace();
		}catch (SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return EVAL_BODY_INCLUDE;
	}

	public String getProperty() {
		return property;
	}
	public void setProperty(String property) {
		this.property = property;
	}

	public String getShowValue() {
		return showValue;
	}

	public void setShowValue(String showValue) {
		this.showValue = showValue;
	}

	@Override
	public int doEndTag() throws JspException {
		// TODO Auto-generated method stub
		return EVAL_PAGE;
	}
}

　　第三步：写tld文件

　　　　在WEB-INF文件夹下，新建一个文件ShowBeanTag.tld，其内容如下

<?xml version="1.0" encoding="UTF-8"?>
<taglib version="2.0" 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 web-jsptaglibrary_2_0.xsd">
	<tlib-version>1.0</tlib-version>
	<jsp-version>2.0</jsp-version>
	<short-name>b</short-name>
	<uri>/showBeanTag</uri>
	<tag>
		<name>showBeanTag</name>
		<tag-class>com.wuyu.tags.ShowBeanTag</tag-class>
		<body-content>scriptless</body-content>
		<attribute>
			<name>test</name>
			<required>false</required>
			<rtexprvalue>true</rtexprvalue>
		</attribute>
	</tag>
	<tag>
		<name>displayColumnTag</name>
		<tag-class>com.wuyu.tags.DisplayColumnTag</tag-class>
		<body-content>empty</body-content>
		<attribute>
			<name>property</name>
			<required>true</required>
			<rtexprvalue>true</rtexprvalue>
		</attribute>
		<attribute>
			<name>showValue</name>
			<required>false</required>
			<rtexprvalue>true</rtexprvalue>
		</attribute>
	</tag>
</taglib>

　　第四步：在web.xml中配置

　　

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <jsp-config>
  	<taglib>
  		<taglib-uri>/showBeanTag</taglib-uri>
  		<taglib-location>/WEB-INF/ShowBeanTag.tld</taglib-location>
  	</taglib>
  </jsp-config>
</web-app>

　　第五步：新建一个JavaBean  User.java

package com.wuyu.bean;

public class User {
	private String userName;
	private int age;
	private String email;
	public String getUserName() {
		return userName;
	}
	public void setUserName(String userName) {
		this.userName = userName;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public String getEmail() {
		return email;
	}
	public void setEmail(String email) {
		this.email = email;
	}
}

　　

　　第六步，在index.jsp中使用

<%@ page language="java" contentType="text/html; charset=UTF-8"
   import="com.wuyu.bean.User,java.util.*" pageEncoding="UTF-8"%>
<%@ taglib uri="/showBeanTag" prefix="b" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<%
	User user = new User();
	user.setUserName("wuyu");
	user.setAge(24);
	user.setEmail("[e-mail]");
	pageContext.setAttribute("user", user);
%>

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
	<b:showBeanTag test="user">
		<b:displayColumnTag property="userName" showValue="用户名"/>
		<b:displayColumnTag property="age" showValue="年龄"/>
	</b:showBeanTag>
</body>
</html>