死磕源码系列【StandardServletEnvironment源码解析】

今天药忘吃喽~ 2022-11-21 03:34 175阅读 0赞

> spring中的StandardServletEnvironment将由基于servlet的web应用程序使用，所有基于servlet的web相关ApplicationContext类将会初始化一个StandardServletEnvironment实例。

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通过上面的图标可以清楚StandardServletEnvironment类的继承关系，PropertyResolver接口是用于针对任何基础源解析属性的接口；ConfigurablePropertyResolver接口是PropertyResolver的子接口，提供了将属性值从一种类型转换为另外一种类型的转换服务；Environment接口代表正在运行的应用程序的环境（包含配置文件Profile、属性Properties）;AbstractEnvironment抽象类是Environment接口的抽象实现，支持设置默认文件名，并允许指定激活和默认的配置文件；StandardEnvironment是Environment接口的实现，适用于标准（即非web）应用程序的实现，提供了两个标准的属性源systemEnvironment、systemProperties；ConfigurableWebEnvironment接口允许在ServletContext、ServletConfig变为可用的早期初始化servlet相关的PropertySource对象。

StandardServletEnvironment类源码如下：

public class StandardServletEnvironment extends StandardEnvironment implements ConfigurableWebEnvironment { 
    
    	/** servletContext初始化参数属性源名 */
    	public static final String SERVLET_CONTEXT_PROPERTY_SOURCE_NAME = "servletContextInitParams";
    
    	/** ServletConfig初始化参数属性源名 */
    	public static final String SERVLET_CONFIG_PROPERTY_SOURCE_NAME = "servletConfigInitParams";
    
    	/** JNDI属性源名 */
    	public static final String JNDI_PROPERTY_SOURCE_NAME = "jndiProperties";
    
    
    	@Override
    	protected void customizePropertySources(MutablePropertySources propertySources) { 
        //新增servletConfig属性源配置，使用占位属性源对象，会被后面的后置处理器替换掉
    		propertySources.addLast(new StubPropertySource(SERVLET_CONFIG_PROPERTY_SOURCE_NAME));
        //新增servletContext属性源配置，使用占位属性源对象，会被后面的后置处理器替换掉
    		propertySources.addLast(new StubPropertySource(SERVLET_CONTEXT_PROPERTY_SOURCE_NAME));
    		if (JndiLocatorDelegate.isDefaultJndiEnvironmentAvailable()) { 
          //新增JNDI属性源配置
    			propertySources.addLast(new JndiPropertySource(JNDI_PROPERTY_SOURCE_NAME));
    		}
        //调用父类StandardEnvironment方法
        //新增PropertiesPropertySource属性原配置，name是systemProperties
        //新增SystemEnvironmentPropertySource属性源配置，name是systemEnvironment
    		super.customizePropertySources(propertySources);
    	}
    	//此方法用于替换掉servletContext、servletConfig对应的占位属性源配置
    	@Override
    	public void initPropertySources(@Nullable ServletContext servletContext, @Nullable ServletConfig servletConfig) { 
    		WebApplicationContextUtils.initServletPropertySources(getPropertySources(), servletContext, servletConfig);
    	}
    
    }

org.springframework.web.context.support.WebApplicationContextUtils\#initServletPropertySources方法：

public static void initServletPropertySources(MutablePropertySources sources,
    			@Nullable ServletContext servletContext, @Nullable ServletConfig servletConfig) { 
    
    		Assert.notNull(sources, "'propertySources' must not be null");
    		String name = StandardServletEnvironment.SERVLET_CONTEXT_PROPERTY_SOURCE_NAME;
    		if (servletContext != null && sources.get(name) instanceof StubPropertySource) { 
          //替换掉servletContextInitParams占位属性源配置
    			sources.replace(name, new ServletContextPropertySource(name, servletContext));
    		}
    		name = StandardServletEnvironment.SERVLET_CONFIG_PROPERTY_SOURCE_NAME;
    		if (servletConfig != null && sources.get(name) instanceof StubPropertySource) { 
          //替换掉servletConfigInitParams占位属性源配置
    			sources.replace(name, new ServletConfigPropertySource(name, servletConfig));
    		}
    	}

在springboot框架中Environment对象初始化过程如org.springframework.boot.SpringApplication\#prepareEnvironment方法：

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
    			ApplicationArguments applicationArguments) { 
    		// 创建environment对象
    		ConfigurableEnvironment environment = getOrCreateEnvironment();
        //对属性源及配置文件进行配置
    		configureEnvironment(environment, applicationArguments.getSourceArgs());
        //环境Environment附加ConfigurationPropertySource属性配置源支持
    		ConfigurationPropertySources.attach(environment);
        //通过后置处理程序加载配置文件
    		listeners.environmentPrepared(environment);
    		bindToSpringApplication(environment);
    		if (!this.isCustomEnvironment) { 
    			environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
    					deduceEnvironmentClass());
    		}
    		ConfigurationPropertySources.attach(environment);
    		return environment;
    	}

org.springframework.boot.SpringApplication\#getOrCreateEnvironment方法创建Environment对象：

private ConfigurableEnvironment getOrCreateEnvironment() { 
    		if (this.environment != null) { 
    			return this.environment;
    		}
    		switch (this.webApplicationType) { 
            //当前环境类型是servlet,所以就创建StandardServletEnvironment对象
    		case SERVLET:
    			return new StandardServletEnvironment();
    		case REACTIVE:
    			return new StandardReactiveWebEnvironment();
    		default:
    			return new StandardEnvironment();
    		}
    	}

org.springframework.boot.SpringApplication\#configureEnvironment模板代理方法源码：

protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) { 
    		if (this.addConversionService) { 
    			ConversionService conversionService = ApplicationConversionService.getSharedInstance();
          //设置属性转换对象
    			environment.setConversionService((ConfigurableConversionService) conversionService);
    		}
        //配置属性源
    		configurePropertySources(environment, args);
        //配置配置文件
    		configureProfiles(environment, args);
    	}

org.springframework.boot.SpringApplication\#configurePropertySources方法对应用程序的环境的PropertySource进行新增、删除或者冲新排序：

protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) { 
    		//获取应用程序环境中的属性源集合
      	MutablePropertySources sources = environment.getPropertySources();
    		if (this.defaultProperties != null && !this.defaultProperties.isEmpty()) { 
    			sources.addLast(new MapPropertySource("defaultProperties", this.defaultProperties));
    		}
      	//设置命令行参数的PropertySource对象
    		if (this.addCommandLineProperties && args.length > 0) { 
    			String name = CommandLinePropertySource.COMMAND_LINE_PROPERTY_SOURCE_NAME;
    			if (sources.contains(name)) { 
    				PropertySource<?> source = sources.get(name);
    				CompositePropertySource composite = new CompositePropertySource(name);
    				composite.addPropertySource(
    						new SimpleCommandLinePropertySource("springApplicationCommandLineArgs", args));
    				composite.addPropertySource(source);
    				sources.replace(name, composite);
    			}
    			else { 
    				sources.addFirst(new SimpleCommandLinePropertySource(args));
    			}
    		}
    	}

org.springframework.boot.SpringApplication\#configureProfiles方法设置激活的配置文件：

protected void configureProfiles(ConfigurableEnvironment environment, String[] args) { 
    		Set<String> profiles = new LinkedHashSet<>(this.additionalProfiles);
    		profiles.addAll(Arrays.asList(environment.getActiveProfiles()));
    		environment.setActiveProfiles(StringUtils.toStringArray(profiles));
    	}

org.springframework.boot.context.properties.source.ConfigurationPropertySources\#attach方法附加ConfigurationPropertySourcesPropertySource支持：

public static void attach(Environment environment) { 
    		Assert.isInstanceOf(ConfigurableEnvironment.class, environment);
        //获取属性配置源
    		MutablePropertySources sources = ((ConfigurableEnvironment) environment).getPropertySources();
        //获取属性配置源name为configurationProperties的对象
    		PropertySource<?> attached = sources.get(ATTACHED_PROPERTY_SOURCE_NAME);
    		if (attached != null && attached.getSource() != sources) { 
    			sources.remove(ATTACHED_PROPERTY_SOURCE_NAME);
    			attached = null;
    		}
    		if (attached == null) { 
          //新增属性配置源
    			sources.addFirst(new ConfigurationPropertySourcesPropertySource(ATTACHED_PROPERTY_SOURCE_NAME,
    					new SpringConfigurationPropertySources(sources)));
    		}
    	}

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GitHub源码：[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/20221120/00fb1ff06ebd4acdb48a075ddf4e563f.png
[https_github.com_mingyang66_spring-parent]: https://github.com/mingyang66/spring-parent