NIO核心组件Channel
# NIO核心组件 - Channel
## SocketChannel 和 ServerSocketChannel
学习此部分可以对比Socket和ServerSocket
服务端代码
```java
public class NioSocketServer01 {
public static void main(String[] args) {
try {
// ServerSocketChannel 支持阻塞/非阻塞
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
// 设置成非阻塞。默认阻塞true
serverSocketChannel.configureBlocking(false);
serverSocketChannel.socket().bind(new InetSocketAddress(8080));
// 循环监听客户端连接
while (true) {
// 如果有客户端连接，则返回一个socketChannel实例，否则socketChannel=null
SocketChannel socketChannel = serverSocketChannel.accept();
// 代码执行到此处，说明有客户端链接
if (socketChannel != null) {
// 读取客户端发送的数据，并输出
ByteBuffer buffer = ByteBuffer.allocate(1024);
socketChannel.read(buffer);
System.err.println(new String(buffer.array()));
// 将数据在写会客户端
buffer.flip();
socketChannel.write(buffer);
//验证客户端 socketChannel设置成false时，从服务端read数据的操作变成非阻塞的
//ByteBuffer buffer = ByteBuffer.allocate(1024);
//buffer.put("this is server!");
//buffer.flip();
//socketChannel.write(buffer);
} else {
Thread.sleep(1000L);
System.err.println("no client");
}
}
} catch (IOException | InterruptedException e) {
e.printStackTrace();
}
}
}
```
客户端代码
```java
public class NioSocketClient1 {
public static void main(String[] args) {
try {
SocketChannel socketChannel = SocketChannel.open();
// 默认阻塞IO true
socketChannel.configureBlocking(false);
socketChannel.connect(new InetSocketAddress("localhost", 8080));
// finishConnect的主要作用就是确认通道连接已建立，方便后续IO操作（读写）不会因连接没建立而导致NotYetConnectedException异常。
if (socketChannel.isConnectionPending()) {
// finishConnect一直阻塞到connect建立完成
socketChannel.finishConnect();
}
ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
byteBuffer.put("hello world".getBytes());
byteBuffer.flip();
socketChannel.write(byteBuffer);
byteBuffer.clear();
int r = socketChannel.read(byteBuffer); // 非阻塞方法 byteBuffer的数据还是上面put的
if (r > 0) {
System.out.println("get msg:{}" + new String(byteBuffer.array()));
} else {
System.out.println("server no back");
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
```