Question

作为Spring Boot项目的一部分，我试图在按如下方式创建Spring ApplicationContext之前先阅读application.properties，

主班

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;

@SpringBootApplication
public class DemoApplication {
    public static void main(String[] args) {
        ConfigurationClass con = new ConfigurationClass();
        con.readProperties();
        ApplicationContext c = SpringApplication.run(DemoApplication.class, args);
    }
}

配置类

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.core.env.Environment;

@Configuration
@PropertySource("classpath:application.properties")
public class ConfigurationClass {

    private String value1;

    private String value2;

    @Autowired
    private Environment env;

    public void readProperties() {
        value1 = env.getProperty("app.value1");
        value2 = env.getProperty("app.value2");
    }

    public String getValue1() {
        return value1;
    }

    public String getValue2() {
        return value2;
    }
}

我想从application.properties获取一些基本值并进行一些配置。此代码发生的事情是，由于nullpointerexception在env期间为空，因此它抛出了value1 = env.getProperty("app.value1");。

我在这里做错了什么？

如何在创建springapplication上下文之前的这个时间点读取application.properties中的值？

任何帮助将不胜感激！

Answer 1

    @Configuration
    @PropertySource("classpath:application.properties")
    public class ConfigurationClass {
        @Value("${app.value1}")    
        private String value1;

        @Value("${app.value2}")    
        private String value2;

        public String getValue1() {
        return value1;
        }

        public String getValue2() {
        return value2;
       }
 }

然后调用

 @SpringBootApplication
public class DemoApplication {

   public static void main(String[] args) {

    ApplicationContext c = SpringApplication.run(DemoApplication.class, args);
    ConfigurationClass  con = c.getBean(ConfigurationClass.class);
    System.out.println(con.getValue1());
    System.out.println(con.getValue2());
     }
}

Answer 2

Spring只会将依赖项注入到Spring Bean中，例如，如果您使用new关键字显式创建任何对象，则它不是Spring Bean，例如

ConfigurationClass con = new ConfigurationClass();

我也知道实例变量不能在静态区域中访问，这可能会使您无法使用new关键字创建对象，因此有两种方法可以解决此问题

第一种方法：建议使用ApplicationRunner

package com.example.demo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;

@SpringBootApplication
public class DemoApplication implements ApplicationRunner {

   @Autowire
   private ConfigurationClass  con;

   public static void main(String[] args) {

    ApplicationContext c = SpringApplication.run(DemoApplication.class, args);
}


@Override
public void run(ApplicationArguments args) throws Exception {
    con.readProperties();
    System.out.println(con.getValue1());
    System.out.println(con.getValue2());
    }
}

第二种方法仅用于共享知识

package com.example.demo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;

@SpringBootApplication
public class DemoApplication {

   public static void main(String[] args) {

    ApplicationContext c = SpringApplication.run(DemoApplication.class, args);
    ConfigurationClass  con = c.getBean(ConfigurationClass.class);
    con.readProperties();
    System.out.println(con.getValue1());
    System.out.println(con.getValue2());
     }
}

注意：：您还可以使用@Value批注来读取属性

在创建Spring应用程序上下文之前阅读application.properties

2 个答案: