通过反射获得注解信息

通过反射获得注解信息

示例代码如下：

    package com.han.reflection;
    
    import java.lang.annotation.*;
    import java.lang.reflect.Field;
    
    /*
    通过反射获得注解信息
     */
    public class Test02 {
        public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
            Class  c1 = Class.forName("com.han.reflection.Student");
            //通过反射获得注解
            Annotation[] annotations = c1.getAnnotations();
            for (Annotation annotation : annotations) {
                System.out.println(annotation);//@com.han.reflection.TableHan(value=db_student)
            }
    
            System.out.println("===============================================================");
    
            //获得注解value的值
            TableHan tableHan = (TableHan)c1.getAnnotation(TableHan.class);
            System.out.println(tableHan.value());//db_student
    
            System.out.println("===============================================================");
    
            Field f = c1.getDeclaredField("name");
            FiledHan annotation = f.getAnnotation(FiledHan.class);
            System.out.println(annotation.columnName());//db_name
            System.out.println(annotation.type());//varchar
            System.out.println(annotation.length());//5
        }
    }
    
    @TableHan("db_student")
    class Student{
        @FiledHan(columnName="db_id",type = "int",length = 10)
        private int id;
        @FiledHan(columnName="db_age",type = "int",length = 8)
        private int age;
        @FiledHan(columnName="db_name",type = "varchar",length = 5)
        private String name;
    
        public Student() {
        }
    
        public Student(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 setName(String name) {
            this.name = name;
        }
    
        @Override
        public String toString() {
            return "Student{" +
                    "id=" + id +
                    ", age=" + age +
                    ", name='" + name + '\'' +
                    '}';
        }
    }
    
    //类名的注解
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @interface TableHan{
        String value();
    }
    
    //属性的注解
    @Target(ElementType.FIELD)
    @Retention(RetentionPolicy.RUNTIME)
    @interface FiledHan{
        String columnName();
        String type();
        int length();
    }