死磕SpringBoot系列--- 第一章

死磕SpringBoot系列— 第一章

序

最近，想要了解一下spring boot的原理，加上重来没有好好的看一次spring的源码，什么东西都是只了解了个大概。想坚持看看spring源码。对于初学者来说，spring源码是最快提升自己的方式。Blog中记录一下学习的东西，这里会写很多章。看不懂的标注下来，可能随着工作年限的增加，再次回顾完善。
————Apollo写于工作1年

第一章

SpringBoot SpringApplication启动

从入口开始

//1.入口
public static void main(String[] args) {
  SpringApplication.run(DemointegrationApplication.class, args);
}
//2.进入SpringApplication
public static ConfigurableApplicationContext run(Class<?> primarySource,
    String... args) {
  return run(new Class<?>[] { primarySource }, args);
}

//3.新建SpringApplication，并调用run方法
public static ConfigurableApplicationContext run(Class<?>[] primarySources,
    String[] args) {
  return new SpringApplication(primarySources).run(args);
}

上文代码step.3中，我们首先看创建 SpringApplication 做了什么

@SuppressWarnings({ "unchecked", "rawtypes" })
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
  //1.此时resourceLoader=null
  this.resourceLoader = resourceLoader;
  Assert.notNull(primarySources, "PrimarySources must not be null");
  //2.设置主类
  this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
  //3.确定Application的类型
  this.webApplicationType = deduceWebApplicationType();
  //4。设置spring Initializer
  setInitializers((Collection) getSpringFactoriesInstances(
      ApplicationContextInitializer.class));
  //5. 设置spring Listener
  setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
  this.mainApplicationClass = deduceMainApplicationClass();
}

上面代码1和2没什么展开的，展开一下3,4,5。

  • 3.确定Application的类型:
    private WebApplicationType deduceWebApplicationType() {
//如果路径存在org.springframework.web.reactive.DispatcherHandler但不存在org.springframework.web.servlet.DispatcherServlet，就是REACTIVE
if (ClassUtils.isPresent(REACTIVE_WEB_ENVIRONMENT_CLASS, null)
  && !ClassUtils.isPresent(MVC_WEB_ENVIRONMENT_CLASS, null)) {
return WebApplicationType.REACTIVE;
}
//如果不存在javax.servlet.Servlet或者org.springframework.web.context.ConfigurableWebApplicationContext就是NONE类型app
for (String className : WEB_ENVIRONMENT_CLASSES) {
if (!ClassUtils.isPresent(className, null)) {
  return WebApplicationType.NONE;
}
}
//一般返回，servlet类型
return WebApplicationType.SERVLET;
}

  • 4.设置spring Initializer

    //这里type = ApplicationContextInitializer.class，就是要从SpringFactory中拿到ApplicationContextInitializer的实例
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
    return getSpringFactoriesInstances(type, new Class<?>[] {});
}

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
        Class<?>[] parameterTypes, Object... args) {
    //获取当前线程ClassLoader
    ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
    // Use names and ensure unique to protect against duplicates
    //4.1这里是获取实现了ApplicationContextInitializer的Set
    Set<String> names = new LinkedHashSet<>(
            SpringFactoriesLoader.loadFactoryNames(type, classLoader));
    //反射实例化
    List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
            classLoader, args, names);
    //根据bean的@Order sort一下
    AnnotationAwareOrderComparator.sort(instances);
    return instances;
}

    SpringFactoriesLoader是一个重点类，我们需要展开4.1、4.2、4.3

    • 4.1
      public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
    String factoryClassName = factoryClass.getName();
//比较关键的方法，这里调用下面的private方法
    return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
}
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
//首先去cache中取
    MultiValueMap<String, String> result = cache.get(classLoader);
    if (result != null)
        return result;
    try {
        //这里会去加载spring jar包下所有/META-INF/spring.factories文件里面的配置
        Enumeration<URL> urls = (classLoader != null ?
                classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
                ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
        result = new LinkedMultiValueMap<>();
        while (urls.hasMoreElements()) {
            URL url = urls.nextElement();
            UrlResource resource = new UrlResource(url);
            Properties properties = PropertiesLoaderUtils.loadProperties(resource);
            for (Map.Entry<?, ?> entry : properties.entrySet()) {
                List<String> factoryClassNames = Arrays.asList(
                        StringUtils.commaDelimitedListToStringArray((String) entry.getValue()));
                result.addAll((String) entry.getKey(), factoryClassNames);
            }
        }
        //把加载的资源放入cache下次调用加载速度
        cache.put(classLoader, result);
        return result;
    }
    catch (IOException ex) {
        throw new IllegalArgumentException("Unable to load factories from location [" +
                FACTORIES_RESOURCE_LOCATION + "]", ex);
    }
}
      这里的扫描，在我调用的时候，分别扫描了如下地方：
      jar:file:/C:/Users/Administrator/.m2/repository/org/springframework/spring-beans/5.0.4.RELEASE/spring-beans-5.0.4.RELEASE.jar!/META-INF/spring.factories
jar:file:/C:/Users/Administrator/.m2/repository/org/springframework/boot/spring-boot/2.0.0.RELEASE/spring-boot-2.0.0.RELEASE.jar!/META-INF/spring.factories
jar:file:/C:/Users/Administrator/.m2/repository/org/springframework/boot/spring-boot-autoconfigure/2.0.0.RELEASE/spring-boot-autoconfigure-2.0.0.RELEASE.jar!/META-INF/spring.factories
jar:file:/C:/Users/Administrator/.m2/repository/org/springframework/data/spring-data-mongodb/2.0.5.RELEASE/spring-data-mongodb-2.0.5.RELEASE.jar!/META-INF/spring.factories
jar:file:/C:/Users/Administrator/.m2/repository/org/springframework/data/spring-data-commons/2.0.5.RELEASE/spring-data-commons-2.0.5.RELEASE.jar!/META-INF/spring.factories
      得到的result中实现ApplicationContextInitializer.class的有如下
      org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,
org.springframework.boot.context.ContextIdApplicationContextInitializer,
org.springframework.boot.context.config.DelegatingApplicationContextInitializer,
org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer,
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,
org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener
      这里贴一个spring.factories文件，这里只是部分，其实就是定义接口与实现
      # Application Context Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\
org.springframework.boot.context.ContextIdApplicationContextInitializer,\
org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\
org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer
    • 5设置spring Listener
      这里跟4很像，就不展开了。都是通过spring.factory找接口实现类，再实例化.

到这里，我们new SpringApplication()就完成了，我们回顾一下创建SpringApplicationg过程

  1. 设置resourceLoader
  2. 设置primarySources主程序入口
  3. 判定项目类型，从WebApplicationType.REACTIVE，WebApplicationType.NONE，WebApplicationType.SERVLET中选取，一般web项目都是WebApplicationType.SERVLET。
  4. 扫描/META-INF/spring.factories文件，找到ApplicationContextInitializer接口的实现，并设置给SpringApplication的initializers。
  5. 扫描/META-INF/spring.factories文件，找到ApplicationListener接口的实现，并设置给SpringApplication的listeners。
  6. 设置主程序class

SpringApplication创建完成后，我们调用run核心方法。见下一章