Callback Pattern in Java
//[C] 2002 Sun Microsystems, Inc.---
import java.io.IOException;
public class RunCallbackPattern {
public static void main(String [] arguments){
System.out.println("Example for the Callback pattern");
System.out.println("This code will run two RMI objects to demonstrate");
System.out.println(" callback capability. One will be CallbackClientImpl,");
System.out.println(" which will request a project from the other remote");
System.out.println(" object, CallbackServerImpl.");
System.out.println("To demonstrate how the Callback pattern allows the");
System.out.println(" client to perform independent processing, the main");
System.out.println(" progam thread will go into a wait loop until the");
System.out.println(" server sends the object to its client.");
System.out.println();
System.out.println("Running the RMI compiler (rmic)");
System.out.println();
try{
Process p1 = Runtime.getRuntime().exec("rmic CallbackServerImpl");
Process p2 = Runtime.getRuntime().exec("rmic CallbackClientImpl");
p1.waitFor();
p2.waitFor();
}
catch (IOException exc){
System.err.println("Unable to run rmic utility. Exiting application.");
System.exit(1);
}
catch (InterruptedException exc){
System.err.println("Threading problems encountered while using the rmic utility.");
}
System.out.println("Starting the rmiregistry");
System.out.println();
Process rmiProcess = null;
try{
rmiProcess = Runtime.getRuntime().exec("rmiregistry");
Thread.sleep(15000);
}
catch (IOException exc){
System.err.println("Unable to start the rmiregistry. Exiting application.");
System.exit(1);
}
catch (InterruptedException exc){
System.err.println("Threading problems encountered when starting the rmiregistry.");
}
System.out.println("Creating the client and server objects");
System.out.println();
CallbackServerImpl callbackServer = new CallbackServerImpl();
CallbackClientImpl callbackClient = new CallbackClientImpl();
System.out.println("CallbackClientImpl requesting a project");
callbackClient.requestProject("New Java Project");
try{
while(!callbackClient.isProjectAvailable()){
System.out.println("Project not available yet; sleeping for 2 seconds");
Thread.sleep(2000);
}
}
catch (InterruptedException exc){}
System.out.println("Project retrieved: " + callbackClient.getProject());
}
}
import java.rmi.Naming;
import java.rmi.server.UnicastRemoteObject;
public class CallbackServerImpl implements CallbackServer{
private static final String CALLBACK_SERVER_SERVICE_NAME = "callbackServer";
public CallbackServerImpl(){
try {
UnicastRemoteObject.exportObject(this);
Naming.rebind(CALLBACK_SERVER_SERVICE_NAME, this);
}
catch (Exception exc){
System.err.println("Error using RMI to register the CallbackServerImpl " + exc);
}
}
public void getProject(String projectID, String callbackMachine,
String callbackObjectName){
new CallbackServerDelegate(projectID, callbackMachine, callbackObjectName);
}
}
import java.rmi.Remote;
import java.rmi.RemoteException;
public interface CallbackServer extends Remote{
public void getProject(String projectID, String callbackMachine,
String callbackObjectName) throws RemoteException;
}
import java.net.InetAddress;
import java.net.MalformedURLException;
import java.net.UnknownHostException;
import java.rmi.Naming;
import java.rmi.server.UnicastRemoteObject;
import java.rmi.NotBoundException;
import java.rmi.RemoteException;
public class CallbackClientImpl implements CallbackClient{
private static final String CALLBACK_CLIENT_SERVICE_NAME = "callbackClient";
private static final String CALLBACK_SERVER_SERVICE_NAME = "callbackServer";
private static final String CALLBACK_SERVER_MACHINE_NAME = "localhost";
private Project requestedProject;
private boolean projectAvailable;
public CallbackClientImpl(){
try {
UnicastRemoteObject.exportObject(this);
Naming.rebind(CALLBACK_CLIENT_SERVICE_NAME, this);
}
catch (Exception exc){
System.err.println("Error using RMI to register the CallbackClientImpl " + exc);
}
}
public void receiveProject(Project project){
requestedProject = project;
projectAvailable = true;
}
public void requestProject(String projectName){
try{
String url = "//" + CALLBACK_SERVER_MACHINE_NAME + "/" + CALLBACK_SERVER_SERVICE_NAME;
Object remoteServer = Naming.lookup(url);
if (remoteServer instanceof CallbackServer){
((CallbackServer)remoteServer).getProject(projectName,
InetAddress.getLocalHost().getHostName(),
CALLBACK_CLIENT_SERVICE_NAME);
}
projectAvailable = false;
}
catch (RemoteException exc){}
catch (NotBoundException exc){}
catch (MalformedURLException exc){}
catch (UnknownHostException exc){}
}
public Project getProject(){ return requestedProject; }
public boolean isProjectAvailable(){ return projectAvailable; }
}
import java.net.MalformedURLException;
import java.rmi.Naming;
import java.rmi.NotBoundException;
import java.rmi.RemoteException;
public class CallbackServerDelegate implements Runnable{
private Thread processingThread;
private String projectID;
private String callbackMachine;
private String callbackObjectName;
public CallbackServerDelegate(String newProjectID, String newCallbackMachine,
String newCallbackObjectName){
projectID = newProjectID;
callbackMachine = newCallbackMachine;
callbackObjectName = newCallbackObjectName;
processingThread = new Thread(this);
processingThread.start();
}
public void run(){
Project result = getProject();
sendProjectToClient(result);
}
private Project getProject(){
return new Project(projectID, "Test project");
}
private void sendProjectToClient(Project project){
try{
String url = "//" + callbackMachine + "/" + callbackObjectName;
Object remoteClient = Naming.lookup(url);
if (remoteClient instanceof CallbackClient){
((CallbackClient)remoteClient).receiveProject(project);
}
}
catch (RemoteException exc){}
catch (NotBoundException exc){}
catch (MalformedURLException exc){}
}
}
import java.net.MalformedURLException;
import java.rmi.Naming;
import java.rmi.NotBoundException;
import java.rmi.RemoteException;
public class CallbackServerWorkThread implements Runnable{
private Thread processingThread;
private String projectID;
private String callbackMachine;
private String callbackObjectName;
public CallbackServerWorkThread(String newProjectID, String newCallbackMachine,
String newCallbackObjectName){
projectID = newProjectID;
callbackMachine = newCallbackMachine;
callbackObjectName = newCallbackObjectName;
processingThread = new Thread(this);
processingThread.start();
}
public void run(){
Project result = getProject();
sendProjectToClient(result);
}
private Project getProject(){
return new Project(projectID, "Test project");
}
private void sendProjectToClient(Project project){
try{
String url = "//" + callbackMachine + "/" + callbackObjectName;
Object remoteClient = Naming.lookup(url);
if (remoteClient instanceof CallbackClient){
((CallbackClient)remoteClient).receiveProject(project);
}
}
catch (RemoteException exc){}
catch (NotBoundException exc){}
catch (MalformedURLException exc){}
}
}
public class Command implements java.io.Serializable{
public static final int GET_PROJECT = 1;
public static final int GET_TASK = 2;
public static final int CREATE_CONTACT = 4;
public static final int ADD_ADDRESS = 8;
public static final int REMOVE_ADDRESS = 16;
public static final int FINALIZE_CONTACT = 32;
private int command;
private Object [] arguments;
public int getCommand(){
return command;
}
public Object [] getArguments(){
return arguments;
}
public void setArguments(Object [] newArguments){
arguments = newArguments;
}
public void setCommand(int newCommand){
command = newCommand;
}
public Command(int name, Object [] argumentList){
command = name;
arguments = argumentList;
}
}
import java.util.ArrayList;
public class Project implements ProjectItem{
private String name;
private String description;
private ArrayList projectItems = new ArrayList();
public Project(){ }
public Project(String newName, String newDescription){
name = newName;
description = newDescription;
}
public String getName(){ return name; }
public String getDescription(){ return description; }
public ArrayList getProjectItems(){ return projectItems; }
public void setName(String newName){ name = newName; }
public void setDescription(String newDescription){ description = newDescription; }
public void addProjectItem(ProjectItem element){
if (!projectItems.contains(element)){
projectItems.add(element);
}
}
public void removeProjectItem(ProjectItem element){
projectItems.remove(element);
}
public String toString(){ return name + ", " + description; }
}
import java.net.Socket;
import java.util.Date;
import java.io.*;
public class ServerWorkThread implements Runnable{
private Thread processingThread;
private Socket requestSocket;
private Command command;
public ServerWorkThread(Socket clientRequestSocket){
requestSocket = clientRequestSocket;
processingThread = new Thread(this);
processingThread.start();
}
private void retrieveCommand(){
try{
ObjectInputStream in = new ObjectInputStream(requestSocket.getInputStream());
Object request = in.readObject();
requestSocket.close();
if (request instanceof Command){
command = (Command)request;
}
}
catch (ClassNotFoundException exc){
}
catch (IOException exc){
}
}
protected void processCommand(){
}
public void run(){
retrieveCommand();
processCommand();
}
public Command getCommand(){
return command;
}
protected Socket getRequestSocket(){
return requestSocket;
}
}
import java.util.ArrayList;
public class Task implements ProjectItem{
private String name;
private ArrayList projectItems = new ArrayList();
private double timeRequired;
public Task(){ }
public Task(String newName, double newTimeRequired){
name = newName;
timeRequired = newTimeRequired;
}
public String getName(){ return name; }
public ArrayList getProjectItems(){ return projectItems; }
public double getTimeRequired(){ return timeRequired; }
public void setName(String newName){ name = newName; }
public void setTimeRequired(double newTimeRequired){ timeRequired = newTimeRequired; }
public void addProjectItem(ProjectItem element){
if (!projectItems.contains(element)){
projectItems.add(element);
}
}
public void removeProjectItem(ProjectItem element){
projectItems.remove(element);
}
}
import java.net.ServerSocket;
import java.net.Socket;
import java.io.IOException;
public class ThreadedServer{
private static final int DEFAULT_SERVER_PORT = 2001;
private boolean shutdown;
private int serverPort = DEFAULT_SERVER_PORT;
public void runServer(){
try{
ServerSocket mainServer = new ServerSocket(serverPort);
while (!shutdown){
Socket requestSocket = mainServer.accept();
new ServerWorkThread(requestSocket);
}
}
catch (IOException exc){
}
}
public int getServerPort(){
return serverPort;
}
public boolean isShutdown(){
return shutdown;
}
public void setShutdown(boolean isShutdown){
shutdown = isShutdown;
}
public void setServerPort(int newServerPort){
serverPort = newServerPort;
}
}
import java.rmi.Remote;
import java.rmi.RemoteException;
public interface CallbackClient extends Remote{
public void receiveProject(Project project) throws RemoteException;
}
import java.io.Serializable;
import java.util.ArrayList;
public interface ProjectItem extends Serializable{
public ArrayList getProjectItems();
}
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