springboot源码解析-管中窥豹系列之web服务器（七）

一、前言

• Springboot源码解析是一件大工程，逐行逐句的去研究代码，会很枯燥，也不容易坚持下去。
• 我们不追求大而全，而是试着每次去研究一个小知识点，最终聚沙成塔，这就是我们的springboot源码管中窥豹系列。

二、web服务器

• 以前的的spring项目或者springmvc项目都需要一个web服务器，tomcat,或者其它的
• 使用springboot之后，我们不再需要配置web服务器，因为springboot帮我们集成了
• 今天我们来分析一下源码，看看在哪里实现的，知其然知其所以然

三、源码分析

• 还是从SpringApplication的run方法开始看
• 不熟悉的可以看之前的文章：springboot源码解析-管中窥豹系列之总体结构（一）

SpringApplication.java
public ConfigurableApplicationContext run(String... args) {

    ...

    try {

        ...

        refreshContext(context);

        ...

    }
    catch (Throwable ex) {

        ...

    }

    ...

    return context;
}

• 接着进入到 refreshContext(context) 里面

AbstractApplicationContext.java

@Override
public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {

        ...

        try {

            ...

            // Initialize other special beans in specific context subclasses.
            onRefresh();

            ...
        }

        catch (BeansException ex) {

            ...

        }

        finally {

            ...

        }
    }
}

• 进入到 onRefresh() 方法

protected void onRefresh() throws BeansException {
    // For subclasses: do nothing by default.
}

• 注意这个是一个protected方法，我们进入到子实现里面
• 具体用的哪个context，请看之前的文章：springboot源码解析-管中窥豹系列之项目类型（二）

public static final String DEFAULT_CONTEXT_CLASS = "org.springframework.context."
        + "annotation.AnnotationConfigApplicationContext";

public static final String DEFAULT_SERVLET_WEB_CONTEXT_CLASS = "org.springframework.boot."
        + "web.servlet.context.AnnotationConfigServletWebServerApplicationContext";

public static final String DEFAULT_REACTIVE_WEB_CONTEXT_CLASS = "org.springframework."
        + "boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext";

protected ConfigurableApplicationContext createApplicationContext() {
    Class<?> contextClass = this.applicationContextClass;
    if (contextClass == null) {
        try {
            switch (this.webApplicationType) {
            case SERVLET:
                contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
                break;
            case REACTIVE:
                contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
                break;
            default:
                contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
            }
        }
        catch (ClassNotFoundException ex) {
            throw new IllegalStateException(
                    "Unable create a default ApplicationContext, please specify an ApplicationContextClass", ex);
        }
    }
    return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}

• 最常用的就是普通web项目，我们看这一个
• 我们到org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext里面找 onRefresh() 方法
• 没找到，在父类ServletWebServerApplicationContext里面找到了

ServletWebServerApplicationContext.java

@Override
protected void onRefresh() {
    super.onRefresh();
    try {
        createWebServer();
    }
    catch (Throwable ex) {
        throw new ApplicationContextException("Unable to start web server", ex);
    }
}

• 我们到 createWebServer() 方法里面

private void createWebServer() {
    WebServer webServer = this.webServer;
    ServletContext servletContext = getServletContext();
    if (webServer == null && servletContext == null) {
        ServletWebServerFactory factory = getWebServerFactory();
        this.webServer = factory.getWebServer(getSelfInitializer());
    }
    else if (servletContext != null) {
        try {
            getSelfInitializer().onStartup(servletContext);
        }
        catch (ServletException ex) {
            throw new ApplicationContextException("Cannot initialize servlet context",
                    ex);
        }
    }
    initPropertySources();
}

• 用的工厂模式，先找到工厂getWebServerFactory()
• 再用工厂生成webServer, factory.getWebServer(getSelfInitializer())
• 先看看 getWebServerFactory() 这个方法

protected ServletWebServerFactory getWebServerFactory() {
    // Use bean names so that we don't consider the hierarchy
    String[] beanNames = getBeanFactory()
            .getBeanNamesForType(ServletWebServerFactory.class);
    if (beanNames.length == 0) {
        throw new ApplicationContextException(
                "Unable to start ServletWebServerApplicationContext due to missing "
                        + "ServletWebServerFactory bean.");
    }
    if (beanNames.length > 1) {
        throw new ApplicationContextException(
                "Unable to start ServletWebServerApplicationContext due to multiple "
                        + "ServletWebServerFactory beans : "
                        + StringUtils.arrayToCommaDelimitedString(beanNames));
    }
    return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
}

• 获取唯一的工厂：ServletWebServerFactory，多了少了都不行
• 在哪加载进springboot的呢？

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter</artifactId>
    <scope>compile</scope>
</dependency>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-autoconfigure</artifactId>
    <scope>compile</scope>
</dependency>

• spring-boot-starter-web里面是包含了spring-boot-starter依赖的
• spring-boot-starter里面包含了spring-boot-autoconfigure依赖
• spring-boot-autoconfigure里面有一个类：ServletWebServerFactoryConfiguration
• 这个类里面有一个静态类: EmbeddedTomcat

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass({ Servlet.class, Tomcat.class, UpgradeProtocol.class })
@ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
static class EmbeddedTomcat {

    @Bean
    TomcatServletWebServerFactory tomcatServletWebServerFactory(
            ObjectProvider<TomcatConnectorCustomizer> connectorCustomizers,
            ObjectProvider<TomcatContextCustomizer> contextCustomizers,
            ObjectProvider<TomcatProtocolHandlerCustomizer<?>> protocolHandlerCustomizers) {
        TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory();
        factory.getTomcatConnectorCustomizers()
                .addAll(connectorCustomizers.orderedStream().collect(Collectors.toList()));
        factory.getTomcatContextCustomizers()
                .addAll(contextCustomizers.orderedStream().collect(Collectors.toList()));
        factory.getTomcatProtocolHandlerCustomizers()
                .addAll(protocolHandlerCustomizers.orderedStream().collect(Collectors.toList()));
        return factory;
    }

}

• ConditionOnClass : 它依赖 Servlet.class, Tomcat.class, UpgradeProtocol.class
• ConditionalOnMissingBean： 防止重复加载
• 至此，factory怎么加载进spring就找到了
• 我们多看一点，这个类ServletWebServerFactoryConfiguration还有两个静态类

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass({ Servlet.class, Server.class, Loader.class, WebAppContext.class })
@ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
static class EmbeddedJetty {

    @Bean
    JettyServletWebServerFactory JettyServletWebServerFactory(
            ObjectProvider<JettyServerCustomizer> serverCustomizers) {
        JettyServletWebServerFactory factory = new JettyServletWebServerFactory();
        factory.getServerCustomizers().addAll(serverCustomizers.orderedStream().collect(Collectors.toList()));
        return factory;
    }

}

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass({ Servlet.class, Undertow.class, SslClientAuthMode.class })
@ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
static class EmbeddedUndertow {

    @Bean
    UndertowServletWebServerFactory undertowServletWebServerFactory(
            ObjectProvider<UndertowDeploymentInfoCustomizer> deploymentInfoCustomizers,
            ObjectProvider<UndertowBuilderCustomizer> builderCustomizers) {
        UndertowServletWebServerFactory factory = new UndertowServletWebServerFactory();
        factory.getDeploymentInfoCustomizers()
                .addAll(deploymentInfoCustomizers.orderedStream().collect(Collectors.toList()));
        factory.getBuilderCustomizers().addAll(builderCustomizers.orderedStream().collect(Collectors.toList()));
        return factory;
    }

}

• 一个是生成jetty服务器工厂，一个是生成undertow服务器工厂
• 它们的加载，取决于依赖的class是否存在
• tomcat: Servlet.class, Tomcat.class, UpgradeProtocol.class
• jetty: Servlet.class, Server.class, Loader.class, WebAppContext.class
• undertow: Servlet.class, Undertow.class, SslClientAuthMode.class

假如我们想换成undertow服务器，依赖改了就行了

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-undertow</artifactId>
</dependency>

假如我们想换成jetty服务器，同理

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jetty</artifactId>
</dependency>

• 思维拉回来，工厂有了，我们看看工厂怎么生成的webServer

TomcatServletWebServerFactory.java
@Override
public WebServer getWebServer(ServletContextInitializer... initializers) {
    if (this.disableMBeanRegistry) {
        Registry.disableRegistry();
    }
    Tomcat tomcat = new Tomcat();
    File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
    tomcat.setBaseDir(baseDir.getAbsolutePath());
    Connector connector = new Connector(this.protocol);
    connector.setThrowOnFailure(true);
    tomcat.getService().addConnector(connector);
    customizeConnector(connector);
    tomcat.setConnector(connector);
    tomcat.getHost().setAutoDeploy(false);
    configureEngine(tomcat.getEngine());
    for (Connector additionalConnector : this.additionalTomcatConnectors) {
        tomcat.getService().addConnector(additionalConnector);
    }
    prepareContext(tomcat.getHost(), initializers);
    return getTomcatWebServer(tomcat);
}

• 这个方法我们就不分析了，就是生成tomcat服务器，和spring关联不大，改天我们专门分析tomcat源码
• 至此，整个springboot的加载web服务器过程就完了

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