Lakmali Erandi Baminiwatta’s blog

Recently I came across a requirement to validate all the elements in a collection and return an output based on that. Let me explain it with an example. I have a XML document containing information about users including a collection to indicate the roles of the person. Source Document <users> <user> <first_name></first_name> <roles> <role> admin </role> <role> subscriber </role> <role> creator </role> </roles> </user> </users> Destination Document I want to map this into a destination profile which has elements to indicate whther the user is an admin or a subsriber. <users> <user> <isAdmin> true </isAdmin> <isSubscriber> true </isSubscriber> <user> <users> </users> In order to achieve this I have to write a map funtion. But for a map funtion, we can't input a collection. If we map the "roles" collect...

This is something I learnt recently. Assume that you want to execute the same code when the switch variable value is one of multiple values. This can be dine without repeating the same code in multiple case statements. For example consider below code. There two case statements that check value for 3 or 4, executes same code block.  We can do this without duplicating the code. switch ( number ) { case ( 1 ): System . out . println ( "Number is 1" ); break ; case ( 2 ): System . out . println ( "Number is 2" ); break ; case ( 3 ): System . out . println ( "Number is 3 or 4" ); break ; case ( 4 ): System . out . println ( "Number is 3 or 4" ); break ; default : System . out . println ( "Number is not 1, 2, 3 or 4" ); break ; } See below. switch ( number ) { case ( 1 ): System . out . println ( "Number is 1" ); break ; case ( 2 ): System...

There two AND operators in Java that we can use. & - Bitwise AND operator && - Conditional AND operator. In Java both above operators can be used in if conditions. However there is a difference how each works. Let's see with an example. (x != 0) & (x > 1)  - With bitwise AND, it evaluates both (x !=0) and (x > 1) conditions. Then takes the AND of the two results. (x != 0) && (x > 1)   - With conditional AND, it first valuates (x !=0) and only if it is true, (x > 1) condition will be evaluated. Then takes the AND of the two results. If (x!= 0) was false, it simply returns false. What is the problem with using & in a condition? There are cases where we can only execute a condition only some other condition is true. See the example below. (x != 0) & (3/x  > 1) - This will throw an exception if the x=0. So for such cases we can only use &&. So in summary, it is always advisable to use conditional AND (...

In my previous post , I described about Lamda expression and its usages. Now I am going to write about method references in Java 8. What is a method reference? As I described in my previous post , a lamda expression is an anonymous function. However, sometimes lamda expression is only calling an existing method. On the other hand, if the function code in the lamda expression is too complicated or has many lines, it makes sense to include it in a separate method. This is when method references comes in handy. Instead of writing a lamda expression, we can refer to an existing method. Based on the method type, there are 4 types of method reference syntax. Type Syntax Reference to a static method ContainingClass::staticMethodName Reference to an instance method of a particular object containingObject::instanceMethodName Reference to an instance method of an arbitrary object of a particular type ContainingType::methodName ...

Lamda expression in Java was introduced in Java 8. This is one of my favorite, cool features of Java 8. This blog is intended to help understanding what is it, where and how can we use it. What is lamda expression? In simple words, Lamda expression in java is an anonymous function. It is defined with the parameter list and the function body. Below is the syntax of lamda expression. { parameter list } -> { function body } So what is actually meant by this definition? Although we define an anonymous function here, this is actually like an implementation to a method in an interface. Also, we can assign this lamda expression to a reference of the interface type. See example below. interface MyInterface { public String sayWelcome ( String name ); } public class LamdaExpSample { public static void main ( String args []) { MyInterface myIn = ( name ) -> { return "Welcome " + name ; }; } } ...

REST APIs being exposed over HTTP mainly, there is a great advantage for APIs through HTTP Caching. Why caching is important for REST APIs?  Reduced server load, Low response time Save bandwidth The biggest gain through caching for REST APIs is reduced server load, because the clients can store a cached response for sometime in their local store and access it without hitting the server. So it will result in a low response time to the client making things faster for them. Further, using E-tags (Entity tags), clients have the ability to check with the server whether the response has updated or not. The response body is sent to the client only if the response has changed from what client has cached. Otherwise a 304 Not-Modified response is sent without a response body.  We'll discuss about ETags more later in this post. What to cache?  In your REST API, there can be data that doesn't change more frequently and also data that changes frequently. We can...