java 開發jsp 自訂標籤

此文目的，糾正網上一些不正確的文章！

開發步驟：

首先建立一個類：

繼承BodyTagSupport

然後設定欄位 產生set方法

類：

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;//需要擷取的屬性public void setValue(String value) {this.value = value;}public String getValue() {return value;}@Overridepublic int doEndTag() throws JspException {// TODO Auto-generated method stubreturn super.doEndTag();}@Overridepublic 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 blocke.printStackTrace();}}return super.doStartTag();}}

特別注意：

輸出內容需要用：

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

tld配置：

建立一個tld檔案，tld檔案需要放在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>