javaweb 实现文件下载的方法及实例代码

package com.cpsec.tang.chemical.action;

import java.io.file;
import java.io.fileinputstream;
import java.io.filenotfoundexception;
import java.io.fileoutputstream;
import java.io.ioexception;
import java.io.inputstream;
import java.io.outputstream;
import java.text.simpledateformat;
import java.util.calendar;
import java.util.list;
import java.util.random;

import javax.annotation.resource;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;

import org.apache.struts2.servletactioncontext;
import org.springframework.stereotype.controller;
import com.cpsec.tang.chemical.biz.documentbiz;
import com.cpsec.tang.chemical.entity.document;
import com.cpsec.tang.chemical.util.pager;
import com.opensymphony.xwork2.actionsupport;

@controller("documentaction")
public class documentaction extends actionsupport{private string filename;
  public string downloadfile(){
    system.out.println(filename);
    try {
      httpservletresponse response=servletactioncontext.getresponse();
      //设置文件mime类型 
      response.setcontenttype(servletactioncontext.getservletcontext().getmimetype(filename)); 
      //设置content-disposition 
      response.setheader("content-disposition", "attachment;filename="+filename); 
      //获取目标文件的绝对路径 
      string fullfilename = servletactioncontext.getservletcontext().getrealpath("/files/" + filename); 
      //system.out.println(fullfilename); 
      //读取文件 
      inputstream in = new fileinputstream(fullfilename); 
      //读取目标文件，通过response将目标文件写到客户端
      outputstream out = response.getoutputstream(); 
      //写文件 
      int b; 
      while((b=in.read())!= -1) 
      { 
        out.write(b); 
      } 
      in.close(); 
      out.close(); 
    } catch (exception e) {
      e.printstacktrace();
    }
    return success;
  }
  
}