java学习——NIO篇2
在前面写的nio学习中是采取的简单的demo，后来在网上看到一个demo，一个用来多线程下载的demo，在这个demo里才会体现nio的高性能之处。充分体现nio的优势。
场景：一个服务端，然后100个客户端同时连接服务端，然后下载一个文件下来。服务端只需要一个连接来处理这些来自客户端的连接。其中对文件的传递采用的是nio中的FileChannel?。很好用的一个东西。
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忘记从哪里转过来的代码了。。。
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服务端：
import java.io.FileInputStream;import java.io.IOException;import java.net.InetSocketAddress;import java.nio.ByteBuffer;import java.nio.CharBuffer;import java.nio.channels.FileChannel;import java.nio.channels.SelectionKey;import java.nio.channels.Selector;import java.nio.channels.ServerSocketChannel;import java.nio.channels.SocketChannel;import java.nio.charset.Charset;import java.nio.charset.CharsetDecoder;import java.util.Iterator;public class NIOServer { static int BLOCK = 4096; // 处理与客户端的交互 public class HandleClient { protected FileChannel channel; protected ByteBuffer buffer; public HandleClient() throws IOException { this.channel = new FileInputStream(filename).getChannel(); this.buffer = ByteBuffer.allocate(BLOCK); } public ByteBuffer readBlock() { try { buffer.clear(); int count = channel.read(buffer); buffer.flip(); if (count <= 0) return null; } catch (IOException e) { e.printStackTrace(); } return buffer; } public void close() { try { channel.close(); } catch (IOException e) { e.printStackTrace(); } } } protected Selector selector; protected String filename = "d:\\test.jpg"; // a big file protected ByteBuffer clientBuffer = ByteBuffer.allocate(BLOCK); protected CharsetDecoder decoder; public NIOServer(int port) throws IOException { selector = this.getSelector(port); Charset charset = Charset.forName("GB2312"); decoder = charset.newDecoder(); } // 获取Selector protected Selector getSelector(int port) throws IOException { ServerSocketChannel server = ServerSocketChannel.open(); Selector sel = Selector.open(); server.socket().bind(new InetSocketAddress(port)); server.configureBlocking(false); server.register(sel, SelectionKey.OP_ACCEPT); return sel; } // 监听端口 public void listen() { try { for (;;) { selector.select(); Iterator iter = selector.selectedKeys().iterator(); while (iter.hasNext()) { SelectionKey key = (SelectionKey) iter.next(); iter.remove(); handleKey(key); } } } catch (IOException e) { e.printStackTrace(); } } // 处理事件 protected void handleKey(SelectionKey key) throws IOException { if (key.isAcceptable()) { // 接收请求 ServerSocketChannel server = (ServerSocketChannel) key.channel(); SocketChannel channel = server.accept(); channel.configureBlocking(false); channel.register(selector, SelectionKey.OP_READ); } else if (key.isReadable()) { // 读信息 System.out.println("能读"); SocketChannel channel = (SocketChannel) key.channel(); int count = channel.read(clientBuffer); if (count > 0) { clientBuffer.flip(); CharBuffer charBuffer = decoder.decode(clientBuffer); System.out.println("Client >>" + charBuffer.toString()); SelectionKey wKey = channel.register(selector, SelectionKey.OP_WRITE); wKey.attach(new HandleClient()); } else channel.close(); clientBuffer.clear(); } else if (key.isWritable()) { // 写事件 System.out.println("能写"); SocketChannel channel = (SocketChannel) key.channel(); HandleClient handle = (HandleClient) key.attachment(); ByteBuffer block = handle.readBlock(); if (block != null) channel.write(block); else { handle.close(); channel.close(); } } } public static void main(String[] args) { int port = 12345; try { NIOServer server = new NIOServer(port); System.out.println("Listernint on " + port); while (true) { server.listen(); } } catch (IOException e) { e.printStackTrace(); } }}?客户端：
import java.io.File;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.net.InetSocketAddress;import java.nio.ByteBuffer;import java.nio.CharBuffer;import java.nio.channels.FileChannel;import java.nio.channels.SelectionKey;import java.nio.channels.Selector;import java.nio.channels.SocketChannel;import java.nio.charset.Charset;import java.nio.charset.CharsetEncoder;import java.util.Iterator;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public class NIOClient { static int SIZE = 10; static InetSocketAddress ip = new InetSocketAddress("localhost", 12345); static CharsetEncoder encoder = Charset.forName("GB2312").newEncoder(); static FileChannel[] filechannel = new FileChannel[SIZE]; static class Download implements Runnable { protected int index; public Download(int index) { this.index = index; } public void run() { try { long start = System.currentTimeMillis(); SocketChannel client = SocketChannel.open(); client.configureBlocking(false); Selector selector = Selector.open(); client.register(selector, SelectionKey.OP_CONNECT); client.connect(ip); ByteBuffer buffer = ByteBuffer.allocate(8 * 1024); int total = 0; boolean flag = true; while (flag) { selector.select(); Iterator iter = selector.selectedKeys().iterator(); while (iter.hasNext()) { SelectionKey key = iter.next(); iter.remove(); if (key.isConnectable()) { SocketChannel channel = (SocketChannel) key.channel(); if (channel.isConnectionPending()) channel.finishConnect(); channel.write(encoder.encode(CharBuffer.wrap("Hello from " + index))); channel.register(selector, SelectionKey.OP_READ); } else if (key.isReadable()) { SocketChannel channel = (SocketChannel) key.channel(); int count = channel.read(buffer); if (count > 0) { writeToFile(buffer, index); total += count; buffer.clear(); } else { filechannel[index].close(); client.close(); flag = false; } } } } double last = (System.currentTimeMillis() - start) * 1.0 / 1000; System.out.println("Thread " + index + " downloaded " + total + "bytes in " + last + "s."); } catch (IOException e) { e.printStackTrace(); } } } public static synchronized void writeToFile(ByteBuffer bb, int index) { try { if (filechannel[index] == null) { filechannel[index] = new FileOutputStream(new File("test" + index + ".jpg")).getChannel(); } bb.flip(); filechannel[index].write(bb); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public static void main(String[] args) throws IOException { ExecutorService exec = Executors.newFixedThreadPool(SIZE); for (int index = 0; index < SIZE; index++) { exec.execute(new Download(index)); } exec.shutdown(); }}?