java自定义注解教程

1、定义注解类

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

　2、定义使用注解的类

@Data
public class User {
    @IniterValue(value = "2")
    private Integer age;
    @IniterValue(value = "小明")
    private String name;
}

　3、定义注解解析器

public class UserFactory {
    public static <T> T create(Class<T> t) throws IllegalAccessException, InstantiationException {
        T t1 = t.newInstance();
        Field[] fields = t1.getClass().getDeclaredFields();
        for (Field field:fields) {
            if(field.isAnnotationPresent(IniterValue.class)){
                IniterValue annotation = field.getAnnotation(IniterValue.class);
                try {
                    field.setAccessible(true);
                    Class<?> type = field.getType();
                    Object obj=null;
                    if(type == Integer.class){
                        obj = Integer.valueOf(annotation.value());

                    }
                    if(type==String.class){
                        obj=annotation.value();
                    }
                    field.set(t1,obj);

                   // method.invoke(t1,annotation.value(),annotation.intValue());
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
            }
        }
        return t1;

    }
}

　4、测试

public class Test {
    public static void main(String[] args) throws InstantiationException, IllegalAccessException {
        User user = UserFactory.create(User.class);
        System.out.println(user.getAge());
    }
}