文件下载是一个很常见的功能，用struts2实现文件下载的步骤：

一）定义一个Action类，FileDownload.java

package com.struts2.filedownload;

import java.io.InputStream;


import org.apache.struts2.ServletActionContext;


import com.opensymphony.xwork2.ActionSupport;

//文件下载
public class FileDownload extends ActionSupport{

  private int number ;

  private String fileName;

  public int getNumber() {
    return number;
  }

  public void setNumber(int number) {
    this.number = number;
  }

  public String getFileName() {
    return fileName;
  }

  public void setFileName(String fileName) {
    this.fileName = fileName;
  }

  //返回一个输入流，作为一个客户端来说是一个输入流，但对于服务器端是一个 输出流
  public InputStream getDownloadFile() throws Exception
  {
    if(1 == number)
    {
       this.fileName = "Dream.jpg" ;
       //获取资源路径
       return ServletActionContext.getServletContext().getResourceAsStream("upload/Dream.jpg") ;
    }

    else if(2 == number)
    {
      this.fileName = "jd2chm源码生成chm格式文档.rar" ;
      //解解乱码
      this.fileName = new String(this.fileName.getBytes("GBK"),"ISO-8859-1");
      return ServletActionContext.getServletContext().getResourceAsStream("upload/jd2chm源码生成chm格式文档.rar") ;
    }
    else
       return null ;
  }

  @Override
  public String execute() throws Exception {

    return SUCCESS;
  }

}


二)在struts.xml文件中配置相关信息

<struts>      
   <package name="struts2" extends="struts-default">      
       <action name="FileDownload" class="com.struts2.filedownload.FileDownload">
           <result name="success" type="stream">
               <param name="contentType">text/plain</param>
               <param name="contentDisposition">attachment;fileName="${fileName}"</param>
               <param name="inputName">downloadFile</param>
               <param name="bufferSize">1024</param>
           </result>
       </action>

   </package>

</struts>

1.结果类型必须要写成 type="stream"  ,与之对应的处理类是 org.apache.struts2.dispatcher.StreamResult


2.涉及到的参数：

3.

1)  <param name="contentDisposition">attachment;fileName="${fileName}"</param>

     contentDisposition默认是 inline（内联的), 比如说下载的文件是文本类型的，就直接在网页上打开，不能直接打开的才会打开下载框自己选择

2)  attachment ：下载时会打开下载框

3)  fileName="${fileName}" ：在这定义的名字是一个动态的，该名字是显示在下载框上的文件名字


4.<param name="inputName">downloadFile</param>，这个downloadFile名字要和FileDownload.java类中的getDownloadFile()方法名去掉get 一致


三）用于显示下载的链接界面 filedownload.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">

    <title>My JSP 'filedownload.jsp' starting page</title>

  <meta http-equiv="pragma" content="no-cache">
  <meta http-equiv="cache-control" content="no-cache">
  <meta http-equiv="expires" content="0">    
  <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
  <meta http-equiv="description" content="This is my page">
  <!--
  <link rel="stylesheet" type="text/css" href="styles.css">
  -->

  </head>

  <body>

    <h2>文件下载内容：</h2><br/>
    Dream.jpg:<a href="FileDownload.action?number=1">点击下载</a><br/>
    jd2chm源码生成chm格式文档.rar:<a href="FileDownload.action?number=2">点击下载2</a>


  </body>
</html>