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SpringBoot的两种启动方式原理解析(配置方案)

2025-01-16 08:54:09 作者：seven97_top

本文介绍了Spring Boot中两种启动方式,使用内置Tomcat启动和使用外置Tomcat部署,在使用内置Tomcat启动时,可以通过IDEA的main函数启动,也可以使用nohup命令在后台运行,这篇文章主要介绍了SpringBoot的两种启动方式原理 ,需要的朋友可以参考下

使用内置tomcat启动

配置案例

启动方式

IDEA中main函数启动
mvn springboot-run

java -jar XXX.jar
使用这种方式时，为保证服务在后台运行，会使用nohup

nohup java -jar -Xms128m -Xmx128m -Xss256k -XX:+PrintGCDetails -XX:+PrintHeapAtGC -Xloggc:/data/log/web-gc.log web.jar >/data/log/web.log &

使用java -jar默认情况下，不会启动任何嵌入式Application Server，该命令只是启动一个执行jar main的JVM进程，当spring-boot-starter-web包含嵌入式tomcat服务器依赖项时，执行java -jar则会启动Application Server

配置内置tomcat属性

关于Tomcat的属性都在 org.springframework.boot.autoconfigure.web.ServerProperties 配置类中做了定义，我们只需在application.properties配置属性做配置即可。通用的Servlet容器配置都以 server 作为前缀

#配置程序端口，默认为8080
server.port= 8080
#用户会话session过期时间，以秒为单位
server.session.timeout=
#配置默认访问路径，默认为/
server.context-path=

而Tomcat特有配置都以 server.tomcat 作为前缀

# 配置Tomcat编码,默认为UTF-8
server.tomcat.uri-encoding=UTF-8
# 配置最大线程数
server.tomcat.max-threads=1000

注意：使用内置tomcat不需要有tomcat-embed-jasper和spring-boot-starter-tomcat依赖，因为在spring-boot-starter-web依赖中已经集成了tomcat

原理

从main函数说起

public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
    return run(new Class[]{primarySource}, args);
}
// 这里run方法返回的是ConfigurableApplicationContext
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
 	return (new SpringApplication(primarySources)).run(args);
}

public ConfigurableApplicationContext run(String... args) {
 ConfigurableApplicationContext context = null;
 Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
 this.configureHeadlessProperty();
 SpringApplicationRunListeners listeners = this.getRunListeners(args);
 listeners.starting();
 Collection exceptionReporters;
 try {
  ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
  ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
  this.configureIgnoreBeanInfo(environment);
  //打印banner，这里可以自己涂鸦一下，换成自己项目的logo
  Banner printedBanner = this.printBanner(environment);
  //创建应用上下文
  context = this.createApplicationContext();
  exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
  //预处理上下文
  this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
  //刷新上下文
  this.refreshContext(context);
  //再刷新上下文
  this.afterRefresh(context, applicationArguments);
  listeners.started(context);
  this.callRunners(context, applicationArguments);
 } catch (Throwable var10) {
 }
 try {
  listeners.running(context);
  return context;
 } catch (Throwable var9) {
 }
}

既然我们想知道tomcat在SpringBoot中是怎么启动的，那么run方法中，重点关注创建应用上下文（createApplicationContext）和刷新上下文（refreshContext）。

创建上下文

//创建上下文
protected ConfigurableApplicationContext createApplicationContext() {
 Class<?> contextClass = this.applicationContextClass;
 if (contextClass == null) {
  try {
   switch(this.webApplicationType) {
    case SERVLET:
                    //创建AnnotationConfigServletWebServerApplicationContext
        contextClass = Class.forName("org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext");
     break;
    case REACTIVE:
     contextClass = Class.forName("org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext");
     break;
    default:
     contextClass = Class.forName("org.springframework.context.annotation.AnnotationConfigApplicationContext");
   }
  } catch (ClassNotFoundException var3) {
   throw new IllegalStateException("Unable create a default ApplicationContext, please specify an ApplicationContextClass", var3);
  }
 }
 return (ConfigurableApplicationContext)BeanUtils.instantiateClass(contextClass);
}

这里会创建AnnotationConfigServletWebServerApplicationContext类。而AnnotationConfigServletWebServerApplicationContext类继承了ServletWebServerApplicationContext，而这个类是最终集成了AbstractApplicationContext。

刷新上下文

//SpringApplication.java
//刷新上下文
private void refreshContext(ConfigurableApplicationContext context) {
 this.refresh(context);
 if (this.registerShutdownHook) {
  try {
   context.registerShutdownHook();
  } catch (AccessControlException var3) {
  }
 }
}
//这里直接调用最终父类AbstractApplicationContext.refresh()方法
protected void refresh(ApplicationContext applicationContext) {
 ((AbstractApplicationContext)applicationContext).refresh();
}

//AbstractApplicationContext.java
public void refresh() throws BeansException, IllegalStateException {
 synchronized(this.startupShutdownMonitor) {
  this.prepareRefresh();
  ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
  this.prepareBeanFactory(beanFactory);
  try {
   this.postProcessBeanFactory(beanFactory);
   this.invokeBeanFactoryPostProcessors(beanFactory);
   this.registerBeanPostProcessors(beanFactory);
   this.initMessageSource();
   this.initApplicationEventMulticaster();
   //调用各个子类的onRefresh()方法，也就说这里要回到子类：ServletWebServerApplicationContext，调用该类的onRefresh()方法
   this.onRefresh();
   this.registerListeners();
   this.finishBeanFactoryInitialization(beanFactory);
   this.finishRefresh();
  } catch (BeansException var9) {
   this.destroyBeans();
   this.cancelRefresh(var9);
   throw var9;
  } finally {
   this.resetCommonCaches();
  }
 }
}

//ServletWebServerApplicationContext.java
//在这个方法里看到了熟悉的面孔，this.createWebServer，神秘的面纱就要揭开了。
protected void onRefresh() {
 super.onRefresh();
 try {
  this.createWebServer();
 } catch (Throwable var2) {
 }
}
//ServletWebServerApplicationContext.java
//这里是创建webServer，但是还没有启动tomcat，这里是通过ServletWebServerFactory创建，那么接着看下ServletWebServerFactory
private void createWebServer() {
 WebServer webServer = this.webServer;
 ServletContext servletContext = this.getServletContext();
 if (webServer == null && servletContext == null) {
  ServletWebServerFactory factory = this.getWebServerFactory();
  this.webServer = factory.getWebServer(new ServletContextInitializer[]{this.getSelfInitializer()});
 } else if (servletContext != null) {
  try {
   this.getSelfInitializer().onStartup(servletContext);
  } catch (ServletException var4) {
  }
 }
 this.initPropertySources();
}
//接口
public interface ServletWebServerFactory {
    WebServer getWebServer(ServletContextInitializer... initializers);
}
//实现
AbstractServletWebServerFactory
JettyServletWebServerFactory
TomcatServletWebServerFactory
UndertowServletWebServerFactory

这里ServletWebServerFactory接口有4个实现类，对应着四种容器：

而其中我们常用的有两个：TomcatServletWebServerFactory和JettyServletWebServerFactory。

//TomcatServletWebServerFactory.java
//这里我们使用的tomcat，所以我们查看TomcatServletWebServerFactory。到这里总算是看到了tomcat的踪迹。
@Override
public WebServer getWebServer(ServletContextInitializer... initializers) {
 Tomcat tomcat = new Tomcat();
 File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
 tomcat.setBaseDir(baseDir.getAbsolutePath());
    //创建Connector对象
 Connector connector = new Connector(this.protocol);
 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);
}
protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
 return new TomcatWebServer(tomcat, getPort() >= 0);
}
//Tomcat.java
//返回Engine容器，看到这里，如果熟悉tomcat源码的话，对engine不会感到陌生。
public Engine getEngine() {
    Service service = getServer().findServices()[0];
    if (service.getContainer() != null) {
        return service.getContainer();
    }
    Engine engine = new StandardEngine();
    engine.setName( "Tomcat" );
    engine.setDefaultHost(hostname);
    engine.setRealm(createDefaultRealm());
    service.setContainer(engine);
    return engine;
}
//Engine是最高级别容器，Host是Engine的子容器，Context是Host的子容器，Wrapper是Context的子容器

getWebServer这个方法创建了Tomcat对象，并且做了两件重要的事情：把Connector对象添加到tomcat中，configureEngine(tomcat.getEngine());

getWebServer方法返回的是TomcatWebServer。

//TomcatWebServer.java
//这里调用构造函数实例化TomcatWebServer
public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
 Assert.notNull(tomcat, "Tomcat Server must not be null");
 this.tomcat = tomcat;
 this.autoStart = autoStart;
 initialize();
}
private void initialize() throws WebServerException {
    //在控制台会看到这句日志
 logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));
 synchronized (this.monitor) {
  try {
   addInstanceIdToEngineName();
   Context context = findContext();
   context.addLifecycleListener((event) -> {
    if (context.equals(event.getSource()) && Lifecycle.START_EVENT.equals(event.getType())) {
     removeServiceConnectors();
    }
   });
   //===启动tomcat服务===
   this.tomcat.start();
   rethrowDeferredStartupExceptions();
   try {
    ContextBindings.bindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
   }
   catch (NamingException ex) {
   }
            //开启阻塞非守护进程
   startDaemonAwaitThread();
  }
  catch (Exception ex) {
   stopSilently();
   destroySilently();
   throw new WebServerException("Unable to start embedded Tomcat", ex);
  }
 }
}

//Tomcat.java
public void start() throws LifecycleException {
 getServer();
 server.start();
}
//这里server.start又会回到TomcatWebServer的
public void stop() throws LifecycleException {
 getServer();
 server.stop();
}

//TomcatWebServer.java
//启动tomcat服务
@Override
public void start() throws WebServerException {
 synchronized (this.monitor) {
  if (this.started) {
   return;
  }
  try {
   addPreviouslyRemovedConnectors();
   Connector connector = this.tomcat.getConnector();
   if (connector != null && this.autoStart) {
    performDeferredLoadOnStartup();
   }
   checkThatConnectorsHaveStarted();
   this.started = true;
   //在控制台打印这句日志，如果在yml设置了上下文，这里会打印
   logger.info("Tomcat started on port(s): " + getPortsDescription(true) + " with context path '"
     + getContextPath() + "'");
  }
  catch (ConnectorStartFailedException ex) {
   stopSilently();
   throw ex;
  }
  catch (Exception ex) {
   throw new WebServerException("Unable to start embedded Tomcat server", ex);
  }
  finally {
   Context context = findContext();
   ContextBindings.unbindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
  }
 }
}
//关闭tomcat服务
@Override
public void stop() throws WebServerException {
 synchronized (this.monitor) {
  boolean wasStarted = this.started;
  try {
   this.started = false;
   try {
    stopTomcat();
    this.tomcat.destroy();
   }
   catch (LifecycleException ex) {
   }
  }
  catch (Exception ex) {
   throw new WebServerException("Unable to stop embedded Tomcat", ex);
  }
  finally {
   if (wasStarted) {
    containerCounter.decrementAndGet();
   }
  }
 }
}

使用外置tomcat部署

配置案例

外置Tomcat启动SpringBoot源码点击这里

继承SpringBootServletInitializer

外部容器部署的话，就不能依赖于Application的main函数了，而是要以类似于web.xml文件配置的方式来启动Spring应用上下文，此时需要在启动类中继承SpringBootServletInitializer，并重写configure方法；还添加 @SpringBootApplication 注解，这是为了能扫描到所有Spring注解的bean

方式一：启动类继承SpringBootServletInitializer实现configure：

@SpringBootApplication
public class SpringBootHelloWorldTomcatApplication extends SpringBootServletInitializer {
	@Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
        return builder.sources(Application.class);
    }
}

这个类的作用与在web.xml中配置负责初始化Spring应用上下文的监听器作用类似，只不过在这里不需要编写额外的XML文件了。

方式二：新增加一个类继承SpringBootServletInitializer实现configure：

public class ServletInitializer extends SpringBootServletInitializer {
    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
        //此处的Application.class为带有@SpringBootApplication注解的启动类
        return builder.sources(Application.class);
    }
}

pom.xml修改tomcat相关的配置

首先需要将 jar 变成war <packaging>war</packaging>

如果要将最终的打包形式改为war的话，还需要对pom.xml文件进行修改，因为spring-boot-starter-web中包含内嵌的tomcat容器，所以直接部署在外部容器会冲突报错。因此需要将内置tomcat排除

<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>

在这里需要移除对嵌入式Tomcat的依赖，这样打出的war包中，在lib目录下才不会包含Tomcat相关的jar包，否则将会出现启动错误。

但是移除了tomcat后，原始的sevlet也被移除了，因此还需要额外引入servet的包

<dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>3.0.1</version>
</dependency>

注意的问题

此时打成的包的名称应该和 application.properties 的 server.context-path=/test 保持一致

<build>
    <finalName>test</finalName>
</build>

如果不一样发布到tomcat的webapps下上下文会变化

原理

tomcat不会主动去启动springboot应用，，所以tomcat启动的时候肯定调用了SpringBootServletInitializer的SpringApplicationBuilder ，就会启动springboot。

ServletContainerInitializer的实现放在jar包的META-INF/services文件夹下，有一个名为javax.servlet.ServletContainerInitializer的文件，内容就是ServletContainerInitializer的实现类的全类名。当servlet容器启动时候就会去该文件中找到ServletContainerInitializer的实现类，从而创建它的实例调用onstartUp。这里就是用了SPI机制

HandlesTypes(WebApplicationInitializer.class)

@HandlesTypes传入的类为ServletContainerInitializer感兴趣的
容器会自动在classpath中找到 WebApplicationInitializer，会传入到onStartup方法的webAppInitializerClasses中
Set<Class<?>> webAppInitializerClasses这里面也包括之前定义的TomcatStartSpringBoot

@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {

@Override
public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
      throws ServletException {
   List<WebApplicationInitializer> initializers = new LinkedList<>();
   if (webAppInitializerClasses != null) {
      for (Class<?> waiClass : webAppInitializerClasses) {
        // 如果不是接口 不是抽象 跟WebApplicationInitializer有关系  就会实例化
         if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
               WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
            try {
               initializers.add((WebApplicationInitializer)
                     ReflectionUtils.accessibleConstructor(waiClass).newInstance());
            }
            catch (Throwable ex) {
               throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
            }
         }
      }
   }
   if (initializers.isEmpty()) {
      servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
      return;
   }
   servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
   // 排序
   AnnotationAwareOrderComparator.sort(initializers);
   for (WebApplicationInitializer initializer : initializers) {
      initializer.onStartup(servletContext);
   }
}

@Override
public void onStartup(ServletContext servletContext) throws ServletException {
   // Logger initialization is deferred in case an ordered
   // LogServletContextInitializer is being used
   this.logger = LogFactory.getLog(getClass());
   WebApplicationContext rootApplicationContext = createRootApplicationContext(servletContext);
   if (rootApplicationContext != null) {
      servletContext.addListener(new SpringBootContextLoaderListener(rootApplicationContext, servletContext));
   }
   else {
      this.logger.debug("No ContextLoaderListener registered, as createRootApplicationContext() did not "
            + "return an application context");
   }
}

SpringBootServletInitializer

protected WebApplicationContext createRootApplicationContext(ServletContext servletContext) {
   SpringApplicationBuilder builder = createSpringApplicationBuilder();
   builder.main(getClass());
   ApplicationContext parent = getExistingRootWebApplicationContext(servletContext);
   if (parent != null) {
      this.logger.info("Root context already created (using as parent).");
      servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, null);
      builder.initializers(new ParentContextApplicationContextInitializer(parent));
   }
   builder.initializers(new ServletContextApplicationContextInitializer(servletContext));
   builder.contextClass(AnnotationConfigServletWebServerApplicationContext.class);
   // 调用configure
   builder = configure(builder); //①
   builder.listeners(new WebEnvironmentPropertySourceInitializer(servletContext));
   SpringApplication application = builder.build();//②
   if (application.getAllSources().isEmpty()
         && MergedAnnotations.from(getClass(), SearchStrategy.TYPE_HIERARCHY).isPresent(Configuration.class)) {
      application.addPrimarySources(Collections.singleton(getClass()));
   }
   Assert.state(!application.getAllSources().isEmpty(),
         "No SpringApplication sources have been defined. Either override the "
               + "configure method or add an @Configuration annotation");
   // Ensure error pages are registered
   if (this.registerErrorPageFilter) {
      application.addPrimarySources(Collections.singleton(ErrorPageFilterConfiguration.class));
   }
   application.setRegisterShutdownHook(false);
   return run(application);//③
}

① 当调用configure就会来到TomcatStartSpringBoot .configure，将Springboot启动类传入到builder.source

@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
    return builder.sources(Application.class);
}

② 调用SpringApplication application = builder.build(); 就会根据传入的Springboot启动类来构建一个SpringApplication

public SpringApplication build(String... args) {
   configureAsChildIfNecessary(args);
   this.application.addPrimarySources(this.sources);
   return this.application;
}

③ 调用 return run(application); 就会启动springboot应用

protected WebApplicationContext run(SpringApplication application) {
   return (WebApplicationContext) application.run();
}

也就相当于Main函数启动：

public static void main(String[] args) {
    SpringApplication.run(Application.class, args);
}

之后的流程就与上面使用内置Tomcat的Main函数一致了

到此这篇关于SpringBoot的两种启动方式原理解析的文章就介绍到这了,更多相关SpringBoot启动方式原理内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家！

SpringBoot的两种启动方式原理解析(配置方案)

使用内置tomcat启动

配置案例

启动方式

配置内置tomcat属性

原理

从main函数说起

创建上下文

刷新上下文

使用外置tomcat部署

配置案例

继承SpringBootServletInitializer

pom.xml修改tomcat相关的配置

注意的问题

原理

HandlesTypes(WebApplicationInitializer.class)

SpringBootServletInitializer

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