NIO主要原理和适用。
NIO 有一个主要的类Selector,这个类似一个观察者，只要我们把需要探知的socketchannel告诉Selector,我们接着做别的事情，当有 事件发生时，他会通知我们，传回一组SelectionKey,我们读取这些Key,就会获得我们刚刚注册过的socketchannel,然后，我们从 这个Channel中读取数据，放心，包准能够读到，接着我们可以处理这些数据。
Selector内部原理实际是在做一个对所注册的channel的轮询访问，不断的轮询(目前就这一个算法)，一旦轮询到一个channel有所注册的事情发生，比如数据来了，他就会站起来报告，交出一把钥匙，让我们通过这把钥匙来读取这个channel的内容。
jdk供的无阻塞I/O（NIO）有效解决了多线程服务器存在的线程开销问题，但在使用上略显得复杂一些。在NIO中使用多线程，主要目的已不是为了应对 每个客户端请求而分配独立的服务线程，而是通过多线程充分使用用多个CPU的处理能力和处理中的等待时间，达到提高服务能力的目的。
这段时间在研究NIO，写篇博客来记住学过的东西。还是从最简单的Hello World开始，
client多线程请求server端，server接收client的名字，并返回Hello! ＋名字的字符格式给client。当然实际应用并不这么简单，实际可能是访问文件或者数据库获取信息返回给client。非阻塞的NIO有何神秘之处？代码：
1)server端代码
public class HelloWorldServer {
static int BLOCK = 1024;
static String name = "";
protected Selector selector;
protected ByteBuffer clientBuffer = ByteBuffer.allocate(BLOCK);
protected CharsetDecoder decoder;
static CharsetEncoder encoder = Charset.forName("GB2312").newEncoder();
public HelloWorldServer(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();
process(key);
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
// 处理事件
protected void process(SelectionKey key) throws IOException {
if (key.isAcceptable()) { // 接收请求
ServerSocketChannel server = (ServerSocketChannel) key.channel();
SocketChannel channel = server.accept();
//设置非阻塞模式
channel.configureBlocking(false);
channel.register(selector, SelectionKey.OP_READ);
} else if (key.isReadable()) { // 读信息
SocketChannel channel = (SocketChannel) key.channel();
int count = channel.read(clientBuffer);
if (count > 0) {
clientBuffer.flip();
CharBuffer charBuffer = decoder.decode(clientBuffer);
name = charBuffer.toString();
// System.out.println(name);
SelectionKey sKey = channel.register(selector,
SelectionKey.OP_WRITE);
sKey.attach(name);
} else {
channel.close();
}
clientBuffer.clear();
} else if (key.isWritable()) { // 写事件
SocketChannel channel = (SocketChannel) key.channel();
String name = (String) key.attachment();
ByteBuffer block = encoder.encode(CharBuffer
.wrap("Hello !" + name));
channel.write(block);
//channel.close();
}
}
public static void main(String[] args) {
int port = 8888;
try {
HelloWorldServer server = new HelloWorldServer(port);
System.out.println("listening on " + port);
server.listen();
} catch (IOException e) {
e.printStackTrace();
}
}
}
2)client端代码
public class HelloWorldClient {
static int SIZE = 10;
static InetSocketAddress ip = new InetSocketAddress("localhost", 8888);
static CharsetEncoder encoder = Charset.forName("GB2312").newEncoder();
static class Message implements Runnable {
protected String name;
String msg = "";
public Message(String index) {
this.name = index;
}
public void run() {
try {
long start = System.currentTimeMillis();
//打开Socket通道
SocketChannel client = SocketChannel.open();
//设置为非阻塞模式
client.configureBlocking(false);
//打开选择器
Selector selector = Selector.open();
//注册连接服务端socket动作
client.register(selector, SelectionKey.OP_CONNECT);
//连接
client.connect(ip);
//分配内存
ByteBuffer buffer = ByteBuffer.allocate(8 * 1024);
int total = 0;
_FOR: for (;;) {
selector.select();
Iterator iter = selector.selectedKeys().iterator();
while (iter.hasNext()) {
SelectionKey key = (SelectionKey) iter.next();
iter.remove();
if (key.isConnectable()) {
SocketChannel channel = (SocketChannel) key
.channel();
if (channel.isConnectionPending())
channel.finishConnect();
channel
.write(encoder
.encode(CharBuffer.wrap(name)));
channel.register(selector, SelectionKey.OP_READ);
} else if (key.isReadable()) {
SocketChannel channel = (SocketChannel) key
.channel();
int count = channel.read(buffer);
if (count > 0) {
total += count;
buffer.flip();
while (buffer.remaining() > 0) {
byte b = buffer.get();
msg += (char) b;
}
buffer.clear();
} else {
client.close();
break _FOR;
}
}
}
}
double last = (System.currentTimeMillis() - start) * 1.0 / 1000;
System.out.println(msg + "used time :" + last + "s.");
msg = "";
} catch (IOException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) throws IOException {
String names[] = new String[SIZE];
for (int index = 0; index < SIZE; index++) {
names[index] = "jeff[" + index + "]";
new Thread(new Message(names[index])).start();
}
}
}