死磕源码系列【SystemEnvironmentPropertySourceEnvironmentPostProcessor、SpringApplicationJsonEnvironmentPostP

女爷i 2022-11-20 08:20 228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][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhb21pbmd5YW5n_size_16_color_FFFFFF_t_70_pic_center]

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

GitHub地址：[https://github.com/mingyang66/spring-parent][https_github.com_mingyang66_spring-parent]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhb21pbmd5YW5n_size_16_color_FFFFFF_t_70_pic_center]: /images/20221120/53f6692dd78f435fb5fcb592d5321f0f.png
[https_github.com_mingyang66_spring-parent]: https://github.com/mingyang66/spring-parent