Question

On my Client/Server Desktop application. I have this problem of how I should properly code my JDBC class with my Models to ensure all persistence request can support concurrency. i.e., multiple models want to request update to its persistence counterpart simultaneously [without atmost delay].

The scenario goes like this. Following the classes located in the server application.

Persitence Package:

abstract class AbstractService {
  // other fields
  private final String tName, tId;
  private final String sqlStatement;
  public AbstractService(final String tName, final String tId) {
    this.tName = tName;
    this.tId = tId;
    this.sqlStatement = ""; // SELECT statement
  }
  // java.sql.Connection() createConnection()
  // methods
}
public class T1Service extends AbstractService {
  private final String sqlDMLStatements;
  public T1Service() {
    super("t1", "t1Id");
    this.sqlDMLStatements = ""; // other DML statements
  }      
  // methods having return types of List<E>, Object, Boolean, etc.
  // i.e., public List<E> listAll()
}

Communication class [Client class]

import java.net.*;
import java.io.*;
public class Client extends Observable{
  private Socket socket;
  private ObjectInputStream input;
  private ObjectOutputStream output;
  private Object message;
  // Constructor
  // Getters/Setters
  // Other methods like open or close input/output
  private class ReceiverRunnable implements Runnable
    @Override
    public void run() {
       while(running) { // if socket is still open and I/O stream are open/initialized
          try { message = input.readObject(); } 
          catch(Exception e) {}
          finally { setChanged(); notifyObservers(); }  
       } 
    }
  }
}

The Main Class [Server class]

import java.net.*;
public class Server {
   private List<Client> clientList; // holds all active connections with the server
   private T1Service    t1Service
   private class ConnectionRunnable implements Runnable {
      @Override public void run() {
         while(running) { // serverSocket is open
           Client client = new Client(ServerSocket.accept(), /* other parameters */);
           client.addObserver(new ClientObserver(client));
           clientList.add(client);
         }
      } 
   }
   private class ClientObserver implements Observer {
      private Client client;
      // Constructor
      public void update(Observable o, Object arg) {
         // Check the contents of 'message' to determine what to reply
         // i.e., message.equals("Broadcast") {
         // synchronized(clientList) {
         //   for(Client element : clientList) {
         //     element.getOutput().writeObject(replyObject);
         //     element.getOutput()..flush();
         //   }
         // }
         // i.e., message.equals("T1") {
         // synchronized(t1Service) {
         //     client.getOutput().writeObject(t1.findAll());
         //     client.getOutput().flush();
         // }
      } 
   } 
}

Since this is a Client/Server applcation, multiple request from the client are simultaneously feed to the server. The server process the request sending the appropriate reply to the approriate client. Note: All of the objects sent between Client & Server an instance of java.io.Serializable.

Having this kind of scenario and looking into the block of Server.ClientServer.update() we may have a performance issue or I should say a delay in processing the N client(s) request due to Intrinsic Locks. But since I have to the rules concurrency and synchronization to ensure that Server.T1Service won’t get confused to the queue of N clients request to it. Here’s are the questions:

1. According to the Item 1 of Effective Java – Second Edition regarding Static Factory, would this let me create a new class reference to the methods inside the classes of Persistence package?
2. Would each Client element inside List<Client> would form a concurrency issue having N client update their message field simultaneously triggering the ClientObsver.update() wherein the reference object(s) of this Observer is only a single instance in the parent class. I was avoiding creating multiple instance of T1Service due to memory concerns.
3. If we are going to go by the contents of Effective Java – Second Edition, how can I convert my persitence class in a way they can be read easily, easily instantiated, and support concurreny?

Answer 1

Is my theory of [Item 1] Static Factory correct?

Yes, you can use a static factory instead of constructors. Typically this is when you the construction logic is complex and shared between various subtypes to warrant a factory pattern. Additionally the factory may provide means for dependency injection outside of a DI framework.

Would it then solve the concurrency issue of the converted static factory global objects?

If you need to synchronize construction, then a static factory works well, just add synchronized to the method declaration on your factory methods. If you need to synchronize methods on the objects themselves then this will not help.

Is it advisable for me to convert to static factory if where dealing with concurrent access to a global object and where wanted real-time access to the methods of each global object?

As I answered above, it depends on what you are trying to achieve. For constructor synchronization use a factory.