使用 Socket 進行 Client-Server 檔案傳送：從 Client 端將檔案傳送給 Server 端

參考資料：
1、官方 Socket 文件（Client 端用來與 Server 連線的 Socket）
2、官方 ServerSocket 文件（Server 端用來接受 Client 端連線的 Socket）


Client 端的語法：

InetAddress addressOfServer = InetAddress.getByName("127.0.0.1");
int portOfServer = 22;

// File to be transmitted
File file = new File("/home/user/test.img");
// Create buffer
byte[] buffer = new byte[2048];
int bytesReaded;

// Socket connection for connecting to the server
Socket socketFromClient = null;
// Output stream for transmitting file to the server
DataOutputStream outputStream = null;
// Input stream for reading local file
FileInputStream fis = null;

try {
　　// Create socket
　　socketFromClient = new Socket(addressOfServer, portOfServer);

　　// Create output stream for transmitting file
　　outputStream = new DataOutputStream(socketFromClient.getOutputStream());
　　// Create input Stream for reading file
　　FileInputStream fis = new FileInputStream(file);

　　// Start transmitting
　　while( (bytesReaded = fis.read(buffer)) > -1 ) {
　　　　outputStream.write(buffer, 0, bytesReaded);
　　　　outputStream.flush();
　　}
} finally {
　　// Close the stream objects
　　if(outputStream != null) outputStream.close();
　　if(fis != null) fis.close();
}

// Close the connection of socket
if(socketFromClient != null) socketFromClient.close();

Server 端語法：

int portOfServer = 22;

// Start listening to port 22
ServerSocket serverSocket = new ServerSocket(serverPort);
Socket clientSocket = serverSocket.accept();

// Reader for accepting the transmission from client
BufferedInputStream bis = null;
DataInputStream dis = null;
// File writer for writing the file transmitted from the client
File writtenFile = null;
FileWriter fw = null;
BufferedWriter bw = null;

try {
　　// Get the address of the connecting client
　　String addressOfClient = clientSocket.getRemoteSocketAddress().toString();
　　// Get the stream which the client tranmits
　　bis = new BufferedInputStream(clientSocket.getInputStream());
　　dis = new DataInputStream(bis);

　　// Create file writer
　　writtenFile = new File("transmittedFile");
　　fw = new FileWriter(writtenFile);
　　bw = new BufferedWriter(fw);

　　// Create buffer
　　byte[] buffer = new byte[2048];
　　int bytesReaded;

　　// Accept and write the file
　　while( (bytesReaded = dis.read(buffer)) > -1) {
　　　　bw.write(buffer, 0, bytesReaded);
　　　　bw.flush();
　　}
}finally {
　　// Close the stream and writer objects
　　if(bw != null) bw.close();
　　if(fw != null) fw.close();
　　if(dis != null) dis.close();
　　if(bis != null) bis.close();
}

如果只是要傳送字串資料，而不是傳送檔案的話，作法好像是一樣的，可以參考以下的連結。

參考資料：
3、簡單的Socket Client Server