Nio建立socket使用注意事項

最近做區塊鏈DEMO時，用到NIO 來建立socket。 初步體驗了該API，總的來說 優缺點並存。 不過使用時需要注意:

1. selectorKey 中OP_WRITE註冊

    爲什麼註冊該事件，是因爲需要底層緩存區準備就緒，在上一次寫操作完成後，或者緩衝區足夠大的前提下。已經是就緒的。 但是最好把寫操作放在 selectorKey.isWritable() 條件後。

2.爲什麼客戶端向服務端發出了消息，服務端無法收到。 這個問題困擾了很久。 而且socket編程中竟然沒有說明...  寫完一條後 需要以\r\n結束。否則對端無法知道已經寫完成。

3.bytebuffer這個東東的設計有點奇葩。構造方法問題會出現大坑很浪費時間...

實例代碼如下:

Server端:

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.util.Iterator;
import java.util.Set;


public class Server {
static Selector selector = null;
private static int BLOCK = 4096;
static int flag;
private static ByteBuffer sendbuffer = ByteBuffer.allocate(BLOCK);
private static ByteBuffer receivebuffer = ByteBuffer.allocate(BLOCK);


public static void main(String[] args) {
initServer();
try {
listen();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}


private static void initServer() {
try {
ServerSocketChannel ss = ServerSocketChannel.open();// (8001);
ss.socket().bind(new InetSocketAddress(8001));
ss.configureBlocking(false);
selector = Selector.open();
ss.register(selector, SelectionKey.OP_ACCEPT);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}


private static void listen() throws IOException {
while (true) {
selector.select();
Set<SelectionKey> selectionKeys = selector.selectedKeys();
Iterator<SelectionKey> iterator = selectionKeys.iterator();
while (iterator.hasNext()) {
SelectionKey selectionKey = iterator.next();
iterator.remove();
handleKey(selectionKey);
}
}
}


private static void handleKey(SelectionKey selectionKey) throws IOException {
ServerSocketChannel server = null;
SocketChannel client = null;
String receiveText;
String sendText;
int count = 0;
if (selectionKey.isAcceptable()) {
server = (ServerSocketChannel) selectionKey.channel();
client = server.accept();
client.configureBlocking(false);
client.register(selector, SelectionKey.OP_READ);
} else if (selectionKey.isReadable()) {
client = (SocketChannel) selectionKey.channel();
receivebuffer.clear();
count = client.read(receivebuffer);
if (count > 0) {
receiveText = new String(receivebuffer.array(), 0, count);
System.out.println("client send:" + receiveText);
client.register(selector, SelectionKey.OP_WRITE);
// back
if (receiveText != null && !"".equals(receiveText)) {
ByteBuffer buffer = ByteBuffer.allocate(256);
if (receiveText.contains("client hello")) {
byte[] backInfo = new String("server hello\r\n").getBytes("UTF-8");
buffer = ByteBuffer.wrap(backInfo);
}
if (receiveText.contains("client ack")) {
byte[] backInfo = new String("server ack\r\n").getBytes("UTF-8");
buffer = ByteBuffer.wrap(backInfo);
}


client.write(buffer);
buffer.rewind();
System.out.println("server send:" + new String(buffer.array()));
}
}
} else if (selectionKey.isWritable()) {
client = (SocketChannel) selectionKey.channel();
client.register(selector, SelectionKey.OP_READ);
}
}
}

Client端:

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;


public class ClientTest {


public static void main(String[] args) {


try {
InetAddress address = InetAddress.getLocalHost();
String ip = address.getHostAddress();
Socket socket = new Socket(ip, 8001);
OutputStream os = socket.getOutputStream();// 字節輸出流
InputStream is = socket.getInputStream();
BufferedWriter pw = new BufferedWriter(new OutputStreamWriter(os));
BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
pw.write("client hello");
pw.newLine();
pw.flush();
while (true) {


// System.out.println("client say");
String text = br.readLine();
if (text != null) {
if ("server hello".equals(text)) {
pw.write("client ack");
pw.newLine();
pw.flush();
} else if ("server ack".equals(text)) {
// 完成握手
System.out.println("handshake complete");
}
}
Thread.sleep(1000);
}
} catch (UnknownHostException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}


}
}