Spring Boot 原理分析

spring-boot.version：2.4.3.RELEASE

Spring Boot 依赖管理

spring-boot-starter-parent

配置文件管理

<resources>
<resource>
<directory>${basedir}/src/main/resources</directory>
<filtering>true</filtering>
<includes>
<include>**/application*.yml</include>
<include>**/application*.yaml</include>
<include>**/application*.properties</include>
</includes>
</resource>
<resource>
<directory>${basedir}/src/main/resources</directory>
<excludes>
<exclude>**/application*.yml</exclude>
<exclude>**/application*.yaml</exclude>
<exclude>**/application*.properties</exclude>
</excludes>
</resource>
</resources>

spring-boot-dependencies

1.常用技术的版本号管理

2.常用技术的依赖管理

<dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>org.apache.activemq</groupId>
        <artifactId>activemq-amqp</artifactId>
        <version>${activemq.version}</version>
      </dependency>

3.插件管理

<build>
    <pluginManagement>
      <plugins>
        <plugin>
          <groupId>org.codehaus.mojo</groupId>
          <artifactId>build-helper-maven-plugin</artifactId>
          <version>${build-helper-maven-plugin.version}</version>
        </plugin>

spring-boot-starter-web

<dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter</artifactId>
      <version>2.3.7.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-json</artifactId>
      <version>2.3.7.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-tomcat</artifactId>
      <version>2.3.7.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-web</artifactId>
      <version>5.2.12.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>5.2.12.RELEASE</version>
      <scope>compile</scope>
    </dependency>
</dependencies>

Spring Boot 自动配置

由@SpringBootApplication配置springboot

源码：

@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {

@SpringBootConfiguration

@Configuration
public @interface SpringBootConfiguration {

说明是一个配置类，相当于XML配置文件

@EnableAutoConfiguration

@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {

@AutoConfigurationPackage

@Import(AutoConfigurationPackages.Registrar.class)
public @interface AutoConfigurationPackage {

static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {

       @Override
       public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
           register(registry, new PackageImports(metadata).getPackageNames().toArray(new String[0]));
       }

new PackageImports(metadata).getPackageNames().toArray(new String[0]):获取主程序启动类所在包

AutoConfigurationImportSelector.class中

有个方法getAutoConfigurationEntry（）中

List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);：获取自动配置类

# 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,\

。。。。。。

configurations = getConfigurationClassFilter().filter(configurations);：选出符合当前项目的自动配置类

@ComponentScan

扫描主程序启动类所在包下的组件

Spring Boot 执行流程

SpringApplication.run(Springboot11Application.class, args);

public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
return run(new Class<?>[] { primarySource }, args);
}

public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
return new SpringApplication(primarySources).run(args);
}

由上面代码看出，程序会创建SpringApplication实例并初始化和调用run方法启动项目

SpringApplication实例并初始化

public SpringApplication(Class<?>... primarySources) {
this(null, primarySources);
}

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
       this.resourceLoader = resourceLoader;
       Assert.notNull(primarySources, "PrimarySources must not be null");
       this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
       this.webApplicationType = WebApplicationType.deduceFromClasspath();//判断web应用类型，servlet应用还是reactive应用
       setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));//设置SpringApplication应用的初始化器
       setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));//设置SpringApplication应用的监听器
       this.mainApplicationClass = deduceMainApplicationClass();//推断主程序启动类
   }

static WebApplicationType deduceFromClasspath() {
       if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null) && !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)
               && !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {
           return WebApplicationType.REACTIVE;
       }
       for (String className : SERVLET_INDICATOR_CLASSES) {
           if (!ClassUtils.isPresent(className, null)) {
               return WebApplicationType.NONE;
           }
       }
       return WebApplicationType.SERVLET;
   }

run方法

public ConfigurableApplicationContext run(String... args) {
       StopWatch stopWatch = new StopWatch();
       stopWatch.start();
       ConfigurableApplicationContext context = null;
       Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
       configureHeadlessProperty();
       SpringApplicationRunListeners listeners = getRunListeners(args);//获取监听器
       listeners.starting();//启动监听器
       try {
           ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
           ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);// Create and configure the environment
           configureIgnoreBeanInfo(environment);//
           Banner printedBanner = printBanner(environment);
           context = createApplicationContext();
           exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
                   new Class[] { ConfigurableApplicationContext.class }, context);
           prepareContext(context, environment, listeners, applicationArguments, printedBanner);
           refreshContext(context);
           afterRefresh(context, applicationArguments);
           stopWatch.stop();
           if (this.logStartupInfo) {
               new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
           }
           listeners.started(context);
           callRunners(context, applicationArguments);//调用自定义的执行器，在启动项目后立即执行一些特定程序
       }
       catch (Throwable ex) {
           handleRunFailure(context, ex, exceptionReporters, listeners);
           throw new IllegalStateException(ex);
       }

try {

/**
   * Called immediately before the run method finishes, when the application context has
   * been refreshed and all {@link CommandLineRunner CommandLineRunners} and
   * {@link ApplicationRunner ApplicationRunners} have been called.
   * @param context the application context.
   * @since 2.0.0
   */
           listeners.running(context);//
       }
       catch (Throwable ex) {
           handleRunFailure(context, ex, exceptionReporters, null);
           throw new IllegalStateException(ex);
       }
       return context;
   }