Java tutorial
/* * Copyright (c) 2004 David Flanagan. All rights reserved. * This code is from the book Java Examples in a Nutshell, 3nd 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, * including teaching and use in open-source projects. * You may distribute it non-commercially as long as you retain this notice. * For a commercial use license, or to purchase the book, * please visit http://www.davidflanagan.com/javaexamples3. */ //package je3.nio; import java.io.FileOutputStream; import java.io.IOException; import java.net.InetSocketAddress; import java.net.SocketAddress; import java.net.URI; import java.nio.BufferUnderflowException; import java.nio.ByteBuffer; import java.nio.CharBuffer; import java.nio.channels.Channels; import java.nio.channels.SocketChannel; import java.nio.channels.WritableByteChannel; import java.nio.charset.Charset; public class HttpGet { public static void main(String[] args) { SocketChannel server = null; // Channel for reading from server FileOutputStream outputStream = null; // Stream to destination file WritableByteChannel destination; // Channel to write to it try { // Exception handling and channel closing code follows this block // Parse the URL. Note we use the new java.net.URI, not URL here. URI uri = new URI(args[0]); // Now query and verify the various parts of the URI String scheme = uri.getScheme(); if (scheme == null || !scheme.equals("http")) throw new IllegalArgumentException("Must use 'http:' protocol"); String hostname = uri.getHost(); int port = uri.getPort(); if (port == -1) port = 80; // Use default port if none specified String path = uri.getRawPath(); if (path == null || path.length() == 0) path = "/"; String query = uri.getRawQuery(); query = (query == null) ? "" : '?' + query; // Combine the hostname and port into a single address object. // java.net.SocketAddress and InetSocketAddress are new in Java 1.4 SocketAddress serverAddress = new InetSocketAddress(hostname, port); // Open a SocketChannel to the server server = SocketChannel.open(serverAddress); // Put together the HTTP request we'll send to the server. String request = "GET " + path + query + " HTTP/1.1\r\n" + // The request "Host: " + hostname + "\r\n" + // Required in HTTP 1.1 "Connection: close\r\n" + // Don't keep connection open "User-Agent: " + HttpGet.class.getName() + "\r\n" + "\r\n"; // Blank // line // indicates // end of // request // headers // Now wrap a CharBuffer around that request string CharBuffer requestChars = CharBuffer.wrap(request); // Get a Charset object to encode the char buffer into bytes Charset charset = Charset.forName("ISO-8859-1"); // Use the charset to encode the request into a byte buffer ByteBuffer requestBytes = charset.encode(requestChars); // Finally, we can send this HTTP request to the server. server.write(requestBytes); // Set up an output channel to send the output to. if (args.length > 1) { // Use a specified filename outputStream = new FileOutputStream(args[1]); destination = outputStream.getChannel(); } else // Or wrap a channel around standard out destination = Channels.newChannel(System.out); // Allocate a 32 Kilobyte byte buffer for reading the response. // Hopefully we'll get a low-level "direct" buffer ByteBuffer data = ByteBuffer.allocateDirect(32 * 1024); // Have we discarded the HTTP response headers yet? boolean skippedHeaders = false; // The code sent by the server int responseCode = -1; // Now loop, reading data from the server channel and writing it // to the destination channel until the server indicates that it // has no more data. while (server.read(data) != -1) { // Read data, and check for end data.flip(); // Prepare to extract data from buffer // All HTTP reponses begin with a set of HTTP headers, which // we need to discard. The headers end with the string // "\r\n\r\n", or the bytes 13,10,13,10. If we haven't already // skipped them then do so now. if (!skippedHeaders) { // First, though, read the HTTP response code. // Assume that we get the complete first line of the // response when the first read() call returns. Assume also // that the first 9 bytes are the ASCII characters // "HTTP/1.1 ", and that the response code is the ASCII // characters in the following three bytes. if (responseCode == -1) { responseCode = 100 * (data.get(9) - '0') + 10 * (data.get(10) - '0') + 1 * (data.get(11) - '0'); // If there was an error, report it and quit // Note that we do not handle redirect responses. if (responseCode < 200 || responseCode >= 300) { System.err.println("HTTP Error: " + responseCode); System.exit(1); } } // Now skip the rest of the headers. try { for (;;) { if ((data.get() == 13) && (data.get() == 10) && (data.get() == 13) && (data.get() == 10)) { skippedHeaders = true; break; } } } catch (BufferUnderflowException e) { // If we arrive here, it means we reached the end of // the buffer and didn't find the end of the headers. // There is a chance that the last 1, 2, or 3 bytes in // the buffer were the beginning of the \r\n\r\n // sequence, so back up a bit. data.position(data.position() - 3); // Now discard the headers we have read data.compact(); // And go read more data from the server. continue; } } // Write the data out; drain the buffer fully. while (data.hasRemaining()) destination.write(data); // Now that the buffer is drained, put it into fill mode // in preparation for reading more data into it. data.clear(); // data.compact() also works here } } catch (Exception e) { // Report any errors that arise System.err.println(e); System.err.println("Usage: java HttpGet <URL> [<filename>]"); } finally { // Close the channels and output file stream, if needed try { if (server != null && server.isOpen()) server.close(); if (outputStream != null) outputStream.close(); } catch (IOException e) { } } } }