package com.sinosoft;

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

public class Test02 {

    public static void main(String[] args) throws ClassNotFoundException,NoSuchFieldException{
        Class c1 = Class.forName("com.sinosoft.Student");
        //通過反射獲得註解
        Annotation[] annotations = c1.getAnnotations();

        for (Annotation annotation: annotations) {
            System.out.println(annotation);
        }

        //獲得註解的value值 註解的名字
        TableName tableName =(TableName) c1.getAnnotation(TableName.class);
        String value = tableName.value();
        System.out.println(value);


        //獲取屬性註解的value值
        Field name = c1.getDeclaredField("name");
        FieldName fieldName = (FieldName)name.getAnnotation(FieldName.class);
        String fname = fieldName.columnName();
        int length = fieldName.length();
        String type = fieldName.type();
        System.out.println("name:"+fname+"\nlength:"+length+"\ntype:"+type);


    }

}
@TableName(value = "db_student")
class Student {
    @FieldName(columnName = "db_name",type="int",length = 30)
    private String name;
    @FieldName(columnName = "db_age",type="int",length = 10)
    private int age;
    @FieldName(columnName = "db_id",type="int",length = 10)
    private int id;

    public Student() {
    }

    public Student(String name, int age, int id) {
        this.name = name;
        this.age = age;
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public int getId() {
        return id;
    }

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

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", id=" + id +
                '}';
    }
}

//類名的註解
@Target(ElementType.TYPE)//表示這個註解只能作用在類上
@Retention(RetentionPolicy.RUNTIME)//表示作用在執行時
@interface TableName {
  String value();
}

//屬性的註解
@Target(ElementType.FIELD)//表示這個註解只能作用在屬性上
@Retention(RetentionPolicy.RUNTIME)//表示作用在執行時
@interface FieldName{
    String columnName();
    String type();
    int length();
}

執行結果：

@com.sinosoft.TableName(value=db_student)
db_student
name:db_name
length:30
type:int