Friday, May 18, 2018

Integrate Apache Keycloak with Spring Boot

Security, I know this is so boring. But this is must. Years ago we have to expend much more time to implement the security of our enterprise applications, basically I'm talking about Web application security. But nowadays there are some Identity management tools that can be used to make easier our lives.

What is an Identity management tool ?

Simply it can be used as a security provider. We can delegate our security to a third party. It is just like hiring a security person or hiring a bodyguard. 

What is Apache Keycloak ?

This is one of the best tools that can be used as an authentication management tool. Actually it is an identity provider. You can very easily integrate it to your Spring Boot applications and if you want you can integrate it with Spring Security also.

Advantages of Apache Keycloak ?
  • It is light weight and fast.
  • Single sign on
  • It uses standard protocols such as OAuth 2.0, OpenID, SAML 2.0...etc.
  • Can be managed easily. 
  • Very easy to use with Keycloak adapters.
  • Very easy to enable social logins.

Here I'm not going to explain more details about Security concerns. I just wanted to explain the integration of Apache Keycloak with Spring Boot.

First of all lets create a simple web application using Spring Boot. Go through following link to get started with Spring Boot if you are new to Spring Boot.

Here I'm going to create a simple web application to demonstrate this.


import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;

public class ReservationController {

    public String home(){
        return "index";

    public String getReservations(){
        return "reservations";

    public String logout(HttpServletRequest request) throws ServletException {
        return "index";


<html xmlns:th="">
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />

    <h1>Home page</h1>
    <a href="/reservation">My Reservations</a>


<html xmlns:th="">
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />

    <h2>Reservations page</h2>

    <a href="/logout">Logout</a>


I changed the default server port to 8090 in file. Just go to following links and check your application is working or not. 

How to use Apache Keycloak server

  • Unzip it in your machine.
  • Go to bin folder. If you are on Windows OS just you can run standalone.bat file or if you are using a Linux distribution, you may use file to start the server. 
  • Normally it will run on port 8080. But you can change it as your wish, go to standalone\configuration\standalone.xml and change the port.
  • Once you run the server, go to http://localhost:8080/auth/

You will be able to see as follows.

This is to create an admin user. You can give any username and password you like. Once you create an admin user, you will be redirected to following page. 

You can see the red square "Administration Console". Just click it and then you will be redirected to following page which asks your admin credentials for the admin you've already created.

Once you are logged, then you can see below page.

Then you have to create a Realm. Just point your mouse to left side and then you will be able to see a button like below image.

Then you can create a realm by giving a realm name. 

Once you create a realm you will be able to see following page.

Then you need to create a client for you application. Click on Client in the left menu.

Then you can give any name for Client ID, I'm using it as "reservations". Once you created a client, scroll down and then you will be able to see "Valid redirect URIs".

It is the entry point to your application after you logged in to it. You may use the port which your Spring Boot application is running. My application is running on port 8090.

Then you have to add new Role. Go to Roles in the menu and click on Add Role.

Once you click, you will be able to see like this.

Add role name, I use it as "user". We need to use this role in our Spring Boot application. Once you save your role, Click again on Roles in menu. Then go to Default Roles.

Then you need to add your role to Default Roles. Select your role and click Add selected.

Now you can create a new user. Click on Users in the menu.

Then click on Add users and give an username and click save. I used it as "client".

Once you saved, just go to Credentials tab in your user and reset your password. Turn off temporary tab for the password. 

Now everything is done on Keycloak configuration side. Ready to go with Spring Boot app.

Configure Spring Boot application

It is actually simple application. What you need to do is, add Keycloak dependencies to your pom.xml and add configurations to file. 


<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="" xmlns:xsi=""


 <description>Demo project for Spring Boot</description>

  <relativePath/> <!-- lookup parent from repository -->






   <name>Spring Snapshots</name>
   <name>Spring Milestones</name>

   <name>Spring Snapshots</name>
   <name>Spring Milestones</name>


#server port of Spring Boot application is running

#specify the url that keycloak server is running

#realm name which you used when you configured keycloak
#client name you created

#created user, when you configured keycloak[0].auth-roles[0]=user
#url pattern needs to be secured[0].security-collections[0].patterns[0]=/reservation/*

This is a simple example of Spring Boot and Apache Keycloak integration. You will be able to see more details, if you can go to Realm settings and then Login tab. Then you can very easily add functionalities for User registration, Remember me, Forgot password, Verify email...ect. You can download the full Spring Boot project from below.

Apache Keycloak can be used with Spring Security also. I'll explain this in later.

Friday, April 20, 2018

Interviews FAQ 1

Here I'm not going to explain detailed overview of questions, it is just main points of FAQs that can be asked and this is a part one.

What are the features of Java ?

  • It is simple (Easy learning curve)
  • Robust (both compiletime/runtime error checking, Memory is managed by itself using Garbage collector)
  • Platform independent
  • High performance (With JVM)
  • Very secure (Java files to class files)

What is a class ?

  • Class is a blueprint of which object is created.
  • We can represent a real world object using a class.

What is an interface ?

  • Interface is a blueprint of a class.
  • Interfaces allow a class to behave like multiple types.

Why we need interfaces ?

  • Interfaces are mainly used for data abstraction.
  • We can achieve multiple inheritance using interfaces.

Interfaces vs Abstract class

What is a Java Bean ?

  • Java bean is a class which follows some conventions. 
  • It has no-arg constructor
  • It is serializable.
  • Its fields can only be accessed by getters and setters
  • Its instance variables are final.

What is a hashcode ?

  • Every object has a hashcode, it is unique number.
  • This is assigned by JVM.
  • Hash related data structures use this. (HashMap, HashList...etc)

What is called Serialization ?

  • This is the process of converting an object into a series of bytes.
  • This is very useful when transferring data, store them in sessions...etc

What is called String pool ?

  • It is a separate area of Heap which consist of String objects.
  • This is maintained by JVM.

Difference between == vs equals() 

  • == are used to compare reference and address.
  • equals() method is used to content comparison. 

Web server vs Application server

  • Application server is the super one.
  • Each application server contains a web server.
  • If you are not satisfied with inbuilt server, you can add another server.

Web serverApplication server
Ex: Tomcat, Jetty, ResinEx: Glassfish, Wildfly, JBoss, WebSphere
Not J2EE compatibleJ2EE compatible
Can be run web applications onlyCan be run both web and enterprise applications
Support for HTML, JSP, Servlets...Support for HTML, JSP, Servlets, EJB, JMS...etc

What is the garbage collector ?

  • Garbage collector is a part of JVM.
  • This is used to manage memory.
  • It runs on its own thread with own algorithm.
  • This will destroy useless data(objects without reference) from memory.

StringBuffer vs StringBuilder

Introduced in Java 1.0Introduced in Java 1.5
Every method is synchronizedNo method is synchronized
At a time only one thread is allow to operate.Multiple threads are allow to operate
Thread safeNot thread safe
Slow performances Fast performances 

What is toString() method ?

  • This is called when we trying to print object reference.
  • In collection framework, StringBuffer, StringBuilder, String class already override the toSting() method. 
  • If we didn't override toString() method, object's class toString() method will be called.

What is "volatile" keyword ?

Explain uses of "final" keyword

  • This can be applied to classes, methods and variables.
  • Final classes cannot be extended.
  • Final methods cannot be overridden.
  • Final variables cannot be changed, they are just constants. 

What is "ACID" in databases ?

  • A - Atomicity
  • C - Consistency 
  • I  - Isolation
  • D - Durability

To be continued...