web文件下载

第一种形式，是以流的开式直接response,适用于数据量不是很大的情况下。
第二种形式，是先将要下载的文件写到后台的一个文件中，然后再进行下载。

package com.lh446.action;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.actions.MappingDispatchAction;

public class ExportAction extends MappingDispatchAction {
 /**
  * 直接通过流导出
  * @param arg0
  * @param arg1
  * @param arg2
  * @param arg3
  * @return
  * @throws Exception
  */
 public ActionForward export(ActionMapping arg0, ActionForm arg1, HttpServletRequest req, HttpServletResponse res) throws Exception {
  
  String msg="倒萨大额外人玩儿完";
  String fileName="test1.txt";
  //fileName=new String(fileName.getBytes("iso-8859-1"),"utf-8");
  res.setContentType("text/plain;charset=GBK");
  res.addHeader("Content-disposition", "attachment;filename="+fileName);
  BufferedOutputStream out=new BufferedOutputStream(res.getOutputStream());
  out.write(msg.getBytes("GBK"));
  out.close();
  return null;
 }
 /**
  * 先将数据保存在本地（本实例通过TXT文本演示）在下载
  * @param arg0
  * @param arg1
  * @param arg2
  * @param arg3
  * @return
  * @throws Exception
  */
 public ActionForward export2(ActionMapping arg0, ActionForm arg1, HttpServletRequest req, HttpServletResponse res) throws Exception {
  String msg="倒萨大额外人玩儿完";
  String path = new String((this.getServlet().getServletContext()
    .getRealPath("/") + "/export/").getBytes(), "GBK");// 存放路径
  File file=new File(path+"导出测试二.txt");
  //创建新文件
  if(file.exists()){
   file.delete();
  }
  file.getParentFile().mkdirs();
  file.createNewFile();
  FileOutputStream fout=new FileOutputStream(file);
  BufferedOutputStream buf=new BufferedOutputStream(fout);
  buf.write(msg.getBytes());
  buf.close();//写入都本地文件中
  res.setContentType("text/plain;charset=GBK");
  res.addHeader("Content-disposition", "attachment;filename=test2.txt");
  BufferedOutputStream out=new BufferedOutputStream(res.getOutputStream());
  FileInputStream in=new FileInputStream(path+"导出测试二.txt");
  byte[] b=new byte[1024];
  int i=0;
  while((i=in.read(b))>0){
   out.write(b, 0, i);
   out.flush();
  }
  if(in!=null){
   in.close();
  }
  if(out!=null){
   out.close();
  }
  return null;
 }
 /**
  * 先将数据保存在本地并压缩处理(保存为zip文件)在下载
  * @param arg0
  * @param arg1
  * @param arg2
  * @param arg3
  * @return
  * @throws Exception
  */
 public ActionForward export3(ActionMapping arg0, ActionForm arg1, HttpServletRequest req, HttpServletResponse res) throws Exception {
  String msg="倒萨大额外人玩儿完";
  String path = new String((this.getServlet().getServletContext()
    .getRealPath("/") + "/export/").getBytes(), "GBK");// 存放路径
  List<String> fileNames=new ArrayList<String>();
  fileNames.add("test3.txt");
  File file=new File(path+"test3.txt");
//  创建新文件
  if(file.exists()){
   file.delete();
  }
  file.getParentFile().mkdirs();
  file.createNewFile();
  FileOutputStream fout=new FileOutputStream(file);
  BufferedOutputStream buf=new BufferedOutputStream(fout);
  buf.write(msg.getBytes());
  buf.close();//写入都本地文件中
  String zipName="test3.zip";
  tozip(fileNames,path,zipName);
  res.setContentType("application/zip zip;charset=UTF-8");
  res.addHeader("Content-Disposition", "attachment;filename="
    + zipName);
  OutputStream outp = res.getOutputStream();
  FileInputStream in=new FileInputStream(path+zipName);
  byte[] b = new byte[1024];
  int i = 0;
  while ((i = in.read(b)) > 0) {
   outp.write(b, 0, i);
   outp.flush();
  }
  if (in != null) {
   in.close();
   in = null;
  }
  if (outp != null) {
   outp.close();
   outp = null;
  }
  return null;
 }
 //压缩处理：
 public void tozip(List<String> fileNames,String path,String zipName) throws IOException{
//  新建zip文件
   ZipOutputStream zipout=null;
   FileOutputStream fout=new FileOutputStream(path+zipName);
   zipout=new ZipOutputStream(new BufferedOutputStream(fout));
   for(int i=0;i<fileNames.size();i++){
   ZipEntry zipEntry=new ZipEntry(fileNames.get(i));//设置zip文件中每个文件的名称
   zipout.putNextEntry(zipEntry);
   FileInputStream in=new FileInputStream(path+fileNames.get(i));//通过文件流取得当前要压缩文件的数据
   byte[] b=new byte[1024];
   int a=0;
   while((a=in.read(b))>0){
   zipout.write(b, 0, a);//写入到当前设置的zipEntry中，即zip文件中的一个压缩文件
   zipout.flush();
   }
   in.close();
   }
   zipout.close();
 }
}

页面请求代码：（通过form表单请求）

function exportData(){
   var form=document.dataForm;
   var url="/test/export.do";
   form.action=url;
   form.submit();
}

假如页面是二级页面（即通过window.showModalDialog(src,window,style)打开）则此时无法打开下载框。
解决方法：1。在form中设置target="_self"，此时会新打开一个页面下载（不友好）
2。。通过iframe框架解决:

<iframe id="hidden_iframe" name="hidden_iframe" style="display: none"></iframe>
<form id="dataform" name="dataform" method="post" target="hidden_iframe"></form>