简介

从Spring Boot 1.3开始，我们可以在应用程序上下文刷新之前使用EnvironmentPostProcessor来自定义应用程序的Environment。Environment表示当前应用程序运行的环境，它可以统一访问各种属性源中的属性，如属性文件、JVM系统属性、系统环境变量和Servlet上下文参数。使用EnvironmentPostProcessor可以在bean初始化之前对Environment进行修改。

示例

在 custom.properties 中定义一些配置，配置如下：

jdbc.root.user=mysql
jdbc.root.password=123456

1.实现EnvironmentPostProcessor

定义MyEnvironmentPostProcessor实现EnvironmentPostProcessor接口

public class MyEnvironmentPostProcessor implements EnvironmentPostProcessor {

    @Override
    public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
        try{
            InputStream inputStream = new FileInputStream("/Users/SpringBoot/custom.properties");
            Properties properties = new Properties();
            properties.load(inputStream);
            PropertiesPropertySource propertiesPropertySource = new PropertiesPropertySource("my",properties);
            environment.getPropertySources().addLast(propertiesPropertySource);
        }catch (IOException e){
            e.printStackTrace();
        }
    }

}

如果你希望EnvironmentPostProcessor按照特定的顺序被调用，可以实现Ordered接口，或者使用@Order注解。

2.注册实现类

想要在Spring Boot启动过程中调用这个实现类，我们还需要在项目的resources目录中定义一个META-INF文件夹，然后在其下面先建spring.factories文件，在其中指定注册这个实现类：

org.springframework.boot.env.EnvironmentPostProcessor=com.test.springboot.processor.MyEnvironmentPostProcessor

3.测试

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(Application.class,args);
        String username = context.getEnvironment().getProperty("jdbc.root.user");
        String password = context.getEnvironment().getProperty("jdbc.root.password");
        System.out.println("username==="+username);
        System.out.println("password==="+password);
    }
}

 EnvironmentPostProcessor接口官网说明

官方文档如下

Allows for customization of the application's {@link Environment} prior to the application context being refreshed.
允许定制应用的上下文的应用环境优于应用的上下文之前被刷新。（意思就是在spring上下文构建之前可以设置一些系统配置）

EnvironmentPostProcessor implementations have to be registered in
META-INF/spring.factories, using the fully qualified name of this class as the key.
EnvironmentPostProcessor的实现类必须要在META-INF/spring.factories文件中去注册，并且注册的是全类名。

EnvironmentPostProcessor processors are encouraged to detect whether Spring's
org.springframework.core.Ordered Ordered interface has been implemented or if the @org.springframework.core.annotation.Order Order annotation is present and to sort instances accordingly if so prior to invocation.
鼓励EnvironmentPostProcessor处理器检测Org.springframework.core.Ordered注解，这样相应的实例也会按照@Order注解的顺序去被调用。