和TCP的SocketChannel类似,UDP的
DatagramChannel能充分利用NIO的优势。
服务端:Selector,
DatagramChannel, ByteBuffer
客户端:
DatagramChannel, ByteBuffer
区别:
a. 服务端没有与TCP的ServerSocketChannel相对应的Channel,服务端和客户端之间更趋于平等,不过服务端的端口号还是固定的。
b. Selector在处理完读取操作后,会触发写操作:发送数据到客户端。
1. 服务端
public class UDPEchoServerSelector {
private static final int TIMEOUT = 4000; // 超时 (毫秒)
private static final int CAPACITY = 255;
public static void main(String[] args) throws IOException {
args = new String[1];
args[0] = "4451";
int servPort = Integer.parseInt(args[0]);
Selector sel = Selector.open(); // 创建选择器,可以处理多路通道。
DatagramChannel channel = DatagramChannel.open();
channel.configureBlocking(false);
channel.socket().bind(new InetSocketAddress(servPort)); // 通道关联的socket绑定地址
channel.register(sel, SelectionKey.OP_READ, new ClientData());
while (true) { // 持续运行,接收和返回数据
if (sel.select(TIMEOUT) == 0) {
System.out.println("No I/O needs to be processed");
continue;
}
Iterator<SelectionKey> iter = sel.selectedKeys().iterator(); // 获取可操作的选择键集合
while (iter.hasNext()) {
SelectionKey key = iter.next(); // 键为位掩码
if (key.isReadable()) { // 客户端有数据发送过来
handleRead(key);
}
if (key.isValid() && key.isWritable()) { // 通道正常,且客户端需要响应
handleWrite(key);
}
iter.remove(); // 从集合中移除选择键
}
}
}
private static void handleRead(SelectionKey key) throws IOException {
DatagramChannel channel = (DatagramChannel) key.channel();
ClientData clntDat = (ClientData) key.attachment();
clntDat.buffer.clear();
clntDat.clientAddress = channel.receive(clntDat.buffer); // 获取客户端的地址,用以发送响应
if (clntDat.clientAddress != null) { // 接收到数据
key.interestOps(SelectionKey.OP_WRITE); // 关注客户端读取响应
}
}
private static void handleWrite(SelectionKey key) throws IOException {
DatagramChannel channel = (DatagramChannel) key.channel();
ClientData clntDat = (ClientData) key.attachment();
clntDat.buffer.flip(); // 从起始位置开始发送
int bytesSent = channel.send(clntDat.buffer, clntDat.clientAddress);
if (bytesSent != 0) {
key.interestOps(SelectionKey.OP_READ); // 关注客户端发送数据
}
}
public static class ClientData {
public SocketAddress clientAddress;
public ByteBuffer buffer = ByteBuffer.allocate(CAPACITY);
}
}
2. 客户端
public class UDPEchoClient {
private static final int CAPACITY = 255;
private static final String UTF8 = "UTF-8";
public static void main(String[] args) throws IOException {
args = new String[2];
args[0] = "localhost";
args[1] = "4451";
String servName = args[0];
int servPort = Integer.parseInt(args[1]);
DatagramChannel clntChan = DatagramChannel.open();
clntChan.configureBlocking(false);
clntChan.connect(new InetSocketAddress(servName, servPort));
ByteBuffer sentBuffer = ByteBuffer.wrap("Hello UDP".getBytes(UTF8));
int bytesSent = clntChan.write(sentBuffer); // 向服务器发送数据
System.out.println("UDP client sent " + bytesSent + " bytes");
ByteBuffer recvBuffer = ByteBuffer.allocate(CAPACITY);
clntChan.receive(recvBuffer); // 读取响应
recvBuffer.flip();
System.out.println("UDP client received: " + new String(recvBuffer.array(), UTF8));
}
}
客户端连接服务器后,发送数据可以用write或send方法:
...
clntChan.connect(new InetSocketAddress(servName, servPort));
...
int bytesSent = clntChan.write(sentBuffer);
...
clntChan.connect(new InetSocketAddress(servName, servPort));
...
int bytesSent = clntChan.send(sentBuffer, new InetSocketAddress(servName, servPort)); // 发送地址必须和前面的连接地址相同,否则报java.lang.IllegalArgumentException: Connected address not equal to target address
客户端没有连接服务器,需要用send方法指定目标地址:
...
int bytesSent = clntChan.send(sentBuffer, new InetSocketAddress(servName, servPort)); // 使用write方法会报java.nio.channels.NotYetConnectedException