java - 我无法将对象从服务器发送到客户端

Question

在尝试从服务器获取表格时，我得到:

java.io.StreamCorruptedException: invalid type code: 00

还有

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: Cannot set a null TableModel

为什么会发生这种情况以及如何解决它？

这是我编写函数的客户端类:

public class Client {

    private Socket client;
    private DataInputStream dis;
    private DataOutputStream dos;
    private ObjectInputStream ois;
    private ObjectOutputStream oos;



    private int id;
    private String name;
    private String surname;



    public void setClientInfo(int id, String name, String surname) {
        this.id = id;
        this.name = name;
        this.surname = surname;
    }

    public int getId() {
        return id;
    }

    public void connectServer() {
        try {

            client = new Socket("localhost", 3000);
            dis = new DataInputStream(client.getInputStream());
            dos = new DataOutputStream(client.getOutputStream());

            oos = new ObjectOutputStream(client.getOutputStream());
            ois = new ObjectInputStream(client.getInputStream());



            System.out.println("I/O streams for client created");

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void closeConnection() {
        try {
            sendUTFDataToServer("EXIT");
            dis.close();
            dos.close();
            client.close();
            System.out.println("CLIENT END");
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public boolean sendUTFDataToServer(String msg) {

        if (client != null) {
            try {
                dos.writeUTF(msg);
                return true;
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return false;
    }

    public boolean sendIntDataToServer(int num) {

        if (client != null) {
            try {
                dos.writeInt(num);
                return true;
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return false;
    }

    public boolean sendDoubleDataToServer(double num) {

        if (client != null) {
            try {
                dos.writeDouble(num);
                return true;
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return false;
    }

    public String getUTFDataFromServer() {
        String res = "";
        if (client != null) {
            try {
                res = dis.readUTF();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return res;
    }

    public int getIntDataFromServer() {
        int res = 0;
        if (client != null) {
            try {
                res = dis.readInt();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return res;
    }

    public double getDoubleDataFromServer() {
        double res = 0;
        if (client != null) {
            try {
                res = dis.readDouble();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return res;
    }

    public void sendObjectToServer(Object obj) {

        if (client != null) {
            try {
                oos.writeObject(obj);
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

    }

    public Object getObjectFromServer() {
        Object obj = null;
        if (client != null) {
            try {

                obj = (DefaultTableModel) ois.readObject();

            } catch (ClassNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return obj;
    }
    public DefaultTableModel showBook(){
        DefaultTableModel dtm=null;
        try {
            dos.writeUTF("showbooks");

            dtm = (DefaultTableModel) ois.readObject();

        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return dtm;
    }
    public String addBook(int id,String author,String name,int library_id)
    {
        String mes="";
        try {
            dos.writeUTF("ADD");
            dos.writeInt(id);
            dos.writeUTF(author);
            dos.writeUTF(name);
            dos.writeInt(library_id);

            mes =dis.readUTF();

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    return mes;
    }



    public static void main(String[] args) {
        Client client=new Client();
        client.connectServer();
        Login_Frame frame = new Login_Frame(client);
        frame.setVisible(true);
    }

}

这是我的服务器类；

public class Server {

    private int port = 3000;
    private ServerSocket server;
    public static int count = 0;
    public static int activeClientCount = 0;

    public Server() {

        try {
            server = new ServerSocket(port);
            System.out.println("Server Started");

            DB.initializeDB();
            System.out.println("Database Connection established");

            while (true) {
                System.out
                        .println("Server: Server is waiting for client connetion");
                Socket clientSocket = server.accept();
                count++;
                activeClientCount++;

                System.out.println("Server: Client connection is provided "
                        + count);
                System.out.println("Active Client  " + activeClientCount);

                MyClientThread mt = new MyClientThread(clientSocket);
                mt.start();
            }

        }  catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        System.out.println("END SERVER");

    }

    public static void main(String[] args) {
        Server server = new Server();
    }

    class MyClientThread extends Thread {


        DataInputStream dis;
        DataOutputStream dos;

        ObjectInputStream ois;
        ObjectOutputStream oos;

        Socket clientsocket;
        public MyClientThread(Socket csocket) {
            this.clientsocket = csocket;
            System.out.println("Client connected");
            try {
                dis = new DataInputStream(clientsocket.getInputStream());
                dos = new DataOutputStream(clientsocket.getOutputStream());

                ois = new ObjectInputStream(clientsocket.getInputStream());
                oos = new ObjectOutputStream(clientsocket.getOutputStream());



                System.out.println("I/O streams are created");

            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

        @Override
        public void run() {

            try {
                while (true && clientsocket != null) {

                    System.out.println("waiting for opp command");
                    String opp = dis.readUTF();

                    String res = "";

                    if (opp.equals("LOGIN")) {

                        String un = dis.readUTF();
                        String pw = dis.readUTF();
                        String type=dis.readUTF();

                        ResultSet rs = ServerSys.login(un, pw,type);


                        if(rs.next()==false)
                        {
                            dos.writeUTF("nouser");

                        }
                        else
                        {
                                dos.writeUTF("YES");
                                dos.writeInt(rs.getInt(1));
                                dos.writeUTF(rs.getString(2));
                                dos.writeUTF(rs.getString(3));      

                        }

                        }
                    else if(opp.equals("showbooks"))
                    {
                        System.out.println("book'a girdi");
                        dos.writeUTF("YES");
                        dos.writeUTF("HEllo");
                        ResultSet rs=DB.executeQ("select * from book");

                        DefaultTableModel dtm= DB.showTables(rs);
                        System.out.println(dtm.getValueAt(1,1));
                        oos.writeObject(dtm);


                    }


                    }


            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

和server_function类；

public class ServerSys {
    public static ResultSet login(String un, String pw,String type) {
        String sql="";
        if(type.equalsIgnoreCase("client"))
        {   
            sql = "select * from client where clientName ='" + un
                    + "' and clientPass='" + pw + "'";

        }
        else
        {
            sql = "select * from admin where adminName ='" + un
                    + "' and adminPassword='" + pw + "'";
        }


        ResultSet rs = DB.executeQ(sql);
        return rs;

    }

    public static void insertBook(int id,String bookauthor,String name,int libraryid) {
        String sql = "insert into book values(" + id + ",'" + bookauthor + "',"+libraryid+
                 ")";
        try {
            DB.executeQ(sql);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

                }

    public static DefaultTableModel showTable(String sql){
        DefaultTableModel dtm = new DefaultTableModel();        
        ResultSet rs;
        try {
            rs = DB.executeQ(sql);

            ResultSetMetaData rsmd= (ResultSetMetaData) rs.getMetaData();
            Vector header= new Vector();
            Vector datarows = new Vector();

            int columnumber = rsmd.getColumnCount();
            for(int i=1; i<columnumber; i++){
                header.add(rsmd.getColumnName(i));
            }

            while(rs.next()){
                Vector row=new Vector();
                for(int i=1; i<columnumber; i++){
                    row.add(rs.getObject(i));
                }               
                datarows.add(row);
            }
            dtm.setDataVector(datarows, header);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        return dtm;

    }

}

顺便说一下，我可以使用 objectoutputstream 发送例如字符串数组，所以我猜问题仅出在 defaulttablemodel 上。

Answer 1

我在你的代码中看到:

        dis = new DataInputStream(client.getInputStream());
        dos = new DataOutputStream(client.getOutputStream());

        oos = new ObjectOutputStream(client.getOutputStream());
        ois = new ObjectInputStream(client.getInputStream());

我认为你不应该这样做:你有两个不同的高级流在同一个低级流中写入或读取。根据它们缓冲数据的方式，这将导致灾难。只需使用 ObjectOutputStream，因为 ObjectOutputStream 实现了 DataOutput，所以您也可以从中编写原语。所以去掉 dis 和 dos 就可以了。