如何使用配置类在Spring Boot中为我的应用程序配置属性？

Question

我正在尝试使用春季配置类为项目设置配置。我创建了一个新的试用项目，因为我不想编辑我的原始项目（对不起，所有这些废话，但是如果用户是新的，该系统几乎没有宽恕所有代码帖子）

demoapplication.java.java：config.java：config.java

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {

    @Autowired
    public static Config configuration;

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
        String fullname = configuration.name + " " + configuration.surname + " " + configuration.age;
        System.out.println(fullname);   
    }

}

---

：

package com.example.demo;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;

@Configuration
@PropertySource("classpath:application.yml")
public class Config {
    @Value("${person.name}")
    public String name;

    @Value("${person.surname}")
    public String surname;

    @Value("${person.age}")
    public Integer age;

}

application.yml：

person:
  name: name1
  surname: surname1
  age: 25

---

例外：

Exception in thread "restartedMain" java.lang.reflect.InvocationTargetException
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49)
Caused by: java.lang.NullPointerException
        at com.example.demo.DemoApplication.main(DemoApplication.java:15)
        ... 5 more

---

我做错了什么？

Answer 1

这是问题所在的问题

@Autowired
public ---> static <---- Config configuration;

。您需要从自动化字段中删除静态

，然后您将无法在main方法中使用此字段，因为main将其声明为静态。这里的解决方案是以下内容。在应用程序上下文通过编程加载后，您需要检索bean，而无需使用@Autowired

@SpringBootApplication
public class DemoApplication {

public static void main(String[] args) {

    ConfigurableApplicationContext ctx = SpringApplication.run(DemoApplication.class, args);

    Config configuration = ctx.getBean(Config.class);   

    String fullname = configuration.name + " " + configuration.surname + " " + configuration.age;
    System.out.println(fullname);   
  }

}

Answer 2

配置对象是静态的，因此它首先会创建，这对于弹簧容器接管对象的创建为时已晚。

Answer 3

您获得Null指针异常的原因，您不能这样初始化Spring。您的静态变量未初始化。

我的建议：

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication implements ApplicationRunner{

    @Autowired
    private Config configuration;

    public static void main(String[] args) {
       
        SpringApplication.run(DemoApplication.class, args);
   } 

    @Override
    public void run(ApplicationArguments args) {
        String fullname = configuration.name + " " + configuration.surname + " " + configuration.age;
        System.out.println(fullname);
   } 

}