java nio 第一弹

浏览数：24 / 时间：2015年06月08日

java NIO 第一弹----概览

摘要：

Non-blocking I/O (usually called NIO, and sometimes called "New I/O") is a collection of Java programming language APIs that offer features for intensive I/Ooperations. It was introduced with the J2SE 1.4 release of Java by Sun Microsystems to complement an existing standard I/O. NIO was developed under the Java Community Process as JSR 51.^[1]

大意：非阻塞I/O(通常叫做NIO，有时也叫新的I/O),是一组提供了加强版I/O操作特性的java api。在java1.4时由sun公司引入。

本系列主要着眼于网络部分，对本地文件操作没有涉及。接下来先看一段代码，展示了最简单Echo服务端。

代码示例

 1         ByteBuffer bb = ByteBuffer.allocate(1024);
 2         /**创建选择器*/
 3         Selector selector = Selector.open();
 4         /**打开一个服务端通道*/
 5         ServerSocketChannel ssc = ServerSocketChannel.open();
 6         /**设置为非阻塞*/
 7         ssc.configureBlocking(false);
 8         /**从通道中拿到服务端socket*/
 9         ServerSocket ss = ssc.socket();
10         /**绑定一个端口*/
11         InetSocketAddress addr = new InetSocketAddress(1234);
12         ss.bind(addr);
13         /**注册感兴趣事件，服务端通道只能注册接受事件*/
14         ssc.register(selector, SelectionKey.OP_ACCEPT);
15         String receivedMsg = "";
16         /**主循环*/
17         while(true){
18             int num = selector.select();
19             System.out.println(num+"个事件发生。。。");
20             Set<SelectionKey> selectedKeys = selector.selectedKeys();
21             Iterator<SelectionKey> it = selectedKeys.iterator();
22             
23             /**循环处理每个通道事件*/
24             while(it.hasNext()){
25                 SelectionKey key = it.next();
26                 it.remove();
27                 if(key.readyOps() == SelectionKey.OP_ACCEPT){
28                     System.out.println("新连接建立事件");
29                     ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel();
30                     SocketChannel sc = serverSocketChannel.accept();
31                     sc.configureBlocking(false);
32                     sc.register(selector, SelectionKey.OP_READ);
33                 }else if((key.readyOps()&SelectionKey.OP_READ) == SelectionKey.OP_READ){
34                     System.out.println("读事件");
35                     SocketChannel sc = (SocketChannel) key.channel();
36                     sc.read(bb);
37                     receivedMsg = new String(bb.array(),0,bb.position());
38                     bb.clear();
39                     sc.register(selector, SelectionKey.OP_WRITE);
40                 }else if(key.readyOps() == SelectionKey.OP_WRITE){
41                     System.out.println("写数据");
42                     SocketChannel sc = (SocketChannel) key.channel();
43                     sc.write(ByteBuffer.wrap(receivedMsg.getBytes()));
44                     /**没有cancel就会一直循环进入此处，因为只要通道不阻塞会一直有写事件，所以使用完需要取消*/
45                     key.cancel();
46                 }else{
47                     System.out.println("other event");
48                 }
49             }
50         }