java注解和反射例子

 

 

package com.wang.test01;
import java.lang.annotation.*;
import java.lang.reflect.Field;

//反射和注解
public class test {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
        Class c1= Class.forName("com.wang.test01.User");
        //通过反射获得注解
        Annotation[] annotations = c1.getAnnotations();
        for (Annotation annotation : annotations) {
            System.out.println(annotation);
        }
        Table Tableannotation = (Table) c1.getAnnotation(Table.class);
        String value = Tableannotation.value();
        System.out.println(value);

        //获得类指定的注解
        Field f = c1.getDeclaredField("name");
        Fieldwang fAnnotation = f.getAnnotation(Fieldwang.class);
        System.out.println(fAnnotation.columnName());
        System.out.println(fAnnotation.type());
        System.out.println(fAnnotation.length());
    }
}

//实体类
@Table("学生")
class User{
    @Fieldwang(columnName = "db_name",type = "int",length = 10)
    private String name;
    @Fieldwang(columnName = "db_id",type = "int",length = 10)
    private int id;
    @Fieldwang(columnName = "db_age",type = "int",length = 10)
    private int age;

    public User() {
    }

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

    public int getAge() {
        return age;
    }

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

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

@Target(ElementType.TYPE) //只允许注解类
@Retention(RetentionPolicy.RUNTIME)
@interface Table {
    String value();
}

@Target(ElementType.FIELD) //只允许属性注解
@Retention(RetentionPolicy.RUNTIME)
@interface Fieldwang{
    String columnName();
    String type();
    int length();
}