Showing posts with label GWT. Show all posts
Showing posts with label GWT. Show all posts

Friday, January 25, 2013

Realization of dream of multitenancy with Google App Engine and MongoDB on cloud.

Multitenancy and the problem of managing the data

Multitenancy refers to a principle in software architecture where a single instance of the software runs on a server, serving multiple client organizations (tenants). Multitenancy is contrasted with a multi-instance architecture where separate software instances (or hardware systems) are set up for different client organizations. With a multitenant architecture, a software application is designed to virtually partition its data and configuration, and each client organization works with a customized virtual application instance. [WIKI]

What if i want to migrate my existing system to any cloud engine?
Move all of code/business logic to app engine, perfect, no problem, but what if my database is already on another physical infrastructure(and which is shredded,etc)?


Of-course app engine/GAE gives you the ability to scale, security, high availability, etc. but with their own terms.You need to use the database which is supported only by the app engine.
Which is one of the major drawback for the GAE and similarly other cloud engines.

I wanted to use MongoDB with Google App Engine(GAE) and could not see the possibility because we can't run MongoDB on GAE and supposed to use Google datastore.

There are few more issues as GAE's highly restricted sandbox. As GAE's docs says your application can only access other computers on the internet through the provided URL fetch and email services (and fewer more ways). Other computers can only connect to the application by making HTTP/HTTPS requests on the standard port. If you want to open a socket from your business logic, its not allowed and GAE will raise an exception.

Few good things happened in this direction, when google annoucned back in 2011 about Google Cloud SQL webservice to support MySQL - https://developers.google.com/cloud-sql/
Some of the other cloud engines have provided more options such as Amazon RDS supports MySQL, Oracle or Microsoft SQL Server database engine. This means that the code, applications, and tools you already use today with your existing databases can be used with Amazon RDS.

I was adamant to move from MongoDB and to use my application with the GAE and mongolab became the savior. Why i want to use my own choice of database because i have already have my own hosted database servers because i want to manage data on my own (security reason, business reason, etc)

Here is the steps how can we use GAE with MongoDB, when your MongoDB instance is hosted on DB cloud.

1) Signup, login and create a database on mongolab


This is going to create mongodb as the database.


2) Create a collection
    Creation of collection (table) can be done by going to database and click on "Add".

3) Open collection which is currently empty and open the API view.
    Connection information on the top of the "Collections" tab is the url which we are going to use interact
    with "mongodb" database created in step1, mongolab has provided REST based methods for database
    interactions.



    At this point we are done with our database part.

    Lets move to GWT(Google Web Toolkit) to create a project.

4) Create a Web Application Project and make sure that "Use Google App Engine" is checked.


    Create a GWT based application, i have used the almost same application which i have created earlier,
    you can refer the steps for the application creation here GWT RPC - Server communication with 
    MongoDB

    The only change here is that the mongodb is hosted on some cloud, and because of that implementation
    for is going to change.

5) Insert a recod and retrive records from cloud database.
    Inserting a record into the databased using the apache's HTTPClient to connect to mongodb hosted on
    cloud, which interacts with the REST based webservice.



    Get all available users from the database.


   As i mentioned earlier about the sandbox security of GAE, i could not use HttpClient directly to invoke
   webserivce and get the data, and had to tweak it bit to make it happen. Shortly going to update about the
  problem as well in this post, which will be describing about GAEConnectionManager.

6) In order to deploy the developed application on cloud, create an an application identifier on app engine.  
    After creation you can see the application as follows:


    Update in /war/WEB-INF/appengine-web.xml and place it under "application" tag.



7) Login to google account from eclipse(you can find it in the bottom left) and deploy the app on the app
    engine.




   And we are done!,  app is available and hosted.
   You can access it from here: http://mongocloudapp.appspot.com/

    I would like to say that overall it is a very nice experience with the app development with GAE and
    without loosing the my own preferred database.

Tuesday, July 24, 2012

GWT RPC - Server communication with MongoDB

Further to the client tutorial in the previous blog, here i am going to present how client communicates with the server with the help of GWT RPC (Remote Procedure Call).
Using RPC which works asynchronously only specific part of the client components can be updated without updating the complete client.














Pre-Requisite:
Java, Eclipse with GWT plugin, MongoDB.



In this example i have extended the previous client to
  a) save data i.e. user data to database and
  b) authentication user

Client can send/receive serializable objects to/from the server. In this example server is going to use that data and insert in into DB, which is MongoDB in our case.


Create Modal
As the client can send serializable java objects over HTTP. Lets create a modal first.


User.java



Create Service
Now we need to have a service which a client can use.
In our case we name it as MongoDBService and it implements RemoteService


MongoDBService.java



@RemoteServiceRelativePath("dbservice") is annotation used for the service identification and calling, which should match with the service path defined in web.xml for servlet-mapping tag.

We need to create Asynchronous service for our MongoDBService, client is actually going to call RPC through MongoDBServiceAsync. All methods of MongoDBService will have extra parameter which is of type AsyncCallback. Client call will be notified when any asynchronous service call completes.

MongoDBServiceAsync.java



Implement service at the server side
Create class MongoDBServiceImpl which extends RemoteServiceServlet and implements MongoDBService. Basically MongoDBServiceImpl is a servlet which is extending from RemoteServiceServlet rather than the HttpServlet directly.



Updating web.xml with servlet details
make sure that all the service which are created with the annotation RemoteServiceRelativePath are added properly for each servlet.

web.xml



url pattern tag path should be formed using module/service.
In this case module name is gwtwebappdemo ( see in GwtWebAppDemo.gwt.xml for rename-to value) and service in dbservice.


Client Service Call
calling service from client





Running application

1) Start MongoDB
    In this case i have started DB without authentication and on default port.
    Default port is 27017 which we have used to connect to database in the code. See DBUtil.java in the
   example.



2) Add user into database.
    Client calls asynchronous call to server, server starts the processing. Once request processing is finished it calls back with the call back handler provided in the request. Client gets call in onFailure in case of failure and onSuccess in case of request processing successful.


    In the server side, server received the User object and sets the data into User collection which is in the mymongodb database using BasicDBObject.

MongoDBServiceImpl.java


3) Check the collection ( table) creation in dbs (database)
    In this example mymongodb is the database and User is the collection which we are using.
    Initially both database and collection is not present, when the first save happens. Both gets automatically
    created.



4) Check User Authentication with wrong input.



Download complete example from here in GwtWebAppDemo_server.rar file.

Tuesday, July 17, 2012

Google Web Toolkit - step by step GWT client tutorial

Its free!
Its opensource!
Its makes development faster!
Its amazing!
Faster development of web application with an ease.
AJAX based app develop in java and run in all browser.
Works well with Android/iPhone.

Google has done preaching on their site and blog about GWT, find more details their.
Ofcourse believers of those preaching also wrote a lot about it on their blog(s), website(s), papers, etc,
So, moving to example.:

Pre-requisetes
   Eclipse, Java.


Download and install GWT plugin for eclipse, in my case its for indigo and link is as follows:
http://dl.google.com/eclipse/plugin/3.7

for complete instruction use the following link
https://developers.google.com/eclipse/docs/install-eclipse-3.7


Create a Google Web Project -> GwtWebAppDemo

     Click on next.

    Un-check the checkbox "Use Google App Engine" as we are going to use internal app server.
    Click on finish.
    A new google web project is created with default project files.
 
    Delete all default java files from client, server and shared package.
    Add a new Entry-Point class into the client package.



One entry will be added into GwtWebAppDemo.gwt.xml.
Verify that entry point is correct in GwtWebAppDemo.gwt.xml. In this case its





Change the class in entry-point tag if you have changed/added the class manually and not as Entry Point Class.


Add RootPanel to the entry point class i.e. GwtDemoAppClient.java in onModuleLoad() method.



RootPanel rootPanel = RootPanel.get();

RootPanle is a panel to which all other widgets must ultimately be added.
RootPanels are never created directly. Rather, they are accessed via get().
Most applications will add widgets to the default root panel in their EntryPoint.onModuleLoad() methods.



After that right client on GwtDemoAppClient.java and open with GWT Designer
We are ready for adding the components by drag and drop.


I have selected LayoutPanel as it allows its children to be positioned using arbitrary constraints.



After adding the components you can see the generated code:





Add few componets to the layoutPanel and test the demo without web app to see it as preview.




If its fine than go ahead and create a web app/deploy to internal app server which is jetty.
Else go and add/remove/update components in the panel.

Change the default html content of GwtWebAppDemo.html in the war/WEB-INF folder.



Right click on the project and click on Run As Web Application
It will start new tab as development mode, copy the link and paste into your browser







For the first time it will ask for installing the plugin for gwt. 
Install it and see the application running.


Do remember to close the client running the the IDE before launching it again.



You can download sample from here  --> GwtWebAppDemo.rar 

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