Java 网络编程 —— 实现非阻塞式的客户端
创建阻塞的 EchoClient
客户程序一般不需要同时建立与服务器的多个连接，因此用一个线程，按照阻塞模式运行就能满足需求
public class EchoClient {
private SocketChannel socketChannel = null;
public EchoClient() throws IOException {
socketChannel = SocketChannel.open();
InetAddress ia = InetAddress,getLocalHost();
InetSocketAddress isa = new InetSocketAddress(ia,8000);
socketChannel.connect(isa); //连接服务器
}
public static void main(String args[])throws IOException {
new EchoClient().talk();
}
private PrintWriter getWriter(Socket socket) throws IOException {
OutputStream socketOut = socket.getOutputStream();
return new PrintWriter(socketOut,true);
}
private BufferedReader getReader(Socket socket) throws IOException {
InputStream socketIn = socket.getInputStream();
return new BufferedReader(new InputStreamReader(socketIn));
}
public void talk() throws IOException {
try {
BufferedReader br = getReader(socketChannel.socket());
PrintWriter pw = getWriter(socketChannel.socket());
BufferedReader localReader = new BufferedReader(new InputStreamReader(System.in));
String msq = null;
while((msg = localReader.readLine()) != null) {
pw.println(msg);
System.out.println(br.readLine());
if(msq.equals("bye")) {
break;
}
}
} catch(IOException e) {
e.printStackTrace();
} finally {
try {
socketChannel.close();
} catch(IOException e) {
e.printStackTrace();
}
}
}
}
创建非阻塞的 EchoClient
对于客户与服务器之间的通信，按照它们收发数据的协调程度来区分，可分为同步通信和异步通信
同步通信指甲方向乙方发送了一批数据后，必须等接收到了乙方的响应数据后，再发送下一批数据。同步通信要求一个 IO 操作完成之后，才能完成下一个 IO 操作，用阻塞模式更容易实现
异步通信指发送数据和接收数据的操作互不干扰，各自独立进行。异步通信允许发送数据和接收数据的操作各自独立进行，用非阻塞模式更容易实现
值得注意的是，通信的两端并不要求都采用同样的通信方式，当一方采用同步通信时，另一方可以采用异步通信
public class EchoClient {
private SocketChannel socketChannel = null;
private ByteBuffer sendBuffer = ByteBuffer.allocate(1024);
private ByteBuffer receiveBuffer = ByteBuffer.allocate(1024);
private Charset charset = Charset.forName("GBK");
private Selector selector;
public EchoClient() throws IOException {
socketChannel = SocketChannel.open();
InetAddress ia = InetAddress.getLocalHost();
InetSocketAddress isa = new InetSocketAddress(ia, 8000);
socketChannel.connect(isa); //采用阻塞模式连接服务器
socketChannel.configureBlocking(false); //设置为非阻塞模式
selector = Selector.open();
}
public static void main(String args[]) throws IOException {
final EchoClient client = new EchoClient();
Thread receiver=new Thread() {
public void run() {
client.receiveFromUser(); //接收用户向控制台输入的数据
}
};
receiver.start();
client.talk();
}
/** 接收用户从控制台输入的数据，放到sendBuffer中 */
public void receiveFromUser() {
try {
BufferedReader localReader = new BufferedReader(new InputStreamReader(System.in));
String msg = null;
while((msg = localReader.readLine()) != null) {
synchronized(sendBuffer) {
sendBuffer.put(encode(msg + "\r\n"));
}
if (msg.equals("bye")) {
break;
}
}
} catch(IOException e) {
e.printStackTrace();
}
}
//接收和发送数据
public void talk() throws IOException {
socketChannel.register(selector, SelectionKey.OP_READ | SelectionKey.OP_WRITE);
while (selector.select() > 0 ) {
Set readyKeys = selector.selectedKeys();
Iterator it = readyKeys.iterator();
while (it.hasNext()) {
SelectionKey key = null;
try {
key = (SelectionKey) it.next();
it.remove();
if (key.isReadable()) {
receive(key);
}
if (key.isWritable()) {
send(key);
}
} catch(IOException e) {
e.printStackTrace();
try {
if(key != null) {
key.cancel();
key.channel().close() ;
}
} catch(Exception ex) {
e.printStackTrace();
}
}
}
}
}
public void send(SelectionKey key) throws IOException {
//发送sendBuffer的数据
SocketChannel socketChannel = (SocketChannel)key.channel();
synchronized(sendBuffer) {
sendBuffer.flip(); //把极限设为位置，把位置设为0
socketChannel.write(sendBuffer); //发送数据
sendBuffer.compact(); //删除已经发送的数据
}
}
public void receive(SelectionKey key) throws IOException {
//接收EchoServer发送的数据，把它放到receiveBuffer
//如果receiveBuffer有一行数据，就打印这行数据，然后把它从receiveBuffer删除
SocketChannel socketChannel = (SocketChannel) key.channel();
socketChannel.read(receiveBuffer):
receiveBuffer.flip();
String receiveData = decode (receiveBuffer);
if(receiveData.indexOf("\n") == -1) return;
String outputData = receiveData.substring(0, receiveData.indexOf("\n") + 1):
System.out.print(outputData);
if(outputData.equals("echo:bye\r\n")) {
key.cancel():
socketChannel.close();
selector.close();
System.exit(0);
}
ByteBuffer temp = encode(outputData);
receiveBuffer.position(temp.limit());
receiveBuffer.compact(): //删除已经打印的数据
}
//解码
public String decode(ByteBuffer buffer) {
CharBuffer charBuffer= charset.decode(buffer);
return charBuffer.toString();
}
//编码
public ByteBuffer encode(String str) {
return charset.encode(str);
}
}