java 开发jsp 自定义标签

此文目的，纠正网上一些不正确的文章！

开发步骤：

首先建立一个类：

继承BodyTagSupport

然后设置字段 生成set方法

类：

package org.pan.tags;

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

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;

public class SessionProperty extends BodyTagSupport{

private static final long serialVersionUID = 1L;

private String value;	//需要获取的属性

public void setValue(String value) {
this.value = value;
}

public String getValue() {
return value;
}

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

@Override
public int doStartTag() throws JspException {

System.out.println("ok");
HttpServletRequest request=(HttpServletRequest)pageContext.getRequest();
HttpSession session=request.getSession();

Object object=session.getAttribute(value);
if(object==null)return EVAL_PAGE;

if(object instanceof String){

try {
pageContext.getOut().write(object.toString());
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

return super.doStartTag();
}

}

特别注意：

输出内容需要用：

pageContext.getOut().write(object.toString());

tld配置：

建立一个tld文件，tld文件需要放在WEB-INF 中

<?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>JSTL 1.1 core library</description>
<display-name>JSTL core</display-name>
<tlib-version>1.1</tlib-version>
<short-name>w</short-name>
<uri>http:/winter.baletu.com/</uri>
<tag>
<description>Obtained from the session attribute</description>
<name>property</name>
<tag-class>org.pan.tags.SessionProperty</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>value</name>
<required>true</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
</tag>
</taglib>