servlet文件上传及下载

servlet3.0中提供了对文件上传的直接支持，不需要借助任何第三方上传组件，直接使用Servlet3.0提供的API就能够实现文件上传功能。

servlet 代码：

package ni.jun.yang.servlet;

import java.io.File;
import java.io.IOException;
import java.util.UUID;
import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;


@WebServlet("/Upload")
@MultipartConfig    //必须使用此注解，标志此servlet 支持文件上传
public class Upload extends HttpServlet {
    private static final long serialVersionUID = 1L;
 
    public Upload() {
        
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //设置请求编码
        request.setCharacterEncoding("utf-8");  
        //(part)此类表示在multipart/form-dataPOST请求中收到的部分或表单项 。
        //
        Part part = request.getPart("filename");
        //获取上下文对象，再获取某文件夹的位置
        String path = request.getServletContext().getRealPath("file");
        //获得头部信息
        String headName = part.getHeader("content-disposition");
　　　　 System.out.println(headName);
        //截取文件后缀名
        String end = headName.substring(headName.indexOf("."), headName.length()-1);
        //随机生成一个文件名，并拼接完整路径
        String filename = path +File.separator+UUID.randomUUID().toString()+end;
        System.out.println(filename);
        //将上传的项目写入磁盘的方便方法。
        part.write(filename);        
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        
        doGet(request, response);
    }
}

part接口：http://docs.oracle.com/javaee/6/api/javax/servlet/http/Part.html

html代码：文件上传一定要将enctype的值改为：enctype="multipart/form-data"

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>文件上传</title>
</head>
<body>
	<form action="Upload" method="post" enctype="multipart/form-data">
	<input type="file" name="filename"><br/><br/>
	<input type="submit" value="上传">
	</form>
</body>
</html>

请求头信息：

效果：

下载：

package ni.jun.yang.servlet;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


@WebServlet("/DownServlet")
public class downServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.获取要下载的文件的绝对路径
        String realPath = this.getServletContext().getRealPath("111.txt");
        System.out.println(realPath);
        //2.获取要下载的文件名
        String fileName = realPath.substring(realPath.lastIndexOf(File.separator)+1);
        String userAgent = request.getHeader("User-Agent");
        //针对IE或者以IE为内核的浏览器：
        if (userAgent.contains("MSIE")||userAgent.contains("Trident")) {
            fileName = java.net.URLEncoder.encode(fileName, "UTF-8");
        } else {
        //非IE浏览器的处理：
            fileName = new String(fileName.getBytes("UTF-8"),"ISO-8859-1");
        }
        //3.设置content-disposition响应头控制浏览器以下载的方式打开文件
        response.setHeader("content-disposition","attachment;filename="+fileName);
        //4.获取要下载的文件输入流
        InputStream in = new FileInputStream(realPath);

        int len = 0;
        //5.创建书缓冲区
        byte[] buffer = new byte[1024];
        //6.通过response对象获取OutputStream输出流对象
        OutputStream os = response.getOutputStream();
        //7.将FileInputStream流对象写入到buffer缓冲区
        while((len=in.read(buffer))>0){
            os.write(buffer,0,len);
        }
        //8.关闭流
        in.close();
        os.close();
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}