Java sockets 101

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

public class URLClient {
    protected HttpURLConnection connection;
    public String getDocumentAt(String urlString) {
        StringBuffer document = new StringBuffer();
        try {
            URL url = new URL(urlString);
            URLConnection conn = url.openConnection();
            BufferedReader reader = 
              new BufferedReader(new InputStreamReader(conn.getInputStream()));

            String line = null;
            while ((line = reader.readLine()) != null)
                document.append(line + "\n");

            reader.close();
        } catch (MalformedURLException e) {
            System.out.println("Unable to connect to URL: " + urlString);
        } catch (IOException e) {
            System.out.println("IOException when connecting to URL: " + urlString);
        }

        return document.toString();
    }
    public static void main(String[] args) {
        URLClient client = new URLClient();
        String yahoo = client.getDocumentAt("http://www.yahoo.com");

        System.out.println(yahoo);
    }
}

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

public class RemoteFileClient {
    protected BufferedReader socketReader;
    protected PrintWriter socketWriter;
    protected String hostIp;
    protected int hostPort;

    public RemoteFileClient(String aHostIp, int aHostPort) {
        hostIp = aHostIp;
        hostPort = aHostPort;
    }
    public String getFile(String fileNameToGet) {
        StringBuffer fileLines = new StringBuffer();

        try {
            socketWriter.println(fileNameToGet);
            socketWriter.flush();

            String line = null;
            while ((line = socketReader.readLine()) != null)
                fileLines.append(line + "\n");
        } catch (IOException e) {
            System.out.println("Error reading from file: " + fileNameToGet);
        }

        return fileLines.toString();
    }
    public static void main(String[] args) {
        RemoteFileClient remoteFileClient = new RemoteFileClient("127.0.0.1", 3000);
        remoteFileClient.setUpConnection();
        String fileContents = 
          remoteFileClient.getFile("C:\\WINNT\\Temp\\RemoteFile.txt");
        remoteFileClient.tearDownConnection();

        System.out.println(fileContents);
    }
    public void setUpConnection() {
        try {
            Socket client = new Socket(hostIp, hostPort);

            socketReader = 
              new BufferedReader(new InputStreamReader(client.getInputStream()));
            socketWriter = new PrintWriter(client.getOutputStream());

        } catch (UnknownHostException e) {
            System.out.println("Error setting up socket connection: 
              unknown host at " + hostIp + ":" + hostPort);
        } catch (IOException e) {
            System.out.println("Error setting up socket connection: " + e);
        }
    }
    public void tearDownConnection() {
        try {
            socketWriter.close();
            socketReader.close();
        } catch (IOException e) {
            System.out.println("Error tearing down socket connection: " + e);
        }
    }
}

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

public class RemoteFileServer {
    int listenPort;
    public RemoteFileServer(int aListenPort) {
        listenPort = aListenPort;
    }
    public void acceptConnections() {
        try {
            ServerSocket server = new ServerSocket(listenPort);
            Socket incomingConnection = null;
            while (true) {
                incomingConnection = server.accept();
                handleConnection(incomingConnection);
            }
        } catch (BindException e) {
            System.out.println("Unable to bind to port " + listenPort);
        } catch (IOException e) {
            System.out.println("Unable to instantiate a 
              ServerSocket on port: " + listenPort);
        }
    }
    public void handleConnection(Socket incomingConnection) {
        try {
            OutputStream outputToSocket = incomingConnection.getOutputStream();
            InputStream inputFromSocket = incomingConnection.getInputStream();

            BufferedReader streamReader = 
              new BufferedReader(new InputStreamReader(inputFromSocket));

            FileReader fileReader = new FileReader(new File(streamReader.readLine()));

            BufferedReader bufferedFileReader = new BufferedReader(fileReader);
            PrintWriter streamWriter = 
              new PrintWriter(incomingConnection.getOutputStream());
            String line = null;
            while ((line = bufferedFileReader.readLine()) != null) {
                streamWriter.println(line);
            }

            fileReader.close();
            streamWriter.close();
            streamReader.close();
        } catch (Exception e) {
            System.out.println("Error handling a client: " + e);
        }
    }
    public static void main(String[] args) {
        RemoteFileServer server = new RemoteFileServer(3000);
        server.acceptConnections();
    }
}

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

public class MultithreadedRemoteFileServer {
    protected int listenPort;
    public MultithreadedRemoteFileServer(int aListenPort) {
        listenPort = aListenPort;
    }
    public void acceptConnections() {
        try {
            ServerSocket server = new ServerSocket(listenPort, 5);
            Socket incomingConnection = null;
            while (true) {
                incomingConnection = server.accept();
                handleConnection(incomingConnection);
            }
        } catch (BindException e) {
            System.out.println("Unable to bind to port " + listenPort);
        } catch (IOException e) {
            System.out.println("Unable to instantiate a 
              ServerSocket on port: " + listenPort);
        }
    }
    public void handleConnection(Socket connectionToHandle) {
        new Thread(new ConnectionHandler(connectionToHandle)).start();
    }
    public static void main(String[] args) {
        MultithreadedRemoteFileServer server = 
          new MultithreadedRemoteFileServer(3000);
        server.acceptConnections();
    }
}

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

public class ConnectionHandler implements Runnable {
    protected Socket socketToHandle;
    public ConnectionHandler(Socket aSocketToHandle) {
        socketToHandle = aSocketToHandle;
    }
    public void run() {
        try {
            PrintWriter streamWriter = 
              new PrintWriter(socketToHandle.getOutputStream());
            BufferedReader streamReader = 
              new BufferedReader(new InputStreamReader(socketToHandle.getInputStream()));
 
            String fileToRead = streamReader.readLine();
            BufferedReader fileReader = 
              new BufferedReader(new FileReader(fileToRead));

            String line = null;
            while ((line = fileReader.readLine()) != null)
                streamWriter.println(line);

            fileReader.close();
            streamWriter.close();
            streamReader.close();
        } catch (Exception e) {
            System.out.println("Error handling a client: " + e);
        }
    }
}

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

public class PooledRemoteFileServer {
    protected int maxConnections;
    protected int listenPort;
    protected ServerSocket serverSocket;
    public PooledRemoteFileServer(int aListenPort, int maxConnections) {
        listenPort = aListenPort;
        this.maxConnections = maxConnections;
    }
    public void acceptConnections() {
        try {
            ServerSocket server = new ServerSocket(listenPort, 5);
            Socket incomingConnection = null;
            while (true) {
                incomingConnection = server.accept();
                handleConnection(incomingConnection);
            }
        } catch (BindException e) {
            System.out.println("Unable to bind to port " + listenPort);
        } catch (IOException e) {
            System.out.println("Unable to instantiate a 
              ServerSocket on port: " + listenPort);
        }
    }
    protected void handleConnection(Socket connectionToHandle) {
        PooledConnectionHandler.processRequest(connectionToHandle);
    }
    public static void main(String[] args) {
        PooledRemoteFileServer server = new PooledRemoteFileServer(3000, 3);
        server.setUpHandlers();
        server.acceptConnections();
    }
    public void setUpHandlers() {
        for (int i = 0; i < maxConnections; i++) {
            PooledConnectionHandler currentHandler =
              new PooledConnectionHandler();
            new Thread(currentHandler, "Handler " + i).start();
        }
    }
}

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

public class PooledConnectionHandler implements Runnable {
    protected Socket connection;
    protected static List pool = new LinkedList();
    public PooledConnectionHandler() {
    }
    public void handleConnection() {
        try {
            PrintWriter streamWriter = new PrintWriter(connection.getOutputStream());
            BufferedReader streamReader = 
              new BufferedReader(new InputStreamReader(connection.getInputStream()));

            String fileToRead = streamReader.readLine();
            BufferedReader fileReader = new BufferedReader(new FileReader(fileToRead));

            String line = null;
            while ((line = fileReader.readLine()) != null)
                streamWriter.println(line);

            fileReader.close();
            streamWriter.close();
            streamReader.close();
        } catch (FileNotFoundException e) {
            System.out.println("Could not find requested file on the server.");
        } catch (IOException e) {
            System.out.println("Error handling a client: " + e);
        }
    }
    public static void processRequest(Socket requestToHandle) {
        synchronized (pool) {
            pool.add(pool.size(), requestToHandle);
            pool.notifyAll();
        }
    }
    public void run() {
        while (true) {
            synchronized (pool) {
                while (pool.isEmpty()) {
                    try {
                        pool.wait();
                    } catch (InterruptedException e) {
                        return;
                    }
                }
                connection = (Socket) pool.remove(0);
            }
            handleConnection();
        }
    }
}