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我正在尝试用 Java 编写 RemoteDesktop 的实现。我在套接字上使用 ObjectOutputStream 和 ObjectInputStream 来发送数据。为了发送数据，我使用了我创建的一个名为“Packet”的类：

import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import javax.swing.ImageIcon;

/**
 * Holds data to send over network connection
 */
class Packet<T extends Serializable> implements Serializable {

    private T payload;

    public Packet() {
        super();
    }

    public Packet(T data) {
        super();
        setPayload(data);
    }

    public T getPayload() {
        return payload;
    }

    public void setPayload(T payload) {
        this.payload = payload;
    }

    public static void send(String message, ObjectOutputStream out) throws IOException {
        out.writeObject(new Packet<>(message));
        out.flush();
    }

    public static void send(Integer value, ObjectOutputStream out) throws IOException {
        out.writeObject(new Packet<>(value));
        out.flush();
    }

    public static void send(Block block, ObjectOutputStream out) throws IOException {
        out.writeObject(new Packet<>(block));
        out.flush();
    }

    public static void send(BufferedImage[][] images, ObjectOutputStream out) throws IOException {
        //convert to ImageIcon
        ImageIcon icons[][] = new ImageIcon[images.length][images[0].length];
        for (int x = 0; x < images.length; x++) {
            for (int y = 0; y < images[0].length; y++) {
                icons[x][y] = new ImageIcon(images[x][y]);
            }
        }
        out.writeObject(new Packet<>(icons));
        out.flush();
    }
}

首次建立连接时，服务器会发送一个二维 ImageIcon 数组，其中包含屏幕的不同“块”。屏幕被分成这组块。然后，服务器会定期截取屏幕截图，并将屏幕的每个“块”与最后一个进行比较，看看它是否发生了变化。如果有变化，那么服务器将在一个名为“Block”的类中发送新的屏幕区域，该类包含该块的 x 和 y 坐标以及 ImageIcon：

import java.awt.image.BufferedImage;
import java.io.Serializable;
import javax.swing.ImageIcon;

/**
 * Holds an image and its x and y coordinates on the screen
 */
class Block implements Serializable {

    private ImageIcon img;
    private int x;
    private int y;

    public Block() {
        super();
    }

    public Block(BufferedImage image, int x, int y) {
        img = new ImageIcon(image);
        this.x = x;
        this.y = y;
    }

    public Block(ImageIcon image, int x, int y) {
        img = image;
        this.x = x;
        this.y = y;
    }

    public int getx() {
        return x;
    }

    public int gety() {
        return y;
    }

    public ImageIcon getImage() {
        return img;
    }
}

这是服务器的主要代码：

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class Server {

    public static void main(String args[]) throws IOException {

        ServerSocket s = new ServerSocket(5000);
        do {
            Socket c;
            ObjectOutputStream out;
            ObjectInputStream in;

            //start listening
            echo("Listening on port: 5000");

            //accept connection
            c = s.accept();
            echo("Connected to client at address " + c.getInetAddress().getHostAddress());

            //open IO streams
            out = new ObjectOutputStream(c.getOutputStream());
            in = new ObjectInputStream(c.getInputStream());

            ServerSession rdsession = new ServerSession(in, out); //start session
        } while (true);
    }

    private static void err(String message) {
        //prints error message and exits
        System.err.println(message);
        System.exit(1);
    }

    private static void echo(String message) {
        //prints message
        System.out.println(message);
    }
}

因此，当建立连接时，服务器会创建一个“ServerSession”类的实例。此类通过确定何时在“块”对象中发送新图像来处理 RD 会话。当它需要向客户端更新一个块时，它使用 Packet.send(Block, ObjectOutputStream) 方法。

该对象使用以下代码从流中读取对象：

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
import javax.swing.ImageIcon;

public class Client {

    public static void main(String[] args) throws IOException, ClassNotFoundException {
        Socket c;
        ObjectOutputStream out;
        ObjectInputStream in;
        String serverIP = "127.0.0.1"; //replace with server IP
        int port = 5000;

        //open connection and streams
        c = new Socket(serverIP, port);
        out = new ObjectOutputStream(c.getOutputStream());
        in = new ObjectInputStream(c.getInputStream());

        ClientSession cs = null;

        do {
                Packet<?> p;
                Object o = in.readObject();
                if (o instanceof Packet) {
                    p = (Packet<?>) o;
                } else {
                    continue;
                }
                if (p.getPayload() instanceof String) { //check if string
                    echo("Server>" + p.getPayload());
                } else if (p.getPayload() instanceof Block) { //check if block
                    Block b = (Block) p.getPayload();
                    if (cs != null) {
                        cs.setImage(b.getImage(), b.getx(), b.gety());
                    }
                } else if (p.getPayload() instanceof ImageIcon[][]) { //check if 2-D image array
                    cs = new ClientSession(in, out, (ImageIcon[][]) p.getPayload()); //create session with image array
                }
        } while (true);
    }

    private static void err(String message) {
        System.err.println(message);
        System.exit(1);
    }

    private static void echo(String message) {
        System.out.println(message);
    }
}

ClientSession 类只存储屏幕图像并处理 GUI。

当我一起运行服务器和客户端时，在发送初始 ImageIcon[][] 数组后，每次客户端尝试读取“块”实例时，都会出现无数错误。这些是经常抛出的错误：

1：

Exception in thread "main" java.io.InvalidClassException: Block; invalid descriptor for field 
    at java.io.ObjectStreamClass.readNonProxy(ObjectStreamClass.java:710)
    at java.io.ObjectInputStream.readClassDescriptor(ObjectInputStream.java:828)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1599)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1515)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1769)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1348)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1989)
    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 Client.main(Client.java:46)
Caused by: java.lang.IllegalArgumentException: illegal signature
    at java.io.ObjectStreamField.<init>(ObjectStreamField.java:122)
    at java.io.ObjectStreamClass.readNonProxy(ObjectStreamClass.java:708)
    ... 11 more

2：

Exception in thread "main" java.io.InvalidClassException: Block; invalid descriptor for field sq ~ sq
    at java.io.ObjectStreamClass.readNonProxy(ObjectStreamClass.java:710)
    at java.io.ObjectInputStream.readClassDescriptor(ObjectInputStream.java:828)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1599)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1515)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1769)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1348)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1989)
    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.defaultReadFields(ObjectInputStream.java:1989)
    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.defaultReadFields(ObjectInputStream.java:1989)
    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 Client.main(Client.java:25)
Caused by: java.lang.IllegalArgumentException: illegal signature
    at java.io.ObjectStreamField.<init>(ObjectStreamField.java:122)
    at java.io.ObjectStreamClass.readNonProxy(ObjectStreamClass.java:708)
    ... 19 more

3：

Exception in thread "main" java.io.EOFException
    at java.io.DataInputStream.readInt(DataInputStream.java:392)
    at java.io.ObjectInputStream$BlockDataInputStream.readInt(ObjectInputStream.java:2818)
    at java.io.ObjectInputStream.readInt(ObjectInputStream.java:969)
    at javax.swing.ImageIcon.readObject(ImageIcon.java:481)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    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.defaultReadFields(ObjectInputStream.java:1989)
    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.defaultReadFields(ObjectInputStream.java:1989)
    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 Client.main(Client.java:25)

4：

Exception in thread "main" java.io.StreamCorruptedException: invalid type code: 73
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1518)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1769)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1348)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1989)
    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.defaultReadFields(ObjectInputStream.java:1989)
    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 Client.main(Client.java:25)

感谢您花时间阅读这篇文章。任何建议将不胜感激。谢谢！

4

3 回答 3

3

在花了很多时间检查我的代码之后，我确定问题与我在服务器上实现多线程的方式有关。线程将尝试同时写入输出流，这导致流损坏。谢谢大家的意见。

于 2013-08-14T05:17:51.433 回答
2

您的序列化和数据传输/交换不同步 - 客户端不再对齐和读取，服务器发送（序列化）有效对象的位置开始。

这大概就是你得到 InvalidClassException: Block; 的原因。字段和 StreamCorruptedException 的描述符无效。

您的数据传输代码主要取决于序列化和 ImageIcon。

并不是说这种方法是错误的，而是有许多必要的假设才能使它起作用：

  1. 类版本完全相同，
  2. SerialVersion UID 匹配，
  3. ImageIcon 是可序列化的，
  4. ImageIcon 内部数据在平台之间是兼容的，
  5. 序列化和小/大端格式兼容。

尝试去掉部分（比如 ImageIcon 的东西），看看你是否可以保持链接同步和良好的顺序。一旦您确定了导致链接不同步的原因，您就可以调查原因。

于 2013-07-29T00:19:19.747 回答
1

您的 Block.class 文件有问题。我会重新编译，重新部署到两端，然后重新测试。

EOFException是意料之中的：您试图读取ObjectInputStream. 你需要单独抓住它才能摆脱你的do/while (true).

注意您应该在启动线程的方法中ObjectOutputStream创建服务器端。目前，您正在循环内创建它们，并且两者都执行可以阻止接受线程接受其他客户端的 I/O。ObjectInputStreamrun()accept()

于 2013-07-29T00:06:29.247 回答