socket问题

public class NetworkActionServer extends Thread{ private static  final int serverport = 8899;

private Socket serversocket;
 DBAction db=new DBAction();

NetworkActionServer(Socket i){
this.serversocket=i;
}

//获得C发来的消息，返回验证消息
public void run() {
try {

            //get client mes
            ObjectInputStream InputStream = new ObjectInputStream(serversocket.getInputStream());
            User usr=(User) InputStream.readObject();
            //do client mes
            db.insertInto(usr);
            //返回验证消息
            ObjectOutputStream OutputStream = new ObjectOutputStream(serversocket.getOutputStream());
            User[] dbusr=db.selectall();
            for(int i=0;i<dbusr.length;i++){
                System.out.println(dbusr[i].getName());
             OutputStream.writeObject("a");////////////
                   /////////////////////////在这里写不不了对象,有              socket                         write error
             //Thread.sleep(3000);
            }
            OutputStream.flush();
} catch (Exception e) {
e.printStackTrace();
}
}

public static void main(String arg[]){
try{
ServerSocket servercon = new ServerSocket(serverport);
while(true){
Socket s=servercon.accept();
Thread t=new NetworkActionServer(s);
t.start();
}
}catch(Exception e){
e.printStackTrace();
}

}
}
就是
socket write error.....大家帮忙,谢谢