通过反射获取类注解的value值和属性

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通过反射获取注解
以及获取注解的value值
以及注解的属性

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import java.lang.annotation.*;
import java.lang.reflect.Field;

public class Test16 {

        public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
                Class c1 = Class.forName("com.test.reflection.Student2");
                //通过反射获取注解
                Annotation[] annotations = c1.getAnnotations(); //获取c1的注解
                for (Annotation annotation : annotations) {
                        System.out.println(annotation);  //遍历输出
                }

                //通过反射获取类注解的value值
                Student2.Tablehe tablehe = (Student2.Tablehe)c1.getAnnotation(Student2.Tablehe.class);
                System.out.println(tablehe.value());

                // 通过反射获取指定的注解，例如获取类属性
                Field f = c1.getDeclaredField("id"); //获取“name”属性
                Student2.Fieldhe annotation = f.getAnnotation(Student2.Fieldhe.class);  //得到注解所属的类
                System.out.println(annotation.columnName()); //输出属性注解的value
                System.out.println(annotation.type());
                System.out.println(annotation.length());
        }
}


@Student2.Tablehe("db_student") //数据库表的注解
class Student2{
        @Fieldhe(columnName = "db_age",type = "int",length = 10) //输入定义的三个值
        private int age;
        @Fieldhe(columnName = "db_name",type = "String",length = 20)
        private String name;
        @Fieldhe(columnName = "db_int",type = "int",length = 10)
        private int id;


        // 类名的注解
        @Target(ElementType.TYPE)
        @Retention(RetentionPolicy.RUNTIME)
        @interface Tablehe{
                String value();
        }

        // 属性的注解
        @Target(ElementType.FIELD)
        @Retention(RetentionPolicy.RUNTIME)
        @interface Fieldhe{
                //定义了三个值
                String columnName();
                String type();
                int length();

        }


        // 定义类的无参构造器
        public Student2() {
        }

        // 定义类的有参构造器
        public Student2(int age, String name, int id) {
                this.age = age;
                this.name = name;
                this.id = id;
        }

        @Override
        public java.lang.String toString() {
                return "Student2{" +
                        "age=" + age +
                        ", name=" + name +
                        ", 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;
        }

        public int getId() {
                return id;
        }

        public void setId(int id) {
                this.id = id;
        }


}