java如何定义一个全局变量（内存中）

前言

java如何定义一个全局变量（内存中），项目启动时，通过读取配置文件来构建一个实体类对象，然后在之后可以直接使用，而不是每次使用都要进行构建

前置准备

实体类结构

package cn.daenx.demo;

import lombok.Data;
@Data
public class Person {
    private  String info;
}

配置文件

spring:
  profiles:
    active: dev

test:
  name: daen
  age: 18

方式一

新建一个类

package cn.daenx.demo;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;

@Component
public class MyTestCom {
    private static String name;
    private static Integer age;

    @Value("${test.name}")
    public void setName(String name) {
        MyTestCom.name = name;
    }

    @Value("${test.age}")
    public void setAge(Integer age) {
        MyTestCom.age = age;
    }


    @Bean
    public Person doInit() {
        Person person = new Person();
        System.out.println("@Bean初始化");
        person.setInfo("姓名：" + name + "，年龄：" + age);
        return person;
    }
}

使用

package cn.daenx.demo.controller;

import cn.daenx.demo.Person;
import org.springframework.web.bind.annotation.*;

import javax.annotation.Resource;

@RestController
@RequestMapping("/test")
public class TestController {
    @Resource
    private Person person;

    @GetMapping(value = "/02")
    @ResponseBody
    private String req02() {
        System.out.println("02");
        return person.getInfo();
    }
}

方式二

新建一个类

package cn.daenx.demo;
public class GlobalInfo {

    private static Person person;

    public static Person getPerson() {
        return person;
    }

    public static void setPerson(Person person) {
        GlobalInfo.person = person;
    }

}

新建一个实体类，并实现ApplicationRunner

package cn.daenx.demo;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.stereotype.Component;

@Component
public class AppRunImpl implements ApplicationRunner {
    @Value("${test.name}")
    private String name;

    @Value("${test.age}")
    private Integer age;

    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("ApplicationRunner初始化");
        Person person = new Person();
        person.setInfo("姓名："+name + "，年龄：" + age);
        GlobalInfo.setPerson(person);
    }
}

使用

package cn.daenx.demo.controller;

import cn.daenx.demo.Person;
import cn.daenx.demo.GlobalInfo;
import org.springframework.web.bind.annotation.*;

import javax.annotation.Resource;

@RestController
@RequestMapping("/test")
public class TestController {

    @GetMapping(value = "/01")
    @ResponseBody
    private String req01() {
        System.out.println("01");
        return GlobalInfo.getPerson().getInfo();
    }
}