自定义注解

示例出自《java编程思想》

自定义注解：

package demo;

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

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface UseCase {
	public int id();
	public String description() default "no description";

}

注解处理器：

package demo;

import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

//注解处理器 使用反射机制查找@UseCase标记
public class UseCaseTracker {
	public static void trackUseCases(List<Integer> useCases, Class<?> cl){
		for(Method m: cl.getDeclaredMethods()){
			UseCase uc = m.getAnnotation(UseCase.class);
			if(uc != null){
				System.out.println("Found Use Case:" + uc.id() + " " + uc.description());
				useCases.remove(new Integer(uc.id()));
			}
		}
		for(int i: useCases){
			System.out.println("Warning: Missing use case-" + i);
		}
	}
	
	public static void main(String[] args) {
		
		List<Integer> useCases = new ArrayList<>();
		Collections.addAll(useCases, 47,48,49,50);
		trackUseCases(useCases, PasswordUtils.class);
	}
}

// 输出结果：
// Found Use Case:49 password muset contain at least one numeric
// Found Use Case:47 password muset contain at least one numeric
// Found Use Case:48 password muset contain at least one numeric
// Warning: Missing use case-50

注解示例：

package demo;

public class PasswordUtils {

	@UseCase(id=47, description="password muset contain at least one numeric")
	public boolean validatePassword(String password){
		return (password.matches("\w*\d\w*"));
	}

	@UseCase(id=48, description="password muset contain at least one numeric")
	public boolean encryptPassword(String password){
		return (password.matches("\w*\d\w*"));
	}
	
	@UseCase(id=49, description="password muset contain at least one numeric")
	public boolean checkForNewPassword(String password){
		return (password.matches("\w*\d\w*"));
	}
}