SocketException：使用ObjectInputStream在服务器上重置连接

Question

我试图绕过 ObjectInputStream / ObjectOutputStream ，所以我创建了一个非常简单的服务器-
客户端应用程序，其中客户端通过创建的流发送HashMap对象，服务器接收并打印该对象。

这是我的服务器代码：

import java.io.*;
import java.net.*;

public class Server {

    public static void main(String[] args) throws IOException, ClassNotFoundException {
        ServerSocket server = new ServerSocket(4444);
        while (true) {
            Socket socket = server.accept();
            ObjectInputStream objIn = new ObjectInputStream(socket.getInputStream());

            if (objIn.readObject() != null) {
                System.out.println(objIn.readObject());
            }
        }    
    }
}

这是我的客户代码：

import java.io.*;
import java.net.InetAddress;
import java.net.Socket;
import java.util.HashMap;

public class Client {

    public static void main(String[] args) throws IOException {
        Socket sock;
        int port = 4444;
        HashMap<Integer, String>  mapSend= new HashMap<>();
        mapSend.put(1,"row1");
        mapSend.put(2,"row2");

        sock = new Socket(InetAddress.getLocalHost(), port);
        ObjectOutputStream objOut = new ObjectOutputStream(sock.getOutputStream());

        objOut.writeObject(mapSend);
        objOut.flush();
    }
}

我运行服务器文件，它运行正常。
然后运行客户端文件，并在服务器上收到以下错误：

    Exception in thread "main" java.net.SocketException: Connection reset
    at java.net.SocketInputStream.read(SocketInputStream.java:189)
    at java.net.SocketInputStream.read(SocketInputStream.java:121)
    at java.io.ObjectInputStream$PeekInputStream.read(ObjectInputStream.java:2308)
    at java.io.ObjectInputStream$BlockDataInputStream.read(ObjectInputStream.java:2716)
    at java.io.ObjectInputStream$BlockDataInputStream.readFully(ObjectInputStream.java:2740)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1978)
    at java.io.ObjectInputStream.defaultReadObject(ObjectInputStream.java:499)
    at java.util.HashMap.readObject(HashMap.java:1115)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1017)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1891)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1796)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1348)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
    at iotest.Server.main(Server.java:17)
Java Result: 1

PS我不知道我是否需要做一些事情来序列化HashMap，但是我想我在某处看到了它是由Java内部处理的。我可能很难错。

在Aaron回答后进行编辑 我按照Aaron的建议在服务器中实现了这一部分：

Object objRead=objIn.readObject();
            if (objRead != null) {
                System.out.println(objRead);
            }

现在我在运行客户端后再次从服务器收到此错误：

Exception in thread "main" java.net.SocketException: Connection reset
    at java.net.SocketInputStream.read(SocketInputStream.java:189)
    at java.net.SocketInputStream.read(SocketInputStream.java:121)
    at java.io.ObjectInputStream$PeekInputStream.read(ObjectInputStream.java:2308)
    at java.io.ObjectInputStream$BlockDataInputStream.read(ObjectInputStream.java:2716)
    at java.io.ObjectInputStream$BlockDataInputStream.readFully(ObjectInputStream.java:2740)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1978)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1913)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1796)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1348)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
    at java.util.HashMap.readObject(HashMap.java:1154)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1017)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1891)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1796)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1348)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
    at iotest.Server.main(Server.java:17)
Java Result: 1

Answer 1

您正在读取对象两次，但是仅第二次打印。因此，当您尝试第二次读取时，客户端可能已关闭，因此套接字已在远程端关闭，因此是异常。

您正在读取！=空值检查上的对象。您不打印它。然后，您尝试再次阅读它，它会炸弹。

从流中读取后，它就会被读取。它是流，而不是缓冲区。您可能想要缓冲读取的内容，然后可以根据需要检查该缓冲区。

最简单的例子

Object o = outputStream.readObject();
if(o != null) {
 system.out.println(o);
}