struts2实现文件下载所出现的乱码，解决方法

<pre class="java" name="code">package com.ifless.struts2;import java.io.InputStream;import org.apache.struts2.ServletActionContext;import com.opensymphony.xwork2.ActionSupport;public class DownloadAction2 extends ActionSupport {private int number;private String filename;    public String getFilename() {return filename;}public void setFilename(String filename) {this.filename = filename;}public int getNumber() {return number;}public void setNumber(int number) {this.number = number;}public InputStream getDownloadFile(){try {if (1== number) {this.filename="Ajax.ppt";this.filename= new String(this.filename.getBytes("gbk"),"8859_1");//防止中文乱码的return ServletActionContext.getServletContext().getResourceAsStream("/upload/Ajax.ppt");}else {this.filename="student.txt";this.filename= new String(this.filename.getBytes("gbk"),"8859_1");//防止中文乱码的return ServletActionContext.getServletContext().getResourceAsStream("/upload/student.txt");}} catch (Exception e) {e.printStackTrace();}return null;}@Overridepublic String execute() throws Exception {return SUCCESS;}}