发布于 2017-11-08 20:43:04 | 53 次阅读 | 评论: 0 | 来源: 网友投递

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Spring Boot

Spring Boot 项目旨在简化创建产品级的 Spring 应用和服务。你可通过它来选择不同的 Spring 平台。可创建独立的 Java 应用和 Web 应用,同时提供了命令行工具来允许 'spring scripts'.


这篇文章主要介绍了Spring Boot启动过程完全解析(一),需要的朋友可以参考下

之前在排查一个线上问题时,不得不仔细跑了很多遍Spring Boot的代码,于是整理一下,我用的是1.4.3.RELEASE。

  首先,普通的入口,这没什么好说的,我就随便贴贴代码了:


SpringApplication.run(Application.class, args);
-->
  public static ConfigurableApplicationContext run(Object source, String... args) {
    return run(new Object[] { source }, args);
  }
  public static ConfigurableApplicationContext run(Object[] sources, String[] args) {
    return new SpringApplication(sources).run(args);
  }

   也就是一个静态方法,调用了构造函数创建实例,构造的参数是Object数组,这里new这个数组的时候传入了一个元素就是启动类的类对象实例(一般就是“new Object[] { Application.class” }),构造函数里调用了一个initialize方法。

  SpringApplication的initialize方法,首先在Object数组有值的情况下将数组放入一个final的类实例私有Object的Set集合中;然后用deduceWebEnvironment方法判断当前应用环境是否是web环境,判断逻辑是看Classpath是否同时存在javax.servlet.Servlet和org.springframework.web.context.ConfigurableWebApplicationContext,缺一就认为不是。然后,调用setInitializers方法,设置类实例的私有List<ApplicationContextInitializer<?>>类型变量initializers:


 public void setInitializers(
   Collection<? extends ApplicationContextInitializer<?>> initializers) {
  this.initializers = new ArrayList<ApplicationContextInitializer<?>>();
  this.initializers.addAll(initializers);
 }

  设置的时候会先new,也就是说这方法每次都是整体更换,不会追加。这个方法的参数都是各个模块中配置在META-INF/spring.factories中的key为org.springframework.context.ApplicationContextInitializer的值,这些类都是接口ApplicationContextInitializer<C extends ConfigurableApplicationContext>的泛型实现。


 private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type,
   Class<?>[] parameterTypes, Object... args) {
  ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
  // Use names and ensure unique to protect against duplicates
  Set<String> names = new LinkedHashSet<String>(
    SpringFactoriesLoader.loadFactoryNames(type, classLoader));
  List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
    classLoader, args, names);
  AnnotationAwareOrderComparator.sort(instances);
  return instances;
 }

  使用SpringFactoriesLoader.loadFactoryNames方法去取上面说的被配置的ApplicationContextInitializer的名字放进Set<String>中,并用反射创建这些名字的实例。

  setInitializers方法之后又是setInitializers,参数同上都是getSpringFactoriesInstances方法获取,只不过这次参数Class<T> type泛型类型是org.springframework.context.ApplicationListener。

   initialize方法的最后一个步是设置实例的Class<?>类型私有属性mainApplicationClass,获取设置值的方法deduceMainApplicationClass:


private Class<?> deduceMainApplicationClass() {
  try {
   StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
   for (StackTraceElement stackTraceElement : stackTrace) {
    if ("main".equals(stackTraceElement.getMethodName())) {
     return Class.forName(stackTraceElement.getClassName());
    }
   }
  }
  catch (ClassNotFoundException ex) {
   // Swallow and continue
  }
  return null;
 }

  实例化SpringApplication后调用了它的run实例方法(注意不是上面的静态方法)。一进run方法首先启动了StopWatch,这个StopWatch的功能在类的注释写可,大概意思是这是个简单的秒表,用于在开发过程中方便程序员调试性能等,非线程安全,不建议用于生产。configureHeadlessProperty设置使用Headless,对于只有远程登录使用的服务器来说这样性能要好一些。接着是加载用于这个run方法启动过程的监听器,依然是getSpringFactoriesInstances方法,这次的类型是org.springframework.boot.SpringApplicationRunListener:


# Run Listeners
org.springframework.boot.SpringApplicationRunListener=\
org.springframework.boot.context.event.EventPublishingRunListener
  


 SpringApplicationRunListeners(Log log,
   Collection<? extends SpringApplicationRunListener> listeners) {
  this.log = log;
  this.listeners = new ArrayList<SpringApplicationRunListener>(listeners);
 }

  先是加载所有可用监听,然后初始化SpringApplicationRunListeners对象,最后循环启动所有SpringApplicationRunListener监听。启动监听的方法:


 @Override
 public void started() {
  this.initialMulticaster
    .multicastEvent(new ApplicationStartedEvent(this.application, this.args));
 }

  ApplicationStartedEvent实例化传了两个参数,先看第一个参数this.application是怎么来的,实例的SpringApplication的run方法中,用于获取SpringApplicationRunListener,也就是前面说的getSpringFactoriesInstances被调用时:


 private SpringApplicationRunListeners getRunListeners(String[] args) {
  Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
  return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances(
    SpringApplicationRunListener.class, types, this, args));
 }

  getSpringFactoriesInstances方法的参数包含SpringApplication.class和this,这两个参数被传入createSpringFactoriesInstances方法:

  可以看到,是通过反射创建实例的时候,将SpringApplication中的this传进来EventPublishingRunListener构造的,然后EventPublishingRunListener构造:


public EventPublishingRunListener(SpringApplication application, String[] args) {
  this.application = application;
  this.args = args;
  this.initialMulticaster = new SimpleApplicationEventMulticaster();
  for (ApplicationListener<?> listener : application.getListeners()) {
   this.initialMulticaster.addApplicationListener(listener);
  }
 }

  最后在构造ApplicationStartedEvent时传给它的基类EventObject的protected不可序列化属性source。实例化ApplicationStartedEvent后instance.getClass()并包装为ResolvableType类型以保存类型信息,并将它和event作为参数传入SimpleApplicationEventMulticaster的multicastEvent方法。multicastEvent首先获取ApplicationListener,使用getApplicationListeners方法,这个方法中抛开对listener做了一些缓存类工作外,主要就是将事件和对应的监听器做了下是否支持的验证,返回通过了retrieveApplicationListeners中通过了supportsEvent验证的监听器集合,这里就体现出了ResolvableType的作用,它保存了类型的信息同时对泛型类型也支持。

   得到了这些匹配的监听器后,判断当前Executor是否被设置过,如果为null则同步循环执行所有:invokeListener(listener, event);如果不为null则:           


executor.execute(new Runnable() {
     @Override
     public void run() {
      invokeListener(listener, event);
     }
    });

  监听器执行的时候也会先判断是否是该由自己处理的事件,例如:


 @Override
 public void onApplicationEvent(ApplicationEvent event) {
  if (event instanceof ApplicationEnvironmentPreparedEvent) {
   onApplicationEnvironmentPreparedEvent(
     (ApplicationEnvironmentPreparedEvent) event);
  }
  if (event instanceof ApplicationPreparedEvent) {
   onApplicationPreparedEvent(event);
  }
 }

  监听启动后,只准备一些启动参数,和环境变量prepareEnvironment方法先是读取了应用的启动参数和profile配置,然后用listeners.environmentPrepared(environment)传给监听器:


 public void environmentPrepared(ConfigurableEnvironment environment) {
  this.initialMulticaster.multicastEvent(new ApplicationEnvironmentPreparedEvent(
    this.application, this.args, environment));
 }

   接着判断如果environment是org.springframework.web.context.ConfigurableWebEnvironment的实例,但webEnvironment不是true,也就是说存在org.springframework.web.context.ConfigurableWebEnvironmen但不存在javax.servlet.Servlet的情况,会多执行一步environment = convertToStandardEnvironment(environment)转换。

  之后的printBanner就不细说了,如果你在resource下自定义了一个banner.txt文件,启动时会输出内容,否则输出:

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v1.4.3.RELEASE)

   接着创建ConfigurableApplicationContext实例,方法也很简单,如果是web环境就BeanUtils.instantiate一个org.springframework.boot.context.embedded. AnnotationConfigEmbeddedWebApplicationContext的实例并强转为ConfigurableApplicationContext,否则用org.springframework.context.annotation. AnnotationConfigApplicationContext的实例强转。

  创建FailureAnalyzers实例,记录了ConfigurableApplicationContext实例中需要关注的部分,如果启动出错了可以据此分析,可以配置,具体的逻辑依然是老方法spring.factories:

  不同的Analyzer关注不同的部分,自己可以扩展配置,最后prepareFailureAnalyzers方法给所有Analyzer实例setBeanFactory(context.getBeanFactory()),一旦启动过程进入catch,被注册的Analyzer实例的analyze方法就会被触发执行,分析结果会被loggedExceptions.add(exception)加入到抛出的异常中:


private FailureAnalysis analyze(Throwable failure, List<FailureAnalyzer> analyzers) {
  for (FailureAnalyzer analyzer : analyzers) {
   FailureAnalysis analysis = analyzer.analyze(failure);
   if (analysis != null) {
    return analysis;
   }
  }
  return null;
 }

例如:NoSuchBeanDefinitionFailureAnalyzer


 @Override
 protected FailureAnalysis analyze(Throwable rootFailure,
   NoSuchBeanDefinitionException cause, String description) {
  if (cause.getNumberOfBeansFound() != 0) {
   return null;
  }
  List<AutoConfigurationResult> autoConfigurationResults = getAutoConfigurationResults(
    cause);
  StringBuilder message = new StringBuilder();
  message.append(String.format("%s required %s that could not be found.%n",
    description == null ? "A component" : description,
    getBeanDescription(cause)));
  if (!autoConfigurationResults.isEmpty()) {
   for (AutoConfigurationResult provider : autoConfigurationResults) {
    message.append(String.format("\t- %s%n", provider));
   }
  }
  String action = String.format("Consider %s %s in your configuration.",
    (!autoConfigurationResults.isEmpty()
      ? "revisiting the conditions above or defining" : "defining"),
    getBeanDescription(cause));
  return new FailureAnalysis(message.toString(), action, cause);
 }

   prepareContext方法中postProcessApplicationContext会在this.beanNameGenerator存在的情况下加载自定义命名策略,然后在this.resourceLoader存在的情况下为context设置resourceLoader和classLoader。applyInitializers方法调用之前加载的Initializer的实例并执行其initialize方法,例如加载环境变量信息、注册EmbeddedServletContainerInitializedEvent的监听、注册CachingMetadataReaderFactoryPostProcessor等。listeners.contextPrepared(context)由于EventPublishingRunListener的contextPrepared是空的,先不说了。logStartupInfo部分初始化了logger,然后根据配置情况打印了启动或运行以及profile是否配置的日志:


protected void logStartupInfo(boolean isRoot) {
  if (isRoot) {
   new StartupInfoLogger(this.mainApplicationClass)
     .logStarting(getApplicationLog());
  }
 }
 protected Log getApplicationLog() {
  if (this.mainApplicationClass == null) {
   return logger;
  }
  return LogFactory.getLog(this.mainApplicationClass);
 }
 public void logStarting(Log log) {
  Assert.notNull(log, "Log must not be null");
  if (log.isInfoEnabled()) {
   log.info(getStartupMessage());
  }
  if (log.isDebugEnabled()) {
   log.debug(getRunningMessage());
  }
 }
 protected void logStartupProfileInfo(ConfigurableApplicationContext context) {
  Log log = getApplicationLog();
  if (log.isInfoEnabled()) {
   String[] activeProfiles = context.getEnvironment().getActiveProfiles();
   if (ObjectUtils.isEmpty(activeProfiles)) {
    String[] defaultProfiles = context.getEnvironment().getDefaultProfiles();
    log.info("No active profile set, falling back to default profiles: "
      + StringUtils.arrayToCommaDelimitedString(defaultProfiles));
   }
   else {
    log.info("The following profiles are active: "
      + StringUtils.arrayToCommaDelimitedString(activeProfiles));
   }
  }
 }

   接着prepareContext中注册启动参数(applicationArguments)到bean工厂,包括logger、commandLineArgs等。然后加载bean定义的来源并根据其中配置加载bean,这里的sources就是初始化启动类时传进来的那个sources:


 BeanDefinitionLoader(BeanDefinitionRegistry registry, Object... sources) {
    Assert.notNull(registry, "Registry must not be null");
    Assert.notEmpty(sources, "Sources must not be empty");
    this.sources = sources;
    this.annotatedReader = new AnnotatedBeanDefinitionReader(registry);
    this.xmlReader = new XmlBeanDefinitionReader(registry);
    if (isGroovyPresent()) {
      this.groovyReader = new GroovyBeanDefinitionReader(registry);
    }
    this.scanner = new ClassPathBeanDefinitionScanner(registry);
    this.scanner.addExcludeFilter(new ClassExcludeFilter(sources));
  }

  注意下面的sources是待加载的,和上面这段不是同一个:


 public int load() {
    int count = 0;
    for (Object source : this.sources) {
      count += load(source);
    }
    return count;
  }
  private int load(Object source) {
    Assert.notNull(source, "Source must not be null");
    if (source instanceof Class<?>) {
      return load((Class<?>) source);
    }
    if (source instanceof Resource) {
      return load((Resource) source);
    }
    if (source instanceof Package) {
      return load((Package) source);
    }
    if (source instanceof CharSequence) {
      return load((CharSequence) source);
    }
    throw new IllegalArgumentException("Invalid source type " + source.getClass());
  }

  类型不同加载过程不同,其中Class<?>加载过程大概是通过BeanDefinitionLoader调用AnnotatedBeanDefinitionReader的registerBean方法:


public void registerBean(Class<?> annotatedClass, String name, Class<? extends Annotation>... qualifiers) {
    AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
    if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
      return;
    }
    ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
    abd.setScope(scopeMetadata.getScopeName());
    String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
    AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
    if (qualifiers != null) {
      for (Class<? extends Annotation> qualifier : qualifiers) {
        if (Primary.class == qualifier) {
          abd.setPrimary(true);
        }
        else if (Lazy.class == qualifier) {
          abd.setLazyInit(true);
        }
        else {
          abd.addQualifier(new AutowireCandidateQualifier(qualifier));
        }
      }
    }
    BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
    definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
    BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
  }

  可以看到有生成方法名,设置默认注入的实例、延迟以及过滤等等,注入的过程包括初始化一些信息,如构造、内部类、注解等: 


protected AbstractBeanDefinition(ConstructorArgumentValues cargs, MutablePropertyValues pvs) {
    setConstructorArgumentValues(cargs);
    setPropertyValues(pvs);
  }
  public StandardAnnotationMetadata(Class<?> introspectedClass, boolean nestedAnnotationsAsMap) {
    super(introspectedClass);
    this.annotations = introspectedClass.getAnnotations();
    this.nestedAnnotationsAsMap = nestedAnnotationsAsMap;
  }

   其他三种比如有的有输入流什么的就不细总结了,这部分介绍Spring IOC的相关文章应该不少。

   prepareContext方法最后listeners.contextLoaded(context),加载监听器到context并广播ApplicationPreparedEvent事件。

咱最近用的github:https://github.com/saaavsaaa

以上所述是小编给大家介绍的Spring Boot启动过程完全解析(一),希望对大家有所帮助,如果大家有任何疑问请给我留言,小编会及时回复大家的。在此也非常感谢大家对PHPERZ网站的支持!



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