例子中有些写法参考自Netty4源码，建议在实际运用中采用Netty，而非原生的Java NIO（小心epoll空转）。
1. 服务器端
public class NioServer {
static SelectorProvider provider = SelectorProvider.provider();
static Selector selector = null;
static ServerSocketChannel server = null;
private static void accept() throws IOException {
SocketChannel channel = null;
try {
channel = server.accept(); // 接受连接
channel.configureBlocking(false); // 非阻塞模式
channel.register(selector, SelectionKey.OP_READ, null); // 监听读就绪
} catch (IOException e) {
if (channel != null)
channel.close();
}
}
private static int read(SocketChannel channel) throws IOException {
try {
ByteBuffer buffer = ByteBuffer.allocate(1024); // 分配HeapByteBuffer
int len = channel.read(buffer); // 直到没有数据 || buffer满
if (len > 0)
System.out.println(new String(buffer.array(), 0, len, Charset.forName("UTF-8"))); // buffer.array()：取HeapByteBuffer中的原始byte[]
return len;
} catch (IOException e) {
if (channel != null)
channel.close();
return -1;
}
}
private static void write(SocketChannel channel, String msg) throws IOException {
try {
byte[] bytes = msg.getBytes(Charset.forName("UTF-8"));
ByteBuffer buffer = ByteBuffer.allocate(bytes.length); // 分配HeapByteBuffer
buffer.put(bytes);
buffer.flip(); // 切换为读模式
channel.write(buffer);
} catch (IOException e) {
if (channel != null)
channel.close();
}
}
public static void main(String[] args) throws IOException {
try {
selector = provider.openSelector();
server = provider.openServerSocketChannel();
server.configureBlocking(false); // 非阻塞模式
SelectionKey key = server.register(selector, 0, null); // 注册
if (server.bind(new InetSocketAddress(8888)).socket().isBound()) // 绑定成功
key.interestOps(SelectionKey.OP_ACCEPT); // 监听连接请求
while (true) {
selector.select(); // 监听就绪事件
Iterator<SelectionKey> it = selector.selectedKeys().iterator();
while (it.hasNext()) {
key = it.next();
it.remove(); // 从已选择键集中移除key
if (key.isAcceptable()) { // 连接请求到来
System.out.println("accept...");
accept();
} else {
SocketChannel channel = (SocketChannel) key.channel();
if (key.isWritable()) { // 写就绪
System.out.println("write...");
write(channel, "Hello NioClient!");
key.interestOps(key.interestOps() & ~SelectionKey.OP_WRITE); // 取消写就绪，否则会一直触发写就绪（写就绪为代码触发）
key.channel().close(); // 关闭channel（key将失效）
}
if (key.isValid() && key.isReadable()) { // key有效（避免在写就绪时关闭了channel或者取消了key） && 读就绪
System.out.println("read...");
int len = read(channel);
if (len >= 0)
key.interestOps(key.interestOps() | SelectionKey.OP_WRITE); // 写就绪，准备写数据
else if (len < 0) // 客户端已关闭socket
channel.close(); // 关闭channel（key将失效）
}
}
}
}
} finally {
if (server != null)
server.close();
if (selector != null)
selector.close();
}
}
}2. 客户端
public class NioClient {
static SelectorProvider provider = SelectorProvider.provider();
static Selector selector = null;
static SocketChannel client = null;
static boolean close = false;
private static void write(String msg) throws IOException {
byte[] bytes = msg.getBytes(Charset.forName("UTF-8"));
ByteBuffer buffer = ByteBuffer.allocate(bytes.length); // 建立HeapByteBuffer（DirectByteBuffer以后有机会再讨论）
buffer.put(bytes);
buffer.flip(); // 切换为读模式
client.write(buffer);
}
private static int read() throws IOException {
ByteBuffer buffer = ByteBuffer.allocate(1024); // 分配HeapByteBuffer
int len = client.read(buffer); // 直到没有数据 || buffer满
if (len > 0)
System.out.println(new String(buffer.array(), 0, len, Charset.forName("UTF-8"))); // buffer.array()：取HeapByteBuffer中的原始byte[]
return len;
}
public static void main(String[] args) throws IOException {
try {
selector = provider.openSelector();
client = provider.openSocketChannel();
client.configureBlocking(false); // 非阻塞模式
SelectionKey key = client.register(selector, 0, null); // 注册
if (client.connect(new InetSocketAddress("127.0.0.1", 8888))) { // 连接成功（很难）
System.out.println("connected...");
key.interestOps(SelectionKey.OP_READ | SelectionKey.OP_WRITE); // 监听读就绪和写就绪（准备写数据）
} else // 连接失败（正常情况下）
key.interestOps(SelectionKey.OP_CONNECT); // 监听连接就绪
while (!close) {
selector.select(); // 监听就绪事件
Iterator<SelectionKey> it = selector.selectedKeys().iterator();
while (it.hasNext()) {
key = it.next();
it.remove(); // 从已选择键集移除key
if (key.isConnectable()) { // 连接就绪
client.finishConnect(); // 完成连接
System.out.println("connected...");
key.interestOps(key.interestOps() & ~SelectionKey.OP_CONNECT); // 取消监听连接就绪（否则selector会不断提醒连接就绪）
key.interestOps(key.interestOps() | SelectionKey.OP_READ | SelectionKey.OP_WRITE); // 监听读就绪和写就绪
} else {
if (key.isWritable()) { // 写就绪
System.out.println("write...");
write("Hello NioServer!");
key.interestOps(key.interestOps() & ~SelectionKey.OP_WRITE); // 取消写就绪，否则会一直触发写就绪（写就绪为代码触发）
}
if (key.isValid() && key.isReadable()) { // key有效（避免在写就绪时关闭了channel或者取消了key） && 读就绪
System.out.println("read...");
if (read() < 0) // 服务器已关闭socket
close = true; // 退出循环
}
}
}
}
} finally {
if (client != null)
client.close();
if (selector != null)
selector.close();
}
}
}