Streams - ObjectOutputStream给出空

Question

我有两个应用程序协同工作。一种是“服务器”类型的应用程序，它没有任何GUI界面，可以处理对数据库的查询和处理来自客户端的请求。另一个是“客户端”，它主要是一个GUI，用户可以以结构化的方式与数据库信息交互。

问题/麻烦/需要帮助

我遇到的问题是，我可以成功地向服务器发送一个对象( String[])，并且没有任何问题。客户端应用程序发送它，服务器应用程序成功地接收到它的进程。

如果我尝试发送第二个String[]，客户端编译数组并认为它被发送了，但是服务器从来没有接收到is (只获得null)并生成一个IOException。

即使数组包含完全相同的位置数和完全相同的文本，格式和位置也是如此。

printStackTrace()产生的错误是：

Java.io.OptionalDataException
at java.io.ObjectInputStream.readObject0 (ObjectInputStream.java:1367)
at java.io.ObjectInputStream.readObject (ObjectInputStream.java:369)
at server.ConnectionThread.processClientRequests(ConnectionThread:204)
at server.ConnectionThread.processClientRequests(ConnectionThread:50)
at javalang.Thread.run(Thread.java:722) 

第204行的代码，它是从以下位置读取ObjectStream的：

String[] addArray = (String[]) ois.readObject();

ois是一个ObjectInputStream，初始化如下：

private ObjectInputStream ois = new ObjectInputStream(socket.getInputStream());

客户端代码

用于将这些对象发送到服务器应用程序的客户端代码是：

ObjectToServer.writeObject(String[] var);
ObjectToServer.flush();
ObjectToServer.reset();

注释

对我来说没有意义的是，这种完全相同的代码格式被用来成功地从服务器向客户端应用程序发送一些String[]，而不发送"null“。

我已经谷歌搜索了这个和所有的绝对无效。

如果可以的话，谁来帮忙！！

                             ADDITIONAL CODE

// CONNECTION THREAD IS ON SERVER APP, SETS UP STREAMS AND WAITS FOR MESSAGES FROM CLIENT
// HANDLES COMMUNICATION FROM CLIENT AND REST OF SERVER

public class ConnectionThread implements Runnable
{

    private Socket socket;
    private SystemCore core;
    //Streams for connections
    private InputStream is;
    private OutputStream os;
    //Writers and readers for communication of Strings
    private PrintWriter toClient;
    private BufferedReader fromClient;
    // Writers and readers for sending and receiving Objects between server and client.
    private ObjectInputStream ois = null;
    private ObjectOutputStream oos = null;
    //Protocol
    static final String CLIENT_QUITTING = "Exit";

    public ConnectionThread(Socket s, SystemCore aSysCore)
    {
        socket = s;

        // State of the SystemCore as taken from HelloServer
        core = aSysCore;
    }

    public void run()
    {
        try
        {
            openStreams();
            toClient.println(MESSAGE_TO_CLIENT);
            processClientRequests();
            closeStreams();
            this.socket.close();
        }
        catch (OptionalDataException ode )
        {
            System.out.println("OptionalDataException: ");
            System.out.println("length is: " + ode.length);
        }
        catch (IOException ioe)
        {
            System.out.println("IO trouble with a connection in ConnectionThread run() " + ioe.getMessage());
            ioe.printStackTrace();
        }
       catch (ClassNotFoundException cnf)
        {
            System.out.println("Class trouble with a connection in ConnectionThread run() " + cnf.getMessage());
            cnf.printStackTrace();
        }
        catch(ParseException pe)
        {
            System.out.println("Parse trouble with a connection in ConnectionThread run() " + pe.getMessage());
            pe.printStackTrace();
        } 
    }

    /**
     * Opens streams between the server and the client.
     *
     * @throws IOException
     */
    private void openStreams() throws IOException
    {
        final boolean AUTO_FLUSH = true;
        this.is = this.socket.getInputStream();
        this.fromClient = new BufferedReader(new InputStreamReader(is));
        this.os = this.socket.getOutputStream();
        this.toClient = new PrintWriter(os, AUTO_FLUSH);

        //Object streams.
        oos = new ObjectOutputStream(socket.getOutputStream());
        ois = new ObjectInputStream(socket.getInputStream());

        System.out.println("...Streams set up");
    }


    /**
     * Private method that accepts arguments from a client and executes the related
     * commands in the systemcore as long as the command passed from the client
     * is not CLIENT_QUITTING.
     *
     * @throws IOException
     * @throws ClassNotFoundException
     */
    private void processClientRequests() throws IOException, ClassNotFoundException, ParseException
    {
        String commandFromClient;
        commandFromClient = fromClient.readLine();
        while (!(commandFromClient.equals(CLIENT_QUITTING)))
        {
            if (commandFromClient.equals("addProjectPrepare"))
            {
                String[] addArray = (String[]) ois.readObject();
                core.addProjectPrepare(addArray);
            }
            if (commandFromClient.equals("editProjectPrepareDetails"))
            {
                String[] editArray = (String[]) ois.readObject();
                recruit.editProjectPrepareDetails(editArray);               
            }
        }
           commandFromClient = fromClient.readLine();
    }


**// CLIENT SIDE (User GUI) CODE THAT SENDS STRING[] TO THE SERVER**




public void saveAction()
    {
        // TEST TO SEE IF THE DATE ENTERED IS CORRECT FORMAT, IF NOT NO SAVE OCCURRS

    boolean parsedOk = false;

    if (this.arrivalDateTextField.getText().isEmpty() == false)
    {
        try
        {
            // Check if date is correct format. Nothing will be done with 
            // the testDate object

            MyDate testDate = new MyDate(
                    this.arrivalDateTextField.getText());

            //Allow write to server to occur.
            parsedOk = true;
            //If date is okay, send form data to server.
        }
        catch (ParseException pe)
        {
            this.arrivalDateTextField.setText(""); // Set text field to blank
            int messageIcon = javax.swing.JOptionPane.ERROR_MESSAGE;
            JOptionPane.showMessageDialog(this, "Invalid date",
                    "Warning", messageIcon);
        }
    }
    else
    {
        parsedOk = true; // No date entered so allow blank. 
    }
    if (parsedOk == true)
    {
        // WRITE DATA TO SERVER OCCURS HERE: 

        try
        {

            **//getPersonDetails() returns a String[]**

            ManageClientConnections.toServer.println("addNewData");                 
       ManageClientConnections.objectToServer.writeObject(this.getPersonDetails());
            ManageClientConnections.objectToServer.flush();
            ManageClientConnections.objectToServer.reset();
        }
        catch (IOException ioe)
        {
            System.out.println(
                    "While writing new person to server, there was an error: " + ioe.getMessage());
        }

        // And dispose of the GUI, inside the parseok if clause
        this.dispose();
    }
}

Answer 1

不能在同一个套接字输入/输出流上创建多个输入/输出流。那不管用。你需要选择一种类型的溪流并坚持下去。因为您需要发送结构化数据，所以应该只使用对象流并丢弃打印流。如果您需要从客户端发送不同类型的消息到服务器，那么您应该考虑使用包装可序列化的对象类型(例如消息)，它可以包含不同类型的消息。