The application and principle of Picocontainer Core in the Java class library

The application and principle of Picocontainer Core in the Java class library Picocontainer Core (hereinafter referred to as Picocontainer) is a lightweight dependencies inject (DI) container, which is widely used in Java development.Its main goal is the dependency relationship between management, and the responsibilities of the object's creation, assembly and life cycle management are handed over to the container to complete.This article will introduce the application and principles of Picocontainer in the Java class library, and provide the corresponding Java code example. Application scenario: In complex Java applications, there are various dependencies between classes.In order to achieve loose coupling and testability, we often want to hand over the management process of the object and dependencies to the container to complete.At this time, Picocontainer played a very important role. Picocontainer is very simple. First of all, we need to introduce the corresponding dependencies in the project (Maven coordinates are `ORG.PICOCONTAINER: Picocontainer-Core: 2.15`), and then create a picocontainer instance with the following code: import org.picocontainer.DefaultPicoContainer; import org.picocontainer.MutablePicoContainer; public class App { public static void main(String[] args) { // Create a picocontainer example MutablePicoContainer container = new DefaultPicoContainer(); // Register component and their dependence relationship container.addComponent(ServiceA.class); container.addComponent(ServiceB.class); / Third ServiceA serviceA = container.getComponent(ServiceA.class); // Use components serviceA.doSomething(); } } This code demonstrates the basic usage of Picocontainer.After creating the instance of `MutablePicocontainer`, we can register components and their dependencies to the container with the` addComponent () `method.Then, use the `GetComponent ()` method to obtain the component instance in the facilities and perform subsequent processing. Principle introduction: The principle of Picocontainer is very simple. It uses reflex and automatic assembly and other technologies to achieve dependency injection based on information such as the annotations and constructing function parameters. In the above examples, we did not directly specify the dependencies between components. Instead, register the component through the `addComponent ()" method. Picocontainer will automatically analyze the dependency relationship between the components to achieve the creation and assembly of the object. Specifically, when we add components to the container, the Picocontainer will obtain the constructor parameters of the component through the reflection mechanism, and recursively analyzes their dependencies to create a complete dependent object diagram. When we get a component in our veteran, Picocontainer obtains the corresponding instance from the object diagram based on the index of the component.If other components in the object diagram are also needed, they will create them recursively and meet their dependence. Picocontainer also supports life cycle management, which can perform specific logic when component creation and destruction.For example, the initialization operation can be performed during the creation of the component, and the cleaning work can be performed when the component is destroyed. Summarize: Picocontainer is a powerful and flexible dependency injection container, which simplifies the management of dependencies between classes in the Java class library.By using Picocontainer, we can implement loose coupling component design to improve the testability and maintenance of code.It is hoped that this article has a more comprehensive understanding of the application and principle of Picocontainer, and can better understand its usage through the Java code example.