如何使用java socket在客户端和服务器之间实现传输文件

Question

我已经实现了简单的TCP服务器和TCP客户端类，可以将消息从客户端发送到服务器，消息将在服务器端转换为大写，但是如何实现从服务器到客户端的传输文件并上传从客户端到服务器的文件。以下代码就是我所拥有的。

TCPClient.java

        import java.io.*;
        import java.net.*;
        import java.util.Scanner;

 class TCPClient {

public static void main(String args[]) throws Exception {
        int filesize=6022386;
        int bytesRead;
        int current = 0;
    String ipAdd="";
    int portNum=0;
    boolean goes=false;
    if(goes==false){
    System.out.println("please input the ip address of the file server");
    Scanner scan=new Scanner(System.in);
    ipAdd=scan.nextLine();
    System.out.println("please input the port number of the file server");
    Scanner scan1=new Scanner(System.in);
    portNum=scan1.nextInt();
    goes=true;
    }
    System.out.println("input done");
    int timeCount=1;
    while(goes==true){
    //System.out.println("connection establishing");

    String sentence="";
    String modifiedSentence;

    BufferedReader inFromUser = new BufferedReader(new InputStreamReader(
            System.in));

    Socket clientSocket = new Socket(ipAdd, portNum);
    //System.out.println("connecting");
    //System.out.println(timeCount);
    if(timeCount==1){
    sentence="set";
    //System.out.println(sentence);


    }
    if(timeCount!=1)
        sentence = inFromUser.readLine();
            if(sentence.equals("close"))
                clientSocket.close();
            if(sentence.equals("download"))
            {
                byte [] mybytearray  = new byte [filesize];
                InputStream is = clientSocket.getInputStream();
                FileOutputStream fos = new FileOutputStream("C:\\users\\cguo\\kk.lsp");
                BufferedOutputStream bos = new BufferedOutputStream(fos);
                bytesRead = is.read(mybytearray,0,mybytearray.length);
                current = bytesRead;
                do {
   bytesRead =
      is.read(mybytearray, current, (mybytearray.length-current));
   if(bytesRead >= 0) current += bytesRead;
} while(bytesRead > -1);

bos.write(mybytearray, 0 , current);
bos.flush();
long end = System.currentTimeMillis();
//System.out.println(end-start);
bos.close();
clientSocket.close();
            }
           // if(sentence.equals("send"))
               // clientSocket.
    timeCount--;
    //System.out.println("connecting1");
    DataOutputStream outToServer = new DataOutputStream(clientSocket
            .getOutputStream());

    BufferedReader inFromServer = new BufferedReader(new InputStreamReader(
            clientSocket.getInputStream()));


    //System.out.println("connecting2");
    //System.out.println(sentence);
    outToServer.writeBytes(sentence + "\n");

    modifiedSentence = inFromServer.readLine();

    System.out.println("FROM SERVER:" + modifiedSentence);

    clientSocket.close();

}
}

}

---

TCPServer.java

          import java.io.*;
       import java.net.*;

     class TCPServer {
public static void main(String args[]) throws Exception {

    Socket s = null;

    int firsttime=1;


    while (true) {
        String clientSentence;
    String capitalizedSentence="";

        ServerSocket welcomeSocket = new ServerSocket(3248);
        Socket connectionSocket = welcomeSocket.accept();

             //Socket sock = welcomeSocket.accept();


        BufferedReader inFromClient = new BufferedReader(
                new InputStreamReader(connectionSocket.getInputStream()));

        DataOutputStream outToClient = new DataOutputStream(
                connectionSocket.getOutputStream());

        clientSentence = inFromClient.readLine();
        //System.out.println(clientSentence);
                    if(clientSentence.equals("download"))
                    {
                         File myFile = new File ("C:\\Users\\cguo\\11.lsp");
  byte [] mybytearray  = new byte [(int)myFile.length()];
  FileInputStream fis = new FileInputStream(myFile);
  BufferedInputStream bis = new BufferedInputStream(fis);
  bis.read(mybytearray,0,mybytearray.length);
  OutputStream os = connectionSocket.getOutputStream();
  System.out.println("Sending...");
  os.write(mybytearray,0,mybytearray.length);
  os.flush();
  connectionSocket.close();
                    }
        if(clientSentence.equals("set"))
            {outToClient.writeBytes("connection is ");
            System.out.println("running here");
            //welcomeSocket.close();
             //outToClient.writeBytes(capitalizedSentence);
            }



        capitalizedSentence = clientSentence.toUpperCase() + "\n";


    //if(!clientSentence.equals("quit"))
           outToClient.writeBytes(capitalizedSentence+"enter the message or command: ");


        System.out.println("passed");
        //outToClient.writeBytes("enter the message or command: ");
        welcomeSocket.close();
    System.out.println("connection terminated");
    }
}

}

所以，TCPServer.java将首先被执行，然后执行TCPClient.java，我尝试使用TCPServer.java中的if子句来测试用户的输入是什么，现在我真的想实现如何从两边传输文件（下载和上传）。谢谢。

Answer 1

快速浏览消息来源，您似乎并不遥远。以下链接应该有所帮助（我为FTP做了类似的事情）。对于从服务器发送到客户端的文件，您可以从文件实例和字节数组开始。然后，将File读入字节数组，并将字节数组写入OutputStream，与客户端的InputStream对应。

http://www.rgagnon.com/javadetails/java-0542.html

编辑：这是一个有效的超简约文件发送者和接收者。确保您了解代码在双方都在做什么。

package filesendtest;

import java.io.*;
import java.net.*;

class TCPServer {

    private final static String fileToSend = "C:\\test1.pdf";

    public static void main(String args[]) {

        while (true) {
            ServerSocket welcomeSocket = null;
            Socket connectionSocket = null;
            BufferedOutputStream outToClient = null;

            try {
                welcomeSocket = new ServerSocket(3248);
                connectionSocket = welcomeSocket.accept();
                outToClient = new BufferedOutputStream(connectionSocket.getOutputStream());
            } catch (IOException ex) {
                // Do exception handling
            }

            if (outToClient != null) {
                File myFile = new File( fileToSend );
                byte[] mybytearray = new byte[(int) myFile.length()];

                FileInputStream fis = null;

                try {
                    fis = new FileInputStream(myFile);
                } catch (FileNotFoundException ex) {
                    // Do exception handling
                }
                BufferedInputStream bis = new BufferedInputStream(fis);

                try {
                    bis.read(mybytearray, 0, mybytearray.length);
                    outToClient.write(mybytearray, 0, mybytearray.length);
                    outToClient.flush();
                    outToClient.close();
                    connectionSocket.close();

                    // File sent, exit the main method
                    return;
                } catch (IOException ex) {
                    // Do exception handling
                }
            }
        }
    }
}

---

package filesendtest;

import java.io.*;
import java.io.ByteArrayOutputStream;
import java.net.*;

class TCPClient {

    private final static String serverIP = "127.0.0.1";
    private final static int serverPort = 3248;
    private final static String fileOutput = "C:\\testout.pdf";

    public static void main(String args[]) {
        byte[] aByte = new byte[1];
        int bytesRead;

        Socket clientSocket = null;
        InputStream is = null;

        try {
            clientSocket = new Socket( serverIP , serverPort );
            is = clientSocket.getInputStream();
        } catch (IOException ex) {
            // Do exception handling
        }

        ByteArrayOutputStream baos = new ByteArrayOutputStream();

        if (is != null) {

            FileOutputStream fos = null;
            BufferedOutputStream bos = null;
            try {
                fos = new FileOutputStream( fileOutput );
                bos = new BufferedOutputStream(fos);
                bytesRead = is.read(aByte, 0, aByte.length);

                do {
                        baos.write(aByte);
                        bytesRead = is.read(aByte);
                } while (bytesRead != -1);

                bos.write(baos.toByteArray());
                bos.flush();
                bos.close();
                clientSocket.close();
            } catch (IOException ex) {
                // Do exception handling
            }
        }
    }
}

相关

Byte array of unknown length in java

编辑：以下内容可用于在传输之前和之后指纹小文件（如果您认为有必要，请使用SHA）：

public static String md5String(File file) {
    try {
        InputStream fin = new FileInputStream(file);
        java.security.MessageDigest md5er = MessageDigest.getInstance("MD5");
        byte[] buffer = new byte[1024];
        int read;
        do {
            read = fin.read(buffer);
            if (read > 0) {
                md5er.update(buffer, 0, read);
            }
        } while (read != -1);
        fin.close();
        byte[] digest = md5er.digest();
        if (digest == null) {
            return null;
        }
        String strDigest = "0x";
        for (int i = 0; i < digest.length; i++) {
            strDigest += Integer.toString((digest[i] & 0xff)
                    + 0x100, 16).substring(1).toUpperCase();
        }
        return strDigest;
    } catch (Exception e) {
        return null;
    }
}