還沒有web.xml，生
配置tomcat
嵌入式Servlet容器：应用打成可执行的jar
优点：简单、便携；
缺点：默认不支持JSP、优化定制比较复杂
使用定制器【ServerProperties、自定义EmbeddedServletContainerCustomizer】，自己编写嵌入式Servlet容器的创建工厂[EmbeddedServletContainerFactory】
外置的Servlet容器：外面安装Tomcat---应用war包的方式打包；
步骤
1）、必须创建一个war项目；（利用idea创建好目录结构）
2）、将嵌入式的Tomcat指定为provided；
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
<scope>provided</scope>
</dependency>
3）、必须编写一个SpringBootServletInitializer的子类，并调用configure方法
public class ServletInitializer extends SpringBootServletInitializer {
@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
//传入SpringBoot应用的主程序
return application.sources(SpringBoot04WebJspApplication.class);
}
}
4）、启动服务器就可以使用；
原理
jar包：执行SpringBoot主类的main方法，启动ioc容器，创建嵌入式的Servlet容器；
war包：启动服务器，服务器启动SpringBoot应用【SpringBootServletInitializer】，启动ioc容器；
规则：(參見servlet3.0（Spring注解版）官方文檔：8.2.4 Shared libraries / runtimes pluggability)
1）、服务器启动（web应用启动）会创建当前web应用里面每一个jar包里面ServletContainerInitializer实例
2）、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
3）、还可以使用@HandlesTypes，在应用启动的时候加载我们感兴趣的类
流程
1）、启动Tomcat
2）、\org\springframework\spring-web\5.1.2.RELEASE\spring-web-5.1.2.RELEASE.jar！ /META-INF/services/javax.servlet.ServletContainerInitializer
package org.springframework.web; //Spring的web模块里面有这个文件 @HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {
//3）、 将@HandlesTypes(WebApplicationInitializer.class)标注的所有这个类型的类都传入到onStartup方法的Set<>類型參數
@Override
public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
throws ServletException { List<WebApplicationInitializer> initializers = new LinkedList<>(); if (webAppInitializerClasses != null) {
for (Class<?> waiClass : webAppInitializerClasses) {
// Be defensive: Some servlet containers provide us with invalid classes,
// no matter what @HandlesTypes says...
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");
AnnotationAwareOrderComparator.sort(initializers);
for (WebApplicationInitializer initializer : initializers) {
initializer.onStartup(servletContext); //4）、每一个WebApplicationInitializer都调用自己的onStartup；
}
} }
5）、 創建War方式的jar包時自動生成的類：会被创建对象，并执行onStartup方法
public class ServletInitializer extends SpringBootServletInitializer {
@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
return application.sources(SpringbootwarApplication.class); //啓動Spring Boot的主類
}
}
6）、創建War方式的jar包時自動生成的類的父類方法onStartup被執行的时候：创建容器
public abstract class SpringBootServletInitializer implements WebApplicationInitializer {
protected Log logger;
private boolean registerErrorPageFilter = true;
public SpringBootServletInitializer() {
}
protected final void setRegisterErrorPageFilter(boolean registerErrorPageFilter) {
this.registerErrorPageFilter = registerErrorPageFilter;
}
public void onStartup(ServletContext servletContext) throws ServletException {
this.logger = LogFactory.getLog(this.getClass());
WebApplicationContext rootAppContext = this.createRootApplicationContext(servletContext);
if (rootAppContext != null) {
servletContext.addListener(new ContextLoaderListener(rootAppContext) {
public void contextInitialized(ServletContextEvent event) {
}
});
} else {
this.logger.debug("No ContextLoaderListener registered, as createRootApplicationContext() did not return an application context");
}
}
//創建IoC容器
protected WebApplicationContext createRootApplicationContext(ServletContext servletContext) {
SpringApplicationBuilder builder = this.createSpringApplicationBuilder();
builder.main(this.getClass());
ApplicationContext parent = this.getExistingRootWebApplicationContext(servletContext);
if (parent != null) {
this.logger.info("Root context already created (using as parent).");
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, (Object)null);
builder.initializers(new ApplicationContextInitializer[]{new ParentContextApplicationContextInitializer(parent)});
}
builder.initializers(new ApplicationContextInitializer[]{new ServletContextApplicationContextInitializer(servletContext)});
builder.contextClass(AnnotationConfigServletWebServerApplicationContext.class);
//调用configure方法，子类重写了这个方法，将SpringBoot的主程序类传入了进来
builder = this.configure(builder);
builder.listeners(new ApplicationListener[]{new SpringBootServletInitializer.WebEnvironmentPropertySourceInitializer(servletContext, null)});
//使用Builder創建Spring應用
SpringApplication application = builder.build();
if (application.getAllSources().isEmpty() && AnnotationUtils.findAnnotation(this.getClass(), Configuration.class) != null) {
application.addPrimarySources(Collections.singleton(this.getClass()));
}
Assert.state(!application.getAllSources().isEmpty(), "No SpringApplication sources have been defined. Either override the configure method or add an @Configuration annotation");
if (this.registerErrorPageFilter) {
application.addPrimarySources(Collections.singleton(ErrorPageFilterConfiguration.class));
}
//开启Spring 应用
return this.run(application);
}
protected SpringApplicationBuilder createSpringApplicationBuilder() {
return new SpringApplicationBuilder(new Class[0]);
}
protected WebApplicationContext run(SpringApplication application) {
return (WebApplicationContext)application.run(new String[0]);
}
private ApplicationContext getExistingRootWebApplicationContext(ServletContext servletContext) {
Object context = servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
return context instanceof ApplicationContext ? (ApplicationContext)context : null;
}
protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
return builder;
}
private static final class WebEnvironmentPropertySourceInitializer implements ApplicationListener<ApplicationEnvironmentPreparedEvent>, Ordered {
private final ServletContext servletContext;
private WebEnvironmentPropertySourceInitializer(ServletContext servletContext) {
this.servletContext = servletContext;
}
public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) {
ConfigurableEnvironment environment = event.getEnvironment();
if (environment instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment)environment).initPropertySources(this.servletContext, (ServletConfig)null);
}
}
public int getOrder() {
return -2147483648;
}
}
}
public class ServletInitializer extends SpringBootServletInitializer {
@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
return application.sources(SpringbootwarApplication.class); //啓動Spring Boot的主類
}
}
Spring Boot项目jar包启动类
@SpringBootApplication
public class SpringbootwarApplication { public static void main(String[] args) {
SpringApplication.run(SpringbootwarApplication.class, args);
}
}
public class SpringApplication {
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
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);
Banner printedBanner = this.printBanner(environment);
context = this.createApplicationContext();
exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
//刷新Ioc容器，IoC容器的初始化
this.refreshContext(context);
this.afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
(new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
}
listeners.started(context);
this.callRunners(context, applicationArguments);
} catch (Throwable var10) {
this.handleRunFailure(context, var10, exceptionReporters, listeners);
throw new IllegalStateException(var10);
}
try {
listeners.running(context);
return context;
} catch (Throwable var9) {
this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null);
throw new IllegalStateException(var9);
}
}
}
总结 （使用外部Servlet容器）
1、 SpringBootServletInitializer – 重写configure
2、SpringApplicationBuilder – builder.source(@SpringBootApplication类)
3、启动原理 – Servlet3.0标准ServletContainerInitializer扫描所有jar包中METAINF/services/javax.servlet.ServletContainerInitializer文件指定的类并加载
– 加载spring web包下的SpringServletContainerInitializer
– 扫描@HandleType(WebApplicationInitializer)
– 加载SpringBootServletInitializer并运行onStartup方法
– 加载@SpringBootApplication主类，启动容器等