摘自《Netty权威指南》
BIO
BIO通信模型：
问题显而易见：每个客户端都需要创建一个线程，并发访问量大时，系统会出现堆栈溢出、创建新线程失败等问题
代码演示
功能：时间服务器
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88public class TimeServer {
public static void main(String[] args) throws IOException {
// 监听8080端口
int port = 8080;
if (args != null && args.length > 0) {
port = Integer.valueOf(args[0]);
}
ServerSocket server = null;
try {
server = new ServerSocket(port);
System.out.println("The time server is start in port : " + port);
Socket socket;
while (true) {
socket = server.accept();
// 这里创建一个线程去执行业务
new Thread(new TimeServerHandler(socket)).start();
}
} finally {
if (server != null) {
System.out.println("The time server close");
server.close();
}
}
}
}
/**
* 具体执行的线程
*/
public class TimeServerHandler implements Runnable{
private Socket socket;
public TimeServerHandler(Socket socket) {
this.socket = socket;
}
public void run() {
BufferedReader in = null;
PrintWriter out = null;
try {
in = new BufferedReader(new InputStreamReader(this.socket.getInputStream()));
out = new PrintWriter(this.socket.getOutputStream(), true);
String currentTime;
String body;
while (true) {
body = in.readLine();
if (body == null) {
break;
}
System.out.println("The time server receive order : " + body);
currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body)
? new Date(System.currentTimeMillis()).toString() : "BAD ORDER";
out.println(currentTime);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
// 释放相关资源
if (in != null) {
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (out != null) {
out.close();
}
if (this.socket != null) {
try {
this.socket.close();
} catch (IOException e) {
e.printStackTrace();
}
this.socket = null;
}
}
}
}
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48public class TimeClient {
public static void main(String[] args) {
int port = 8080;
if (args != null && args.length > 0) {
port = Integer.valueOf(args[0]);
}
Socket socket = null;
BufferedReader in = null;
PrintWriter out = null;
try {
socket = new Socket("127.0.0.1", port);
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
out = new PrintWriter(socket.getOutputStream(), true);
out.println("QUERY TIME ORDER");
System.out.println("Send order 2 server succeed.");
String resp = in.readLine();
System.out.println("Now is : " + resp);
} catch (Exception e) {
e.printStackTrace();
} finally {
// 释放相关资源
if (in != null) {
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (out != null) {
out.close();
}
if (socket != null) {
try {
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
伪异步I/O
伪异步I/O模型图：
可以看到，伪异步I/O只是加入了一个线程池，避免了每次请求都创建线程的问题（这里就不写demo了）
但是通过对输入和输出流的API文档分析，了解到读和写操作都是同步阻塞的，阻塞的时间取决于对方I/O线程的处理速度和网络I/O的传输速度。我们无法保证生产环境的网络状况和对端的应用程序能足够快，所以它的可靠性就非常差。