springboot中使用配置方式有四种，分别是environment、BeanDefinition、@Value、@ConfigurationProperties。具体的原理可以看我之前的一篇文章https://blog.csdn.net/cjc000/article/details/132800290。代码在https://gitee.com/summer-cat001/config-center

原理

environment是存储配置的地方，其他的都是从这里获取的数据。所以只要在他们用到配置之前，把配置放到environment中就可以了，先看下springboot的启动流程图。

可以看到业务代码第一次用到配置的地方是PropertySourcesPlaceholderConfigurer，它是一个BeanFactoryPostProcessor默认的order是最低优先级的，所以只要在执行它之前把配置放到environment对象中即可，如图标红的地方

不过很多三方的jar包可能会会自定义ApplicationContextInitializer和BeanFactoryPostProcessor。所以为了让这些jar包也用到我们的配置，所以要在更早的阶段加载配置，既然springboot提供了加载配置的扩展点，那我们直接注册一个自定义的EnvironmentPostProcessor类即可，不过因为我们加载配置的时候也要使用application.yml的配置，比如设置连接地址什么的，所以需要把我们的EnvironmentPostProcessor的优先级设置的小于ConfigDataEnvironmentPostProcessor，ConfigDataEnvironmentPostProcessor的优先级是Ordered.HIGHEST_PRECEDENCE + 10，我们只要把order设置成Ordered.HIGHEST_PRECEDENCE + 11即可

代码

ConfigCenterClient改为单例

 private static volatile ConfigCenterClient client;

    private ConfigCenterClient(String url) {
        this.url = url;
        //将配置中心的配置转换成property格式，即user.name=xxx
        List<ConfigVO> configList = getAllValidConfig();
        this.configMap = configList2ConfigMap(configList);
    }

    public static ConfigCenterClient getInstance(String url) {
        return Optional.ofNullable(client).orElseGet(() -> {
            synchronized (ConfigCenterClient.class) {
                if (client == null) {
                    client = new ConfigCenterClient(url);
                }
                return client;
            }
        });
    }

自定义EnvironmentPostProcessor

可以看到我们是从application.yml文件中获取了配置中心的地址，然后再把配置中心的配置注入到springboot中

public class ConfigEnvironmentPostProcessor implements EnvironmentPostProcessor {

    @Override
    public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
        String configCenterUrl = environment.getProperty("config.center.url");
        ConfigCenterClient configCenterClient = ConfigCenterClient.getInstance(configCenterUrl);
        Map<String, Object> configProperty = configCenterClient.getConfigProperty();

        MutablePropertySources propertySources = environment.getPropertySources();
        MapPropertySource configCenter = new MapPropertySource("configCenter", configProperty);
        propertySources.addFirst(configCenter);
    }
}

注册EnvironmentPostProcessor

org.springframework.boot.env.EnvironmentPostProcessor=\
com.config.center.config.ConfigEnvironmentPostProcessor

效果

environment对象获取配置

@Autowired
    private Environment environment;

    @Test
    public void configTest() {
        String userName = environment.getProperty("user.name");
        System.out.println(userName);
    }

xml中获取配置

public class User {
    private String userName;

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
	    "
       default-lazy-init="false">

    <bean id="user" class="com.config.center.test.User">
        <property name="userName" value="${user.name}"/>
    </bean>

</beans>

@Value获取配置

    @Value("${user.name}")
    private String name;

    @Test
    public void configTest() {
        System.out.println(name);
    }

@ConfigurationProperties

@Component
@ConfigurationProperties(prefix = "user")
public class UserConfig {
    private String name;
    private int age;
    private List<String> education;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public List<String> getEducation() {
        return education;
    }

    public void setEducation(List<String> education) {
        this.education = education;
    }
}

    @Autowired
    private UserConfig userConfig;

    @Test
    public void configTest() {
        System.out.println(userConfig);
    }

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