使用内置tomcat启动
配置案例
启动方式
-
IDEA中main函数启动
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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nohupnohup 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logoBanner 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AnnotationConfigServletWebServerApplicationContextcontextClass = 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 {@Overrideprotected 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 {@Overrideprotected 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 usedthis.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configurebuilder = configure(builder); //①builder.listeners(new WebEnvironmentPropertySourceInitializer(servletContext));SpringApplication application = builder.build();//②if (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 registeredif (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
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