Java

Google App Engine: Understanding Caching

Reading Time: 3 minutes If you have been following the Google App Engine downtime notify group then you would realize that the datastore has been behaving erratically over the last 2 weeks. Though we had been thinking about exploiting Memcache for caching for a while now, but the last 2 weeks proved to be the perfect alibi. Another reason was the comment that we got on our blog by Continue Reading

Google App Engine More JPA Gotchas

Reading Time: 2 minutes We were in process of porting an application to GAE. The application used JPA for persistence and we decided to use the same for GAE as well. After deploying, the application worked fine on Google App Engine. Over a period of time we started getting errors, which seemed strange. All our tests were running fine and application worked without any issues with our seed data. Continue Reading

Duplicate Code? Chain Constructors

Reading Time: 2 minutes After the ‘Introduction of Null Object’ and the ‘Replace One/Many Distinctions with Composite’ let us do an easy one this time. It is easy but of course it is present in a lot of code samples else we would not be discussing it here. If there are a lot of constructors which have duplicate code then see if there is a reasonable possibility to chain Continue Reading

Google App Engine Some JPA Gotchas

Reading Time: 2 minutes While porting an application to Google App Engine we encountered several issues. Most of them where related to persistence. We were using JPA for persistence in the application. One of the most common mistake we did was in issuing a JPA Query where one or more parameters are of type com.google.appengine.datastore.api.Key class. Key class has two String representations which lead to some confusion. Let’s look Continue Reading

Duplicate Code? Replace One/Many Distinctions with Composite

Reading Time: 3 minutes After the first post on how to introduce Null Object, in this second post on how to write clean(er) code, let us look at one of the very frequent occurrence. At least something that I have seen quite often. You too would have noticed that many APIs provide two methods to do the same thing. One of the methods expects one object and the other Continue Reading

GAE Problems: Slim3 To The Rescue?

Reading Time: 3 minutes For the past few months we have been working on porting a time-sheet application on Google App Engine. The application we were trying to port had Spring for Dependency Injection, Hibernate for persistence and Wicket as the web framework. Looking at the will it play in app engine Hibernate was an easy call, it is not compatible on Google App Engine, wicket works with some Continue Reading

Downloading Datastore Data from a Java Application on Google App Engine

Reading Time: 3 minutes One of the most frequently talked barriers for getting onto the cloud is the data lock-in. In this post we would try to look at how we can download data as a CSV from the app engine datastore. This would help us get the data back from the app engine, just in case you want to move away from the datastore. So there exists a Continue Reading

Combine Multiple BIRT Designs To Generate Single Report

Reading Time: 2 minutes We use BIRT for generating reports in our application. Currently we have a suite of report designs that covers various parts of the application. Reports are generated on demand by the user. The application required the functionality of specifying a list of birt rpt design files, which can then be run to generate a single report for the user. It is quite common to have Continue Reading

Multitenancy in Google App Engine: Scope of NamespaceManager

Reading Time: 2 minutes As you would have read in our previous post, we used the Namespace API to make the SaaS application that we were working on multi-tenant in a matter of four hours. You would have noticed that we set the tenant name in the NamespaceManager [sourcecode language=”java”] NamespaceManager.set(request.getServerName()); [/sourcecode] Our initial assumption was that the NamespaceManager would continue to exist for the lifetime of the session Continue Reading

Implementing Multi-tenancy On Google App Engine

Reading Time: 3 minutes Google recently added support for multi-tenancy for applications via the Namespaces API. We are in process of porting an application to Google App engine. We were thinking of making our application multi-tenant. With the new Namespaces API in our arsenal we decided to give it a try. To our surprise implementing multi-tenancy is easy, we were done with it in couple of hours! With multi-tenancy, Continue Reading

Duplicate Code? Introduce Null Object

Reading Time: 3 minutes One of the most significant code smells is having duplicate code. There are primarily 2 forms of code duplications Explicit – These are the ones where there is blatant copy paste of the code. Methods are repeated within classes and it is easy for the CPD tool of PMD to figure out that lines are copied thus leaving us red faced. Subtle – This is Continue Reading

Improve Performance By Using Keys Only Query on Google App Engine

Reading Time: 2 minutes It has been around two months since we started to port an existing application on Google App engine. It used Hibernate for persistence, Wicket framework for web layer and Spring as an Ioc container. Looking at the will it play on appengine we had to change Hibernate to use either JPA or JDO. We decided on JPA purely on the basis of experience we had Continue Reading

Lock-in, the Overrated Barrier to Cloud Adoption

Reading Time: 4 minutes By definition, lock-in makes a customer dependent on a vendor for products and services, unable to use another vendor without substantial switching costs. That sounds scary. Now let us take a step back and look at all the standards which were available in the traditional world to prevent lock-in. JEE specs sure have a lot of them and that ensures that you would be able Continue Reading