1.前言

通过PropertySourceLoader接口的实现类配合监听器实现加载外部的配置文件，加载properties文件使用PropertiesPropertySourceLoader，加载yml文件使用YamlPropertySourceLoader。.通过监听器将配置文件加载到Spring环境配置中，且可以指定优先级。核心是将配置文件加载PropertySource中并将其添加到spring的MutablePropertySources中，使其可以通过@value等方式获取配置文件中的属性值。

2.加载properties文件

-----1.方法一：PropertiesPropertySourceLoader

public class MyApplicationContextInitializer implements ApplicationContextInitializer {
    
    @Override
    public void initialize(ConfigurableApplicationContext configurableApplicationContext) {
        PropertiesPropertySourceLoader loader = new PropertiesPropertySourceLoader();
        try {
            PropertySource<?> propertySource = loader.load("publicConfiguration", new InputStreamResource(Files.newInputStream(Paths.get("C:\\Users\\fkp12\\Desktop\\application.properties")))).get(0);
            configurableApplicationContext.getEnvironment().getPropertySources().addFirst(propertySource);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

-----2.方法二：PropertiesFactoryBean

public class MyApplicationContextInitializer implements ApplicationContextInitializer {
    
    @Override
    public void initialize(ConfigurableApplicationContext configurableApplicationContext) {
        PropertiesFactoryBean factoryBean = new PropertiesFactoryBean();
        try {
            factoryBean.setLocation(new InputStreamResource(Files.newInputStream(Paths.get("C:\\Users\\fkp12\\Desktop\\application.properties"))));
            Properties object = factoryBean.getObject();
            if(object != null){
                PropertiesPropertySource propertySource = new PropertiesPropertySource("publicConfiguration",object);
                configurableApplicationContext.getEnvironment().getPropertySources().addFirst(propertySource);
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

3.加载yml文件

-----1.方法一：YamlPropertySourceLoader

public class MyApplicationContextInitializer implements ApplicationContextInitializer {
    
    @Override
    public void initialize(ConfigurableApplicationContext configurableApplicationContext) {

        YamlPropertySourceLoader loader = new YamlPropertySourceLoader();
        try {
            PropertySource<?> propertySource = loader.load("externalConfiguration", new InputStreamResource(Files.newInputStream(Paths.get("C:\\Users\\fkp12\\Desktop\\application.yml")))).get(0);
            configurableApplicationContext.getEnvironment().getPropertySources().addFirst(propertySource);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

-----2.方法二：YamlPropertiesFactoryBean

public class MyApplicationContextInitializer implements ApplicationContextInitializer {
    
    @Override
    public void initialize(ConfigurableApplicationContext configurableApplicationContext) {
        YamlPropertiesFactoryBean factoryBean = new YamlPropertiesFactoryBean();
        try {
            factoryBean.setResources(new InputStreamResource(Files.newInputStream(Paths.get("C:\\Users\\fkp12\\Desktop\\application.yml"))));
            Properties object = factoryBean.getObject();
            if(object != null){
                PropertiesPropertySource propertySource = new PropertiesPropertySource("publicConfiguration",object);
                configurableApplicationContext.getEnvironment().getPropertySources().addFirst(propertySource);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

4.配置优先级

通过上述代码可以发现所有方法最后都是通过configurableApplicationContext.getEnvironment().getPropertySources().addFirst(propertySource)将封装好的PropertySource对象加入到Spring配置中的，而都是通过调用addFirst(PropertySource  propertySource)，除了addFirst还有addLast,addBefore,addAfter,这就与优先级有关系了，先说一下addBefore和addAfter,这两个方法参数都是String relativePropertySourceName, PropertySource<?> propertySource，意思就是要将此propertySource添加在名为relativePropertySourceName的propertySource的前边还是后边，放在前边的在读取属性时会优先读取属性值，而addFirst和addLast则是将此propertySource放在整个列表的最前或最后。

对于优先读取该属性的值的解释：

例如项目中的配置文件application.yml中有属性name: zhangsan，外部配置文件externalApplication.yml中有属性name: lisi，通过上述任何方式将外部配置文件加载到Spring配置中后因为两个配置文件中都有name属性，但其值不相同，这个时候如果通过@Value("${name}")取值会取到zhangsan还是lisi呢，答案是在上述PropertySource列表中靠前的会优先生效。如果想让外部的配置文件优先则可以使用addFirst方法添加propertySource。

提到配置文件的优先级就想起了springboot默认读取配置文件的优先级，参考下方说明和链接：

优先级依次递减

1.在执行命令的目录下建config文件夹，然后把配置文件放到这个文件夹下。(在jar包的同一个目录下建config文件夹，执行命令需要在jar包所在目录下才行)
2.直接把配置文件放到jar包的同级目录
3.在classpath下建一个config文件夹，然后把配置文件放进去。
4.在classpath下直接放配置文件。

参考文章：http://t.csdn.cn/ufapd

5.使用的监听器以及加载的时机（监听的事件）

无论使用那种监听器的实现类型，都需要拿到ConfigurableEnvironment这个参数，可以在多个时机加载配置文件，例如environmentPrepared，contextPrepared，下面展示三种方式实现

方法一：

public class MyApplicationContextInitializer implements ApplicationContextInitializer {

    @Override
    public void initialize(ConfigurableApplicationContext configurableApplicationContext) {
        YamlPropertySourceLoader loader = new YamlPropertySourceLoader();
        try {
            PropertySource<?> propertySource = loader.load("externalConfiguration", new InputStreamResource(Files.newInputStream(Paths.get("C:\\Users\\fkp12\\Desktop\\application.yml")))).get(0);
            configurableApplicationContext.getEnvironment().getPropertySources().addFirst(propertySource);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

需要将该类的全限定名配置到spring.factories中

org.springframework.context.ApplicationContextInitializer=com.fkp.springboot_listener.listener.MyApplicationContextInitializer

方法二：

public class MySpringApplicationRunListener implements SpringApplicationRunListener {

    private final SpringApplication springApplication;

    private final String[] args;

    public MySpringApplicationRunListener(SpringApplication springApplication, String[] args) {
        this.springApplication = springApplication;
        this.args = args;
    }

    @Override
    public void starting(ConfigurableBootstrapContext bootstrapContext) {
        System.out.println("SpringApplicationRunListener....starting");
    }

    @Override
    public void environmentPrepared(ConfigurableBootstrapContext bootstrapContext, ConfigurableEnvironment environment) {
        YamlPropertySourceLoader loader = new YamlPropertySourceLoader();
        try {
            PropertySource<?> propertySource = loader.load("externalConfiguration", new InputStreamResource(Files.newInputStream(Paths.get("C:\\Users\\fkp12\\Desktop\\application.yml")))).get(0);
            environment.getPropertySources().addFirst(propertySource);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public void contextPrepared(ConfigurableApplicationContext context) {
        System.out.println("SpringApplicationRunListener....contextPrepared");
    }

    @Override
    public void contextLoaded(ConfigurableApplicationContext context) {
        System.out.println("SpringApplicationRunListener....contextLoaded");
    }

    @Override
    public void started(ConfigurableApplicationContext context) {
        System.out.println("SpringApplicationRunListener....started");
    }

    @Override
    public void running(ConfigurableApplicationContext context) {
        System.out.println("SpringApplicationRunListener....running");
    }

    @Override
    public void failed(ConfigurableApplicationContext context, Throwable exception) {
        System.out.println("SpringApplicationRunListener....failed");
    }
}

需要将该类的全限定名配置到spring.factories中

org.springframework.boot.SpringApplicationRunListener=com.fkp.springboot_listener.listener.MySpringApplicationRunListener

方法三：

public class MyApplicationListener implements ApplicationListener<ApplicationEnvironmentPreparedEvent> {
    @Override
    public void onApplicationEvent(ApplicationEnvironmentPreparedEvent applicationEnvironmentPreparedEvent) {
        YamlPropertySourceLoader loader = new YamlPropertySourceLoader();
        try {
            PropertySource<?> propertySource = loader.load("externalConfiguration", new InputStreamResource(Files.newInputStream(Paths.get("C:\\Users\\fkp12\\Desktop\\application.yml")))).get(0);
            applicationEnvironmentPreparedEvent.getEnvironment().getPropertySources().addFirst(propertySource);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

需要将该类的全限定名配置到spring.factories中

org.springframework.context.ApplicationListener=com.fkp.springboot_listener.listener.MyApplicationListener

备注：通过Environment取Spring配置中的值

Environment或实现该接口的类可以通过多种方式获取，例如上述ApplicationEnvironmentPreparedEvent#getEnvironment()获取ConfigurableEnvironment

通用的一种方法是通过ApplicationContext获取，ApplicationContext#getEnvironment()，ApplicationContext可以从Spring容器中取。

通过Environment的getProperty方法可以取Spring配置中属性的值。