Apache FreeMarker vs MapStruct: What are the differences?

Introduction

Apache FreeMarker and MapStruct are both powerful tools used in web development, but they have key differences that make them suitable for different purposes. Let's explore the main differences between these two technologies.

1. Template engine vs. code generator: Apache FreeMarker is a powerful template engine that allows developers to separate the presentation logic from the data. It provides a flexible and dynamic way to generate output based on templates. On the other hand, MapStruct is a code generation library that focuses on generating mapping code between Java beans. It automates the process of writing repetitive mapping code, making it easier to maintain and update.

2. Data presentation vs. object mapping: FreeMarker excels at generating HTML, XML, or any other text-based output by merging templates with data. It enables dynamic content rendering, control structures, and reusable components. MapStruct, on the other hand, focuses on mapping objects between layers or contexts, such as DTOs and domain entities. It simplifies the mapping process by generating efficient and type-safe mapping code for developers.

3. Flexibility vs. static analysis: FreeMarker provides more flexibility in terms of template design and resource configuration. It allows conditional rendering, loop iteration, and template composition, which makes it suitable for complex logic in presentation layers. MapStruct, on the other hand, performs static analysis of the object's structure at compile-time, ensuring type-safety and avoiding errors in object mapping by generating code based on annotations and conventions.

4. Runtime evaluation vs. compile-time generation: FreeMarker evaluates templates at runtime, which allows dynamic changes to the template's logic and structure without recompiling the code. This flexibility is beneficial for certain use cases where the template logic needs to be modified frequently. MapStruct, on the other hand, generates mapping code during the compilation phase, resulting in highly optimized and efficient mappings without the need for runtime evaluation.

5. Rich expression language vs. automatic mapping: FreeMarker provides a rich expression language that allows developers to manipulate data, perform calculations, and apply complex logic within templates. It supports variables, functions, and control structures, making it a powerful tool for presenting data. In contrast, MapStruct focuses on automatic mapping between objects based on conventions and annotations. It eliminates the need for manual coding of repetitive and boilerplate mapping operations.

6. Widely adopted template engine vs. specialized code generation library: FreeMarker is a widely adopted and mature template engine that has been in use for many years. It has a large community and extensive documentation, making it easy to find support and resources. MapStruct, on the other hand, is a specialized code generation library specifically designed for object mapping in Java. It is gaining popularity due to its simplicity and effectiveness in reducing mapping boilerplate.

In summary, Apache FreeMarker and MapStruct have distinct focuses and purposes. FreeMarker is a versatile and flexible template engine used for generating dynamic and customizable text-based output, while MapStruct is a specialized code generation library that automates object mapping between layers or contexts in Java applications.