Java - File Transfer Example Using Socket

This code snippet demonstrates a very simple file transfer program. In this example the client program sends a file to the server. The client program is a GUI and allows a user to browse for a file to send to the server.
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1. // Client.java
2.  
3. /*
4.  * In this client/server example, the client sends a file to the server.
5.  *
6.  */
7.  
8. import javax.swing.*;
9. import java.awt.*;
10. import java.awt.event.*;
11. import java.net.*;
12. import java.io.*;
13.  
14. public class Client extends JFrame implements ActionListener {
15.  
16.     private JTextField txtFile;
17.    
18.     public static void main(String args[]){
19.  
20.         /* Create and display the client form */
21.  
22.         Client clientForm = new Client();
23.         clientForm.Display();
24.     }
25.  
26.     public void Display(){
27.  
28.         JFrame frame = new JFrame();
29.         frame.setTitle("Client");
30.  
31.         FlowLayout layout = new FlowLayout();
32.         layout.setAlignment(FlowLayout.LEFT);
33.  
34.         JLabel lblFile = new JLabel("Filename:");
35.        
36.         txtFile = new JTextField();
37.         txtFile.setPreferredSize(new Dimension(150,30));
38.  
39.         JButton btnTransfer = new JButton("Transfer");
40.         btnTransfer.addActionListener(this);
41.  
42.         JPanel mainPanel = new JPanel();
43.         mainPanel.setLayout(layout);
44.         mainPanel.add(lblFile);
45.         mainPanel.add(txtFile);
46.         mainPanel.add(btnTransfer);
47.  
48.         frame.getContentPane().add(mainPanel);
49.         frame.pack();
50.         frame.setVisible(true);
51.     }
52.  
53.     public void actionPerformed(ActionEvent e) {
54.  
55.         /* File Open Dialog box allows the user to select a file */
56.  
57.         JFileChooser fileDlg = new JFileChooser();
58.         fileDlg.showOpenDialog(this);
59.         String filename = fileDlg.getSelectedFile().getAbsolutePath();
60.         txtFile.setText(filename);
61.  
62.         try{
63.  
64.             /* Try to connect to the server on localhost, port 5555 */
65.  
66.             Socket sk = new Socket("localhost", 5555);
67.             OutputStream output = sk.getOutputStream();
68.  
69.             /* Send filename to server */
70.  
71.             OutputStreamWriter outputStream = new OutputStreamWriter(sk.getOutputStream());
72.             outputStream.write(fileDlg.getSelectedFile().getName() + "\n");
73.             outputStream.flush();
74.  
75.             /* Get reponse from server */
76.  
77.             BufferedReader inReader = new BufferedReader(new InputStreamReader(sk.getInputStream()));
78.  
79.             String serverStatus = inReader.readLine(); // Read the first line
80.  
81.             /* If server is ready, send the file */
82.  
83.             if ( serverStatus.equals("READY") ){
84.  
85.                 FileInputStream file = new FileInputStream(filename);
86.  
87.                 byte[] buffer = new byte[sk.getSendBufferSize()];
88.  
89.                 int bytesRead = 0;
90.  
91.                 while((bytesRead = file.read(buffer))>0)
92.                 {
93.                     output.write(buffer,0,bytesRead);
94.                 }
95.  
96.                 output.close();
97.                 file.close();
98.                 sk.close();
99.  
100.                 JOptionPane.showMessageDialog(this, "Transfer complete");
101.             }
102.         }
103.         catch (Exception ex){
104.             /* Catch any errors */
105.             JOptionPane.showMessageDialog(this, ex.getMessage());
106.         }
107.     }
108. }
109.  
110.  
111. // Server.java
112.  
113. /*
114.  * Server waits for a connection to be established by client
115.  *
116.  */
117.  
118. import java.io.*;
119. import java.net.*;
120.  
121. class Server
122. {
123.     public static void main(String args[])throws Exception
124.     {
125.         System.out.println("Server running...");
126.  
127.         /* Listen on port 5555 */
128.  
129.         ServerSocket server = new ServerSocket(5555);
130.  
131.         /* Accept the sk */
132.  
133.         Socket sk = server.accept();
134.        
135.         System.out.println("Server accepted client");
136.         InputStream input = sk.getInputStream();
137.         BufferedReader inReader = new BufferedReader(new InputStreamReader(sk.getInputStream()));
138.         BufferedWriter outReader = new BufferedWriter(new OutputStreamWriter(sk.getOutputStream()));
139.  
140.         /* Read the filename */
141.         String filename = inReader.readLine();
142.  
143.         if ( !filename.equals("") ){
144.  
145.             /* Reply back to client with READY status */
146.  
147.             outReader.write("READY\n");
148.             outReader.flush();
149.         }
150.  
151.         /* Create a new file in the tmp directory using the filename */
152.         FileOutputStream wr = new FileOutputStream(new File("C://tmp/" + filename));
153.  
154.         byte[] buffer = new byte[sk.getReceiveBufferSize()];
155.  
156.         int bytesReceived = 0;
157.  
158.         while((bytesReceived = input.read(buffer))>0)
159.         {
160.             /* Write to the file */
161.            wr.write(buffer,0,bytesReceived);
162.         }
163.     }
164. }

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