死磕源码系列【SystemEnvironmentPropertySourceEnvironmentPostProcessor、SpringApplicationJsonEnvironmentPostP-蒲公英云

死磕源码系列【SystemEnvironmentPropertySourceEnvironmentPostProcessor、SpringApplicationJsonEnvironmentPostP

女爷i 2022-11-20 08:20 287阅读 0赞

SystemEnvironmentPropertySourceEnvironmentPostProcessor类是EnvironmentPostProcessor接口的实现类，用来替换Environment环境中的systemEnvironment，systemEnvironment中最初存储的是SystemEnvironmentPropertySource类，现由实现类OriginAwareSystemEnvironmentPropertySource替换，OriginAwareSystemEnvironmentPropertySource提供了获取Origin的方法，即返回SystemEnvironmentOrigin对象。

先看下SystemEnvironmentPropertySource类中存储的系统环境配置：

我们可以看到里面存储的都是操作系统相关的环境变量配置

SystemEnvironmentPropertySourceEnvironmentPostProcessor源码：

public class SystemEnvironmentPropertySourceEnvironmentPostProcessor implements EnvironmentPostProcessor, Ordered { 
   /** * 后置处理器的优先级，其优先级高于SpringApplicationJsonEnvironmentPostProcessor * 值越小优先级越高 */
   public static final int DEFAULT_ORDER = SpringApplicationJsonEnvironmentPostProcessor.DEFAULT_ORDER - 1;
   private int order = DEFAULT_ORDER;
    //后置处理器回调方法
   @Override
   public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) { 
      //获取系统环境配置名，即：systemEnvironment
      String sourceName = StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME;
      //获取环境对象中的系统配置
      PropertySource<?> propertySource = environment.getPropertySources().get(sourceName);
      if (propertySource != null) { 
        //替换系统环境对象中的环境配置
         replacePropertySource(environment, sourceName, propertySource);
      }
   }
   @SuppressWarnings("unchecked")
   private void replacePropertySource(ConfigurableEnvironment environment, String sourceName,
         PropertySource<?> propertySource) { 
     //获取环境配置，转换为字典结构
      Map<String, Object> originalSource = (Map<String, Object>) propertySource.getSource();
     //转换为将要替换的环境对象 
     SystemEnvironmentPropertySource source = new OriginAwareSystemEnvironmentPropertySource(sourceName,
            originalSource);
     //替换环境对象
      environment.getPropertySources().replace(sourceName, source);
   }
   @Override
   public int getOrder() { 
      return this.order;
   }
   public void setOrder(int order) { 
      this.order = order;
   }
   /** * 为SystemEnvironmentPropertySource提供SystemEnvironmentOrigin源 * 其Origin代表的是属性配置最原始的源相关信息 */
   protected static class OriginAwareSystemEnvironmentPropertySource extends SystemEnvironmentPropertySource
         implements OriginLookup<String> { 
      OriginAwareSystemEnvironmentPropertySource(String name, Map<String, Object> source) { 
         super(name, source);
      }
      @Override
      public Origin getOrigin(String key) { 
         String property = resolvePropertyName(key);
         if (super.containsProperty(property)) { 
            return new SystemEnvironmentOrigin(property);
         }
         return null;
      }
   }
}

SpringApplicationJsonEnvironmentPostProcessor类也是EnvironmentPostProcessor环境后置处理器函数，其优先级比SystemEnvironmentPropertySourceEnvironmentPostProcessor高，会将系统属性spring.application.json或SPRING_APPLICATION_JSON解析成JSON,并存储到Environment：

在这里插入图片描述

上述是通过代码的形式传递spring.application.json参数，也可以通过运行jar包时传递：

java -jar demo-0.0.1-SNAPSHOT.jar --spring.application.json='{"a":"bar","b":23}'
 //或
java -Dspring.application.json='{"a":"bar","b":23}' -jar demo-0.0.1-SNAPSHOT.jar