MapStruct Core framework of the annotation processor implementation principle

MapStruct is a Java annotation processor framework. Its goal is to simplify the conversion process between Java objects.In MapStructs, use annotations to mark the conversion method and mapping method, and then generate the conversion code by annotating processor. The principle of implementation of MapStruct's annotation processor is as follows: 1. Comment processor registration: When compiling, the compiler will automatically call the MapStruct annotation processor.In order to enable the annotation processor, you need to specify the dependencies of MapStruct in the construction configuration file of the project and register the annotation processor into the compiler. 2. Note processing process: The annotation processor scan the class and methods with MAPSTRUCT annotations in the items.The main annotations include@MAPPER,@Mapping,@Mappings, etc.Based on these annotations, the annotation processor generates a conversion code. 3. Generate conversion code: Annotation processor analyzes the source code according to the information information, and generates the conversion code.The generated code will copy the attribute value of the source object to the target object according to the mapping relationship defined in the annotation.The generated conversion code contains the specific implementation of the mapping rules, and it can be customized through the configuration in the annotation. 4. Compilation phase: The conversion code generated by the annotation processor will be compiled into bytecode by the compiler.The generated converter class will realize the conversion interface defined by the MapStruct framework, and realize the conversion logic of the source object to the target object. 5. Use converter: The generated converter class can be used in other parts of the project.By calling the conversion method of the converter class, the conversion between objects can be achieved.The conversion logic has contained the conversion logic in the converter class. Developers only need to use the converter class to complete the conversion between objects. It should be noted that the implementation principle of MapStruct's annotation processor does not require developers to directly operate the compilation process. You only need to correctly add the dependency and configuration of the MAPStruct in the project to use it.The annotation processor will automatically generate the conversion code according to the configuration of the annotation, which greatly simplifies the conversion process between objects.