Java 反射操作注解

你的名字 2024-03-27 01:47 76阅读 0赞

### 反射操作注解 ###

*  getAnnotations
 *  getAnnotation

### 练习：ORM ###

*  什么是ORM
    
     *  Object relationship Mapping --> 对象 关系 映射  
        ![在这里插入图片描述][472414deee404a19a2dc8fc4dbe1e35c.png]
     *  类和表结构对应
     *  属性和字段对应
     *  对象和记录对应
 *  要求：利用注解和反射 完成 类和表结构 的映射关系

package com.reflection;
    
    import java.lang.annotation.*;
    import java.lang.reflect.Field;
    
    //练习反射操作注解
    public class Test12 {
        
    
        public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
        
            Class c1 = Class.forName("com.reflection.Student2");
    
            //通过反射获得注解
            Annotation[] annotations = c1.getAnnotations();
            for (Annotation annotation : annotations) {
        
                System.out.println(annotation);
            }
    
            //获得注解的value的值
            TableWang tableWang = (TableWang) c1.getAnnotation(TableWang.class);
            String value = tableWang.value();
            System.out.println(value);
    
    
            //获得类指定的注解
            Field f = c1.getDeclaredField("id");
            FiledWang annotation = f.getAnnotation(FiledWang.class);
            System.out.println(annotation.columnName());
            System.out.println(annotation.type());
            System.out.println(annotation.length());
    
        }
    }
    
    @TableWang("db_student")
    class Student2{
        
        @FiledWang(columnName = "db_id",type = "int",length = 10)
        private int id;
        @FiledWang(columnName = "db_age",type = "int",length = 10)
        private int age;
        @FiledWang(columnName = "db_name",type = "varchar",length = 3)
        private String name;
    
        public Student2() {
        
        }
    
        public Student2(int id, int age, String name) {
        
            this.id = id;
            this.age = age;
            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;
        }
    
        public String getName() {
        
            return name;
        }
    
        public void setAnme(String anme) {
        
            this.name = anme;
        }
    
        @Override
        public String toString() {
        
            return "Student2{" +
                    "id=" + id +
                    ", age=" + age +
                    ", anme='" + name + '\'' +
                    '}';
        }
    
    }
    
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @interface TableWang{
        
        String value();
    }
    
    //属性的注解
    @Target(ElementType.FIELD)
    @Retention(RetentionPolicy.RUNTIME)
    @interface FiledWang{
        
        String columnName();
        String type();
        int length();
    }

[472414deee404a19a2dc8fc4dbe1e35c.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/602149ef6224451480574e0d2713a03e.png