Monday, February 19, 2018

What is SecurityContext and SecurityContextHolder in Spring Security?

The SecurityContext and SecurityContextHolder are two fundamental classes of Spring Security. The SecurityContext is used to store the details of the currently authenticated user, also known as a principle. So, if you have to get the username or any other user details, you need to get this SecurityContext first. The SecurityContextHolder is a helper class, which provide access to the security context. By default, it uses a ThreadLocal object to store security context, which means that the security context is always available to methods in the same thread of execution, even if you don't pass the SecurityContext object around. Don't worry about the ThreadLocal memory leak in web application though, Spring Security takes care of cleaning ThreadLocal.

Sunday, February 18, 2018

How to fix Exception in thread "main" java.lang.NoClassDefFoundError: org/slf4j/LoggerFactory in Java

This error means your code or any external library you are using in your application is using the SLF4J library, an open source logging library, but it is not able to find the required JAR file e.g. slf4j-api-1.7.2.jar hence it's throwing Exception in thread "main" java.lang.NoClassDefFoundError: org/slf4j/LoggerFactory. If you look at the error, you will see that it's saying it is not able to find the class org/slf4j/LoggerFactory or org.slf4j.LoggerFactory. The package name indicates that it's part of SLF4j, hence you need SLF4j JAR files e.g. slf4j-api-1.7.2.jar in your application's classpath. So, go ahead and download the JAR file from SLFj website or from Maven Central repository and restart your application.

Monday, February 12, 2018

Top 5 Java Design Pattern Courses for Experienced Java Developers

Hello guys, today, we'll talk about design patterns and some of the best online courses to learn design patterns in Java from scratch. If you are wondering what is a design pattern and why Java developers should learn them? then let me give you a brief overview. Design patterns are nothing but a tried and tested solutions of common programming problems, for example, the creational design patterns deal with the problems of object creation. They exist from a long time but made popular by famous Gang of four of Erich Gamma, John Vlissides, Ralph Johnson and Richard Helm in their classic 1994 book Design Patterns: Elements of Reusable Object-Oriented Software, also known as GOF design patterns. This book documented 24 design patterns which are reusable to solve common programming problems.