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：

[java] 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();
    }

}

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：

[java] pageContext.getOut().write(object.toString());

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

[html] <?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>

补充：Web开发 , Jsp ,