servlet下载文件实现代码详解（五）

本文实例为大家分享了servlet下载文件的具体代码，供大家参考，具体内容如下

1.servlet下载文件

　　servlet下载文件就是将服务器端的文件传输到客户端。

2案例

下载文件servlet类

package com.learn;

import javax.servlet.servletconfig;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;
import java.io.file;
import java.io.ioexception;
import java.io.inputstream;
import java.io.outputstream;

/**
 * created by administrator on 2017/09/24.
 */
public class downloadservlet extends httpservlet {
  private string filepath;

  @override
  public void init(servletconfig config) throws servletexception {
    super.init(config);
    filepath = config.getinitparameter("filepath");
    //初始化路径
    //filepath = config.getservletcontext().getrealpath(filepath);
    system.out.println("初始化文件路径："+filepath);
  }

  @override
  protected void doget(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
    dopost(req,resp);

  }

  @override
  protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {

    outputstream out; //输出流
    inputstream in; //输入流

    string filename = req.getparameter("filename");
    system.out.println("文件名称："+filename);
    //如果把文件名为null则提示用户
    if(filename == null){
      out = resp.getoutputstream();
      out.write("please input filename".getbytes());
      out.close();
    }
    //获取文件流
    in = getservletcontext().getresourceasstream(filepath+ file.separator+filename);
    system.out.println(in==null?true:false);
    int length = in.available();
    
    //设置返回消息头部信息
    resp.setcontenttype("application/force-download");
    resp.setheader("content-length",string.valueof(length));
    resp.setheader("content-disposition","attachment;filename=\""+filename+"\"");
    //输出文件到客户端
    out = resp.getoutputstream();
    int bytesend = 0 ;
    byte[] buff = new byte[512];
    while ((bytesend = in.read(buff))!= -1){
      out.write(buff,0,bytesend);
    }
    in.close();
    out.close();
  }
}

web.xml配置

 <servlet>
  <servlet-name>download</servlet-name>
  <servlet-class>com.learn.downloadservlet</servlet-class>
  <init-param>
    <param-name>filepath</param-name>
    <param-value>file</param-value>
  </init-param>
 </servlet>
 <servlet-mapping>
  <servlet-name>download</servlet-name>
  <url-pattern>/download</url-pattern>
 </servlet-mapping>