一. 测试代码

@SpringBootApplication

public class SbmvcApplication {

    public static void main(String[] args) {

        SpringApplication.run(SbmvcApplication.class, args);

    }

}

此处我的springboot 版本是 2.0.3.RELEASE

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <parent>

        <groupId>org.springframework.boot</groupId>

        <artifactId>spring-boot-starter-parent</artifactId>

        <version>2.0.3.RELEASE</version>

        <relativePath/> <!-- lookup parent from repository -->

    </parent>

    <groupId>com.study.demo</groupId>

    <artifactId>sbmvc</artifactId>

    <version>0.0.1-SNAPSHOT</version>

    <name>sbmvc</name>

    <description>Demo project for Spring Boot</description>

    <properties>

        <java.version>1.8</java.version>

    </properties>

    <dependencies>

        <dependency>

            <groupId>org.springframework.boot</groupId>

            <artifactId>spring-boot-starter-web</artifactId>

        </dependency>

    </dependencies>

    <build>

        <plugins>

            <plugin>

                <groupId>org.springframework.boot</groupId>

                <artifactId>spring-boot-maven-plugin</artifactId>

            </plugin>

        </plugins>

    </build>

</project>

二. 调试

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);

}

1. 创建 SpringApplication

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));
　　//判断运行环境类型

    this.webApplicationType = deduceWebApplicationType();
　　//加载 spring.factories 配置文件, 并设置 ApplicationContextInitializer 配置到 this.initializers 属性中

    setInitializers((Collection) getSpringFactoriesInstances(

            ApplicationContextInitializer.class));
　　//同样是加载配置文件, 设置 ApplicationListener配置 到 this.listeners 属性中

    setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
　　//这里是拿入口类, 如本例中的 Sbmvcapplication

    this.mainApplicationClass = deduceMainApplicationClass();

}

deduceWebApplicationType()

private static final String REACTIVE_WEB_ENVIRONMENT_CLASS = "org.springframework."

            + "web.reactive.DispatcherHandler";

private static final String MVC_WEB_ENVIRONMENT_CLASS = "org.springframework."

            + "web.servlet.DispatcherServlet";

private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",

            "org.springframework.web.context.ConfigurableWebApplicationContext" };

private WebApplicationType deduceWebApplicationType() {

    if (ClassUtils.isPresent(REACTIVE_WEB_ENVIRONMENT_CLASS, null)

            && !ClassUtils.isPresent(MVC_WEB_ENVIRONMENT_CLASS, null)) {

        return WebApplicationType.REACTIVE;

    }

    for (String className : WEB_ENVIRONMENT_CLASSES) {

        if (!ClassUtils.isPresent(className, null)) {

            return WebApplicationType.NONE;

        }

    }

    return WebApplicationType.SERVLET;

}

从这里看, 程序分为3中运行环境,

NONE : 非 web 的运行环境

SERVLET : 普通 web 的运行环境

REACTIVE : 响应式 web 的运行环境

这里主要看的是 SERVLET 启动.

getSpringFactoriesInstances()

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {

    return getSpringFactoriesInstances(type, new Class<?>[] {});

}

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,

        Class<?>[] parameterTypes, Object... args) {

    ClassLoader classLoader = Thread.currentThread().getContextClassLoader();

    // Use names and ensure unique to protect against duplicates

    Set<String> names = new LinkedHashSet<>(

            SpringFactoriesLoader.loadFactoryNames(type, classLoader));

    List<T> instances = createSpringFactoriesInstances(type, parameterTypes,

            classLoader, args, names);

    AnnotationAwareOrderComparator.sort(instances);

    return instances;

}

这里主要看一下 SpringFactoriesLoader.loadFactoryNames() 方法

public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {

    String factoryClassName = factoryClass.getName();

    return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());

}

public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";

private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {

    MultiValueMap<String, String> result = cache.get(classLoader);

    if (result != null) {

        return result;

    }

    try {

        Enumeration<URL> urls = (classLoader != null ?

                classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :

                ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));

        result = new LinkedMultiValueMap<>();

        while (urls.hasMoreElements()) {

            URL url = urls.nextElement();

            UrlResource resource = new UrlResource(url);

            Properties properties = PropertiesLoaderUtils.loadProperties(resource);

            for (Map.Entry<?, ?> entry : properties.entrySet()) {

                List<String> factoryClassNames = Arrays.asList(

                        StringUtils.commaDelimitedListToStringArray((String) entry.getValue()));

                result.addAll((String) entry.getKey(), factoryClassNames);

            }

        }

        cache.put(classLoader, result);

        return result;

    }

    catch (IOException ex) {

        throw new IllegalArgumentException("Unable to load factories from location [" +

                FACTORIES_RESOURCE_LOCATION + "]", ex);

    }

}

看到这, 能明白, 是在加载 META-INF/spring.factories 文件中的配置.

key 就是传入类的引用, value 是配置的值, 多个值之间用英文逗号隔开, 如:

# PropertySource Loaders

org.springframework.boot.env.PropertySourceLoader=\

org.springframework.boot.env.PropertiesPropertySourceLoader,\

org.springframework.boot.env.YamlPropertySourceLoader

# Run Listeners

org.springframework.boot.SpringApplicationRunListener=\

org.springframework.boot.context.event.EventPublishingRunListener

# Error Reporters

org.springframework.boot.SpringBootExceptionReporter=\

org.springframework.boot.diagnostics.FailureAnalyzers

# Application Context Initializers

org.springframework.context.ApplicationContextInitializer=\

org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\

org.springframework.boot.context.ContextIdApplicationContextInitializer,\

org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\

org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer

# Application Listeners

org.springframework.context.ApplicationListener=\

org.springframework.boot.ClearCachesApplicationListener,\

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.context.logging.ClasspathLoggingApplicationListener,\

org.springframework.boot.context.logging.LoggingApplicationListener,\

org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener

# Environment Post Processors

org.springframework.boot.env.EnvironmentPostProcessor=\

org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\

org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor,\

org.springframework.boot.env.SystemEnvironmentPropertySourceEnvironmentPostProcessor

# Failure Analyzers

org.springframework.boot.diagnostics.FailureAnalyzer=\

org.springframework.boot.diagnostics.analyzer.BeanCurrentlyInCreationFailureAnalyzer,\

org.springframework.boot.diagnostics.analyzer.BeanNotOfRequiredTypeFailureAnalyzer,\

org.springframework.boot.diagnostics.analyzer.BindFailureAnalyzer,\

org.springframework.boot.diagnostics.analyzer.BindValidationFailureAnalyzer,\

org.springframework.boot.diagnostics.analyzer.UnboundConfigurationPropertyFailureAnalyzer,\

org.springframework.boot.diagnostics.analyzer.ConnectorStartFailureAnalyzer,\

org.springframework.boot.diagnostics.analyzer.NoUniqueBeanDefinitionFailureAnalyzer,\

org.springframework.boot.diagnostics.analyzer.PortInUseFailureAnalyzer,\

org.springframework.boot.diagnostics.analyzer.ValidationExceptionFailureAnalyzer,\

org.springframework.boot.diagnostics.analyzer.InvalidConfigurationPropertyNameFailureAnalyzer,\

org.springframework.boot.diagnostics.analyzer.InvalidConfigurationPropertyValueFailureAnalyzer

# FailureAnalysisReporters

org.springframework.boot.diagnostics.FailureAnalysisReporter=\

org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter

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;

}

这里调用了非java代码, 跟踪不了具体执行过程, 但是从结果看, 拿到的是 SbmvcApplication 类

总结

在创建 SpringApplication 的时候, 干了以下几件事情:

1. 判断了运行环境类型为 SERVLET

2. 加载了 spring.factories 文件中的 ApplicationContextInitializer 配置到 this.initializers 属性中 - 6个初始化器

# spring-boot 包里面

# Application Context Initializers

org.springframework.context.ApplicationContextInitializer=\

org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\

org.springframework.boot.context.ContextIdApplicationContextInitializer,\

org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\

org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer

# spring-boot-autoconfigure 包里面

# Initializers

org.springframework.context.ApplicationContextInitializer=\

org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\

org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener

3. 加载了 spring.factories 文件中的 ApplicationListener 配置到 this.listeners 属性中 - 10个监听器

# spring-boot 包里面
# Application Listeners

org.springframework.context.ApplicationListener=\

org.springframework.boot.ClearCachesApplicationListener,\

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.context.logging.ClasspathLoggingApplicationListener,\

org.springframework.boot.context.logging.LoggingApplicationListener,\

org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener


# spring-boot-autoconfigure 包里面

# Application Listeners

org.springframework.context.ApplicationListener=\

org.springframework.boot.autoconfigure.BackgroundPreinitializer

4. 拿到入口类SbmvcApplication , 放入 this.mainApplicationClass 属性中.

巴特西

springboot web - 启动(1) 创建SpringApplication