使用反射获取注解信息

Myth丶恋晨 2023-03-14 08:09 17阅读 0赞

1.https://www.bilibili.com/video/BV1p4411P7V3  
根据狂神视频记录。

import java.lang.annotation.*;
    import java.lang.reflect.Field;
    
    public class Test1 { 
        public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException { 
            Class<?> aClass = Class.forName("com.sfw.prac.reflect.Student");
            
            TableAnno annotation = aClass.getAnnotation(TableAnno.class);
            System.out.println(annotation);
            System.out.println(annotation.value());
    
            System.out.println("==========================");
            Field name = aClass.getDeclaredField("name");
            FieldAnno declaredAnnotation = name.getDeclaredAnnotation(FieldAnno.class);
            System.out.println(declaredAnnotation);
            System.out.println(declaredAnnotation.columnName());
            System.out.println(declaredAnnotation.type());
            System.out.println(declaredAnnotation.length());
    
            System.out.println("==========================");
            Field id = aClass.getDeclaredField("id");
            FieldAnno declaredAnnotation1 = id.getDeclaredAnnotation(FieldAnno.class);
            System.out.println(declaredAnnotation1);
            System.out.println(declaredAnnotation1.columnName());
            System.out.println(declaredAnnotation1.type());
            System.out.println(declaredAnnotation1.length());
    
            System.out.println("==========================");
            Field age = aClass.getDeclaredField("age");
            FieldAnno declaredAnnotation2 = age.getDeclaredAnnotation(FieldAnno.class);
            System.out.println(declaredAnnotation2);
            System.out.println(declaredAnnotation2.columnName());
            System.out.println(declaredAnnotation2.type());
            System.out.println(declaredAnnotation2.length());
        }
    }
    
    @TableAnno("db_student")
    class Student{ 
    
        @FieldAnno(columnName = "db_name", type = "varchar", length = 10)
        private String name;
    
        @FieldAnno(columnName = "db_id", type = "int", length = 10)
        private int id;
    
        @FieldAnno(columnName = "db_age", type = "int", length = 3)
        private int age;
    
        public Student() { 
        }
    
        public Student(String name, int id, int age) { 
            this.name = name;
            this.id = id;
            this.age = age;
        }
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    
        public int getId() { 
            return id;
        }
    
        public void setId(int id) { 
            this.id = id;
        }
    
        public int getAge() { 
            return age;
        }
    
        public void setAge(int age) { 
            this.age = age;
        }
    
        @Override
        public String toString() { 
            return "Student{" +
                    "name='" + name + '\'' +
                    ", id=" + id +
                    ", age=" + age +
                    '}';
        }
    }
    
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @interface TableAnno { 
        String value();
    }
    
    @Target(ElementType.FIELD)
    @Retention(RetentionPolicy.RUNTIME)
    @interface FieldAnno { 
        String columnName();
        String type();
        int length();
    }

2.自定义数据校验注解：https://mp.weixin.qq.com/s/gdYysBB3aD\_HmPyvEThFXw