java Annotation使用例子

首先看下面代碼：


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



/**
 * Created by 21405 on 8/21/2017.
 */

public class AppUtil {
    public static void main(String[] args) {
        //1. get the info about fruit
        getFruitInfo();

        //2. trackUserCase
        List<Integer> useCases = new ArrayList<Integer>();
        Collections.addAll(useCases, 47, 48, 49, 50);
        trackUseCases(useCases, PasswordUtils.class);

    }
    public static void getFruitInfo(){
        Class clazz = App.class;
        Field[] fields = clazz.getDeclaredFields();
        System.out.println(Arrays.asList(clazz.getAnnotations()));
        for (Field field : fields) {
            if (field.isAnnotationPresent(FruitName.class)) {
                FruitName fruitName = (FruitName) field.getAnnotation(FruitName.class);
                System.out.println(fruitName.value());
            }

        }
    }

    public static void trackUseCases(List<Integer> useCases, Class<?> cl){
        for(Method m:cl.getDeclaredMethods()){
            UserCase uc = m.getAnnotation(UserCase.class);
            if(uc != null){
                System.out.println("Found Use Case:"+ uc.id()+"　"+uc.decription());
                useCases.remove(new Integer(uc.id()));
            }
        }
        for(int i: useCases){
            System.out.println("Warning Missing use case-"+i);
        }
    }
}

上面代碼中用到的其他類的定義見下面：

FruitName定義如下：

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

/**
 * Created by 21405 on 8/21/2017.

 */
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface FruitName {
    String value() default "";
}

App定義：

/**
 * Created by 21405 on 8/21/2017.
 */
public class App {
    @FruitName(value="mifeng")
    private String appleName;

    public String getAppleName() {
        return appleName;
    }

    public void setAppleName(String appleName) {
        this.appleName = appleName;
    }
}

UserCase 定義：

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

Passworld定義：

import java.util.List;

/**
 * Created by 21405 on 8/21/2017.
 */
public class PasswordUtils
{
    @UserCase(id = 47, decription = "Passwords must contain at least one numeric")
    public boolean validatePassword(String password){
        return (password.matches("\\w*\\d\\w*"));
    }

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

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

    }

}