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Discover how to efficiently map fields from one Java object to another using the `ModelMapper` library, all without rewriting unnecessary code.
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Simplifying Object Mapping in Java: A to B Without Redundant Code

In modern software development, handling object transformations between different data representations is a common challenge. Take, for example, the scenario where you have two classes, ObjectA and ObjectB, both of which inherit from a common superclass ObjectC. They share a significant number of fields—around 100—making it impractical to manually map every single field from one object to another. In this guide, we will explore a solution to automate this process using a powerful library in Java called ModelMapper.

The Challenge: Mapping Fields Between Objects

The Problem

You need to create a mapper that allows you to copy properties from ObjectB to an existing ObjectA instance, as demonstrated below:

You want to avoid the tedious task of manually writing out the mapping for 100 fields.

You wish to utilize a method signature that allows you to pass existing instances, like so:

[[See Video to Reveal this Text or Code Snippet]]

In essence, you want a flexible, reusable solution that efficiently transfers data from one object to another without the overhead of creating new instances.

The Solution: Using ModelMapper

Introduction to ModelMapper

ModelMapper is a Java library that simplifies object mapping by automatically mapping fields between Java objects using reflection. It can handle object copies, nested mapping, and other complex scenarios with minimal configuration, which makes it perfect for our situation.

Setting Up ModelMapper

To implement ModelMapper, you'll need to follow these steps:

Add Dependency: First, ensure you have ModelMapper included in your project dependencies. If you're using Maven, you can add it as follows:

[[See Video to Reveal this Text or Code Snippet]]

Create Your Objects: Next, define your classes similar to the provided example:

[[See Video to Reveal this Text or Code Snippet]]

Implement Mapping Logic: You can now incorporate ModelMapper into your code:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of Code

Creating Objects: Initialize instances of ObjectA and ObjectB and set their fields.

ModelMapper Configuration: By setting SkipNullEnabled, we ensure that if a field in objectB is null, it won't overwrite existing values in objectA.

Mapping Call: The map function of ModelMapper is called to copy values from objectB to objectA.

Result

When run, the provided code will print:

[[See Video to Reveal this Text or Code Snippet]]

This indicates that the fields have been successfully copied according to your requirements, without the necessity of manually coding for each field.

Conclusion

Using ModelMapper is a fantastic approach to automate the mapping between objects in Java, allowing you to focus on more critical aspects of your application while maintaining clean and manageable code. With the ability to configure settings to suit your needs, ModelMapper stands out as a reliable tool for handling object transformations efficiently.

With this solution, you can now map between complex objects effortlessly, significantly enhancing your productivity as a Java developer.