本文基于Spring Boot版本1.3.3, 使用了spring-boot-starter-web。
配置完成后,编写了代码如下:
@SpringBootApplicationpublic class Application { public static void main(String[] args) { SpringApplication.run(Application.class, args); } }@RestControllerpublic class RootController { public static final String PATH_ROOT = "/"; @RequestMapping(PATH_ROOT) public String welcome() { return "Welcome!"; } }
虽然只有几行代码,但是这已经是一个完整的Web程序,当访问url的path部分为"/"时,返回字符串"Welcome!"。
首先是一个非常普通的java程序入口,一个符合约定的静态main方法。在这个main方法中,调用了SpringApplication的静态run方法,并将Application类对象和main方法的参数args作为参数传递了进去。
然后是一个使用了两个Spring注解的RootController类,我们在main方法中,没有直接使用这个类。
以下代码摘自:org.springframework.boot.SpringApplicationpublic 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); }
在这个静态方法中,创建SpringApplication对象,并调用该对象的run方法。
以下代码摘自:org.springframework.boot.SpringApplicationpublic SpringApplication(Object... sources) { initialize(sources); }private void initialize(Object[] sources) { // 为成员变量sources赋值 if (sources != null && sources.length > 0) { this.sources.addAll(Arrays.asList(sources)); } this.webEnvironment = deduceWebEnvironment(); setInitializers((Collection) getSpringFactoriesInstances( ApplicationContextInitializer.class)); setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); this.mainApplicationClass = deduceMainApplicationClass(); }
构造函数中调用initialize方法,初始化SpringApplication对象的成员变量sources,webEnvironment,initializers,listeners,mainApplicationClass。sources的赋值比较简单,就是我们传给SpringApplication.run方法的参数。剩下的几个,我们依次来看看是怎么做的。
以下代码摘自:org.springframework.boot.SpringApplicationprivate boolean webEnvironment; private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet", "org.springframework.web.context.ConfigurableWebApplicationContext" };private void initialize(Object[] sources) { ... // 为成员变量webEnvironment赋值 this.webEnvironment = deduceWebEnvironment(); ... }private boolean deduceWebEnvironment() { for (String className : WEB_ENVIRONMENT_CLASSES) { if (!ClassUtils.isPresent(className, null)) { return false; } } return true; }
可以看到webEnvironment是一个boolean,该成员变量用来表示当前应用程序是不是一个Web应用程序。那么怎么决定当前应用程序是否Web应用程序呢,是通过在classpath中查看是否存在WEB_ENVIRONMENT_CLASSES这个数组中所包含的类,如果存在那么当前程序即是一个Web应用程序,反之则不然。
在本文的例子中webEnvironment的值为true。
initializers成员变量,是一个ApplicationContextInitializer类型对象的集合。 顾名思义,ApplicationContextInitializer是一个可以用来初始化ApplicationContext的接口。
以下代码摘自:org.springframework.boot.SpringApplicationprivate List<ApplicationContextInitializer<?>> initializers;private void initialize(Object[] sources) { ... // 为成员变量initializers赋值 setInitializers((Collection) getSpringFactoriesInstances( ApplicationContextInitializer.class)); ... }public void setInitializers( Collection<? extends ApplicationContextInitializer<?>> initializers) { this.initializers = new ArrayList<ApplicationContextInitializer<?>>(); this.initializers.addAll(initializers); }
可以看到,关键是调用getSpringFactoriesInstances(ApplicationContextInitializer.class),来获取ApplicationContextInitializer类型对象的列表。
以下代码摘自:org.springframework.boot.SpringApplicationprivate <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type) { return getSpringFactoriesInstances(type, new Class<?>[] {}); }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; }
在该方法中,首先通过调用SpringFactoriesLoader.loadFactoryNames(type, classLoader)来获取所有Spring Factories的名字,然后调用createSpringFactoriesInstances方法根据读取到的名字创建对象。最后会将创建好的对象列表排序并返回。
以下代码摘自:org.springframework.core.io.support.SpringFactoriesLoaderpublic static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) { String factoryClassName = factoryClass.getName(); try { Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) : ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION)); List<String> result = new ArrayList<String>(); while (urls.hasMoreElements()) { URL url = urls.nextElement(); Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url)); String factoryClassNames = properties.getProperty(factoryClassName); result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames))); } return result; } catch (IOException ex) { throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() + "] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex); } }
可以看到,是从一个名字叫spring.factories的资源文件中,读取key为org.springframework.context.ApplicationContextInitializer的value。而spring.factories的部分内容如下:
以下内容摘自spring-boot-1.3.3.RELEASE.jar中的资源文件META-INF/spring.factories# 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.context.web.ServerPortInfoApplicationContextInitializer
可以看到,最近的得到的,是ConfigurationWarningsApplicationContextInitializer,ContextIdApplicationContextInitializer,DelegatingApplicationContextInitializer,ServerPortInfoApplicationContextInitializer这四个类的名字。
接下来会调用createSpringFactoriesInstances来创建ApplicationContextInitializer实例。
以下代码摘自:org.springframework.boot.SpringApplicationprivate <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args, Set<String> names) { List<T> instances = new ArrayList<T>(names.size()); for (String name : names) { try { Class<?> instanceClass = ClassUtils.forName(name, classLoader); Assert.isAssignable(type, instanceClass); Constructor<?> constructor = instanceClass.getConstructor(parameterTypes); T instance = (T) constructor.newInstance(args); instances.add(instance); } catch (Throwable ex) { throw new IllegalArgumentException( "Cannot instantiate " + type + " : " + name, ex); } } return instances; }
所以在我们的例子中,SpringApplication对象的成员变量initalizers就被初始化为,ConfigurationWarningsApplicationContextInitializer,ContextIdApplicationContextInitializer,DelegatingApplicationContextInitializer,ServerPortInfoApplicationContextInitializer这四个类的对象组成的list。
下图画出了加载的ApplicationContextInitializer,并说明了他们的作用。至于何时应用他们,且听后面慢慢分解。
以下代码摘自:org.springframework.boot.SpringApplicationprivate List<ApplicationListener<?>> listeners;private void initialize(Object[] sources) { ... // 为成员变量listeners赋值 setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); ... }public void setListeners(Collection<? extends ApplicationListener<?>> listeners) { this.listeners = new ArrayList<ApplicationListener<?>>(); this.listeners.addAll(listeners); }
listeners成员变量,是一个ApplicationListener<?>类型对象的集合。可以看到获取该成员变量内容使用的是跟成员变量initializers一样的方法,只不过传入的类型从ApplicationContextInitializer.class变成了ApplicationListener.class。
看一下spring.factories中的相关内容:
以下内容摘自spring-boot-1.3.3.RELEASE.jar中的资源文件META-INF/spring.factories# Application Listeners org.springframework.context.ApplicationListener=\ org.springframework.boot.builder.ParentContextCloserApplicationListener,\ org.springframework.boot.context.FileEncodingApplicationListener,\ org.springframework.boot.context.config.AnsiOutputApplicationListener,\ org.springframework.boot.context.config.ConfigFileApplicationListener,\ org.springframework.boot.context.config.DelegatingApplicationListener,\ org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener,\ org.springframework.boot.logging.ClasspathLoggingApplicationListener,\ org.springframework.boot.logging.LoggingApplicationListener
也就是说,在我们的例子中,listener最终会被初始化为ParentContextCloserApplicationListener,FileEncodingApplicationListener,AnsiOutputApplicationListener,ConfigFileApplicationListener,DelegatingApplicationListener,LiquibaseServiceLocatorApplicationListener,ClasspathLoggingApplicationListener,LoggingApplicationListener这几个类的对象组成的list。
下图画出了加载的ApplicationListener,并说明了他们的作用。至于他们何时会被触发,等事件出现时,我们再说明。
以下代码摘自:org.springframework.boot.SpringApplicationprivate Class<?> mainApplicationClass;private void initialize(Object[] sources) { ... // 为成员变量mainApplicationClass赋值 this.mainApplicationClass = 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; }
在deduceMainApplicationClass方法中,通过获取当前调用栈,找到入口方法main所在的类,并将其复制给SpringApplication对象的成员变量mainApplicationClass。在我们的例子中mainApplicationClass即是我们自己编写的Application类。
经过上面的初始化过程,我们已经有了一个SpringApplication对象,根据SpringApplication类的静态run方法一节中的分析,接下来会调用SpringApplication对象的run方法。我们接下来就分析这个对象的run方法。
以下代码摘自:org.springframework.boot.SpringApplicationpublic ConfigurableApplicationContext run(String... args) { StopWatch stopWatch = new StopWatch(); stopWatch.start(); ConfigurableApplicationContext context = null; configureHeadlessProperty(); SpringApplicationRunListeners listeners = getRunListeners(args); listeners.started(); try { ApplicationArguments applicationArguments = new DefaultApplicationArguments( args); context = createAndRefreshContext(listeners, applicationArguments); afterRefresh(context, applicationArguments); listeners.finished(context, null); stopWatch.stop(); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass) .logStarted(getApplicationLog(), stopWatch); } return context; } catch (Throwable ex) { handleRunFailure(context, listeners, ex); throw new IllegalStateException(ex); } }
可变个数参数args即是我们整个应用程序的入口main方法的参数,在我们的例子中,参数个数为零。
StopWatch是来自org.springframework.util的工具类,可以用来方便的记录程序的运行时间。
SpringApplication对象的run方法创建并刷新ApplicationContext,算是开始进入正题了。下面按照执行顺序,介绍该方法所做的工作。
以下代码摘自:org.springframework.boot.SpringApplicationprivate static final String SYSTEM_PROPERTY_JAVA_AWT_HEADLESS = "java.awt.headless";private boolean headless = true;public ConfigurableApplicationContext run(String... args) { ... //设置headless模式 configureHeadlessProperty(); ... }private void configureHeadlessProperty() { System.setProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, System.getProperty( SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, Boolean.toString(this.headless))); }
实际上是就是设置系统属性java.awt.headless,在我们的例子中该属性会被设置为true,因为我们开发的是服务器程序,一般运行在没有显示器和键盘的环境。关于java中的headless模式,更多信息可以参考这里。
以下代码摘自:org.springframework.boot.SpringApplicationpublic ConfigurableApplicationContext run(String... args) { ... SpringApplicationRunListeners listeners = getRunListeners(args); listeners.started(); /** * 创建并刷新ApplicationContext * context = createAndRefreshContext(listeners, applicationArguments); **/ listeners.finished(context, null); ... }private SpringApplicationRunListeners getRunListeners(String[] args) { Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class }; return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances( SpringApplicationRunListener.class, types, this, args)); }
run方法中,加载了一系列SpringApplicationRunListener对象,在创建和更新ApplicationContext方法前后分别调用了listeners对象的started方法和finished方法, 并在创建和刷新ApplicationContext时,将listeners作为参数传递到了createAndRefreshContext方法中,以便在创建和刷新ApplicationContext的不同阶段,调用listeners的相应方法以执行操作。所以,所谓的SpringApplicationRunListeners实际上就是在SpringApplication对象的run方法执行的不同阶段,去执行一些操作,并且这些操作是可配置的。
同时,可以看到,加载SpringApplicationRunListener时,使用的是跟加载ApplicationContextInitializer和ApplicationListener时一样的方法。那么加载了什么,就可以从spring.factories文件中看到了:
以下内容摘自spring-boot-1.3.3.RELEASE.jar中的资源文件META-INF/spring.factories# Run Listeners org.springframework.boot.SpringApplicationRunListener=\ org.springframework.boot.context.event.EventPublishingRunListener
可以看到,在我们的例子中加载的是org.springframework.boot.context.event.EventPublishingRunListener。我们看一看这个SpringApplicationRunListener究竟做了点什么工作了?
以下代码摘自:org.springframework.boot.context.event.EventPublishingRunListenerpublic EventPublishingRunListener(SpringApplication application, String[] args) { this.application = application; this.args = args; this.multicaster = new SimpleApplicationEventMulticaster(); for (ApplicationListener<?> listener : application.getListeners()) { this.multicaster.addApplicationListener(listener); } }@Overridepublic void started() { publishEvent(new ApplicationStartedEvent(this.application, this.args)); }@Overridepublic void environmentPrepared(ConfigurableEnvironment environment) { publishEvent(new ApplicationEnvironmentPreparedEvent(this.application, this.args, environment)); }@Overridepublic void contextPrepared(ConfigurableApplicationContext context) { registerApplicationEventMulticaster(context); }@Overridepublic void contextLoaded(ConfigurableApplicationContext context) { for (ApplicationListener<?> listener : this.application.getListeners()) { if (listener instanceof ApplicationContextAware) { ((ApplicationContextAware) listener).setApplicationContext(context); } context.addApplicationListener(listener); } publishEvent(new ApplicationPreparedEvent(this.application, this.args, context)); }@Overridepublic void finished(ConfigurableApplicationContext context, Throwable exception) { publishEvent(getFinishedEvent(context, exception)); }
EventPublishingRunListener在对象初始化时,将SpringApplication对象的成员变量listeners全都保存下来,然后在自己的public方法被调用时,发布相应的事件,或执行相应的操作。可以说这个RunListener是在SpringApplication对象的run方法执行到不同的阶段时,发布相应的event给SpringApplication对象的成员变量listeners中记录的事件监听器。
下图画出了SpringApplicationRunListeners相关的类结构,虽然我们的例子中只有一个SpringApplicationRunListener,但在这样的设计下,想要扩展是非常容易的!
接下来,我们看一下在调用listeners的started方法。在我们的例子中,也就是发布了ApplicationStartedEvent时,我们已经加载的事件监听器都做了什么操作。至于其它事件的发布,我们按照代码执行的顺序在后面的章节在介绍。
ParentContextCloserApplicationListener不监听ApplicationStartedEvent,没有操作;
FileEncodingApplicationListener不监听ApplicationStartedEvent,没有操作;
AnsiOutputApplicationListener不监听ApplicationStartedEvent,没有操作;
ConfigFileApplicationListener不监听ApplicationStartedEvent,没有操作;
DelegatingApplicationListener不监听ApplicationStartedEvent,没有操作;
LiquibaseServiceLocatorApplicationListener监听ApplicationStartedEvent,会检查classpath中是否有liquibase.servicelocator.ServiceLocator并做相应操作;
以下代码摘自:org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener@Overridepublic void onApplicationEvent(ApplicationStartedEvent event) { if (ClassUtils.isPresent("liquibase.servicelocator.ServiceLocator", null)) { new LiquibasePresent().replaceServiceLocator(); } }
我们的例子中,classpath中不存在liquibase,所以不执行任何操作。
ClasspathLoggingApplicationListener监听ApplicationStartedEvent,会打印classpath到debug日志;
@Overridepublic void onApplicationEvent(ApplicationEvent event) { if (event instanceof ApplicationStartedEvent) { if (this.logger.isDebugEnabled()) { this.logger.debug("Application started with classpath: " + getClasspath()); } ... }private String getClasspath() { ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); if (classLoader instanceof URLClassLoader) { return Arrays.toString(((URLClassLoader) classLoader).getURLs()); } return "unknown"; }
因为是debug级别的日志,而SpringBoot的默认日志级别是info级,所以我们在控制台不会看到classpath的输出。
LoggingApplicationListener监听ApplicationStartedEvent,会根据classpath中的类情况创建相应的日志系统对象,并执行一些初始化之前的操作;
@Overridepublic void onApplicationEvent(ApplicationEvent event) { if (event instanceof ApplicationStartedEvent) { onApplicationStartedEvent((ApplicationStartedEvent) event); } ... }private void onApplicationStartedEvent(ApplicationStartedEvent event) { this.loggingSystem = LoggingSystem .get(event.getSpringApplication().getClassLoader()); this.loggingSystem.beforeInitialize(); }
我们的例子中,创建的是org.springframework.boot.logging.logback.LogbackLoggingSystem类的对象,Logback是SpringBoot默认采用的日志系统。下图画出了SpringBoot中的日志系统体系:
好了,ApplicationStartedEvent事件的处理这样就结束了。以后在介绍事件处理的时候,我们只介绍监听该事件的监听器的操作,而不监听的,就不再说明了。
以下代码摘自:org.springframework.boot.SpringApplicationpublic ConfigurableApplicationContext run(String... args) { ... try { ApplicationArguments applicationArguments = new DefaultApplicationArguments( args); context = createAndRefreshContext(listeners, applicationArguments); afterRefresh(context, applicationArguments); ... } catch (Throwable ex) { handleRunFailure(context, listeners, ex); throw new IllegalStateException(ex); } }
首先是创建一个DefaultApplicationArguments对象,之后调用createAndRefreshContext方法创建并刷新一个ApplicationContext,最后调用afterRefresh方法在刷新之后做一些操作。
以下代码摘自:org.springframework.boot.DefaultApplicationArgumentsDefaultApplicationArguments(String[] args) { Assert.notNull(args, "Args must not be null"); this.source = new Source(args); this.args = args; }private static class Source extends SimpleCommandLinePropertySource { Source(String[] args) { super(args); } ... } 以下代码摘自:org.springframework.core.env.SimpleCommandLinePropertySourcepublic SimpleCommandLinePropertySource(String... args) { super(new SimpleCommandLineArgsParser().parse(args)); }
可以看到是把main函数的args参数当做一个PropertySource来解析。我们的例子中,args的长度为0,所以这里创建的DefaultApplicationArguments也没有实际的内容。
以下代码摘自:org.springframework.boot.SpringApplicationprivate ConfigurableEnvironment environment;private boolean webEnvironment;private ConfigurableApplicationContext createAndRefreshContext( SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) { ConfigurableApplicationContext context; // 创建并配置Environment ConfigurableEnvironment environment = getOrCreateEnvironment(); configureEnvironment(environment, applicationArguments.getSourceArgs()); listeners.environmentPrepared(environment); if (isWebEnvironment(environment) && !this.webEnvironment) { environment = convertToStandardEnvironment(environment); } ... return context; }private ConfigurableEnvironment getOrCreateEnvironment() { if (this.environment != null) { return this.environment; } if (this.webEnvironment) { return new StandardServletEnvironment(); } return new StandardEnvironment(); }
Spring Application的Environment代表着程序运行的环境,主要包含了两种信息,一种是profiles,用来描述哪些bean definitions是可用的;一种是properties,用来描述系统的配置,其来源可能是配置文件、JVM属性文件、操作系统环境变量等等。
首先要调用getOrCreateEnvironment方法获取一个Environment对象。在我们的例子中,执行到此处时,environment成员变量为null,而webEnvironment成员变量的值为true,所以会创建一个StandardServletEnvironment对象并返回。
之后是调用configureEnvironment方法来配置上一步获取的Environment对象,代码如下:
以下代码摘自:org.springframework.boot.SpringApplicationprivate Map<String, Object> defaultProperties;private boolean addCommandLineProperties = true;private Set<String> additionalProfiles = new HashSet<String>();protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) { configurePropertySources(environment, args); configureProfiles(environment, args); }protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) { MutablePropertySources sources = environment.getPropertySources(); if (this.defaultProperties != null && !this.defaultProperties.isEmpty()) { sources.addLast( new MapPropertySource("defaultProperties", this.defaultProperties)); } 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( name + "-" + args.hashCode(), args)); composite.addPropertySource(source); sources.replace(name, composite); } else { sources.addFirst(new SimpleCommandLinePropertySource(args)); } } }protected void configureProfiles(ConfigurableEnvironment environment, String[] args) { environment.getActiveProfiles(); // ensure they are initialized // But these ones should go first (last wins in a property key clash) Set<String> profiles = new LinkedHashSet<String>(this.additionalProfiles); profiles.addAll(Arrays.asList(environment.getActiveProfiles())); environment.setActiveProfiles(profiles.toArray(new String[profiles.size()])); }
configureEnvironment方法先是调用configurePropertySources来配置properties,然后调用configureProfiles来配置profiles。
configurePropertySources首先查看SpringApplication对象的成员变量defaultProperties,如果该变量非null且内容非空,则将其加入到Environment的PropertySource列表的最后。然后查看SpringApplication对象的成员变量addCommandLineProperties和main函数的参数args,如果设置了addCommandLineProperties=true,且args个数大于0,那么就构造一个由main函数的参数组成的PropertySource放到Environment的PropertySource列表的最前面(这就能保证,我们通过main函数的参数来做的配置是最优先的,可以覆盖其他配置)。在我们的例子中,由于没有配置defaultProperties且main函数的参数args个数为0,所以这个函数什么也不做。
configureProfiles首先会读取Properties中key为spring.profiles.active的配置项,配置到Environment,然后再将SpringApplication对象的成员变量additionalProfiles加入到Environment的active profiles配置中。在我们的例子中,配置文件里没有spring.profiles.active的配置项,而SpringApplication对象的成员变量additionalProfiles也是一个空的集合,所以这个函数没有配置任何active profile。
到现在,Environment就算是配置完成了。接下来调用SpringApplicationRunListeners类的对象listeners发布ApplicationEnvironmentPreparedEvent事件:
以下代码摘自:org.springframework.boot.context.event.EventPublishingRunListener@Overridepublic void environmentPrepared(ConfigurableEnvironment environment) { publishEvent(new ApplicationEnvironmentPreparedEvent(this.application, this.args, environment)); }
好,现在来看一看我们加载的ApplicationListener对象都有哪些响应了这个事件,做了什么操作:
FileEncodingApplicationListener响应该事件,检查file.encoding配置是否与spring.mandatory_file_encoding一致:
以下代码摘自:org.springframework.boot.context.FileEncodingApplicationListener@Overridepublic void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) { RelaxedPropertyResolver resolver = new RelaxedPropertyResolver( event.getEnvironment(), "spring."); if (resolver.containsProperty("mandatoryFileEncoding")) { String encoding = System.getProperty("file.encoding"); String desired = resolver.getProperty("mandatoryFileEncoding"); if (encoding != null && !desired.equalsIgnoreCase(encoding)) { logger.error("System property 'file.encoding' is currently '" + encoding + "'. It should be '" + desired + "' (as defined in 'spring.mandatoryFileEncoding')."); logger.error("Environment variable LANG is '" + System.getenv("LANG") + "'. You could use a locale setting that matches encoding='" + desired + "'."); logger.error("Environment variable LC_ALL is '" + System.getenv("LC_ALL") + "'. You could use a locale setting that matches encoding='" + desired + "'."); throw new IllegalStateException( "The Java Virtual Machine has not been configured to use the " + "desired default character encoding (" + desired + ")."); } } }
在我们的例子中,因为没有spring.mandatory_file_encoding的配置,所以这个响应方法什么都不做。
AnsiOutputApplicationListener响应该事件,根据spring.output.ansi.enabled和spring.output.ansi.console-available对AnsiOutput类做相应配置:
以下代码摘自:org.springframework.boot.context.config.AnsiOutputApplicationListener@Overridepublic void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) { RelaxedPropertyResolver resolver = new RelaxedPropertyResolver( event.getEnvironment(), "spring.output.ansi."); if (resolver.containsProperty("enabled")) { String enabled = resolver.getProperty("enabled"); AnsiOutput.setEnabled(Enum.valueOf(Enabled.class, enabled.toUpperCase())); } if (resolver.containsProperty("console-available")) { AnsiOutput.setConsoleAvailable( resolver.getProperty("console-available", Boolean.class)); } }
我们的例子中,这两项配置都是空的,所以这个响应方法什么都不做。
ConfigFileApplicationListener加载该事件,从一些约定的位置加载一些配置文件,而且这些位置是可配置的。
以下代码摘自:org.springframework.boot.context.config.ConfigFileApplicationListener@Overridepublic void onApplicationEvent(ApplicationEvent event) { if (event instanceof ApplicationEnvironmentPreparedEvent) { onApplicationEnvironmentPreparedEvent( (ApplicationEnvironmentPreparedEvent) event); } if (event instanceof ApplicationPreparedEvent) { onApplicationPreparedEvent(event); } }private void onApplicationEnvironmentPreparedEvent( ApplicationEnvironmentPreparedEvent event) { List<EnvironmentPostProcessor> postProcessors = loadPostProcessors(); postProcessors.add(this); AnnotationAwareOrderComparator.sort(postProcessors); for (EnvironmentPostProcessor postProcessor : postProcessors) { postProcessor.postProcessEnvironment(event.getEnvironment(), event.getSpringApplication()); } }List<EnvironmentPostProcessor> loadPostProcessors() { return SpringFactoriesLoader.loadFactories(EnvironmentPostProcessor.class, getClass().getClassLoader()); } 以下内容摘自spring-boot-1.3.3.RELEASE.jar中的资源文件META-INF/spring.factories# Environment Post Processors org.springframework.boot.env.EnvironmentPostProcessor=\ org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\ org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor
可以看到,ConfigFileApplicationListener从META-INF/spring.factories文件中读取EnvironmentPostProcessor配置,加载相应的EnvironmentPostProcessor类的对象,并调用其postProcessEnvironment方法。在我们的例子中,会加载CloudFoundryVcapEnvironmentPostProcessor和SpringApplicationJsonEnvironmentPostProcessor并执行,由于我们的例子中没有CloudFoundry和Json的配置,所以这个响应,不会加载任何的配置文件到Environment中来。
DelegatingApplicationListener响应该事件,将配置文件中key为context.listener.classes的配置项,加载在成员变量multicaster中:
以下内容摘自:org.springframework.boot.context.config.DelegatingApplicationListenerprivate static final String PROPERTY_NAME = "context.listener.classes";private SimpleApplicationEventMulticaster multicaster;@Overridepublic void onApplicationEvent(ApplicationEvent event) { if (event instanceof ApplicationEnvironmentPreparedEvent) { List<ApplicationListener<ApplicationEvent>> delegates = getListeners( ((ApplicationEnvironmentPreparedEvent) event).getEnvironment()); if (delegates.isEmpty()) { return; } this.multicaster = new SimpleApplicationEventMulticaster(); for (ApplicationListener<ApplicationEvent> listener : delegates) { this.multicaster.addApplicationListener(listener); } } if (this.multicaster != null) { this.multicaster.multicastEvent(event); } }@SuppressWarnings("unchecked")private List<ApplicationListener<ApplicationEvent>> getListeners( ConfigurableEnvironment env) { String classNames = env.getProperty(PROPERTY_NAME); List<ApplicationListener<ApplicationEvent>> listeners = new ArrayList<ApplicationListener<ApplicationEvent>>(); if (StringUtils.hasLength(classNames)) { for (String className : StringUtils.commaDelimitedListToSet(classNames)) { try { Class<?> clazz = ClassUtils.forName(className, ClassUtils.getDefaultClassLoader()); Assert.isAssignable(ApplicationListener.class, clazz, "class [" + className + "] must implement ApplicationListener"); listeners.add((ApplicationListener<ApplicationEvent>) BeanUtils .instantiateClass(clazz)); } catch (Exception ex) { throw new ApplicationContextException( "Failed to load context listener class [" + className + "]", ex); } } } AnnotationAwareOrderComparator.sort(listeners); return listeners; }
我们的例子中,因为没有key为context.listener.classes的Property,所以不会加载任何listener到该监听器中。
LoggingApplicationListener响应该事件,并对在ApplicationStarted时加载的LoggingSystem做一些初始化工作:
以下代码摘自:org.springframework.boot.logging.LoggingApplicationListener@Overridepublic void onApplicationEvent(ApplicationEvent event) { if (event instanceof ApplicationStartedEvent) { onApplicationStartedEvent((ApplicationStartedEvent) event); } else if (event instanceof ApplicationEnvironmentPreparedEvent) { onApplicationEnvironmentPreparedEvent( (ApplicationEnvironmentPreparedEvent) event); } else if (event instanceof ApplicationPreparedEvent) { onApplicationPreparedEvent((ApplicationPreparedEvent) event); } else if (event instanceof ContextClosedEvent && ((ContextClosedEvent) event) .getApplicationContext().getParent() == null) { onContextClosedEvent(); } }private void onApplicationEnvironmentPreparedEvent( ApplicationEnvironmentPreparedEvent event) { if (this.loggingSystem == null) { this.loggingSystem = LoggingSystem .get(event.getSpringApplication().getClassLoader()); } initialize(event.getEnvironment(), event.getSpringApplication().getClassLoader()); }protected void initialize(ConfigurableEnvironment environment, ClassLoader classLoader) { LogFile logFile = LogFile.get(environment); setSystemProperties(environment, logFile); initializeEarlyLoggingLevel(environment); initializeSystem(environment, this.loggingSystem, logFile); initializeFinalLoggingLevels(environment, this.loggingSystem); registerShutdownHookIfNecessary(environment, this.loggingSystem); }
在我们的例子中,是对加载的LogbackLoggingSystem做一些初始化工作。关于日志系统更详细的讨论,值得再写一篇文章,就不在这里展开讨论了。
以下代码摘自:org.springframework.boot.SpringApplicationprivate Banner banner;private Banner.Mode bannerMode = Banner.Mode.CONSOLE;public static final String BANNER_LOCATION_PROPERTY = "banner.location";public static final String BANNER_LOCATION_PROPERTY_VALUE = "banner.txt";private static final Banner DEFAULT_BANNER = new SpringBootBanner();private ConfigurableApplicationContext createAndRefreshContext( SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) { ... if (this.bannerMode != Banner.Mode.OFF) { printBanner(environment); } ... }protected void printBanner(Environment environment) { Banner selectedBanner = selectBanner(environment); if (this.bannerMode == Banner.Mode.LOG) { try { logger.info(createStringFromBanner(selectedBanner, environment)); } catch (UnsupportedEncodingException ex) { logger.warn("Failed to create String for banner", ex); } } else { selectedBanner.printBanner(environment, this.mainApplicationClass, System.out); } }private Banner selectBanner(Environment environment) { String location = environment.getProperty(BANNER_LOCATION_PROPERTY, BANNER_LOCATION_PROPERTY_VALUE); ResourceLoader resourceLoader = this.resourceLoader != null ? this.resourceLoader : new DefaultResourceLoader(getClassLoader()); Resource resource = resourceLoader.getResource(location); if (resource.exists()) { return new ResourceBanner(resource); } if (this.banner != null) { return this.banner; } return DEFAULT_BANNER; }private String createStringFromBanner(Banner banner, Environment environment) throws UnsupportedEncodingException { ByteArrayOutputStream baos = new ByteArrayOutputStream(); banner.printBanner(environment, this.mainApplicationClass, new PrintStream(baos)); String charset = environment.getProperty("banner.charset", "UTF-8"); return baos.toString(charset); }
printBanner方法中,首先会调用selectBanner方法得到一个banner对象,然后判断bannerMode的类型,如果是Banner.Mode.LOG,那么将banner对象转换为字符串,打印一条info日志,否则的话,调用banner对象的printbanner方法,将banner打印到标准输出System.out。
在我们的例子中,bannerMode是Banner.Mode.Console,而且也不曾提供过banner.txt这样的资源文件。所以selectBanner方法中得到到便是默认的banner对象,即SpringBootBanner类的对象:
以下代码摘自:org.springframework.boot.SpringBootBannerprivate static final String[] BANNER = { "", " . ____ _ __ _ _", " /\\\\ / ___'_ __ _ _(_)_ __ __ _ \\ \\ \\ \\", "( ( )\\___ | '_ | '_| | '_ \\/ _` | \\ \\ \\ \\", " \\\\/ ___)| |_)| | | | | || (_| | ) ) ) )", " ' |____| .__|_| |_|_| |_\\__, | / / / /", " =========|_|==============|___/=/_/_/_/" };private static final String SPRING_BOOT = " :: Spring Boot :: ";private static final int STRAP_LINE_SIZE = 42;@Overridepublic void printBanner(Environment environment, Class<?> sourceClass, PrintStream printStream) { for (String line : BANNER) { printStream.println(line); } String version = SpringBootVersion.getVersion(); version = (version == null ? "" : " (v" + version + ")"); String padding = ""; while (padding.length() < STRAP_LINE_SIZE - (version.length() + SPRING_BOOT.length())) { padding += " "; } printStream.println(AnsiOutput.toString(AnsiColor.GREEN, SPRING_BOOT, AnsiColor.DEFAULT, padding, AnsiStyle.FAINT, version)); printStream.println(); }
先打印个Spring的图形,然后打印个Spring Boot的文本,再然后打印一下Spring Boot的版本。会在控制台看到如下输出:
以下内容是程序启动后在console的输出: . ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \ ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: (v1.3.3.RELEASE)
我的天。分析启动流程这么久,终于在屏幕有一行输出了,不容易。
private Class<? extends ConfigurableApplicationContext> applicationContextClass;public static final String DEFAULT_CONTEXT_CLASS = "org.springframework.context." + "annotation.AnnotationConfigApplicationContext";public static final String DEFAULT_WEB_CONTEXT_CLASS = "org.springframework." + "boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext";private ConfigurableApplicationContext createAndRefreshContext( SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) { ConfigurableApplicationContext context; ... context = createApplicationContext(); context.setEnvironment(environment); postProcessApplicationContext(context); applyInitializers(context); listeners.contextPrepared(context); if (this.logStartupInfo) { logStartupInfo(context.getParent() == null); logStartupProfileInfo(context); } ... return context; }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); }
createAndRefreshContext中调用createApplicationContext获取创建ApplicationContext,可以看到,当检测到本次程序是一个web应用程序(成员变量webEnvironment为true)的时候,就加载类DEFAULT_WEB_CONTEXT_CLASS,否则的话加载DEFAULT_CONTEXT_CLASS。我们的例子是一个web应用程序,所以会加载DEFAULT_WEB_CONTEXT_CLASS,也就是org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext。我们先来看一看这个AnnotationConfigEmbeddedWebApplicationContext具体有什么功能。下图画出了它的继承体系。
可以看到我们加载的这个AnnotationConfigEmbeddedWebApplicationContext类,从名字就可以看出来,首先是一个WebApplicationContext实现了WebApplicationContext接口,然后是一个EmbeddedWebApplicationContext,这意味着它会自动创建并初始化一个EmbeddedServletContainer,同时还支持AnnotationConfig,会将使用注解标注的bean注册到ApplicationContext中。更详细的过程,后面在例子中再一一剖析。
可以看到在加载类对象AnnotationConfigEmbeddedWebApplicationContext之后,createApplicationContext方法中紧接着调用BeanUtils的instantiate方法来创建ApplicationContext对象,其代码如下:
以下代码摘自:org.springframework.beans.BeanUtilspublic static <T> T instantiate(Class<T> clazz) throws BeanInstantiationException { Assert.notNull(clazz, "Class must not be null"); if (clazz.isInterface()) { throw new BeanInstantiationException(clazz, "Specified class is an interface"); } try { return clazz.newInstance(); } catch (InstantiationException ex) { throw new BeanInstantiationException(clazz, "Is it an abstract class?", ex); } catch (IllegalAccessException ex) { throw new BeanInstantiationException(clazz, "Is the constructor accessible?", ex); } }
通过调用Class对象的newInstance()方法来实例化对象,这等同于直接调用类的空的构造方法,所以我们来看AnnotationConfigEmbeddedWebApplicationContext类的构造方法:
以下代码摘自:org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContextpublic AnnotationConfigEmbeddedWebApplicationContext() { this.reader = new AnnotatedBeanDefinitionReader(this); this.scanner = new ClassPathBeanDefinitionScanner(this); }@Overridepublic void setEnvironment(ConfigurableEnvironment environment) { super.setEnvironment(environment); this.reader.setEnvironment(environment); this.scanner.setEnvironment(environment); }
构造方法中初始化了两个成员变量,类型分别为AnnotatedBeanDefinitionReader和ClassPathBeanDefinitionScanner用以加载使用注解的bean定义。
这样ApplicationContext对象就创建出来了,在createAndRefreshContext方法中创建了ApplicationContext对象之后会紧接着调用其setEnvironment将我们之前准备好的Environment对象赋值进去。之后分别调用postProcessApplicationContext和applyInitializers做一些处理和初始化的操作。
先来看看postProcessApplicationContext:
protected void postProcessApplicationContext(ConfigurableApplicationContext context) { if (this.webEnvironment) { if (context instanceof ConfigurableWebApplicationContext) { ConfigurableWebApplicationContext configurableContext = (ConfigurableWebApplicationContext) context; if (this.beanNameGenerator != null) { configurableContext.getBeanFactory().registerSingleton( AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR, this.beanNameGenerator); } } } if (this.resourceLoader != null) { if (context instanceof GenericApplicationContext) { ((GenericApplicationContext) context) .setResourceLoader(this.resourceLoader); } if (context instanceof DefaultResourceLoader) { ((DefaultResourceLoader) context) .setClassLoader(this.resourceLoader.getClassLoader()); } } }
如果成员变量beanNameGenerator不为Null,那么为ApplicationContext对象注册beanNameGenerator bean。如果成员变量resourceLoader不为null,则为ApplicationContext对象设置ResourceLoader。我们的例子中,这两个成员变量都为Null,所以什么都不做。
之后是applyInitializers方法:
protected void applyInitializers(ConfigurableApplicationContext context) { for (ApplicationContextInitializer initializer : getInitializers()) { Class<?> requiredType = GenericTypeResolver.resolveTypeArgument( initializer.getClass(), ApplicationContextInitializer.class); Assert.isInstanceOf(requiredType, context, "Unable to call initializer."); initializer.initialize(context); } }public Set<ApplicationContextInitializer<?>> getInitializers() { return asUnmodifiableOrderedSet(this.initializers); }private static <E> Set<E> asUnmodifiableOrderedSet(Collection<E> elements) { List<E> list = new ArrayList<E>(); list.addAll(elements); Collections.sort(list, AnnotationAwareOrderComparator.INSTANCE); return new LinkedHashSet<E>(list); }
以上就是有关Spring Boot的启动流程的相关介绍的详细内容,更多请关注php中文网其它相关文章!
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