httpimpl.java

java的经典例子

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


public class HttpImpl extends HttpURLConnection {
    Socket sock = null;

    public HttpImpl(URL url) {
        super(url);
    }

    // Establishes connection to HTTP server and sends request
    // Implementation of abstract method defined in URLConnection
    public void connect() throws IOException {
	if (connected) {
	    return;
	}
        InetAddress dst = InetAddress.getByName(getURL().getHost());
        int port;
        if ((port = getURL().getPort()) == -1)
            port = 80;        // default port number for HTTP
	sock = new Socket(dst, port);
	OutputStream out = sock.getOutputStream();

	send(out, getRequestMethod() + " " + url.toString() + 
	     " HTTP/1.1\r\n");
	send(out, "\r\n");
	connected  = true;
    }


    // Disconnects from HTTP server.
    // Implementation of abstract method defined in HttpURLConnection
    public void disconnect() {
	if (sock != null) {
	    try {
		sock.close();
	    } catch (IOException e) {
	    }
	}
	connected = false;
    }

// START getFollowRedirects
    public Object getContent() throws IOException {
	connect();  // make sure we're connected

	int code = getResponseCode(); // get response code
	if (getFollowRedirects() && (code/100) == 3) {
	    String newLocation = getHeaderField("location");
	    if (newLocation != null) {
		// Very simplistic assumption: use HTTP again
		HttpImpl n = new HttpImpl(new URL(newLocation));
		return n.getContent();
	    }
	}
	// else just continue as before
	return super.getContent();
    }
// END

    // Implementation of abstract method defined in HttpURLConnection
    public boolean usingProxy() {
	return false; // this simple impl does not use proxy
    }

    // Override default provided in URLConnection
    public InputStream getInputStream() throws IOException {
	if (!connected)
	    throw new IOException("Connection not established yet");
	return sock.getInputStream();
    }

    // Override default provided in URLConnection
    public OutputStream getOutputStream() throws IOException {
	if (!connected)
	    throw new IOException("Connection not established yet");
	return sock.getOutputStream();
    }

    // Override default provided in URLConnection
    public String getHeaderField(int n) {
	getHeaders();
	if (n < headers.size()) {
	    return getField((String)headers.elementAt(n));
	}
	return null;
    }

    // Override default provided in URLConnection
    public String getHeaderField(String key) {
	getHeaders();
	return (String)keys.get(key.toLowerCase());
    }

    // Override default provided in URLConnection
    public String getHeaderFieldKey(int n) {
	getHeaders();
	if (n < headers.size()) {
	    return getKey((String)headers.elementAt(n));
	}
	return null;
    }


    // Helper routine to send a string to an output stream
    static void send(OutputStream out, String s) throws IOException {
        for (int i=0; i<s.length(); i++) {
            out.write((byte)s.charAt(i));
        }
        out.flush();
    }

    // Helper routine to read a newline-terminated string from input stream
    static String recv(InputStream in) throws IOException {
        String result = "";
        int c = in.read();

        while (c >= 0 && c != '\n') {
            if (c != '\r') {
                result += (char)c;
            }
            c = in.read();
        }
        return result;
    }


    // Helper routines for parsing header field
    private static final char keySeparator = ':';
    static String getKey(String str) {
	if (str == null)
	    return null;
	int ind = str.indexOf(keySeparator);
	if (ind >= 0)
	    return str.substring(0, ind).toLowerCase();
	return null;
    }

    static String getField(String str) {
	if (str == null)
	    return null;
	int ind = str.indexOf(keySeparator);
	if (ind >= 0)
	    return str.substring(ind+1).trim();
	else
	    return str;
    }


    // Helper routine that reads header from HTTP connection
    Hashtable keys = new Hashtable();
    Vector headers = new Vector();
    boolean gotten = false;
    void getHeaders() {
	if (gotten)
	    return;
	gotten = true;
	try {
	    connect();
	    InputStream in = sock.getInputStream();
	    while (true) {
		String header = recv(in);
		if (header.length() == 0)
		    break;
System.out.println("Header:" + header);
		headers.addElement(header);
		String key = getKey(header);
		if (key != null) {
		    keys.put(key, getField(header));
		 }
	    }
	} catch (IOException e) {
	    e.printStackTrace();
	}
    }
}