19. SpringBoot_web开发-使用外部Servlet容器&JSP支持
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
