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;
  }
  
}