Java下载文件后台代码 处理逻辑

文件下载功能是web开发中经常使用到的功能，使用HttpServletResponse对象就可以实现文件的下载

文件下载功能的实现思路：找到文件路径，取文件名，设置浏览器响应头，获取输入流，获取输出流，将输入流通过buffer转到输出流输出到浏览器

　　1.获取要下载的文件的绝对路径

　　2.获取要下载的文件名

　　3.设置content-disposition响应头控制浏览器以下载的形式打开文件

　　4.获取要下载的文件输入流FileInputStream

　　5.创建数据缓冲区buffer

　　6.通过response对象获取OutputStream流

　　7.将FileInputStream流写入到buffer缓冲区

　　8.使用OutputStream将缓冲区的数据输出到客户端浏览器

文件下载注意事项：编写文件下载功能时推荐使用OutputStream流，避免使用PrintWriter流，因为OutputStream流是字节流，可以处理任意类型的数据，而PrintWriter流是字符流，只能处理字符数据，如果用字符流处理字节数据，会导致数据丢失。



[java] view plain copy

    package gacl.response.study; 
    import java.io.FileInputStream; 
    import java.io.FileNotFoundException; 
    import java.io.FileReader; 
    import java.io.IOException; 
    import java.io.InputStream; 
    import java.io.OutputStream; 
    import java.io.PrintWriter; 
    import java.net.URLEncoder; 
    import javax.servlet.ServletException; 
    import javax.servlet.http.HttpServlet; 
    import javax.servlet.http.HttpServletRequest; 
    import javax.servlet.http.HttpServletResponse; 
    /**
     * @author gacl
     * 文件下载
     */ 
    public class ResponseDemo02 extends HttpServlet { 
     
        public void doGet(HttpServletRequest request, HttpServletResponse response) 
                throws ServletException, IOException { 
            downloadChineseFileByOutputStream(response);//下载中文文件 
        } 
     
        /**
         * 下载中文文件,中文文件下载时，文件名要经过URL编码，否则会出现文件名乱码
         * @param response
         * @throws FileNotFoundException
         * @throws IOException
         */ 
        private void downloadChineseFileByOutputStream(HttpServletResponse response) 
                throws FileNotFoundException, IOException { 
            String realPath = this.getServletContext().getRealPath("/download/张家界国家森林公园.JPG");//获取要下载的文件的绝对路径 
            String fileName = realPath.substring(realPath.lastIndexOf("\\")+1);//获取要下载的文件名 
            //设置content-disposition响应头控制浏览器以下载的形式打开文件，中文文件名要使用URLEncoder.encode方法进行编码，否则会出现文件名乱码 
            response.setHeader("content-disposition", "attachment;filename="+URLEncoder.encode(fileName, "UTF-8")); 
            InputStream in = new FileInputStream(realPath);//获取文件输入流 
            int len = 0; 
            byte[] buffer = new byte[1024]; 
            OutputStream out = response.getOutputStream(); 
            while ((len = in.read(buffer)) > 0) { 
                out.write(buffer,0,len);//将缓冲区的数据输出到客户端浏览器 
            } 
            in.close(); 
        } 
         
        public void doPost(HttpServletRequest request, HttpServletResponse response) 
                throws ServletException, IOException { 
            doGet(request, response); 
        } 
    } 







----------java实现ftp的文件上传和下载 --------------
    import static org.junit.Assert.fail; 
     
    import java.io.File; 
    import java.io.FileInputStream; 
    import java.io.FileOutputStream; 
    import java.io.IOException; 
     
    import org.apache.commons.io.IOUtils; 
    import org.apache.commons.net.ftp.FTPClient; 
    import org.apache.commons.net.ftp.FTPFile; 
    import org.junit.AfterClass; 
    import org.junit.BeforeClass; 
    import org.junit.Test; 
     
    /**
     *
     * @version 创建时间：2015年12月14日 上午9:45:32
     * 
     */ 
    public class JunitFtp { 
     
      private static FTPClient ftpClient; 
      private static String ftpIp = "192.168.0.229"; 
      private static String ftpUser = "ff"; 
      private static String ftpPassWord = "ff"; 
      private static String ftpPort = "21"; 
      private static String workingDirectory = "\\data"; 
      private static String localDirectory = "E:\\home\\ftp\\download"; 
     
      @BeforeClass 
      public static void setUpBeforeClass() throws Exception { 
        // ftp连接 
        ftpClient = new FTPClient(); 
        ftpClient.setControlEncoding("gb2312"); 
        ftpClient.connect(ftpIp, Integer.parseInt(ftpPort)); 
        ftpClient.login(ftpUser, ftpPassWord); 
      } 
     
      @AfterClass 
      public static void tearDownAfterClass() throws Exception { 
     
        ftpClient.disconnect(); 
      } 
     
      /**
       *单个文件下载
       * @throws IOException
       * "JiaYanFei"
       * 2015年12月14日
       */ 
      @Test 
      public void fileDownload() throws IOException { 
        // ftpClient.setControlEncoding("gb2312"); 
        FileOutputStream fos = null; 
        try { 
          ftpClient.connect(ftpIp, Integer.parseInt(ftpPort)); 
          ftpClient.login(ftpUser, ftpPassWord); 
          ftpClient.changeWorkingDirectory(workingDirectory); 
          System.out.println("dir:" + ftpClient.printWorkingDirectory()); 
          FTPFile[] files = ftpClient.listFiles(); 
            // FTP服务器文件路径 
            String remoteFileName = "\\data\\中.txt";// 已经切换到data目录只写 中.txt 也可以 但是 写\\中.txt不行 
            String newFileName = "文.txt"; 
            // 文件下载存放路径 
            fos = new FileOutputStream(localDirectory + File.separator+ newFileName); 
            fos.flush(); 
            ftpClient.setBufferSize(1024); 
            ftpClient.setFileType(FTPClient.BINARY_FILE_TYPE); 
            if (ftpClient.retrieveFile(remoteFileName, fos)) { 
              System.out.println(" 文件下载成功。。"); 
            } else { 
              System.out.println(" 文件下载失败。。"); 
              fail("下载失败"); 
            } 
     
        } catch (Exception e) { 
          e.printStackTrace(); 
        } finally { 
          IOUtils.closeQuietly(fos); 
          ftpClient.disconnect(); 
        } 
     
      } 
     
      @Test 
      public void fileUpload() throws IOException { 
        FileInputStream fis = null; 
        try { 
          ftpClient.connect(ftpIp, Integer.parseInt(ftpPort)); 
          ftpClient.login(ftpUser, ftpPassWord); 
          ftpClient.changeWorkingDirectory("/data"); 
     
          fis = new FileInputStream(new File("E:\\home\\ftp\\data\\o.txt")); 
          if (ftpClient.storeFile("/data/backFile3.txt", fis)) {//  /backFile3.txt backFile3.txt也可以 
            System.out.println("上传成功！"); 
          } else { 
            System.out.println("上传失败"); 
            fail("上传失败"); 
          } 
        } finally { 
          IOUtils.closeQuietly(fis); 
          ftpClient.disconnect(); 
        } 
     
      } 
     
      
      
       
       
      /**
       *目录下载
       * @throws IOException
       * 2015年12月14日
       */ 
      @Test 
      public void downloadDirectory() throws IOException { 
        downloadDirectory("\\data" ,localDirectory+ "\\data"); 
      } 
     
     
      /**
       *目录递归下载
       * @param basePath
       * @param localPath
       * @throws IOException
       * 2015年12月14日
       */ 
      public void downloadDirectory(String basePath, String localPath) throws IOException{ 
        ftpClient.changeWorkingDirectory(basePath); 
        System.out.println(ftpClient.printWorkingDirectory()); 
        FTPFile[] files = ftpClient.listFiles(); 
        if (0 == files.length) {// 目录为空 创建空目录 
          System.out.println("dir name: " +localPath ); 
          new File(localPath ).mkdirs(); 
          return; 
        } 
        File file = null; 
        for(FTPFile f:files){ 
          if(f.isDirectory()){ 
            downloadDirectory(basePath + File.separator + f.getName(), localPath + File.separator + f.getName()); 
          }else{ 
            file = new File(localPath);//先判断本地目录是否存在     --不存在则创建 
            if(!file.exists()){ 
              file.mkdirs(); 
            } 
            FileOutputStream fos = new FileOutputStream( localPath + File.separator + f.getName()); 
            fos.flush(); 
            ftpClient.setBufferSize(1024); 
            ftpClient.setFileType(FTPClient.BINARY_FILE_TYPE); 
            System.out.println("fileName: " + f.getName()); 
            if (ftpClient.retrieveFile(basePath + File.separator +f.getName(), fos)) { 
              System.out.println(" 文件下载成功。。"); 
            } else { 
              System.out.println(" 文件下载失败。。"); 
              fail("下载失败"); 
            } 
          } 
           
        } 
         
      } 
       
    } 





------------------------------------java socket实现文件的上传和下载-------------
import Java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class ServerScoket {
//服务器端
int port= 8822;//设置的端口号
public void UpFile(){//接受客户端上传的文件，并保存
try { 
ServerSocket server= new ServerSocket(port);
           while(true){ 
            Socket socket = server.accept(); 
               DataInputStream is = new  DataInputStream(socket.getInputStream());  
               OutputStream os = socket.getOutputStream();                 
               //1、得到文件名      
               String filename="E:\\";
               filename += is.readUTF();
            
               System.out.println("新生成的文件名为:"+filename); 
               FileOutputStream fos = new FileOutputStream(filename); 
               byte[] b = new byte[1024];
               int length = 0; 
               while((length=is.read(b))!=-1){ 
                   //2、把socket输入流写到文件输出流中去 
                   fos.write(b, 0, length); 
               } 
               fos.flush(); 
               fos.close();              
               is.close(); 
               socket.close(); 
           }              
       } catch (IOException e) { 
           // TODO Auto-generated catch block 
           e.printStackTrace(); 
       }   

}


public void DownFile(String filePath){
//接受客户端的下载请求，将本地文件传输给客户端
       try {
           while (true) {
ServerSocket server= new ServerSocket(port);
            // 选择进行传输的文件
               File fi = new File(filePath);
               System.out.println("文件长度:" + (int) fi.length());
               // public Socket accept() throws
               // IOException侦听并接受到此套接字的连接。此方法在进行连接之前一直阻塞。
               Socket socket = server.accept();
               System.out.println("建立socket链接");
              /* DataInputStream dis = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
               dis.readByte();
               */
               DataInputStream fis = new DataInputStream(new BufferedInputStream(new FileInputStream(filePath)));
               DataOutputStream ps = new DataOutputStream(socket.getOutputStream());
               //将文件名及长度传给客户端。这里要真正适用所有平台，例如中文名的处理，还需要加工，具体可以参见Think In Java 4th里有现成的代码。
               ps.writeUTF(fi.getName());
               System.out.println(fi.getName());
               ps.flush();
              int bufferSize = 8192;
               byte[] buf = new byte[bufferSize];
               while (true) {
                   int read = 0;
                   if (fis != null) {
                       read = fis.read(buf);
                   }
                   if (read == -1) {
                       break;
                   }
                   ps.write(buf, 0, read);
               }
               ps.flush();
               // 注意关闭socket链接哦，不然客户端会等待server的数据过来，
               // 直到socket超时，导致数据不完整。               
               fis.close();
               socket.close();               
               System.out.println("文件传输完成");
           }
       } catch (Exception e) {
           e.printStackTrace();
       }
}
public static void main(String arg[]) {
    //String filepath="D:\\test.txt";
       new ServerScoket().UpFile();
   }

}

********************************************************************************************************************************************************

import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.NET.Socket;

public class ClientScoket {
//客户端
private String ip = "localhost";// 设置成服务器IP
    private int port = 8822;//设置端口号
    public void UpFile(String filePath){
    //上传文件，将本地文件传输到服务器端
        try {
        Socket socket = new Socket(ip,port);
            while (true) {
             // 选择进行传输的文件
                File fi = new File(filePath);
                System.out.println("文件长度:" + (int) fi.length());
               /* DataInputStream dis = new DataInputStream(new BufferedInputStream(s.getInputStream()));
                dis.readByte();
                */
                DataInputStream fis = new DataInputStream(new BufferedInputStream(new FileInputStream(filePath)));
                DataOutputStream ps = new DataOutputStream(socket.getOutputStream());
                //将文件名及长度传给客户端。这里要真正适用所有平台，例如中文名的处理，还需要加工，具体可以参见Think In Java 4th里有现成的代码。
                ps.writeUTF(fi.getName());
                ps.flush();
           
                int bufferSize = 8192;
                byte[] buf = new byte[bufferSize];
                while (true) {
                    int read = 0;
                    if (fis != null) {
                        read = fis.read(buf);
                    }

                    if (read == -1) {
                        break;
                    }
                    ps.write(buf, 0, read);
                }
                ps.flush();
                // 注意关闭socket链接哦，不然客户端会等待server的数据过来，
                // 直到socket超时，导致数据不完整。               
                fis.close();
                socket.close();               
                System.out.println("文件传输完成");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } 
}
   
public void DownFile(){
//从服务器端下载文件
try {
    Socket socket = new Socket(ip,port);
           while(true){ 
               DataInputStream is = new  DataInputStream(socket.getInputStream());  
               OutputStream os = socket.getOutputStream();                 
               //1、得到文件名      
               String filename="E:\\";
               filename += is.readUTF();
            
               System.out.println("新生成的文件名为:"+filename); 
               FileOutputStream fos = new FileOutputStream(filename); 
               byte[] b = new byte[1024];
               int length = 0; 
               while((length=is.read(b))!=-1){ 
                   //2、把socket输入流写到文件输出流中去 
                   fos.write(b, 0, length); 
               } 
               fos.flush(); 
               fos.close();              
               is.close(); 
               socket.close(); 
           } 
            
       } catch (IOException e) { 
           // TODO Auto-generated catch block 
           e.printStackTrace(); 
       }  
} 
public static void main(String arg[]) {
String filepath="D:\\test.txt";
       new ClientScoket().UpFile(filepath);;
   }
}