The technical principles of the Common Annotations 1.2 API framework in the Java class library

The Common Annotations 1.2 API framework in the Java class library is an important part of the Java EE platform. It provides a set of interfaces and classes for writing annotations.In Java programming, the annotation is a technology that adds metadata information for program elements (such as classes, methods, variables, etc.). It can be used to provide information required for program running or generate code during compilation.Common Annotations 1.2 API framework provides developers with a simple and unified way to define and use annotations. The technical principles of Common Annotations 1.2 API framework mainly include the following aspects: 1. Definition of annotation elements: In the Common Annotations 1.2 API framework, developers can define the annotation elements through interfaces. These annotations can include basic data types, enumeration types, and other annotation types.By defining the annotation element, you can provide the required information for the annotation to make it more powerful. 2. Using meta -annotations: Metropolitan annotations are an annotation for annotation of other annotations. Common Annotations 1.2 API framework provides a variety of meta -withs annotations, including@Retention,@Target,@Inherited,@DCument, etc.Developers can use meta -annotations to specify the scope of use, life cycle, and other characteristics of the annotation. 3. Analysis annotation: Common Annotions 1.2 API framework provides interfaces and classes for parsing annotations. Developers can use these tools to obtain annotations used in the program and processes accordingly according to the information provided by the annotation.Through annotations, some specific functions can be achieved, such as custom configuration and enhancement performance. 4. Generate code during runtime: Common Annotations 1.2 Annotation in the API framework can generate additional code when the program is running, these code can be used to achieve some specific functions.For example, AOP (facing surface programming) can be implemented by annotations, and the program is dynamically added to the program without modifying the source code. Below is a simple example of using Common Annotations 1.2 API framework: import javax.annotation.PostConstruct; public class MyClass { @PostConstruct public void init() { // Do some initialization work here } public void doSomething() { // Do something } } In this example, we use the @PostConStruct annotation in the Common Annotations 1.2 API framework to mark the init method, and this method is called to initialize this method when the program initializes. When using the Common Annotations 1.2 API framework, developers need to introduce relevant dependencies in the configuration file of the project and use the corresponding annotations and tools according to specific needs.By using Common Annotations 1.2 API framework, the Java program can have more powerful functions and flexibility.