Dagger framework technical analysis and optimization strategy in the Java class library

The Dagger framework is a dependent injection framework widely used in the Java library. It provides a simple and powerful way to manage the dependencies between objects by using the code generated by annotations and compilation.This article will analyze the technical principles of the Dagger framework and provide some optimization strategies. 1. Analysis of the technical principles of the Dagger framework 1. Annotation processing The core principle of Dagger is to use the annotation processor, which can scan the annotation in the source code during compilation and generate the dependent relationship code required by the annotation.The main annotations used by Dagger are@inject,@module and @Component. -@Inject: Used to mark the dependencies that need to be injected.Can be used for constructing methods, fields and methods. -@Module: Used to mark classes that provide dependencies.Class using @module annotations contains one or more methods marked with @Provides annotation, which returns the required dependencies. -@Component: Components used to mark dependencies.The interface or abstract class using the @Component annotation can be associated with @module and @Inject. 2. Dependency Graph Dagger exists in the form of a dependency diagram based on the code generated by the annotation, which describes the dependency relationship between objects.When a certain object needs to be obtained, Dagger will automatically analyze the dependent relationship diagram and create and provide the required dependencies when needed. 3. The code generated during compilation Dagger will generate some code during compilation, including: -Factory: Dagger generates a factory class for each class with @inject comments to create instances of this class. -ComPonent: Dagger generates a component class for each interface or abstract class with @Component annotation, which is responsible for coordinating the creation and provision of the entire dependent relationship diagram. 2. Optimization strategy of Dagger framework 1. Use local dependencies Dagger can handle a very complicated relying diagram, but too huge maps may lead to too long compilation time.In order to optimize the compilation time, you can divide the dependencies into multiple local dependencies, and then merge them into a global dependencies when needed. 2. Use scope to perform the life cycle management of dependencies Dagger allows the use of customized scope of @SINGLETON and other customized scope to manage the life cycle of the object.By using the scope of the scope, the objects in the same scope can be ensured that the objects in the same scope are single -case, and the objects of repetitive creation and destruction can be avoided. 3. Use Provider and Lazy to delay injection Dagger allows using provider and lazy to delay the injecting dependencies.Provider allows dynamic dependencies when needed, while Lazy allows lazily loading dependencies when needed.Delayed injection can improve the performance and resource use efficiency of the application. The following is a simple example code that demonstrates the use of the Dagger framework: // Define a dependent item class class Car { @Inject public Car() { } } // Define a @module class to provide dependencies @Module class CarModule { @Provides Car provideCar() { return new Car(); } } // Define a component interface, associate @module and @inject @Component(modules = CarModule.class) interface CarComponent { Car getCar(); } // Use components in the application public class Main { public static void main(String[] args) { CarComponent component = DaggerCarComponent.create(); Car car = component.getCar(); // Use CAR object } } Summary: The Dagger framework provides a simple and powerful way to manage the dependencies in the Java library by using the code generated by the annotation processor and compiled.Understanding Dagger's technical principles and optimization strategies can help developers better use the framework to build maintenance and scalable applications.