Java 正在尝试通过套接字将arraylist从服务器发送到客户端

我试图使用ObjectInputStream/ObjectOutputStream通过套接字将ArrayList从服务器发送到客户端，但收到一个错误，即发送的对象为null。 应该发生以下情况（但事实并非如此）： 1.在服务器端，从MySQL数据库填充ArrayList 2.发送到客户端并用于填充jTable

连接文件（服务器端）我认为我的问题是我的无效运行（）

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“我收到一个发送的对象为null的错误。”这只能表示您发送了null。这个等式与MySQL无关，与JTable也几乎无关，但它确实与MySQL有关。我知道这就是问题所在。我不知道如何解决它，这就是我在这里征求意见的原因。呃，如果你不想收到null，就不要发送null？不清楚您需要什么样的建议。在这里的这些行中，它应该发送非空的对象。但出于某种原因，它没有发送。我不知道这是为什么。这个。getTopology（）；this.ooos.writeObject（getTopology（））；不发送任何内容，或发送null而不是对象？事实上，这一切都是最不清楚的。您还没有发布实际的错误消息、堆栈跟踪或任何症状。以目前的形式不负责。

package networkclientserver;  


import java.net.*;  
import java.io.ObjectInputStream;  
import java.io.ObjectOutputStream;  
import java.sql.Connection;  
import java.sql.DriverManager;  
import java.sql.PreparedStatement;  
import java.sql.ResultSet;  
import java.sql.Statement;  
import java.util.ArrayList;  
import java.util.logging.Level;  
import java.util.logging.Logger;  


class ConnectionCW implements Runnable   
  {  
    private Socket s;  
    private ObjectOutputStream ooos;  
    private ObjectInputStream oois;  
    ResultSet rs;  


ConnectionCW(Socket s)  
{  
    this.s = s;  
}  


public void run()  
{  
    try  
    {  
        ObjectOutputStream ooos = new ObjectOutputStream(this.s.getOutputStream());  
        ObjectInputStream oois = new ObjectInputStream(this.s.getInputStream());  

        this.getTopology();  
        this.ooos.writeObject(getTopology());  
        this.ooos.flush();  



    } catch (Exception ex)  
    {  
        Logger.getLogger(ConnectionCW.class.getName()).log(Level.SEVERE, null, ex);  
    }  
}  // end of method run*/  




}  

   public ArrayList<ReadNet> getTopology() throws Exception  
{  
    ArrayList<ReadNet> getTopology2 = new ArrayList<ReadNet>();  

    Connection conn2 = getConnection();  


    String query = "SELECT * FROM  datatopology ";  
    Statement st;  
    st=conn2.createStatement();  
    rs=st.executeQuery(query);  
    ReadNet readNet;  
    while(rs.next())  
    {  
        readNet = new ReadNet(rs.getInt("id"),rs.getInt("numberNodes"),rs.getInt("numberHubs"),rs.getInt("numberSwitches"),rs.getString("topologyStructure"),rs.getString("country"),rs.getString("status"));  
        getTopology2.add(readNet);  
    }  
    return getTopology2;  
}  



public Connection getConnection() throws Exception  
{  
    try  
    {  
        String driver = "com.mysql.jdbc.Driver";  
        String url = "jdbc:mysql://localhost:3306/networkstopology";  
        String username = "user";  
        String password = "pass";  
        Class.forName(driver);  


        Connection conn = DriverManager.getConnection(url, username, password);  
        System.out.println("Connected to MySQL!");  
        return conn;  


    } catch (Exception e)  
    {  
        System.out.println(e);  
    }  
    return null;  
}  
}  

private void buttonReadActionPerformed(java.awt.event.ActionEvent evt)                                           
{                                               

    try
    {
        ArrayList<ReadNet> setTopology = (ArrayList<ReadNet>) ios.readObject();
        DefaultTableModel model = (DefaultTableModel) topologyTable1.getModel();
        Object[] row = new Object[7];
        for (int i = 0; i < setTopology.size(); i++)
        {
            row[0] = setTopology.get(i).getId();
            row[1] = setTopology.get(i).getNNodes();
            row[2] = setTopology.get(i).getNHubs();
            row[3] = setTopology.get(i).getNSwitches();
            row[4] = setTopology.get(i).getCountry();
            row[5] = setTopology.get(i).getTopology();
            row[6] = setTopology.get(i).getStatus();
            model.addRow(row);
        }
    } catch (IOException ex)
    {
        Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
    } catch (ClassNotFoundException ex)
    {
        Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
    }
}     

package networkclientserver;

import java.io.Serializable;

class ReadNet implements Serializable
{
int id;
int nnodes;
int nhubs;
int nswitch;
String topology;
String country;
String status;


ReadNet(int id,int nodes, int hubs, int switches, String countries, String topology, String status)
{
    this.id=id;
    this.nnodes = nodes;
    this.nhubs = hubs;
    this.nswitch = switches;
    this.country = countries;
    this.topology = topology;
    this.status = status;
}

public int getId()
{
return this.id;
}
public int getNNodes()
{
    return this.nnodes;
}

public int getNHubs()
{
    return this.nhubs;
}

public int getNSwitches()
{
    return this.nswitch;
}

String getTopology()
{
    return this.topology;
}

String getCountry()
{
    return this.country;
}

String getStatus()
{
    return this.status;
}
}