《Thinking In Java》注解定义、使用与编写注解处理器 简例

PasswordUtils.java

package annotations;

//: annotations/PasswordUtils.java
// 使用注解
import java.util.*;

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

	@UseCase(id = 48)
	public String encryptPassword(String password) {
		return new StringBuilder(password).reverse().toString();
	}

	@UseCase(id = 49, description = "New passwords can't equal previously used ones")
	public boolean checkForNewPassword(List<String> prevPasswords,
			String password) {
		return !prevPasswords.contains(password);
	}
} ///:~

UseCase.java

package annotations;

//: annotations/UseCase.java
// 定义注解
import java.lang.annotation.*;

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface UseCase {
	public int id();

	public String description() default "no description";
} ///:~

UseCaseTracker.java

package annotations;

//: annotations/UseCaseTracker.java
// 注解处理器
import java.lang.reflect.*;
import java.util.*;

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<Integer>();
		Collections.addAll(useCases, 47, 48, 49, 50);
		trackUseCases(useCases, PasswordUtils.class);
	}
} /* Output:
Found Use Case:47 Passwords must contain at least one numeric
Found Use Case:48 no description
Found Use Case:49 New passwords can't equal previously used ones
Warning: Missing use case-50
*///:~