尝试显示从服务器对象检索到的值时显示空值

Posted 2023-04-17

【中文标题】尝试显示从服务器对象检索到的值时显示空值

【英文标题】：Displaying null value when attempting to display value retrieved from Server object

【发布时间】：2016-01-11 23:19:57

【问题描述】：

为了更新问题，我已将 Product 和 Customer 类附加在 Server 和 Client 类下方

如果我不清楚，我会提前在这里道歉。我试图在JTextField 中显示ArrayList 中包含的String 值。 String 值确实显示，但 null 值也显示，我想显示 String 值。这是JTextField 中显示的示例String 值

[nullDamonTholsonnull0, nullSylvesterStallonenull0, nullMisterTnull0]
[nullDamonTholsonnull0, nullSylvesterStallonenull0, nullMisterTnull0]
[nullDamonTholsonnull0, nullSylvesterStallonenull0, nullMisterTnull0]

在我的程序中，我有客户端用户界面从 Server Object 请求 String 值，然后在 JTextField 中显示它们。这是客户端接口代码：

private void jButtonDisplaycNamesActionPerformed(java.awt.event.ActionEvent evt) 
    
        try 
            Socket socket = new Socket("localhost", 67);
            ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
            ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
            DataRequest request = new DataRequest(DataRequest.NAME);
            out.writeObject(request);
            out.flush();

            List<Customer> customerNames = (List<Customer>) in.readObject();
            jTextAreaOutput.setText("");

            for (Customer customerName : customerNames) 
                jTextAreaOutput.append(customerNames.toString());
                jTextAreaOutput.append("\n");
            
            socket.close();
         catch (Exception ex) 
            JOptionPane.showMessageDialog(this, "unable to contact Server");
            Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
         // TODO add your handling code here:
    

    // TODO add your handling code here:


private void jButtonDisplaycIDActionPerformed(java.awt.event.ActionEvent evt) 
    try 

        Socket socket = new Socket("localhost", 67);
        ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
        ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
        DataRequest request = new DataRequest(DataRequest.ID);
        out.writeObject(request);
        out.flush();
        List<Customer> customerIDs = (List<Customer>) in.readObject();
        jTextAreaOutput.setText("");
        for (Customer customerID : customerIDs) 
            jTextAreaOutput.append(customerIDs.toString());
            jTextAreaOutput.append("\n");
        
        socket.close();
     catch (Exception ex) 
        JOptionPane.showMessageDialog(this, "unable to contact Server");
        Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
     // TODO add your handling code here:


private void jButtonDisplaypIDActionPerformed(java.awt.event.ActionEvent evt) 
    
        try 

            Socket socket = new Socket("localhost", 67);
            ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
            ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
            DataRequest request = new DataRequest(DataRequest.PRODUCTID);
            out.writeObject(request);
            out.flush();

            List<Product> productIDs = (List<Product>) in.readObject();
            jTextAreaOutput.setText("");

            for (Product procuctID : productIDs) 
                jTextAreaOutput.append(productIDs.toString());
                jTextAreaOutput.append("\n");
            
            socket.close();
         catch (Exception ex) 
            JOptionPane.showMessageDialog(this, "unable to contact Server");
            Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
         // TODO add your handling code here:
    

这是服务器对象代码

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

    ServerSocket server = new ServerSocket(67);
    while (true) 
        Socket socket = server.accept();
        ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
        ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());

        DataRequest request = (DataRequest) in.readObject();

        switch (request.getDataType()) 
            case DataRequest.NAME:
                out.writeObject(getCustomerName());
                out.flush();
                break;

            case DataRequest.ID:
                out.writeObject(getCustomerID());
                out.flush();
                break;

            case DataRequest.PASSWORD:
                out.writeObject(getCustomerPassword());
                out.flush();
                break;

            case DataRequest.DESCRIPTION:
                out.writeObject(getProductDescription());
                out.flush();
                break;
            case DataRequest.PRODUCTID:
                out.writeObject(getProductDescription());
                out.flush();
                break;

            case DataRequest.PRICE:
                out.writeObject(getProductDescription());
                out.flush();
                break;

        
    


private static List<Customer> getCustomerName() 
    List<Customer> names = new ArrayList<Customer>();
    in.readObject;
    Customer name = new Customer();
    name.setcFirstName("Damon");

    name.setcLastName("Tholson");

    names.add(name);

    name = new Customer();

    name.setcFirstName("Sylvester");
    name.setcLastName("Stallone");
    names.add(name);

    name = new Customer();

    name.setcFirstName("Mister");
    name.setcLastName("T");
    names.add(name);

    return names;

公共类客户实现可序列化

private String cID;
private String cFirstName;
private String cLastName;
private String cPassword;
private int dataType;




/**
 * @return the cID
 */
public String getcID() 
    return cID;


/**
 * @param cID the cID to set
 */
public void setcID(String cID) 
    this.cID = cID;


/**
 * @return the cFirstName
 */
public String getcFirstName() 
    return cFirstName;


/**
 * @param cFirstName the cFirstName to set
 */
public void setcFirstName(String cFirstName) 
    this.cFirstName = cFirstName;


/**
 * @return the cLastName
 */
public String getcLastName() 
    return cLastName;


/**
 * @param cLastName the cLastName to set
 */
public void setcLastName(String cLastName) 
    this.cLastName = cLastName;


/**
 * @return the cPassword
 */
public String getcPassword() 
    return cPassword;


/**
 * @param cPassword the cPassword to set
 */
public void setcPassword(String cPassword) 
    this.cPassword = cPassword;


/**
 * @return the dataType
 */
public int getDataType() 
    return dataType;


/**
 * @param dataType the dataType to set
 */
public void setDataType(int dataType) 
    this.dataType = dataType;


@Override
public String toString() 
    return  cID + cFirstName + cLastName +  cPassword +  dataType ;

公共类产品实现可序列化

private String pID;

private String pDescription;
private String pPrice;
private int dataType;



/**
 * @return the pID
 */
public String getpID() 
    return pID;


/**
 * @param pID the pID to set
 */
public void setpID(String pID) 
    this.pID = pID;


/**
 * @return the pName
 */
/**
 * @return the pDescription
 */
public String getpDescription() 
    return pDescription;


/**
 * @param pDescription the pDescription to set
 */
public void setpDescription(String pDescription) 
    this.pDescription = pDescription;


/**
 * @return the pPrice
 */
public String getpPrice() 
    return pPrice;


/**
 * @param pPrice the pPrice to set
 */
public void setpPrice(String pPrice) 
    this.pPrice = pPrice;


public int getDataType() 
    return dataType;


/**
 * @param dataType the dataType to set
 */
public void setDataType(int dataType) 
    this.dataType = dataType;


@Override
public String toString() 
    return pID + pDescription + pPrice;


/**
 * @return the dataType
 */

【问题讨论】：

你很快就会想看看Concurrency in Swing

Customer 类是什么样的？考虑提供一个runnable example 来证明您的问题。这不是代码转储，而是您正在做的事情的一个例子，它突出了您遇到的问题。这将减少混乱并获得更好的响应

您可以发布客户和产品类代码吗？或者至少，该类的 toString 方法。也许可以通过修改这些方法来解决问题。

你永远不会关闭接受的套接字。

我以为我在 Server 类的 switch 语句的末尾用命令 socket.close(); 关闭了它；

【参考方案1】：

问题出在调用 Customer 类中 toString 方法的输出的 Client 类中。我在 toString 方法中有多个返回，但我只调用一个返回，所以我收到了我调用的变量和我没有调用的变量的空值。所以我的 toString 方法返回以下内容：

@覆盖 公共字符串 toString() 返回 cFirstName + cID + cLastName +cPassword；

但是我的客户端类只调用了该方法中的一个变量

for (客户 customerName : customerNames) jTextAreaOutput.append(customerName.toString());

所以我改为调用一个特定的变量

for (客户 customerName : customerNames) jTextAreaOutput.append(customerName.getcFirstName());