What is the method for java custom aspect enhancement?

java custom aspect enhancement

1. Customize an annotation

@Target(value = { ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
public @interface CacheNullify {
    boolean value = true;
}

2. Implement enhanced logic

@Slf4j
@Aspect
@Component
public class CacheNullifyHandler {

    @AfterReturning("@annotation(com.xxx.CacheNullify)")
    public void afterReturning() {
        log.info("走你");
        CacheServiceUtil.delUserInfoCache();
    }
}

• @annotation: What follows is the annotation you want to enhance (the annotated method), you can directly write the annotation name, But in order to prevent duplicate names, write the full path as much as possible

• ##@AfterReturning: Triggered after the method is executed and returns successfully

• @After: Triggered after the method is completed (including execution completion, or exception thrown)

3. Use

Add the @CacheNullify annotation to the method that needs to be enhanced

Use of aspects and custom annotations

First understand the basic concepts and usage of aspects and custom annotations

Introduction to AOP

AOP is the abbreviation of Aspect Oriented Programming, which means: Aspect-oriented programming, a technology that achieves unified maintenance of program functions through pre-compilation and dynamic agents during runtime.

AOP is the continuation of OOP, a hot spot in software development, an important content in the Spring framework, and a derivative paradigm of functional programming.

AOP can be used to isolate various parts of the business logic, thereby reducing the coupling between the various parts of the business logic, improving the reusability of the program, and improving the efficiency of development.

AOP definition

• Aspect (aspect)

Aspect declaration is similar to a class in Java Statement, the Aspect will contain some Pointcuts and corresponding Advice.

• Joint point

refers to those intercepted points. In spring, these points refer to is the method.

• Pointcut (pointcut)

represents a group of joint points, which may be combined through logical relationships Together, or concentrated through wildcards, regular expressions, etc., it defines where the corresponding Advice will occur.

• Advice (enhancement/notification)

Advice defines what the program points defined in Pointcut should do. Operation, it uses before, after and around to distinguish the code executed before, after or instead of each joint point.

• Introduction

A special notification that can be added dynamically without modifying the source code Some methods.

• Target (target object)

The target object woven into Advice.

• Weaving

The process of connecting Aspect to other objects and creating an Advised object

Introduction to annotations

Annotations are metadata that can be added to Java source code. Methods, classes, parameters and packages can all be modified with annotations.

Annotations can be regarded as a special mark that can be used on methods, classes, parameters and packages. The program can detect these marks and perform some special processing when compiling or running.

Elements and composition

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface MyAnnotation {
    String value() default"";
}

Analysis of the above annotation composition

• ##public: modifier

The access modifier must be public, if not written, it defaults to public;

• @interface: Keyword

The keyword is @interface;

• MyAnnotaion: Annotation name

The annotation name is a custom annotation Name, for example, MyAnnotaion above is the annotation name

• #value: Annotation type element

Annotation type element is in the annotation Content, mark parameters as needed, such as the value of the above annotation;

Meta-annotation

But careful analysis also includes four annotations starting with @@Target, @Retention, @Inherited, @Documented ) These are the four underlying meta-annotations, annotations that annotate other annotations

@Target: used to describe the scope of use of the annotation, where the annotation can be used

Target type Description

##ElementType.TYPE
• Applies to classes, interfaces (including annotation types), and enumerations

ElementType.FIELD
• Applies to properties (including constants in enumerations)

ElementType.METHOD
• Applies to methods

ElementType.PARAMETER
• Applied to the formal parameters of the method

ElementType.CONSTRUCTOR
• Applied to the constructor

ElementType.LOCAL_VARIABLE
• Applies to local variables
  ##ElementType.ANNOTATION_TYPE
Applies to annotation types

• ElementType.PACKAGE
Applies to package

Note: For example, @Target(ElementType.METHOD), the annotation of the flag is used on the method, but if we use this annotation flag on the class, an error will be reported

@Retention: Indicates the life cycle of the annotation

Life cycle type Description

• RetentionPolicy.SOURCE Discarded during compilation, not included In the class file

• RetentionPolicy.CLASS is discarded when the JVM is loaded and included in the class file. The default value is

• RetentionPolicy.RUNTIME Loaded by the JVM, included in the class file, and can be obtained at runtime

@Inherited: It is a mark annotation, @Inherited elaborates An annotated type is inherited. If an annotation type modified with @Inherited is used for a class, this annotation will be used for subclasses of the class.

@Documented: Indicates that the element marked by this annotation can be documented by Javadoc or similar tools

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