Java Config and annotations (reproduced)

Reprinted: https://www.cnblogs.com/Johness/archive/2013/04/17/3026689.html

1. An annotation is essentially a markup. Compared with xml configuration, there is only a difference in the way

2. The annotation itself is also a type and also needs to be declared

package annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Custom annotations to configure methods
 *
 * @author Johness
 *
 */
@Retention(RetentionPolicy.RUNTIME) // Indicates that the annotation still exists at runtime
@Target(ElementType.METHOD) // Indicates that the annotation can be used on the method
public @interface SayHiAnnotation {
    String paramValue() default "johness"; // means my annotation needs a parameter named "paramValue" default value is "johness"
}

3. Use annotations

package element;

import annotation.SayHiAnnotation;

/**
 * The class of the element to use SayHiAnnotation
 * Since we defined that only methods can use our annotations, we use multiple methods for testing
 *
 * @author Johness
 *
 */
public class SayHiEmlement {

    // normal method
    public void SayHiDefault(String name){
        System.out.println("Hi, " + name);
    }
    
    // method using annotations and passing in parameters
    @SayHiAnnotation(paramValue="Jack")
    public void SayHiAnnotation(String name){
        System.out.println("Hi, " + name);
    }
    
    // method using annotation and using default parameters
    @SayHiAnnotation
    public void SayHiAnnotationDefault(String name){
        System.out.println("Hi, " + name);
    }
}

4. Reflection to get the annotated method and perform the corresponding operation

package Main;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import element.SayHiEmlement;
import annotation.SayHiAnnotation;

public class AnnotionOperator {
    public static void main(String[] args) throws IllegalAccessException, IllegalArgumentException, InvocationTargetException, ClassNotFoundException {
        SayHiEmlement element = new SayHiEmblement(); // Initialize an instance for method invocation
        Method[] methods = SayHiEmlement.class.getDeclaredMethods(); // get all methods
        
        for (Method method : methods) {
            SayHiAnnotation annotationTmp = null;
            if((annotationTmp = method.getAnnotation(SayHiAnnotation.class))!=null) // Check if our annotation is used
                method.invoke(element,annotationTmp.paramValue()); // If our annotation is used, we call the method with the "paramValue" parameter value in the annotation as a method parameter
            else
                method.invoke(element, "Rose"); // If we don't use our annotation, we need to use the normal way to call the method
        }
    }
}

5. Results

Hi, Jack
Hi, johness
Hi, Rose

Java Config and annotations (reproduced)

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