JetBrains Java Annotations framework in the Java class library
JetBrains Java Annotations framework in the Java class library
JetBrains Java Annotations (JBA) is a framework used to declare and use annotations in the Java class library.It provides many functions that enable developers to handle and expand the Java class library more flexibly.
1. Notepad summary:
Note is a special mark inserted in the Java source code to provide additional metadata.They can be used to perform different operations for compilers, parsers, operation libraries and other tools.Java 5 introduced the concept of annotation and is now a common practice in Java development.
2. The main features of JBA:
2.1 Statement Note: Use JBA to define your own annotations and apply them to the Java class.This enables developers to use custom annotations to mark and describe code.
2.2 RMB Note Support: JBA supports the use of meta -annotations to define and configure other annotations.This includes the life cycle of marking the annotation, reusable use, etc.
2.3 Note processor: JBA also provides annotation processor for processing annotations during compilation and runtime.This can automatically perform specific tasks, such as generating code, verification constraints, etc.
3. JBA working principle:
3.1 Note definition: First, by defining an annotation interface, a new annotation can be created.
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation {
String value();
}
In this example, we define an annotation called `Myannotation` and specify its retention strategy to run.
3.2 Note Application: Next, the annotations of the application are on the required positions, such as class, methods, or fields.
@MyAnnotation("Hello World")
public class MyClass {
@MyAnnotation("Greeting")
public void greet() {
System.out.println("Hello!");
}
}
In this example, we apply the `Myannotation` annotation to the` MyCLASS` class and the `Greet` method.
3.3 Note processor: JBA realizes the interaction with the annotation by providing an annotation processor.
import java.lang.reflect.Method;
public class MyAnnotationProcessor {
public static void processAnnotations(Class<?> clazz) {
if (clazz.isAnnotationPresent(MyAnnotation.class)) {
MyAnnotation annotation = clazz.getAnnotation(MyAnnotation.class);
System.out.println("Class annotation: " + annotation.value());
}
Method[] methods = clazz.getDeclaredMethods();
for (Method method : methods) {
if (method.isAnnotationPresent(MyAnnotation.class)) {
MyAnnotation annotation = method.getAnnotation(MyAnnotation.class);
System.out.println("Method annotation (" + method.getName() + "): " + annotation.value());
}
}
}
public static void main(String[] args) {
processAnnotations(MyClass.class);
}
}
In this example, we created a simple processor `myannotationProcessor`, which can handle the` myannotation` annotation.Using reflection, it prints the annotation values applied to class and methods.
4 Conclusion:
JetBrains Java Annotions framework provides rich functions for the annotations in the processing and expansion of the Java library.By declarating the customized annotations and applied to the code, developers can use metadata to flexibly describe and process the different aspects of the code.The annotation processor further enhances this capacity, which can automatically perform various tasks and improve development efficiency.
