httpclient.java

164个完整的Java程序源代码,包括了19种Java技术的164个类源代码

/*
 * Copyright (c) 2000 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 2nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book (recommended),
 * visit http://www.davidflanagan.com/javaexamples2.
 */
package com.davidflanagan.examples.net;
import java.io.*;
import java.net.*;

/**
 * This program connects to a Web server and downloads the specified URL
 * from it.  It uses the HTTP protocol directly.
 **/
public class HttpClient {
    public static void main(String[] args) {
        try {
            // Check the arguments
            if ((args.length != 1) && (args.length != 2))
                throw new IllegalArgumentException("Wrong number of args");
            
            // Get an output stream to write the URL contents to
            OutputStream to_file;
            if (args.length == 2) to_file = new FileOutputStream(args[1]);
            else to_file = System.out;
            
            // Now use the URL class to parse the user-specified URL into
            // its various parts.  
            URL url = new URL(args[0]);
            String protocol = url.getProtocol();
            if (!protocol.equals("http")) // Check that we support the protocol
               throw new IllegalArgumentException("Must use 'http:' protocol");
            String host = url.getHost();
            int port = url.getPort();
            if (port == -1) port = 80; // if no port, use the default HTTP port
            String filename = url.getFile();

            // Open a network socket connection to the specified host and port
            Socket socket = new Socket(host, port);

            // Get input and output streams for the socket
            InputStream from_server = socket.getInputStream();
            PrintWriter to_server = new PrintWriter(socket.getOutputStream());
            
            // Send the HTTP GET command to the Web server, specifying the file
            // This uses an old and very simple version of the HTTP protocol
            to_server.print("GET " + filename + "\n\n");
            to_server.flush();  // Send it right now!
            
            // Now read the server's response, and write it to the file
            byte[] buffer = new byte[4096];
            int bytes_read;
            while((bytes_read = from_server.read(buffer)) != -1)
                to_file.write(buffer, 0, bytes_read);
            
            // When the server closes the connection, we close our stuff
            socket.close();
            to_file.close();
        }
        catch (Exception e) {    // Report any errors that arise
            System.err.println(e);
            System.err.println("Usage: java HttpClient <URL> [<filename>]");
        }
    }
}