我正在使用套接字编写多个客户端-Java中的服务器应用程序。我编写了简单的客户端-服务器应用程序,一切正常,但是当我尝试将其更改为多客户端应用程序时,启动客户端时出现了异常:
Exception in thread "pool-1-thread-1" java.lang.NullPointerException
at MiniSerwer.run(Serwer.java:110)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:679)
我还有两个类(线程-输入和输出的InWorker和OutWorker)。
Serwer.java(没有InWorker和OutWorker):
public class Serwer {
Serwer(int port) {
ServerSocket serversocket=null;
ExecutorService exec= Executors.newCachedThreadPool();
try {
serversocket=new ServerSocket(port);
} catch (IOException e) {
e.printStackTrace();
}
while(true) {
Socket socket=null;
try {
socket = serversocket.accept();
} catch (IOException e) {
e.printStackTrace();
}
exec.execute(new MiniSerwer(socket)); // create new thread
}
} }
MiniSerwer-帮助程序类为每个客户端创建拥有线程
class MiniSerwer implements Runnable{
Socket socket=null;
ExecutorService exec=null;
ObjectOutputStream oos=null;
ObjectInputStream ois=null;
MiniSerwer(Socket socket) {
this.socket=socket;
try {
oos=new ObjectOutputStream(socket.getOutputStream());
oos.flush();
ois=new ObjectInputStream(socket.getInputStream());
} catch (IOException e) {
e.printStackTrace();
}
}
public void run() {
while(true) {
exec.execute(new InWorker(socket, ois)); // input stream
exec.execute(new OutWorker(socket, oos)); //output stream
Thread.yield();
}
}
}
我更改了程序,但仍然无法正常工作。还有其他建议吗?
服务器:
public class Serwer implements Runnable{
ServerSocket serversocket=null;
ExecutorService exec= Executors.newCachedThreadPool();
int port;
Serwer(int port) {
this.port=port;
}
public void run() {
try {
serversocket=new ServerSocket(port);
while(true) {
Socket socket=null;
try {
socket = serversocket.accept();
exec.execute(new MiniSerwer(socket)); // create new thread
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
int port;
Scanner in = new Scanner(System.in);
System.out.println("Enter the port:");
port = in.nextInt();
ExecutorService exec=Executors.newCachedThreadPool();
exec.execute(new Serwer(port));
}
}
MiniSerwer:
class MiniSerwer implements Runnable{
Socket socket=null;
ExecutorService exec=Executors.newCachedThreadPool();
ObjectOutputStream oos=null;
ObjectInputStream ois=null;
MiniSerwer(Socket socket) {
this.socket=socket;
}
public void run() {
try {
oos=new ObjectOutputStream(socket.getOutputStream());
oos.flush();
ois=new ObjectInputStream(socket.getInputStream());
} catch (IOException e) {
e.printStackTrace();
}
while(true) {
exec.execute(new InWorker(socket, ois)); // input stream
exec.execute(new OutWorker(socket, oos)); //output stream
Thread.yield();
}
}
}
当我尝试将消息从客户端发送到服务器时,我有很多异常(exception)。
2秒在服务器端连接后(我什么都不发送):
Exception in thread "pool-2-thread-1" java.lang.OutOfMemoryError: unable to create new native thread
at java.lang.Thread.start0(Native Method)
at java.lang.Thread.start(Thread.java:657)
at java.util.concurrent.ThreadPoolExecutor.addWorker(ThreadPoolExecutor.java:943)
at java.util.concurrent.ThreadPoolExecutor.processWorkerExit(ThreadPoolExecutor.java:992)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:679)
最佳答案
您的MiniSerwer
类中的执行程序服务永远不会初始化。这是您的NPE的根本原因。
但是,正如我在评论中提到的那样,您不应在其构造函数中执行所有的Serwer
逻辑。该对象永远不会完全初始化,因为您永远不会退出构造函数。使整个类成为Runnable,然后将该逻辑移至重写的run
方法。然后添加main
方法,以在实际实例化/运行服务器时使用。
另外,在MiniSerwer
中,流初始化可能会失败。您需要先验证流不为null,然后才能在run方法中使用它们。或者只是将它们的初始化逻辑移到run方法的开头。
编辑
您的MiniSerwer
实现中也有一个错误,您产生了无限数量的线程来处理对象的输入和输出流:
while(true) {
exec.execute(new InWorker(socket, ois)); // input stream
exec.execute(new OutWorker(socket, oos)); //output stream
Thread.yield();
}
您要么用完线程,要么用完内存,要么两者都用。老实说,您的解决方案是经过精心设计的,我怀疑In和Out工作人员是否真的需要按现在的方式分开。
关于java - 多个客户端-Java中的服务器,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/14359036/