jsp自定义标签

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自定义标签主要用于移除页面的java代码。
使用自定义标签分成两个步骤：

1、编写一个实现Tag接口的java类，把页面代码移到这个java类中（标签处理器）

[java] view plaincopyprint?

package tab.ctrl.alt.tag;
import java.io.IOException;
import javax.management.RuntimeErrorException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.TagSupport;
public class ViewTag extends TagSupport {
/**
*
*/
private static final long serialVersionUID = 1L;
@Override
public int doStartTag() throws JspException {
HttpServletRequest request = (HttpServletRequest)this.pageContext.getRequest();
JspWriter writer = this.pageContext.getOut();
String ip = request.getRemoteAddr();
try {
writer.print(ip);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
throw new RuntimeException(e);
}
return super.doStartTag();
}
}

package tab.ctrl.alt.tag;import java.io.IOException;import javax.management.RuntimeErrorException;import javax.servlet.http.HttpServletRequest;import javax.servlet.jsp.JspException;import javax.servlet.jsp.JspWriter;import javax.servlet.jsp.tagext.TagSupport;public class ViewTag extends TagSupport {/** *  */private static final long serialVersionUID = 1L;@Overridepublic int doStartTag() throws JspException {HttpServletRequest request = (HttpServletRequest)this.pageContext.getRequest();JspWriter writer = this.pageContext.getOut();String ip = request.getRemoteAddr();try {writer.print(ip);} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();throw new RuntimeException(e);}return super.doStartTag();}}

2、编写标签描述符（tld一个标签。）文件，在tld文件中把标签处理器描述成

[plain] view plaincopyprint?

<?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>itdos</short-name>
<uri>http://itdos.net</uri>
<tag>
<description>view</description>
<name>helloWorld</name>
<tag-class>tab.ctrl.alt.tag.ViewTag</tag-class>
<body-content>empty</body-content>
</tag>
</taglib>

<?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>itdos</short-name>    <uri>http://itdos.net</uri>        <tag><description>view</description>        <name>helloWorld</name><tag-class>tab.ctrl.alt.tag.ViewTag</tag-class><body-content>empty</body-content>    </tag> </taglib>

3、jsp

[plain] view plaincopyprint?

<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%>
<%@taglib uri="http://itdos.net" prefix="itdos" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP '1.jsp' starting page</title>
</head>
<body>
<itdos:helloWorld/>
</body>
</html>

<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%><%@taglib uri="http://itdos.net"  prefix="itdos" %><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>       <title>My JSP '1.jsp' starting page</title>  </head>    <body>    <itdos:helloWorld/>  </body></html>

自定义标签执行过程

1、遇到自定义标签。先实例对应的标签处理器类。
2、调用setPageContext方法，把页面的pagecontext对象传递给标签处理器类
3、看标签是否有父标签，如果有父标签把父标签作为一个对象，调用setParent方法传递给标签处理器类，如果没有传递个null
4、完成标签初始化工作后，服务器开始执行标签。遇到标签的开始标签调用dostart方法
5、如果标签有标签体，服务器一般会执行标签体
6、服务器遇到结束标签，执行结束doend方法
7、整个标签执行完后，服务器一般会调用release()方法，释放变迁工作时占用的资源