Java By Source

In my previous article JPA Auditing: Persisting Audit Logs Automatically using EntityListeners , I have discussed how we can use Spring Data JPA automate Auditing and automatically create audit logs or history records and update CreatedBy, CreatedDate, LastModifiedBy, LastModifiedDate properties. So in order to save history records for our File entity, we were trying to auto-wire EntityManager inside our FileEntityListener class and we have come to know that we can not do this. We can not inject any Spring-managed bean in the EntityListener because EntityListeners are instantiated by JPA before Spring inject anything into it. EntityListeners are not managed Spring so Spring cannot inject any Spring-managed bean e.g. EntityManager in the EntityListeners. And this case is not just with EntityListeners, you can not auto wire any Spring-managed bean into another class (i.e. utility classes) which is not managed by Spring. Because it is a very common problem and can also arise with other c...

In my previous article Spring Data JPA Auditing: Saving CreatedBy, CreatedDate, LastModifiedBy, LastModifiedDate automatically , I have discussed why Auditing is important for any business application and how we can use Spring Data JPA automate it. I have also discussed how Spring Data uses JPA’s EntityListeners and callback methods to automatically update CreatedBy , CreatedDate , LastModifiedBy , LastModifiedDate properties. Well, here in this article I am going dig a little bit more and discuss how we can use JPA EntityListeners to create audit logs and keep information of every insert, update and delete operation on our data. I will take the File entity example from the previous article and walk you through the necessary steps and code portions you will need to include in our project to automate the Auditing process. We will use Spring Boot, Spring Data JPA (Because it gives us complete JPA functionality plus some nice customization by Spring), MySql to demonstrate this. We wi...

In any business application auditing simply means tracking and logging every change we do in the persisted records which simply means tracking every insert, update and delete operation and storing it. Auditing helps us in maintaining history records which can later help us in tracking user activities. If implemented properly auditing can also provide us similar functionality like version control systems. I have seen projects storing these things manually and doing so become very complex because you will need to write it completely by your own which will definitely require lots of code and lots of code means less maintainability and less focus on writing business logic. But why should someone need to go to this path when both JPA and Hibernate provides Automatic Auditing which we can be easily configured in your project. And here in this article, I will discuss how we can configure JPA to persist CreatedBy, CreatedDate, LastModifiedBy, LastModifiedDate columns automatically for any ...

Lombok is a tool that generates code like getters, setters, constructors, equals, hashCode, toString for us in the same way that our IDE does. While IDE generates all these things in our source code file, Lombok generates them directly in the class file. So Lombok basically takes out all these things from your source code to bytecode so we don't need to write them in our source code which means less code in our source code file. And in this article, I am going to explain how Lombok can help us in removing this kind of boilerplate code. To understand it let's suppose we have an entity class Employee  and we want to use it to hold a single employee record. We can use it as a DTO or persistent entity or anything else we want but idea is that we want to use it to store  id , firstName , lastName  and salary  fields. For this requirement, we will need a simple Employee  POJO and according to General directions for creating Plain Old Java Object , Each...

This is my third article on Java Cloning  series, In previous articles Java Cloning and Types of Cloning (Shallow and Deep) in Details with Example  and Java Cloning - Copy Constructor versus Cloning  I had discussed Java cloning in detail and explained every concept like what is cloning, how does it work, what are the necessary steps we need to follow to implement cloning, how to use Object.clone(), what is Shallow and Deep cloning, how to achieve cloning using Serialization and Copy constructors and advantages copy of copy constructors over Java cloning. If you have read those articles you can easily understand why it is good to use Copy constructors over cloning or Object.clone(). In this article, I am going to discuss why copy constructor are not sufficient? Yes, you are reading it right copy constructors are not sufficient by themselves, copy constructors are not polymorphic because constructors do not get inherited to the child class from the parent class. If we ...

In my previous article Java Cloning and Types of Cloning (Shallow and Deep) in Details with Example , I have discussed Java Cloning in details and answered questions about how we can use cloning to copy objects in Java, what are two different types of cloning (Shallow & Deep) and how we can implement both of them, if you haven’t read it please go ahead. In order to implement cloning, we need configure our classes to follow below steps Implement Cloneable interface in our class or its superclass or interface, Define clone() method which should handle CloneNotSupportedException (either throw or log), And in most cases from our clone() method we call the clone() method of the superclass. And super.clone() will call its super.clone() and chain will continue until call will reach to clone() method of the Object class which will create a field by field mem copy of our object and return it back. Like everything Cloning also comes with its advantages and disadvantages. However, Java c...

In my previous article 5 Different ways to create objects in Java with Example , I have discussed 5 different ways (new keyword, Class.newInstance() method, Constructor.newInstance() method, clone() method and deserialization) a developer can use to create objects, if you haven't read it please go ahead. Cloning is also a way of creating an object but in general, cloning is not just about creating a new object. Cloning means creating a new object from an already present object and copying all data of given object to that new object. In order to create a clone of an object we generally design our class in such way that Our class should implement Cloneable interface otherwise, JVM will throw CloneNotSupportedException if we will call clone() on our object. Cloneable interface is a marker interface which JVM uses to analyse whether this object is allowed for cloning or not. According to JVM if yourObject instanceof Cloneable then create a copy of the object otherwise throw ...