【SpringBoot】容器启动

---

title: 【SpringBoot】容器启动
date: 2017-07-10 20:24:11
tags:

• Java
• Spring
  categories: Spring

---

Spring Boot 的启动前面说到了：

• 包文件启动：从JarLauncher的main方法启动，加载各种资源后，开启一个新的线程调用程序的main方法
• SpringApplication实例创建：判断是否是web环境，加载并实例化初始化器和监听器，查找main方法所在类
• 启动监听器：创建SpringApplicationRunListeners实例统一管理监听器。在启动过程中调用不同容器生命周期通知，创建不同的事件类型，由ApplicationEventMulticaster广播对应事件给ApplicationListener

前面做了各种准备工作就是为了最后的容器提供服务，本文以注释的形式记录一下 Spring Boot 容器的启动过程：

    public ConfigurableApplicationContext run(String... args) {
        // ...
        try {
            // 封装应用启动参数
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            // 准备环境
            ConfigurableEnvironment environment = prepareEnvironment(listeners,
                    applicationArguments);
            Banner printedBanner = printBanner(environment);
            // 创建容器
            context = createApplicationContext();
            analyzers = new FailureAnalyzers(context);
            // 准备容器
            prepareContext(context, environment, listeners, applicationArguments,
                    printedBanner);
            // 刷新容器
            refreshContext(context);
            // 运行runner
            afterRefresh(context, applicationArguments);
            listeners.finished(context, null);
            stopWatch.stop();
            if (this.logStartupInfo) {
                new StartupInfoLogger(this.mainApplicationClass)
                        .logStarted(getApplicationLog(), stopWatch);
            }
            return context;
        }
        catch (Throwable ex) {
            // ...
        }
    }

准备环境

    private ConfigurableEnvironment prepareEnvironment(
            SpringApplicationRunListeners listeners,
            ApplicationArguments applicationArguments) {
        // 创建环境
        ConfigurableEnvironment environment = getOrCreateEnvironment();
        // 配置环境
        configureEnvironment(environment, applicationArguments.getSourceArgs());
        // 监听器通知事件
        listeners.environmentPrepared(environment);
        // 处理非web环境
        if (isWebEnvironment(environment) && !this.webEnvironment) {
            environment = convertToStandardEnvironment(environment);
        }
        return environment;
    }

    private ConfigurableEnvironment getOrCreateEnvironment() {
        if (this.environment != null) {
            return this.environment;
        }
        if (this.webEnvironment) {
            return new StandardServletEnvironment();
        }
        return new StandardEnvironment();
    }

    protected void configureEnvironment(ConfigurableEnvironment environment,
            String[] args) {
        // 配置property
        configurePropertySources(environment, args);
        // 配置profiles
        configureProfiles(environment, args);
    }

    public static final String COMMAND_LINE_PROPERTY_SOURCE_NAME = "commandLineArgs";

    protected void configurePropertySources(ConfigurableEnvironment environment,
            String[] args) {
        MutablePropertySources sources = environment.getPropertySources();
        // 判断defaultProperties是否为空
        if (this.defaultProperties != null && !this.defaultProperties.isEmpty()) {
            // MutablePropertySources内部维护一个list>集合
            // addLast先removeIfPresent()然后把defaultProperties加到最后
            sources.addLast(
                    new MapPropertySource("defaultProperties", this.defaultProperties));
        }
        // 判断addCommandLineProperties ==true 和 args的长度
        if (this.addCommandLineProperties && args.length > 0) {
            // name=commandLineArgs
            String name = CommandLinePropertySource.COMMAND_LINE_PROPERTY_SOURCE_NAME;
            if (sources.contains(name)) {
                // 如果列表中包含，替换
                PropertySource source = sources.get(name);
                CompositePropertySource composite = new CompositePropertySource(name);
                composite.addPropertySource(new SimpleCommandLinePropertySource(
                        name + "-" + args.hashCode(), args));
                composite.addPropertySource(source);
                sources.replace(name, composite);
            }
            else {
                // 如果列表中不包含
                // 将配置信息添加在最前面，优先执行
                sources.addFirst(new SimpleCommandLinePropertySource(args));
            }
        }
    }

    protected void configureProfiles(ConfigurableEnvironment environment, String[] args) {
        // spring.active.profile值
        environment.getActiveProfiles();
        // But these ones should go first (last wins in a property key clash)
        Set profiles = new LinkedHashSet(this.additionalProfiles);
        profiles.addAll(Arrays.asList(environment.getActiveProfiles()));
        // 将additionalProfiles和getActiveProfiles的值加到一起设置到环境中
        environment.setActiveProfiles(profiles.toArray(new String[profiles.size()]));
    }

注释比较详细的说明了代码的作用了：

1. 创建环境
2. 配置环境
3. 监听器通知环境准备完毕
4. 对异常环境处理

上面代码注释跳过了web环境相关的配置，猜测里面会有servlet容器相关配置，这里跳过另开一文记录。

创建容器

public static final String DEFAULT_WEB_CONTEXT_CLASS = "org.springframework."
            + "boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext";

public static final String DEFAULT_CONTEXT_CLASS = "org.springframework.context."
            + "annotation.AnnotationConfigApplicationContext";

protected ConfigurableApplicationContext createApplicationContext() {
   Class contextClass = this.applicationContextClass;
   if (contextClass == null) {
      try {
         contextClass = Class.forName(this.webEnvironment
               ? DEFAULT_WEB_CONTEXT_CLASS : DEFAULT_CONTEXT_CLASS);
      }
      catch (ClassNotFoundException ex) {
         throw new IllegalStateException(
               "Unable create a default ApplicationContext, "
                     + "please specify an ApplicationContextClass",
               ex);
      }
   }
   return (ConfigurableApplicationContext) BeanUtils.instantiate(contextClass);
}

这部分没什么可说的，就是根据环境通过反射直接创建对应的容器的实例。

准备容器

private void prepareContext(ConfigurableApplicationContext context,
      ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
      ApplicationArguments applicationArguments, Banner printedBanner) {
   context.setEnvironment(environment);
   postProcessApplicationContext(context);
   applyInitializers(context);
   listeners.contextPrepared(context);
   if (this.logStartupInfo) {
      logStartupInfo(context.getParent() == null);
      logStartupProfileInfo(context);
   }

   // Add boot specific singleton beans
   context.getBeanFactory().registerSingleton("springApplicationArguments",
         applicationArguments);
   if (printedBanner != null) {
      context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
   }

   // Load the sources
   Set