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Java Switch statements : Executing same code for two values without redundant code

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.out.println("Number is 2");break;case(3):case(4): System.out.println("Number is 3 or 4");break;default: System.out.println("Number is not 1,…

Java: Difference between Conditional and Bitwise AND operator - & vs &&

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 if conditions. &…

Understanding Java-8 method references with examples

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.

TypeSyntaxReference to a static methodContainingClass::staticMethodNameReference to an instance method of a particular objectcontainingObject::instanceMethodNameReference to an instance method of an arbitrary object of a particular typeContainingType::methodNameReference to a constructorClassName::new
Example usages

I am going to take the s…

Understanding Java Lamda Expression with examples

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.

interfaceMyInterface{public String sayWelcome(String name);}publicclassLamdaExpSample{publicstaticvoidmain(String args[]){ MyInterface myIn =(name)->{return"Welcome "+ name;};}}
As above, we have defined a Lamda expression to return a greet message. It has implemented the "sayWelcome" me…

REST API Caching

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 timeSave 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 define those data types as near…

What is HTTP/2?

Not so long ago, I happened to do a research about HTTP/2 and how it affects performance of web services for my Masters. In this blog post, I am describing the basic details of the HTTP/2 protocol. 
HTTP/2 the latest version of Hyper Text Transfer Protocol, is an optimized transport for HTTP semantics. Hence, it supports all the core features of HTTP/1.1 [1] . The aim of HTTP/2 is to be more efficient by addressing limitations of HTTP/1.1 [1] .
There are 5 main features of HTTP/2.


MultiplexingHeader CompressionRequest prioritizationServer pushBinary message frames. Connection establishment in HTTP/2 HTTP/2 also uses the same “http” and “https” URI schemas and same port numbers as HTTP/1.1. Therefore, implementations processing requests for target URIs with“http” and “https” should have a way to discover whether the next hop supports HTTP/2 or not. The determination procedure for HTTP/2 support is different for “http” and “https” URIs [1] .

Starting HTTP/2 for “http” URIs A client with…

WSO2 API Manager- Customizing Store User Sign-Up

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WSO2 API Manager allows on boarding new users to the API store through a Sign-up page. The default sign-up page has set of mandatory and optional fields for user to provide details. However, there can be cases where one needs to customize the available fields by modifying available ones or/and adding new fields.

This can be easily achieved in WSO2 API manager since the fields are loaded dynamically from the user claim attributes. So this post explains how we can customize the default Sign-up page.

By default API Store Sign-up looks as below. Note that this blog posts shows how to do this in APIM 2.1.0.



Let's say you want to add a new field called 'City' to Store Sign-up page. This post provides step by step instructions on how to achieve this.

1. Start API Manager 2.1.0 and go to Management Console (https://localhost:9443/carbon/)

2. Go to Claims -> Add -> Add Local Claim



3. Enter the below values for the new claim.


Claim URI : http://wso2.org/claims/city
Display Na…