我有一个程序有两个服务器端进程。一台服务器只是向客户端发送一个ArrayList。另一台服务器首先从客户端获取一个字符串，然后找到与该ID相对应的正确记录并将该记录发回。
我遇到了第二个服务器进程的问题。请参阅下面的println语句，其中显示“卡在这里”。这就是程序挂起的地方。
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);
}
}
}
答案 0 :(得分：2)
你需要首先创建并刷新（）ObjectOutputStream，否则它会在尝试读取标题时卡住，另一端没有发送，因为它等待读取你的标题。
答案 1 :(得分：1)
您需要在两端的ObjectInputStream之前创建ObjectOutputStream。