通过注解和反射配合设计ORM

联系ORM对象关系映射 讲java的类映射到数据库的表

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

public class Test09 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
        Class c1 = Class.forName ("Reflection.Test09.Student2");
        //通过反射获取注解
        Annotation[] annotations = c1.getAnnotations ();
        for (Annotation annotation : annotations) {
            System.out.println (annotation);
        }
        //获得注解的value的值
        Tablekuang tablekuang = (Tablekuang) c1.getAnnotation (Tablekuang.class);
        String value = tablekuang.value ();
        System.out.println (value);
        //获取类指定的注解
        Field f = c1.getDeclaredField ("id");
        Fieldkuang annotation = f.getAnnotation (Fieldkuang.class);
        System.out.println (annotation.columnName ());
        System.out.println (annotation.type ());
        System.out.println (annotation.length ());
    }
}
@Tablekuang ("db_student")
class Student2{
    @Fieldkuang (columnName = "db_id",type = "int",length = 10)
    private int id;
    @Fieldkuang (columnName = "db_age",type = "int",length = 10)
    private int age;
    @Fieldkuang (columnName = "db_name",type = "varchar",length = 10)
    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 setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Student2{" +
                "id=" + id +
                ", age=" + age +
                ", name='" + name + '\'' +
                '}';
    }
}
//类名的注解
@Target (ElementType.TYPE)
@Retention (RetentionPolicy.RUNTIME)
@interface Tablekuang{
    String value();
}
 //属性的注解
@Target (ElementType.FIELD)
@Retention (RetentionPolicy.RUNTIME)
@interface Fieldkuang{
    String columnName();
    String type();
    int length();
}

这个程序有点错误