1 SpringBoot简介
SpringBoot是由Pivotal团队提供的全新框架,其设计目的是用来简化新Spring应用的初始搭建以及开发过程。该框架使用了特定的方式来进行配置,从而使开发人员不再需要定义样板化的配置。通过这种方式,Boot致力于在蓬勃发展的快速应用开发领域(rapid application development)成为领导者。SpringBoot并不是要成为Spring平台里面众多“Foundation”层项目的替代者。SpringBoot的目标不在于为已解决的问题域提供新的解决方案,而是为平台带来另一种开发体验,从而简化对这些已有技术的使用。
SpringBoot主要有如下核心特点:
- 包含执行所需的一切的可执行jar包。包含了运行所需的一切,包括内嵌应用服务器等,并打包为一个可执行jar文件部署,这点在微服务概念里非常重要。
- 约定大于配置理念的完美践行,自动配置模块
- 提供各种各样的starter简化初始配置过程
- 提供各种扩展机制等等
2 一个简单的例子
下面先通过一个简单的例子看一下使用SpringBoot开发项目能有多快捷。我们打算编写一个web服务器,设置启动端口并提供一个简单的页面/index,当浏览该页面时会显示hello world。为了达到这样的效果只需要简单的几步就可以做到:配置pom.xml
- <dependency>
- <groupId>org.springframework.boot</groupId>
- <artifactId>spring-boot-starter-web</artifactId>
- </dependency>
编写项目的启动类
- @SpringBootApplication
- public class SBApplication {
- public static void main(String args[]) throws Exception{
- SpringApplication.run(SBApplication.class, args);
- }
- }
添加Controller
最后,编写页面/index对应的Controller:
- @RestController
- public class TestController {
- @RequestMapping("/index")
- public String index(){
- return "hello world";
- }
- }
默认端口为8080,为了设置自定义端口,我们在项目的/src/main/resources下新建application.properties文件,并在其中加上:
- server.port=7668
如此一来,一个最简单的SpringBoot Web程序就完成了,由于启动类有main方法,我们直接run as application就可以运行这个程序,控制台输出结果为:
- ...................
- 2017-12-30 00:50:35.873 INFO 14033 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX exposure on startup
- 2017-12-30 00:50:35.931 INFO 14033 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 7668 (http)
- 2017-12-30 00:50:35.937 INFO 14033 --- [ main] springbootext.SBApplication : Started SBApplication in 3.752 seconds (JVM running for 4.089)
看到输出的最后几句就表示web服务器启动成功了,端口为我们定义的7668。接下来访问
- http://localhost:7668/index
就能看到页面上显示的hello world,一个基本的web服务器就这么简简单单创建完成了,简直是简单的令人发指。
上面的SpringBoot程序跟一个普通java程序的两点不同在于@SpringBootApplication注释以及SpringApplication类。下面我们介绍这两者的功能及其背后的SpringBoot框架的实现原理。
3 @SpringBootApplication注释
前面例子中为了简洁,直接将@SpringBootApplication打在了主类上,其实更加清晰的写法应该是将主类和SpringBoot配置类分开,如下所示:- @SpringBootApplication
- public class SBConfiguration {
- }
- public class SBApplication {
- public static void main(String args[]) throws Exception{
- SpringApplication.run(SBConfiguration.class, args);
- }
- }
如此一来,就能比较清晰的看出主类SBApplication只是程序的入口,没有什么特殊的。调用了SpringApplication的静态方法run,并使用SpringBoot主配置类SBConfigration.class作为参数。
主配置类就是打上@SpringBootApplication注释的类,首先看一下注释SpringBootApplication的代码:
- @Target(ElementType.TYPE)
- @Retention(RetentionPolicy.RUNTIME)
- @Documented
- @Inherited
- @SpringBootConfiguration
- @EnableAutoConfiguration
- @ComponentScan(excludeFilters = {
- @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
- @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
- public @interface SpringBootApplication {
- ...........................
- }
可以看出,这是一个复合注释,其中@SpringBootConfiguration代表了SpringBoot的配置类,除了测试时有些区别,大体上就是Spring标准@Configuration的替代品。
@EnableAutoConfiguration用于启动SpringBoot的自动配置机制,这是SpringBoot的核心特色之一,自动对各种机制进最大可能的进行配置。
@ComponentScan是Spring原来就有的注释,用于对指定的路径进行扫描,并将其中的@Configuration配置类加载。接下来分别对其一一介绍。
3.1 @SpringBootConfiguration
先看该注释的定义:- @Target(ElementType.TYPE)
- @Retention(RetentionPolicy.RUNTIME)
- @Documented
- @Configuration
- public @interface SpringBootConfiguration {
- }
从代码可见,其本质上就是一个@Configuration。唯一不同的地方是在测试时,如果打上了@SpringBootConfiguration注释,那么SpringBootTest中并不需要指定就可以自动加载该配置类;而当打上@Configuration时,需要通过@SpringBootTest(classes = SBConfiguration.class)来指定加载的SpringBoot配置类。
若不考虑测试时非要省略指定Configuration类的话,该注释可有可无。因为在作为参数传递给SpringApplication.run方法后,只要其中配置了@Bean方法,就会直接被认为是一个配置类进行加载处理,并不需要@Configuration来标识。
应用启动时在springcontext经典的refresh主流程中,当beanFactory创建完成后会执行invokeBeanFactoryPostProcessors阶段,该阶段会调用前面注册的BeanFactoryPostProcessors中的postProcessBeanDefinitionRegistry方法来对beanFactory进一步处理。
其中ConfigurationClassPostProcessor是专门用来处理Configuration类的启动加载进程的。其processConfigBeanDefinitions方法中首先使用:
- String[] candidateNames = registry.getBeanDefinitionNames();
获得所有已注册到registry中的beanDefinitionNames然后对其中的每一个beanDefinitionName判断其是否属于配置类:
- for (String beanName : candidateNames) {
- BeanDefinition beanDef = registry.getBeanDefinition(beanName);
- if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) ||
- ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) {
- if (logger.isDebugEnabled()) {
- logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);
- }
- }
- else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
- configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
- }
- }
其中把判断beanDef是否为Configuration类委托给ConfigurationClassUtils来处理,ConfigurationClassUtils类通过两个方法来确定一个类是否是配置类:
- public static boolean isFullConfigurationCandidate(AnnotationMetadata metadata) {
- return metadata.isAnnotated(Configuration.class.getName());
- }
- public static boolean isLiteConfigurationCandidate(AnnotationMetadata metadata) {
- // Do not consider an interface or an annotation...
- if (metadata.isInterface()) {
- return false;
- }
- // Any of the typical annotations found?
- for (String indicator : candidateIndicators) {
- if (metadata.isAnnotated(indicator)) {
- return true;
- }
- }
- // Finally, let's look for @Bean methods...
- try {
- return metadata.hasAnnotatedMethods(Bean.class.getName());
- }
- catch (Throwable ex) {
- if (logger.isDebugEnabled()) {
- logger.debug("Failed to introspect @Bean methods on class [" + metadata.getClassName() + "]: " + ex);
- }
- return false;
- }
- }
从上述代码可知,当一个类没有标注@Configuration但是其中定义了@Bean方法时,也会被判断为lite configuration(轻量级配置)类。判断过程完成后,委托ConfigurationClassParser来解析前面找到的每一个配置类,具体解析过程在此就不展开了,回头会专门写一篇关于spring context的介绍文章详细介绍。
由此我们可知,如果在springcontext refresh主流程的invokeBeanFactoryPostProcessors阶段之前就将beanDefinition注册到beanDefinitionRegistry,那么这个beanDefinition并不需要非得打上@Configuration注释,也可以通过其内部定义的@Bean方法被认定是一个Configuration类。
而在SpringApplication的run方法中以参数形式传递进去,就是方法之一。
例如,当我们把上述代码修改为:
- @EnableAutoConfiguration
- @ComponentScan
- public class SBConfiguration {
- }
3.2 @EnableAutoConfiguration
EnableAutoConfiguration自动配置机制是SpringBoot的核心特色之一。可根据引入的jar包对可能需要的各种机制进进行默认配置。该注释的定义如下:
- @SuppressWarnings("deprecation")
- @Target(ElementType.TYPE)
- @Retention(RetentionPolicy.RUNTIME)
- @Documented
- @Inherited
- @AutoConfigurationPackage
- @Import(EnableAutoConfigurationImportSelector.class)
- public @interface EnableAutoConfiguration {
- ..........
- }
其中@AutoConfigurationPackage用来指示包含打了该注释的类的包(package)应该被注册到AutoConfigurationPackages中,以备后续扩展机制(例如JPA或Mybatis等)的实体扫描器使用。
@EnableAutoConfiguration真正核心的动作就是通过Import机制加载EnableAutoConfigurationImportSelector.selectImports函数返回的配置类:
- public String[] selectImports(AnnotationMetadata annotationMetadata) {
- if (!isEnabled(annotationMetadata)) {
- return NO_IMPORTS;
- }
- try {
- AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
- .loadMetadata(this.beanClassLoader);
- AnnotationAttributes attributes = getAttributes(annotationMetadata);
- List<String> configurations = getCandidateConfigurations(annotationMetadata,
- attributes);
- configurations = removeDuplicates(configurations);
- configurations = sort(configurations, autoConfigurationMetadata);
- Set<String> exclusions = getExclusions(annotationMetadata, attributes);
- checkExcludedClasses(configurations, exclusions);
- configurations.removeAll(exclusions);
- configurations = filter(configurations, autoConfigurationMetadata);
- fireAutoConfigurationImportEvents(configurations, exclusions);
- return configurations.toArray(new String[configurations.size()]);
- }
- catch (IOException ex) {
- throw new IllegalStateException(ex);
- }
- }
其中比较核心的动作为getCandidateConfigurations(annotationMetadata, attributes),代码如下:
- protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,
- AnnotationAttributes attributes) {
- List<String> configurations = SpringFactoriesLoader.loadFactoryNames(
- getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());
- Assert.notEmpty(configurations,
- "No auto configuration classes found in META-INF/spring.factories. If you "
- + "are using a custom packaging, make sure that file is correct.");
- return configurations;
- }
- protected Class<?> getSpringFactoriesLoaderFactoryClass() {
- return EnableAutoConfiguration.class;
- }
我们注意:
- List<String> configurations = SpringFactoriesLoader.loadFactoryNames(
- getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());
这句,SpringFactoriesLoader是spring framework内部使用的通用的工厂加载机制,其可加载并实例化可能出现在classpath上的多个jar包中的META-INF/spring.factories文件中定义的指定类型的工厂,可视为一种类似于SPI的接口。
SpringBoot利用这种SPI接口实现了autoconfiguration机制:委托SpringFactoriesLoader来加载所有配置在META-INF/spring.factories中的org.springframework.boot.autoconfigure.EnableAutoConfiguration对应的值,spring-boot-autoconfiguration jar包中的META-INF/spring.factories中的EnableAutoConfiguration配置摘录如下:
- # Auto Configure
- org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
- org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
- org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
- org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
- org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
- org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
- org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\
- org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration,\
- ..........................
其中我们可以看到相当多非常熟悉的自动配置类,例如AopAutoConfiguration、CacheAutoConfiguration等等。其中的每一个自动配置类都会在一定条件(@Condition)下启动生效,并对相关的机制进行默认自动的配置。这便是SpringBoot自动配置机制的核心功能所在。
3.3 @ComponentScan
这是spring-context原来就存在的注释,需要在@Configuration标注的类上标注,用来指示扫描某些包及其子包上的组件。可通过配置属性basePackageClasses、basePackages或value来指出需要扫描哪些包(包括其子包),如果没有指定任何一个属性值,则默认扫描当前包及其子包。例如,在前面例子中,如果SBConfiguration所在的包是springbootext,那么由于SBConfiguration打了@ComponentScan注释,那么在springbootext、springbootext.service、springbootext.config等等地方定义的@Configuration、@Component、@Service、@Controller等等组件都可以直接被加载,无需额外配置。而在anotherpackage中定义的组件,无法被直接加载。可以通过设置扫描路径来解决:
- @EnableAutoConfiguration
- @ComponentScan(basePackages={"springbootext", "anotherpackage"})
- public class SBConfiguration{
- }
当然也可以通过借助3.2节中介绍的在spring.factories中定义扩展机制定义EnableAutoConfiguration来实现加载。
启动过程中@ComponentScan起作用的时机是在springcontext refresh主流程的invokeBeanFactoryPostProcessor阶段,也就是BeanFactory创建并准备完毕后通过BeanFactoryPostProcessors来进一步对beanFactory进行处理的阶段。
在该阶段,ConfigurationClassPostProcessor中对于Configuration类的处理里包括了识别其打的@ComponentScan注释,并委托ComponentScanAnnotationParser根据该注释的属性值进行组件扫描。将扫描生成的beanDefinitions注册到beanFactory中供下一个阶段创建beans。
4 SpringApplication一站式程序启动解决方案
当我们执行SpringApplication.run(Object[] sources, String[] args)静态方法时,内部会执行- new SpringApplication(sources).run(args);
因此,我们也可以将前面程序主类的启动过程修改为:
- public class SBApplication {
- public static void main(String args[]) throws Exception{
- SpringApplication sa = new SpringApplication(SBConfiguration.class);
- sa.run(args);
- }
- }
如此一来,我们可以使用到SpringApplication提供的一系列实例方法对其进行配置。
从上面代码看,应用的启动过程分为两部分:首先创建一个SpringApplication对象;然后执行其对象方法run。构造函数中实际业务逻辑都放在了initialize方法中。下面我们分别分析这两部分都干了什么。
4.1 初始化initialize
顾名思义,initialize就是初始化函数,其代码如下:- private void initialize(Object[] sources) {
- 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();
- }
首先,将初始化参数中的Object... sources保存在this.sources中,供后续run方法的prepareContext阶段使用。该参数代表了SpringBoot启动时指定的Configuration类(可多个)。然后通过判断当前是否含有:
- private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",
- "org.springframework.web.context.ConfigurableWebApplicationContext" };
中定义的两个类,来判断当前是否是一个web环境,后续会针对不同的环境创建不同的ApplicationContext。
接着通过两个函数getSpringFactoriesInstances(ApplicationContextInitializer.class)、getSpringFactoriesInstances(ApplicationListener.class)得到以SpringFactoriesLoader扩展方案注册的ApplicationContextInitializer和ApplicationListener类型的实例,并设置到当前SpringApplication的对象中。在这两个函数都调用了:
- 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;
- }
来获取特定类型的实例,又看到了熟悉的SpringFactoriesLoader。查找配置在classpath及各个jar包中的META-INF/spring.factories中配置的ApplicationContextInitializer和ApplicationListener,并实例化。
最后一步得到含有main函数的主类,并保存在mainApplicationClass属性中。
4.2 实际启动过程run
SpringApplication将SpringBoot应用启动流程模板化,并在启动过程的不同时机定义了一系列不同类型的的扩展点,方便我们对其进行定制。下面对整个启动过程代码进行分析:1. 通过SpringFactoriesLoader来获取定义在spring.factories中的SpringApplicationRunListener,SpringBoot框架默认只定义了一个EventPublishingRunListener,其中维护了一个SimpleApplicationEventMulticaster,并将前面initialize阶段中获得的ApplicationListeners注册进去。然后调用其start方法,给所有的SpringApplicationRunListener发送一个start事件,然后EventPublishingRunListener给注册在其中的所有ApplicationListener发送ApplicationStartedEvent。
- SpringApplicationRunListeners listeners = getRunListeners(args);
- listeners.starting();
2. 将参数包装为ApplicationArguments,DefaultApplicationArguments是用来维护命令行参数的,例如可以方便的将命令行参数中的options和non options区分开,以及获得某option的值等。
- ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
3. 通过ApplicationArguments来准备应用环境Environment, Environment包含了两个层面的信息:属性(properties)和轮廓(profiles):
- ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
- private ConfigurableEnvironment prepareEnvironment(
- SpringApplicationRunListeners listeners,
- ApplicationArguments applicationArguments) {
- // Create and configure the environment
- ConfigurableEnvironment environment = getOrCreateEnvironment();
- configureEnvironment(environment, applicationArguments.getSourceArgs());
- listeners.environmentPrepared(environment);
- if (!this.webEnvironment) {
- environment = new EnvironmentConverter(getClassLoader())
- .convertToStandardEnvironmentIfNecessary(environment);
- }
- return environment;
- }
- protected void configureEnvironment(ConfigurableEnvironment environment,
- String[] args) {
- configurePropertySources(environment, args);
- configureProfiles(environment, args);
- }
而轮廓(profile)可以认为是程序的运行环境,典型的环境比如有开发环境(Develop)、生产环境(Production)、测试环境(Test)等等。我们可以定义某个Bean在特定的环境中才生效,这样就可以通过指定profile来方便的切换运行环境。可通过SpringApplication.setAdditionalProfiles()来设置轮廓,environment内通过activeProfiles来维护生效的轮廓(可不止一个)。
在环境配置完毕后,执行所有SpringApplicationRunListeners的environmentPrepared函数,然后EventPublishingRunListener给所有注册其中的ApplicationListeners发送一个“环境准备好了”ApplicationEnvironmentPreparedEvent事件:
- listeners.environmentPrepared(environment);
4. 根据前面判断的是web应用还是普通应用决定创建什么类型的ApplicationContext:
- context = createApplicationContext();
- 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";
- 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);
- }
这两个子类的不同之处在于对内部的DefaultListableBeanFactory的管理:AbstractRefreshableApplicationContext允许多次调用其refreshBeanFactory()函数,每次调用时都会重新创建一个DefaultListableBeanFactory,并将已有的销毁;而GenericApplicationContext不允许刷新beanFactory,只能调用refreshBeanFactory()一次,当多次调用时会抛出异常。
无论AnnotationConfigApplicationContext还是AnnotationConfigEmbeddedWebApplicationContext,它们都是GenericApplicationContext的子类。因此其内部持有的BeanFactory是不可刷新的,并且从初始化开始就一直持有一个唯一的BeanFactory。相关细节会在spring context的介绍中深入讨论。
5. 借助SpringFactoriesLoader获得spring.factories中注册的FailureAnalyzers以供当运行过程中出现异常时进行分析:
- analyzers = new FailureAnalyzers(context);
- List<String> analyzerNames = SpringFactoriesLoader
- .loadFactoryNames(FailureAnalyzer.class, classLoader);
6. 接着就是SpringBoot启动过程中的最核心流程,对第4步创建的ApplicationContext进行准备:
- prepareContext(context, environment, listeners, applicationArguments, printedBanner);
7. 调用ApplicationContext的refresh函数,开启spring context的核心流程,就是根据配置加载bean(spring beans核心功能)以及在各个时机开放的不同扩展机制(spring context):
- refreshContext(context);
8. 获取所有的ApplicationRunner和CommandLineRunner并执行:
- afterRefresh(context, applicationArguments);
- protected void afterRefresh(ConfigurableApplicationContext context,
- ApplicationArguments args) {
- callRunners(context, args);
- }
- private void callRunners(ApplicationContext context, ApplicationArguments args) {
- List<Object> runners = new ArrayList<Object>();
- runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
- runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
- AnnotationAwareOrderComparator.sort(runners);
- for (Object runner : new LinkedHashSet<Object>(runners)) {
- if (runner instanceof ApplicationRunner) {
- callRunner((ApplicationRunner) runner, args);
- }
- if (runner instanceof CommandLineRunner) {
- callRunner((CommandLineRunner) runner, args);
- }
- }
- }
此处又定义了两个扩展机制,我们可以自定义ApplicationRunner或CommandLineRunner并将其配置为Bean,便可以在context refresh完毕后执行。
9. spring-context refresh过程完毕后执行所有SpringApplicationRunListeners的finished函数,然后EventPublishingRunListener给所有注册其中的ApplicationListeners发送一个“应用启动完毕”ApplicationReadyEvent事件:
- listeners.finished(context, null);
10. 当运行时出现异常时,向context发送退出码事件ExitCodeEvent,供其内部listener执行退出前的操作;并使用前面第5步获得的analyzers来打印可能的原因:
- handleRunFailure(context, listeners, analyzers, ex);
- private void handleRunFailure(ConfigurableApplicationContext context,
- SpringApplicationRunListeners listeners, FailureAnalyzers analyzers,
- Throwable exception) {
- try {
- try {
- handleExitCode(context, exception);
- listeners.finished(context, exception);
- }
- finally {
- reportFailure(analyzers, exception);
- if (context != null) {
- context.close();
- }
- }
- }
- catch (Exception ex) {
- logger.warn("Unable to close ApplicationContext", ex);
- }
- ReflectionUtils.rethrowRuntimeException(exception);
- }
至此,SpringApplication的run函数,也就是SpringBoot应用的启动过程就执行完毕了。可以看出,SpringBoot的启动过程是对Spring context启动过程的扩展,在其中定义了若干的扩展点并提供了不同的扩展机制。并提供了默认配置,我们可以什么都不配,也可以进行功能非常强大的配置和扩展。这也正是SpringBoot的优势所在。
4.3 核心过程prepareContext
顾名思义,该函数的功能就是对前面创建的ApplicationContext进行准备,其执行步骤如下:1. 将environment设置到context中:
- context.setEnvironment(environment);
2. 对ApplicationContext应用相关的后处理,子类可以重写该方法来添加任意的后处理功能:
- postProcessApplicationContext(context);
- protected void postProcessApplicationContext(ConfigurableApplicationContext context) {
- if (this.beanNameGenerator != null) {
- context.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());
- }
- }
- }
- org.springframework.context.annotation.internalConfigurationBeanNameGenerator
3. 对initialize阶段得到的通过spring.factories注册进来的所有ApplicationContextInitializer,逐个执行其initialize方法来修改context,并在执行之前对其进行校验:
- 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);
- }
- }
4. 执行所有SpringApplicationRunListeners的contextPrepared函数,注意EventPublishingRunListener并没有给所有注册其中的ApplicationListeners发送对应的事件:
- listeners.contextPrepared(context);
5. 将applicationArguments注册进context.getBeanFactory()中,名字为"SpringApplicationArguments"、若printBanner不为空,将printBanner注册到context.getBeanFactory()中,名字为"SpringBootBanner":
- context.getBeanFactory().registerSingleton("springApplicationArguments",
- applicationArguments);
- if (printedBanner != null) {
- context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
- }
6. 得到所有的sources(可通过SpringApplication的run函数、构造函数和setSources函数指定,代表了一个或多个Configuration类),然后执行load(context, sources)函数:
- Set<Object> sources = getSources();
- Assert.notEmpty(sources, "Sources must not be empty");
- load(context, sources.toArray(new Object[sources.size()]));
- protected void load(ApplicationContext context, Object[] sources) {
- if (logger.isDebugEnabled()) {
- logger.debug(
- "Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
- }
- BeanDefinitionLoader loader = createBeanDefinitionLoader(
- getBeanDefinitionRegistry(context), sources);
- if (this.beanNameGenerator != null) {
- loader.setBeanNameGenerator(this.beanNameGenerator);
- }
- if (this.resourceLoader != null) {
- loader.setResourceLoader(this.resourceLoader);
- }
- if (this.environment != null) {
- loader.setEnvironment(this.environment);
- }
- loader.load();
- }
- 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());
- }
- public void register(Class<?>... annotatedClasses) {
- for (Class<?> annotatedClass : annotatedClasses) {
- registerBean(annotatedClass);
- }
- }
此处已是spring context的功能了,将通过注释定义的Configuration类的BeanDefinition注册到BeanDefinitionRegistry中。(此时尚不解析Configuration类内部定义的@Bean方法)
- listeners.contextLoaded(context);
- public void contextLoaded(ConfigurableApplicationContext context) {
- for (ApplicationListener<?> listener : this.application.getListeners()) {
- if (listener instanceof ApplicationContextAware) {
- ((ApplicationContextAware) listener).setApplicationContext(context);
- }
- context.addApplicationListener(listener);
- }
- this.initialMulticaster.multicastEvent(
- new ApplicationPreparedEvent(this.application, this.args, context));
- }
5 SpringBoot扩展机制
SpringApplication首先提供了一系列的setter方法来进行定制,另外从上面对于SpringBoot启动过程的解读可知,对于SpringBoot有如下几种扩展机制:5.1 SpringApplicationRunListener
SpringApplicationRunListener是SpringBoot独有的概念,用以在SpringBoot应用启动过程的不同时机接收事件通知并执行相应操作,接口定义如下:- public interface SpringApplicationRunListener {
- void starting();
- void environmentPrepared(ConfigurableEnvironment environment);
- void contextPrepared(ConfigurableApplicationContext context);
- void contextLoaded(ConfigurableApplicationContext context);
- void finished(ConfigurableApplicationContext context, Throwable exception);
- }
SpringBoot框架内置定义了一个EventPublishingRunListener用以将定义在spring.factories中的ApplicationListener管理起来,并在SpringBoot应用启动的不同时机通知它们执行各自的业务逻辑。
我们可以自定义一个实现了EventPublishingRunListener接口的类,例如:
- public class MySpringApplicationRunListener implements SpringApplicationRunListener {
- Logger logger = LoggerFactory.getLogger(MySpringApplicationRunListener.class);
- private final SpringApplication application;
- private final String[] args;
- public MySpringApplicationRunListener(SpringApplication application, String[] args){
- this.application = application;
- this.args = args;
- }
- @Override
- public void starting() {
- System.out.println("===============starting");
- }
- @Override
- public void environmentPrepared(ConfigurableEnvironment environment) {
- environment.setActiveProfiles("Develop");
- logger.info("===============environmentPrepared");
- }
- @Override
- public void contextPrepared(ConfigurableApplicationContext context) {
- logger.info("===============contextPrepared");
- }
- @Override
- public void contextLoaded(ConfigurableApplicationContext context) {
- logger.info("===============contextLoaded");
- }
- @Override
- public void finished(ConfigurableApplicationContext context,
- Throwable exception) {
- logger.info("===============finished");
- }
- }
注意:其必须拥有一个SpringApplication类型和String[]类型参数的构造函数:
- public MySpringApplicationRunListener(SpringApplication application, String[] args)
另外,SpringBoot启动过程中,LoggingApplicationListener作为一个注册到spring.factories中的ApplicationListener,其在接收到ApplicationEnvironmentPreparedEvent时,才会执行logging system的初始化,因此在starting方法中是没法使用logger打印日志的。
然后在META-INF/spring.factories中添加如下配置:
- org.springframework.boot.SpringApplicationRunListener=\
- springbootext.runlistener.MySpringApplicationRunListener
此时启动应用,可得到如下的输出:
- ===============starting
- 2017-12-31 02:28:39.647 INFO 16329 --- [ main] s.r.MySpringApplicationRunListener : ===============environmentPrepared
- . ____ _ __ _ _
- /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
- ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
- \\/ ___)| |_)| | | | | || (_| | ) ) ) )
- ' |____| .__|_| |_|_| |_\__, | / / / /
- =========|_|==============|___/=/_/_/_/
- :: Spring Boot :: (v1.5.8.RELEASE)
- 2017-12-31 02:28:39.768 INFO 16329 --- [ main] s.r.MySpringApplicationRunListener : ===============contextPrepared
- 2017-12-31 02:28:39.772 INFO 16329 --- [ main] springbootext.SBApplication : Starting SBApplication on wangd-ThinkPad-T450 with PID 16329 (/home/wangd/work/test/springbootext/target/classes started by wangd in /home/wangd/work/test/springbootext)
- 2017-12-31 02:28:39.773 INFO 16329 --- [ main] springbootext.SBApplication : The following profiles are active: Develop
- 2017-12-31 02:28:39.824 INFO 16329 --- [ main] s.r.MySpringApplicationRunListener : ===============contextLoaded
- 2017-12-31 02:28:39.828 INFO 16329 --- [ main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@58a90037: startup date [Sun Dec 31 02:28:39 CST 2017]; root of context hierarchy
- 2017-12-31 02:28:41.654 INFO 16329 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 7668 (http)
- 2017-12-31 02:28:41.672 INFO 16329 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
- 2017-12-31 02:28:41.673 INFO 16329 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet Engine: Apache Tomcat/8.5.23
- 2017-12-31 02:28:41.802 INFO 16329 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
- 2017-12-31 02:28:41.802 INFO 16329 --- [ost-startStop-1] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 1978 ms
- 2017-12-31 02:28:41.980 INFO 16329 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean : Mapping servlet: 'dispatcherServlet' to [/]
- 2017-12-31 02:28:41.985 INFO 16329 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'characterEncodingFilter' to: [/*]
- 2017-12-31 02:28:41.986 INFO 16329 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
- 2017-12-31 02:28:41.987 INFO 16329 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'httpPutFormContentFilter' to: [/*]
- 2017-12-31 02:28:41.987 INFO 16329 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'requestContextFilter' to: [/*]
- 2017-12-31 02:28:42.390 INFO 16329 --- [ main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@58a90037: startup date [Sun Dec 31 02:28:39 CST 2017]; root of context hierarchy
- 2017-12-31 02:28:42.476 INFO 16329 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/index]}" onto public java.lang.String springbootext.controller.TestController.index()
- 2017-12-31 02:28:42.482 INFO 16329 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
- 2017-12-31 02:28:42.483 INFO 16329 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
- 2017-12-31 02:28:42.526 INFO 16329 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
- 2017-12-31 02:28:42.526 INFO 16329 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
- 2017-12-31 02:28:42.581 INFO 16329 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
- 2017-12-31 02:28:42.786 INFO 16329 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX exposure on startup
- 2017-12-31 02:28:42.852 INFO 16329 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 7668 (http)
- 2017-12-31 02:28:42.858 INFO 16329 --- [ main] s.r.MySpringApplicationRunListener : ===============finished
- 2017-12-31 02:28:42.858 INFO 16329 --- [ main] springbootext.SBApplication : Started SBApplication in 3.469 seconds (JVM running for 3.776)
5.2 ApplicationListener
如5.1所述,SpringBoot框架内置了一个EventPublishingRunListener用以将定义在spring.factories中的ApplicationListener管理起来,并在SpringBoot应用启动的不同时机给他们发送不同的事件。EventPublishingRunListener内部维护了一个ApplicationEventMulticaster,并将SpringApplication初始化时获得的ApplicationListeners注册进去:
- private final ApplicationEventMulticaster initialMulticaster;
- 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);
- }
- }
然后在SpringBoot执行的不同时机被调用不同方法时,将通知封装成不同类型的ApplicationEvent并广播给注册的ApplicationListener:
- @Override
- public void started() {
- this.initialMulticaster.multicastEvent(new ApplicationStartedEvent(
- this.application, this.args));
- }
- @Override
- public void environmentPrepared(ConfigurableEnvironment environment) {
- this.initialMulticaster.multicastEvent(new ApplicationEnvironmentPreparedEvent(
- this.application, this.args, environment));
- }
- @Override
- public void contextPrepared(ConfigurableApplicationContext context) {
- }
- @Override
- public void contextLoaded(ConfigurableApplicationContext context) {
- for (ApplicationListener<?> listener : this.application.getListeners()) {
- if (listener instanceof ApplicationContextAware) {
- ((ApplicationContextAware) listener).setApplicationContext(context);
- }
- context.addApplicationListener(listener);
- }
- this.initialMulticaster.multicastEvent(new ApplicationPreparedEvent(
- this.application, this.args, context));
- }
- @Override
- public void finished(ConfigurableApplicationContext context, Throwable exception) {
- // Listeners have been registered to the application context so we should
- // use it at this point
- context.publishEvent(getFinishedEvent(context, exception));
- }
注意:contextLoaded通知发出时,EventPublishingRunListener会将SpringApplication中的ApplicationListeners统统注册到context中。而在finished通知发出时,直接通知的是context中的所有ApplicationListeners。
我们也可以自定义一个实现了ApplicationListener接口的类,然后通过
- springApplication.addListeners(new MyApplicationListener());
- org.springframework.context.ApplicationListener=\
- springbootext.listener.MyApplicationListener
5.3 ApplicationContextInitializer
ApplicationContextInitializer是Spring context原有的概念,其目的就是在ApplicationContext准备好之后且refresh之前执行,可以对ApplicationContext做进一步的维护。其执行时机是在SpringApplication run阶段的prepareContext时期调用applyInitializers函数来实现的,代码如下:- 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);
- }
- }
我们也可以自定义一个实现了ApplicationContextInitializer接口的类,然后通过
- springApplication.addInitializers(new MyInitializer());
- org.springframework.context.ApplicationContextInitializer=\
- springbootext.initializer.MyInitializer
5.4 CommandLineRunner和ApplicationRunner
这两个runner如此相似,就将他们放在一起说明了。CommandLineRunner和ApplicationRunner接口是在容器启动成功后的最后一步回调,可以认为是挂载了一些开机自启动程序。其执行时机在run的afterRefresh阶段:- protected void afterRefresh(ConfigurableApplicationContext context,
- ApplicationArguments args) {
- callRunners(context, args);
- }
- private void callRunners(ApplicationContext context, ApplicationArguments args) {
- List<Object> runners = new ArrayList<Object>();
- runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
- runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
- AnnotationAwareOrderComparator.sort(runners);
- for (Object runner : new LinkedHashSet<Object>(runners)) {
- if (runner instanceof ApplicationRunner) {
- callRunner((ApplicationRunner) runner, args);
- }
- if (runner instanceof CommandLineRunner) {
- callRunner((CommandLineRunner) runner, args);
- }
- }
- }
由于其执行时机是在applicationContext的refresh完成以后,因此其获取是通过applicationContext.getBeansOfType来得到的,也就是说所有注册在applicationContext(也就是其中的beanFactory)中的CommandLineRunner或ApplicationRunner类型的bean都会被执行。
所以我们可以通过在Configuration类中定义@Bean方法将自定义的Runner注册进来。
两者的执行时机是完全一样的,唯一的区别在于一个接受ApplicationArguments,一个接受String[]类型的原始命令行参数。而ApplicationArguments也只是对原始命令行参数的一个封装,因此本质上是一样的。
6 spring-boot-starter实现原理
SpringBoot中的starter是一种非常重要的机制,能够抛弃以前繁杂的配置,将其统一集成进starter,应用者只需要引入starter jar包,SpringBoot就能自动扫描到要加载的信息并启动相应的默认配置。starter让我们摆脱了各种依赖库的处理,需要配置各种信息的困扰。SpringBoot会自动通过classpath路径下的类发现需要的Bean,并注册进IOC容器。
SpringBoot提供了针对日常企业应用研发各种场景的spring-boot-starter依赖模块。所有这些依赖模块都遵循着约定成俗的默认配置,并允许我们调整这些配置,即遵循“约定大于配置”的理念。SpringBoot提供的starter包括了:
- spring-boot-starter
- spring-boot-starter-logging
- spring-boot-starter-web
- spring-boot-starter-jdbc
- spring-boot-starter-aop
- spring-boot-starter-secutiry
- ......
下面通过一个最常用的web应用场景使用的spring-boot-starter-web来介绍一下starter到底干了什么,以及是如何干的;然后自定义一个starter。
6.1 spring-boot-starter-web详解
打开spring-boot-starter-web-1.5.8.RELEASE.jar看一下,发现结构如下:其中META-INF中并没有定义spring.factories文件,回顾前面介绍的@EnableAutoConfiguration注释的功能,其实这些SpringBoot官方提供的starter的配置类是在spring-boot-autoconfigure模块中注册的,而starter本身只通过pom.xml来定义其依赖的类库,因此其中唯一起作用的就是pom.xml,spring-boot-starter-web相应的pom.xml内容如下:
- <?xml version="1.0" encoding="UTF-8"?>
- <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
- <modelVersion>4.0.0</modelVersion>
- <parent>
- <groupId>org.springframework.boot</groupId>
- <artifactId>spring-boot-starters</artifactId>
- <version>1.5.8.RELEASE</version>
- </parent>
- <artifactId>spring-boot-starter-web</artifactId>
- <name>Spring Boot Web Starter</name>
- <description>Starter for building web, including RESTful, applications using Spring
- MVC. Uses Tomcat as the default embedded container</description>
- <url>http://projects.spring.io/spring-boot/</url>
- <organization>
- <name>Pivotal Software, Inc.</name>
- <url>http://www.spring.io</url>
- </organization>
- <properties>
- <main.basedir>${basedir}/../..</main.basedir>
- </properties>
- <dependencies>
- <dependency>
- <groupId>org.springframework.boot</groupId>
- <artifactId>spring-boot-starter</artifactId>
- </dependency>
- <dependency>
- <groupId>org.springframework.boot</groupId>
- <artifactId>spring-boot-starter-tomcat</artifactId>
- </dependency>
- <dependency>
- <groupId>org.hibernate</groupId>
- <artifactId>hibernate-validator</artifactId>
- </dependency>
- <dependency>
- <groupId>com.fasterxml.jackson.core</groupId>
- <artifactId>jackson-databind</artifactId>
- </dependency>
- <dependency>
- <groupId>org.springframework</groupId>
- <artifactId>spring-web</artifactId>
- </dependency>
- <dependency>
- <groupId>org.springframework</groupId>
- <artifactId>spring-webmvc</artifactId>
- </dependency>
- </dependencies>
- </project>
从上可得,这些starters只是定义了各个场景需要依赖的jar包,而真正做自动化配置的代码的是在spring-boot-autoconfigure里面。SpringBoot会基于你的classpath中的jar包,试图猜测和配置您可能需要的bean。
我们通过在前面介绍的spring-boot-autoconfig包中定义的META-INF/spring.factories中可看到,与web相关的自动配置类有:
- org.springframework.boot.autoconfigure.web.DispatcherServletAutoConfiguration,\
- org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration,\
- org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration,\
- org.springframework.boot.autoconfigure.web.HttpEncodingAutoConfiguration,\
- org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration,\
- org.springframework.boot.autoconfigure.web.MultipartAutoConfiguration,\
- org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration,\
- org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration,\
- org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration,\
- @Configuration
- @ConditionalOnWebApplication
- @ConditionalOnClass({ Servlet.class, DispatcherServlet.class,
- WebMvcConfigurerAdapter.class })
- @ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
- @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
- @AutoConfigureAfter(DispatcherServletAutoConfiguration.class)
- public class WebMvcAutoConfiguration{
- ...............
- }
内部注册了一系列必要的ViewResolver、Converter、Formatter、Filter等等。
其中@AutoConfigureAfter代表需要在DispatcherServletAutoConfiguration之后加载,因此,在此之前需要先加载DispatcherServletAutoConfiguration,其注释信息如下:- @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
- @Configuration
- @ConditionalOnWebApplication
- @ConditionalOnClass(DispatcherServlet.class)
- @AutoConfigureAfter(EmbeddedServletContainerAutoConfiguration.class)
- public class DispatcherServletAutoConfiguration {
- ......
- }
DispatcherServletAutoConfiguration内部通过@EnableConfigurationProperties/@ConfigurationProperties机制使用属性设置DispatcherServlet并注册进IOC容器,然后注册一个ServletRegistrationBean到IOC容器。DispatcherServlet是springframework中web模块的概念,是http请求分发路由的核心枢纽。ServletRegistrationBean是SpringBoot中用来在Servlet容器中注册servlet用的,其作用类似于ServletContext.addServlet(String, Servlet),但是用了更加友好的Spring bean配置注册方式。
在该类的注释中同样使用@AutoConfigureAfter来指示加载本类之前先加载EmbeddedServletContainerAutoConfiguration配置类,其代码如下:
- @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
- @Configuration
- @ConditionalOnWebApplication
- @Import(BeanPostProcessorsRegistrar.class)
- public class EmbeddedServletContainerAutoConfiguration {
- .........
- }
EmbeddedServletContainerAutoConfiguration首先判断是否web应用,若是才会继续。其作用是根据不同的条件(通过判断拥有哪些类来判断引入了哪个包)注册EmbeddedServletContainerCustomizer的具体实现(例如:TomcatEmbeddedServletContainerFactory和JettyEmbeddedServletContainerFactory等),然后通过Import机制为beanFactory注册embeddedServletContainerCustomizerBeanPostProcessor和errorPageRegistrarBeanPostProcessor这两个BeanDefinition。
这两个BeanPostProcessor会在EmbeddedServletContainerCustomizer类型的bean被实例化之后、初始化之前以后对其进行进一步的操作。
EmbeddedServletContainerCustomizerBeanPostProcessor会利用已注册在beanFactory中的EmbeddedServletContainerCustomizers来对ConfigurableEmbeddedServletContainer进行定制:
- @Override
- public Object postProcessBeforeInitialization(Object bean, String beanName)
- throws BeansException {
- if (bean instanceof ConfigurableEmbeddedServletContainer) {
- postProcessBeforeInitialization((ConfigurableEmbeddedServletContainer) bean);
- }
- return bean;
- }
- private void postProcessBeforeInitialization(
- ConfigurableEmbeddedServletContainer bean) {
- for (EmbeddedServletContainerCustomizer customizer : getCustomizers()) {
- customizer.customize(bean);
- }
- }
例如其中有一个名为ServerProperties的customizer,其本身通过标注@ConfigurationProperties(prefix = "server", ignoreUnknownFields = true)来将自身属性设置为以server.开头配置的属性,然后其customize函数代码如下:
- public void customize(ConfigurableEmbeddedServletContainer container) {
- if (getPort() != null) {
- container.setPort(getPort());
- }
- if (getAddress() != null) {
- container.setAddress(getAddress());
- }
- if (getContextPath() != null) {
- container.setContextPath(getContextPath());
- }
- if (getDisplayName() != null) {
- container.setDisplayName(getDisplayName());
- }
- if (getSession().getTimeout() != null) {
- container.setSessionTimeout(getSession().getTimeout());
- }
- container.setPersistSession(getSession().isPersistent());
- container.setSessionStoreDir(getSession().getStoreDir());
- if (getSsl() != null) {
- container.setSsl(getSsl());
- }
- if (getJspServlet() != null) {
- container.setJspServlet(getJspServlet());
- }
- if (getCompression() != null) {
- container.setCompression(getCompression());
- }
- container.setServerHeader(getServerHeader());
- if (container instanceof TomcatEmbeddedServletContainerFactory) {
- getTomcat().customizeTomcat(this,
- (TomcatEmbeddedServletContainerFactory) container);
- }
- if (container instanceof JettyEmbeddedServletContainerFactory) {
- getJetty().customizeJetty(this,
- (JettyEmbeddedServletContainerFactory) container);
- }
- if (container instanceof UndertowEmbeddedServletContainerFactory) {
- getUndertow().customizeUndertow(this,
- (UndertowEmbeddedServletContainerFactory) container);
- }
- container.addInitializers(new SessionConfiguringInitializer(this.session));
- container.addInitializers(new InitParameterConfiguringServletContextInitializer(
- getContextParameters()));
- }
errorPageRegistrarBeanPostProcessor会利用已注册在beanFactory中的ErrorPageRegistrar来对ConfigurableEmbeddedServletContainer进行定制:
- private void postProcessBeforeInitialization(ErrorPageRegistry registry) {
- for (ErrorPageRegistrar registrar : getRegistrars()) {
- registrar.registerErrorPages(registry);
- }
- }
- public void registerErrorPages(ErrorPageRegistry errorPageRegistry) {
- ErrorPage errorPage = new ErrorPage(this.properties.getServletPrefix()
- + this.properties.getError().getPath());
- errorPageRegistry.addErrorPages(errorPage);
- }
除此之外还有:
- org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration,\
- org.springframework.boot.autoconfigure.web.HttpEncodingAutoConfiguration,\
- org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration,\
- org.springframework.boot.autoconfigure.web.MultipartAutoConfiguration,\
- org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration,\
- org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration,\
当我们引入spring-boot-starter-web时,上面的启动条件会满足,因此这些配置类都会被加载生效。于是对于一个web应用,默认就配置完成了。
6.2 自定义starter
SpringBoot官方提供的starter提供了两层有价值的信息:所需依赖的jar包相互之间使用不产生冲突的版本;在spring-boot-autoconfiguration库中提供了对其进行默认配置的配置类并利用Spring框架的扩展协议实现注册。因此,当我们想要自定义一个starter,以实现一旦在pom.xml中引入该starter就能自动工作的效果时,我们需要确保两件事:
- 仔细确定依赖的各个库的jar包的版本,保证它们之间不会产生冲突,或无法合作。
- 提供对所需机制的Configuration类,以实现将需要的功能注入IOC容器。并通过SpringBoot的扩展机制确保引入自定义starter的jar包时Configuration类被加载。
1. 编写pom.xml在其中定义我们的场景需要依赖的jar包,并仔细选择其版本
2. 项目中编写@Configuration配置类以将必要的功能注册进IOC容器
3. 在META-INF/spring.factories中添加
- org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
- mypackage1.MyConfiguration1,\
- mypackage2.MyConfiguration2,\
- .........
4. 打包成jar文件以供使用。
如此一来,每当该starter jar包被引入时,SpringBoot的@EnableAutoConfiguration注释便会借助SpringFactoriesLoader将我们配置的Configuration类加载,并对其进行解析,我们的starter就可以工作起来了。
7 自动配置机制实现原理
7.1 SpringFactoriesLoader
SpringFactoriesLoader是SpringFramework内部使用的通用的工厂加载机制,其可加载并实例化可能出现在classpath上的多个jar包中的META-INF/spring.factories文件中定义的指定类型的工厂。factories文件必须使用Properties格式,也就是多行key=value组成的格式。其中key是指定工厂的抽象类或接口的全限定名,value是用逗号隔开的key指定工厂的具体实现类的全限定名。例如:
- example.MyService=example.MyServiceImpl1,example.MyServiceImpl2
这样配置完后,我们就可以使用SpringFactoriesLoader.loadFactories(Myservice.class, null)来获得MyServiceImpl1和MyServiceImpl2的实例。后续如何处理MyServiceImpl1和MyServiceImpl1,就看各个扩展机制的实际业务逻辑了。
7.2 EnableAutoConfiguration
EnableAutoConfiguration是SpringBoot利用SpringFactoriesLoader扩展机制来实现的一种自动配置机制。EnableAutoConfiguration注释包含两层功能:第一是作为注释,通过Import机制实现标注在类上以表示开启自动配置机制。第二是作为SpringBoot的autoconfiguration模块利用SpringFactoriesLoader扩展的“工厂类”。
在autoconfiguration模块的META-INF/spring.factories中定义了:
- # Auto Configure
- org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
- org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
- org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
- org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
- org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
- org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
- org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\
- org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration,\
- .......
8 属性配置说明
8.1 SpringBoot属性配置顺序
Spring Boot支持多种外部属性源配置方式,并使用非常特别的属性源优先级顺序:1. 命令行参数
2. 来自java:comp/env的JNDI属性
3. Java系统属性(System.getProperties())
4. 操作系统环境变量
5. RandomValuePropertySource配置的random.*属性值
6. jar包外部的application-{profile}.properties或application.yml(带spring.profile)配置文件
7. jar包内部的application-{profile}.properties或application.yml(带spring.profile)配置文件
8. jar包外部的application.properties或application.yml(不带sprin.profile)配置文件
9. jar包内部的application.properties或application.yml(不带spring.profile)配置文件
10. @Configuration注解类上的@PropertySource
11. 通过SpringApplication.setDefaultProperties指定的默认属性
具体使用说明,请参照文档https://docs.spring.io/spring-boot/docs/1.2.3.RELEASE/reference/html/boot-features-external-config.html。
8.2 属性值配置/获取方式
SpringBoot为我们提供的获得属性值的方式有以下几种,其中有Springframework本身就提供了的,也有SpringBoot自己扩展出来的方式:1. environment.getProperty(String key)
任何我们可以获得Environment对象的地方,都可以直接使用这个函数来获得key所定义的属性值。key是类似home.me.name或server.port等等这样的字符串,例如:- environment.getProperty("home.me.name");
- environment.getProperty("server.port");
2. environment.resolvePlaceholders(String placeholder)
同上,能获得environment对象的地方,都可以使用该函数。所不同的是,其参数为placeholder,也就是${home.me.name}或${server.port}并且支持嵌套表达,例如:- environment.resolverPlaceholders("${home.me.name}");
- environment.resolverPlaceholders("${home.me.${test.name}}");
3. @Value
当我们在一个Bean中的某属性上定义@Value("home.me.name")时,IOC容器在创建这个Bean的时候就会将对应的属性值注入(Inject)进去,例如:- @Component
- public class SBConfiguration {
- @Value("${home.me.name:hello}")
- <span style="white-space:pre;"> </span>String name;
- <span style="white-space:pre;"> </span>......
- }
4. @ConfigurationProperties("home.me")
当我们在一个配置类上标注@ConfigurationProperties时,IOC容器会在创建这个配置类时自动为其注入其字段对应的属性(若存在的话)。这是SpringBoot新引入的获取机制。- @Configuration
- @ConfigurationProperties("home.me")
- public class SBConfiguration {
- String name;
- ......
- }
所有这些获取方式都最终都会将实际的属性获取行为委托给spring-core模块中的PropertySourcesPropertyResolver:
- protected <T> T getProperty(String key, Class<T> targetValueType, boolean resolveNestedPlaceholders) {
- if (this.propertySources != null) {
- for (PropertySource<?> propertySource : this.propertySources) {
- if (logger.isTraceEnabled()) {
- logger.trace("Searching for key '" + key + "' in PropertySource '" +
- propertySource.getName() + "'");
- }
- Object value = propertySource.getProperty(key);
- if (value != null) {
- if (resolveNestedPlaceholders && value instanceof String) {
- value = resolveNestedPlaceholders((String) value);
- }
- logKeyFound(key, propertySource, value);
- return convertValueIfNecessary(value, targetValueType);
- }
- }
- }
- if (logger.isDebugEnabled()) {
- logger.debug("Could not find key '" + key + "' in any property source");
- }
- return null;
- }
其中的this.propertySources是从environment中获取过来的。上述代码的意思就是遍历environment中预定义的propertySources,查找属性key对应的值,如有需要递归处理嵌套属性,一旦得到非空的属性值,就返回。因此对于多个propertySources来源而言,排在前面的优先级就高过排在后面的优先级。
8.3 属性源注册顺序
从8.2属性获取及绑定过程可知,属性源优先级顺序其实就取决于属性源在environment中注册完毕后的最终顺序,SpringBoot在启动阶段控制这这个属性源的加载及排序,我们跟踪一下启动过程:
- protected void customizePropertySources(MutablePropertySources propertySources) {
- propertySources.addLast(new StubPropertySource(SERVLET_CONFIG_PROPERTY_SOURCE_NAME));
- propertySources.addLast(new StubPropertySource(SERVLET_CONTEXT_PROPERTY_SOURCE_NAME));
- if (JndiLocatorDelegate.isDefaultJndiEnvironmentAvailable()) {
- propertySources.addLast(new JndiPropertySource(JNDI_PROPERTY_SOURCE_NAME));
- }
- super.customizePropertySources(propertySources);
- }
- protected void customizePropertySources(MutablePropertySources propertySources) {
- propertySources.addLast(new MapPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));
- propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME,
- getSystemEnvironment()));
- }
此时propertySources的顺序为:
- servletConfigInitParams
- servletContextInitParams
- jndiProperties
- systemProperties
- systemEnvironment
2. 然后在configEnvironment阶段:
- 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));
- }
- }
- }
- commandLineArgs
- servletConfigInitParams
- servletContextInitParams
- jndiProperties
- systemProperties
- systemEnvironment
- defaultProperties
3. 在发出environmentPrepared事件后,ConfigFileApplicationListener执行回调函数:
- public void postProcessEnvironment(ConfigurableEnvironment environment,
- SpringApplication application) {
- addPropertySources(environment, application.getResourceLoader());
- configureIgnoreBeanInfo(environment);
- bindToSpringApplication(environment, application);
- }
- protected void addPropertySources(ConfigurableEnvironment environment,
- ResourceLoader resourceLoader) {
- RandomValuePropertySource.addToEnvironment(environment);
- new Loader(environment, resourceLoader).load();
- }
- public static void addToEnvironment(ConfigurableEnvironment environment) {
- environment.getPropertySources().addAfter(
- StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME,
- new RandomValuePropertySource(RANDOM_PROPERTY_SOURCE_NAME));
- logger.trace("RandomValuePropertySource add to Environment");
- }
然后委托Loader来搜索searchLocations路径上的可用的配置文件。默认搜索顺序是file:./config/, file:./, classpath:/config/, classpath:./。我们可以通过设置"spring.config.location"来修改默认搜索路径。
结合environment当前设置的profile,在上述路径中查询特定文件名(默认为"application",可通过设置"spring.config.name"来指定)和特定后缀(properties, xml, yml, yaml)的文件。将所有符合条件的文件封装为不同类型的PropertySource(例如PropertiesPropertySource)。最终将这些PropertySources封装成一个ConfigurationPropertySources(名为:applicationConfigurationProperties)然后添加在如下位置:
- private void addConfigurationProperties(
- ConfigurationPropertySources configurationSources) {
- MutablePropertySources existingSources = this.environment
- .getPropertySources();
- if (existingSources.contains(DEFAULT_PROPERTIES)) {
- existingSources.addBefore(DEFAULT_PROPERTIES, configurationSources);
- }
- else {
- existingSources.addLast(configurationSources);
- }
- }
- commandLineArgs
- servletConfigInitParams
- servletContextInitParams
- jndiProperties
- systemProperties
- systemEnvironment
- random
- applicationConfigurationProperties
- defaultProperties
4. 随后,在context.refresh阶段的invokeBeanFactoryPostProcessors(beanFactory)子阶段,会执行到ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry函数。其中委托ConfigurationClassParser来解析已经注册到beanDefinitionFactory中的@Configuration类,其中调用到doProcessConfigurationClass方法来获得配置在@Configuration类上的propertySource:
- for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
- sourceClass.getMetadata(), PropertySources.class,
- org.springframework.context.annotation.PropertySource.class)) {
- if (this.environment instanceof ConfigurableEnvironment) {
- processPropertySource(propertySource);
- }
- else {
- logger.warn("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
- "]. Reason: Environment must implement ConfigurableEnvironment");
- }
- }
- private void processPropertySource(AnnotationAttributes propertySource) throws IOException {
- String name = propertySource.getString("name");
- if (!StringUtils.hasLength(name)) {
- name = null;
- }
- String encoding = propertySource.getString("encoding");
- if (!StringUtils.hasLength(encoding)) {
- encoding = null;
- }
- String[] locations = propertySource.getStringArray("value");
- Assert.isTrue(locations.length > 0, "At least one @PropertySource(value) location is required");
- boolean ignoreResourceNotFound = propertySource.getBoolean("ignoreResourceNotFound");
- Class<? extends PropertySourceFactory> factoryClass = propertySource.getClass("factory");
- PropertySourceFactory factory = (factoryClass == PropertySourceFactory.class ?
- DEFAULT_PROPERTY_SOURCE_FACTORY : BeanUtils.instantiateClass(factoryClass));
- for (String location : locations) {
- try {
- String resolvedLocation = this.environment.resolveRequiredPlaceholders(location);
- Resource resource = this.resourceLoader.getResource(resolvedLocation);
- addPropertySource(factory.createPropertySource(name, new EncodedResource(resource, encoding)));
- }
- catch (IllegalArgumentException ex) {
- // Placeholders not resolvable
- if (ignoreResourceNotFound) {
- if (logger.isInfoEnabled()) {
- logger.info("Properties location [" + location + "] not resolvable: " + ex.getMessage());
- }
- }
- else {
- throw ex;
- }
- }
- catch (IOException ex) {
- // Resource not found when trying to open it
- if (ignoreResourceNotFound &&
- (ex instanceof FileNotFoundException || ex instanceof UnknownHostException)) {
- if (logger.isInfoEnabled()) {
- logger.info("Properties location [" + location + "] not resolvable: " + ex.getMessage());
- }
- }
- else {
- throw ex;
- }
- }
- }
- }
其功能是获得PropertySource注释的value属性定义的逗号分割的多个locations,为每一个都创建ResourcePropertySource并对其执行addPropertySource方法:
- private void addPropertySource(PropertySource<?> propertySource) {
- String name = propertySource.getName();
- MutablePropertySources propertySources = ((ConfigurableEnvironment) this.environment).getPropertySources();
- if (propertySources.contains(name) && this.propertySourceNames.contains(name)) {
- // We've already added a version, we need to extend it
- PropertySource<?> existing = propertySources.get(name);
- PropertySource<?> newSource = (propertySource instanceof ResourcePropertySource ?
- ((ResourcePropertySource) propertySource).withResourceName() : propertySource);
- if (existing instanceof CompositePropertySource) {
- ((CompositePropertySource) existing).addFirstPropertySource(newSource);
- }
- else {
- if (existing instanceof ResourcePropertySource) {
- existing = ((ResourcePropertySource) existing).withResourceName();
- }
- CompositePropertySource composite = new CompositePropertySource(name);
- composite.addPropertySource(newSource);
- composite.addPropertySource(existing);
- propertySources.replace(name, composite);
- }
- }
- else {
- if (this.propertySourceNames.isEmpty()) {
- propertySources.addLast(propertySource);
- }
- else {
- String firstProcessed = this.propertySourceNames.get(this.propertySourceNames.size() - 1);
- propertySources.addBefore(firstProcessed, propertySource);
- }
- }
- this.propertySourceNames.add(name);
- }
addPropertySource函数主要用来确定ResourcePropertySource的添加次序:
- 如果propertySources已经添加了相同名称的propertySource并且本实例维护的propertySourceNames包含本名称,则说明已经注册过一个相同名称的用@PropertySource标注的属性源,因此需要对已有的属性源进行扩展。将新增加的propertySource插入进去。
- 否则,如果本实例维护的propertySourceNames为空,说明在此之前并没有注册任何通过@PropertySource标注的属性源,则将该属性源添加到propertySources的最后,也就是优先级最低的位置。
- 若本实例维护的propertySourceNames不为空,则说明在此之前已经注册过通过@PropertySource标注的属性源,则将本属性源添加到上一次添加的属性源之前。
- commandLineArgs
- servletConfigInitParams
- servletContextInitParams
- jndiProperties
- systemProperties
- systemEnvironment
- random
- applicationConfigurationProperties
- defaultProperties
- ResourcePropertySource(若干个)
5. 跟着会由PropertySourceOrderingPostProcessor执行postProcessBeanFactory:
- public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)
- throws BeansException {
- reorderSources(this.context.getEnvironment());
- }
- private void reorderSources(ConfigurableEnvironment environment) {
- ConfigurationPropertySources
- .finishAndRelocate(environment.getPropertySources());
- PropertySource<?> defaultProperties = environment.getPropertySources()
- .remove(DEFAULT_PROPERTIES);
- if (defaultProperties != null) {
- environment.getPropertySources().addLast(defaultProperties);
- }
- }
然后将"defaultProperties"删除,如果"defaultProperties"不为空,那么就将其添加到队列的最后,也就是优先级最低的地方。重新排序后最终propertySources的顺序如下:
- commandLineArgs
- servletConfigInitParams
- servletContextInitParams
- jndiProperties
- systemProperties
- systemEnvironment
- random
- PropertiesPropertySource(若干)
- ResourcePropertySource(若干)
- defaultProperties
经过上述的整个过程以后,environment中参数源列表(propertySources)的排序与前面文档中提到的顺序就完全一致了。