java | 反射操作注解

反射操作注解。

package com.redisc;

import java.lang.annotation.*;
import java.lang.reflect.*;
import java.util.List;
import java.util.Map;


// 类名注解
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@interface Table {
    String value();
}

// 属性注解
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@interface TableField {
    String columnName();

    String type();

    int length();
}

@Table("student")
class Student {
    @TableField(columnName = "id", type = "int", length = 10)
    public int id;
    @TableField(columnName = "name", type = "varchar", length = 255)
    public String name;
}


public class Test {

    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
        Class c1 = Class.forName("com.redisc.Student");

        // 通过反射获得注解
        Annotation[] annotations = c1.getAnnotations();
        for (Annotation annotation : annotations) {
            System.out.println(annotation);
        }

        // 获得注解的值
        Table annotation = (Table) c1.getAnnotation(Table.class);
        System.out.println(annotation.value());

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

    }
}

输出

@com.redisc.Table("student")
student
name
varchar