java - ObjectInput and Output streams are not being accepted by client/server

Question

I have one program with two serverside processes. One server just sends an ArrayList to client. The other server first takes a string from client and then finds proper record corresponding to the ID and sends the record back.

I'm having problems with the second server process. See the println statement below where it says "Gets stuck here". That's where the program hangs.

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;


public class CustServer{
    public static void main(String args[]) throws IOException, ClassNotFoundException{
     ServerSocket serverSocket1 = null;
     ServerSocket serverSocket2 = null;
     ArrayList<Customer> list = null;

        String driverName = "sun.jdbc.odbc.JdbcOdbcDriver";
        String connectionURL = "jdbc:odbc:customer";
        Connection con = null;
        Statement stmt = null;
        String sqlStatement = "SELECT ID, CustomerName, Address," +
                " City, State, Zip, Orders FROM Customer";
        ResultSet rs = null;
        try {
            Class.forName(driverName).newInstance();
            con = DriverManager.getConnection(connectionURL);
            stmt = con.createStatement();
            rs = stmt.executeQuery(sqlStatement);
            list = new ArrayList<Customer>(39);
            while(rs.next()){
                list.add(
                    new Customer(
                        rs.getString(1), 
                        rs.getString(2), 
                        rs.getString(3),  
                        rs.getString(4), rs.getString(5), rs.getString(6), 
                        rs.getString(7)));
            }

            rs.close();
            stmt.close();
            con.close();
        }catch (Exception ex) { ex.printStackTrace(); }

    try {
        serverSocket1 = new ServerSocket(8889);
        System.out.println("Customer DB server is running at port 8889");

    } catch (IOException e){
        System.out.println("Could not listen on port: 8889.");
        System.exit(1);
    }

    Socket clientSocket = null;
    try{
        clientSocket = serverSocket1.accept();

    }catch (IOException e){
        System.out.println("Server 1: Accept failed.");
        System.exit(1);
    }
    //A server program which returns a list of customer IDs from the database.
    ObjectOutputStream out = new ObjectOutputStream(clientSocket.getOutputStream());
    out.writeObject(list);
    System.out.println(list.size() + "Customer IDs (list) were sent.");

    out.flush();
    out.close();
    clientSocket.close();
    serverSocket1.close();
    //second server process:
    //Takes a customer  I D and returns the customer record 
    try {
        serverSocket2 = new ServerSocket(8888);
        System.out.println("Customer DB server is running at port 8888");

    } catch (IOException e){
        System.out.println("Could not listen on port: 8889.");
        System.exit(1);
    }
    try{
        clientSocket = serverSocket2.accept();

    }catch (IOException e){
        System.out.println("Server 2: Accept failed.");
        System.exit(1);
    }

    System.out.println("Gets stuck here."); //<<<<<HERE
    ObjectInputStream in = new ObjectInputStream(clientSocket.getInputStream());
    ObjectOutputStream out1 = new ObjectOutputStream(clientSocket.getOutputStream());
    String id = (String) in.readObject();
    String record = null;

    for(Customer c : list){
        if(c.getID().equals(id))
            record = c.toString();
    }

    out1.writeObject(record);

    out1.flush();
    out1.close();
    in.close();
    clientSocket.close();
    serverSocket2.close();
    }
}

Clientside:

    import java.awt.BorderLayout;
import java.awt.Dimension;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.ArrayList;

import javax.swing.DefaultListModel;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextField;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;


public class ClientGUI extends JFrame implements ListSelectionListener{

    //gui components
    JList jlist = null;
    String requestID = null; //Assigned to selected ID in JList. 
    JScrollPane scpane = null;
    JTextField field = null;
    JPanel pane = null;
    DefaultListModel<String> listModel = null;
    ArrayList<String> idList = null;

    //client stuff:
    Socket sock1 = null;
    Socket sock2 = null;
    ObjectInputStream in = null;
    ObjectOutputStream out = null;

    public ClientGUI() throws ClassNotFoundException{
        //get List of IDs from Server1
        try{
            sock1 = new Socket("FahadAhmed-PC", 8889); 
            in = new ObjectInputStream(sock1.getInputStream());
            idList = new ArrayList<String>(29);
            ArrayList<Customer> custList = null;
            custList = (ArrayList<Customer>) in.readObject();
            for(Customer c : custList){
                idList.add(c.getID());
            }

            in.close();
            sock1.close();

            sock2 = new Socket("FahadAhmed-PC", 8888); 



        }catch(UnknownHostException e) {
            System.err.println("Don't know about host: FahadAhmed-PC");
            System.exit(1);
        }catch(IOException e){
            System.err.println(e);
            System.exit(1);
        }

        //Setup GUI
        jlist = new JList(idList.toArray());
        jlist.setVisibleRowCount(10);
        scpane = new JScrollPane(jlist);
        jlist.addListSelectionListener(this);
        pane = new JPanel(new BorderLayout());
        pane.setPreferredSize(new Dimension(300, 300));
        field = new JTextField(29);
        field.setEditable(false);
        pane.add(scpane, BorderLayout.PAGE_START);
        pane.add(field, BorderLayout.PAGE_END);

        this.setContentPane(pane);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.pack();
        this.setVisible(true);
    }

    public static void main(String args[]) throws ClassNotFoundException{
        ClientGUI gui = new ClientGUI();
    }


    @Override
    public void valueChanged(ListSelectionEvent arg0) {
        if(!arg0.getValueIsAdjusting())
            try {
                getRecord(jlist.getSelectedValue().toString());
            } catch (ClassNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }       
    }

    private void getRecord(String getID) throws ClassNotFoundException {
        try{
            in = new ObjectInputStream(sock2.getInputStream());
            out = new ObjectOutputStream(sock2.getOutputStream());
            System.out.println(getID + "sent to getRecord method");
            out.writeObject(getID);

            String rec = (String) in.readObject();

            field.setText(rec);
            out.flush();
            out.close();
            in.close();
        }catch(UnknownHostException e) {
            System.err.println("Don't know about host: FahadAhmed-PC");
            System.exit(1);
        }catch(IOException e){
            System.err.println(e);
            System.exit(1);
        }
    }


}

Answer 1

You need to create and flush() the ObjectOutputStream first, or it will get stuck trying to read the header, the other end hasn't sent because its waiting to read your header.