一、SpringBoot嵌入式Servlet容器與外置Servlet容器的比較
- 嵌入式Servlet容器應用將程序打成Jar包,外置Servlet容器應用將程序打成War包。
- 嵌入式Servlet容器的優點:簡單、便攜。缺點:默認不支持JSP,優化定製較複雜。
嵌入式Servlet容器優化定製的方法:
① 使用定製器:ServerProperties、自定義 EmbeddedServletContainerCustomizer
② 自己編寫嵌入式Servlet容器的創建工廠 【EmbeddedServletContainerFactory】
二、如何使用外置Servlet容器的步驟
1、創建一個War包項目
;File——》New——Project,選中Spring Initializr,然後單擊Next,進入到如下頁面,將默認的Jar包改成War,然後Next,直到Finish。
創建出來的目錄結構:
由於創建的是War包項目,所以以上的目錄結構還不完整,我們需要手動創建web.xml和webapp。有兩種創建方式:
① 手動在src/main下創建webapp目錄及在/src/main/webapp/WEB-INF下創建web.xml文件。
② 在IDEA的Project Structure中完善目錄結構。
點擊Module,選中web,來到如下頁面:
雙擊上圖圈出來的url處,彈出以下對話框:
單擊OK,選擇Yes。
還是在Project Structure頁面,點擊如下圖所示的“+”,彈出如下對話框,修改生成web.xml文件的目錄/src/main/webapp,然後點擊OK。
在上一步中點擊OK後,先點擊Apply,然後選擇OK,即可創建出webapp目錄和web.xml文件。
完善後的目錄結構如下:
2、將嵌入式的tomcat指定爲provided
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
<scope>provided</scope>
</dependency>
3、必須寫一個SpringBootServletInitializer 的實現子類。
目的是調用configure方法,傳入springboot應用的主程序。
public class ServletInitializer extends SpringBootServletInitializer {
@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
return application.sources(SpringBootWebJspApplication.class);
}
}
4、啓動服務器
三、外部Servlet啓動SpringBoot應用原理(1.5.x)
- 將項目打成 jar包啓動方式:執行SpringBoot主類的main方法,啓動IOC容器,創建嵌入式的Servlet容器。
- 將項目打成 war包啓動方式:啓動服務器,服務器啓動SpringBoot應用【
SpringBootServletInitializer
】,然後啓動IOC容器。
在Spring3.0(Spring註解版)的8.2.4 Shared libraries / runtimes pluggability中,有如下規則:
【1】在服務器(web應用)啓動時,會創建當前web應用裏每一個jar包中的ServletContainerInitializer
實例。
【2】ServletContainerInitializer
的實現放在jar包的META-INF/services文件夾下,必須有一個名爲 javax.servlet.ServletContainerInitializer 的文件,內容就是ServletContainerInitializer的實現類的全類名。
【3】還可以使用@HandlesTypes
註解,作用是在應用啓動的時候加載我們感興趣的類。
步驟:
【1】啓動tomcat服務器;
【2】 在../org/springframework/spring-web/4.3.14.RELEASE/spring-web-4.3.14.RELEASE.jar/META-INF/services
目錄下有一個名爲javax.servlet.ServletContainerInitializer
的文件,文件內容是:
org.springframework.web.SpringServletContainerInitializer
相當於在web應用啓動的時候啓動SpringServletContainerInitializer
。
【3】SpringServletContainerInitializer
將@HandlesTypes(WebApplicationInitializer.class)
標註的所有類型的類(感興趣的類)都傳入到onStartup方法的Set<Class<?>> webAppInitializerClasses
,爲這些WebApplicationInitializer
類型的類(不是接口、不是抽象類)創建實例。
【4】每一個WebApplicationInitializer
都調用自己的onStartup
,相當於我們的SpringBootServletInitializer
的類會被創建對象,並執行onStartup
方法。WebApplicationInitializer
是一個接口,它的實現類如下:
//Set<Class<?>> webAppInitializerClasses表示感興趣的類
public void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext) throws ServletException {
List<WebApplicationInitializer> initializers = new LinkedList();
Iterator var4;
if (webAppInitializerClasses != null) {
var4 = webAppInitializerClasses.iterator();
while(var4.hasNext()) {
Class<?> waiClass = (Class)var4.next();
//如果不死接口或者抽象類
if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) && WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
try {
//加入到WebApplicationInitializer對象的集合中
initializers.add((WebApplicationInitializer)waiClass.newInstance());
} catch (Throwable var7) {
throw new ServletException("Failed to instantiate WebApplicationInitializer class", var7);
}
}
}
}
if (initializers.isEmpty()) {
servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
} else {
servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
AnnotationAwareOrderComparator.sort(initializers);
var4 = initializers.iterator();
while(var4.hasNext()) {
WebApplicationInitializer initializer = (WebApplicationInitializer)var4.next();
//每一個WebApplicationInitializer對象調用自己的onStartup方法創建SpringBootServletInitializer對象
initializer.onStartup(servletContext);
}
}
}
public class ServletInitializer extends SpringBootServletInitializer {
@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
return application.sources(SpringBootWebJspApplication.class);
}
}
【5】SpringBootServletInitializer
實例執行onStartup
方法的時候會調用createRootApplicationContext
方法創建容器
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");
}
}
protected WebApplicationContext createRootApplicationContext(ServletContext servletContext) {
//1、創建SpringApplicationBuilder對象
SpringApplicationBuilder builder = this.createSpringApplicationBuilder();
StandardServletEnvironment environment = new StandardServletEnvironment();
environment.initPropertySources(servletContext, (ServletConfig)null);
builder.environment(environment);
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(AnnotationConfigEmbeddedWebApplicationContext.class);
//調用configure方法,在子類重寫了這個方法,傳入SpringBoot的主程序類
builder = this.configure(builder);
//使用builder創建spring應用
SpringApplication application = builder.build();
if (application.getSources().isEmpty() && AnnotationUtils.findAnnotation(this.getClass(), Configuration.class) != null) {
application.getSources().add(this.getClass());
}
Assert.state(!application.getSources().isEmpty(), "No SpringApplication sources have been defined. Either override the configure method or add an @Configuration annotation");
if (this.registerErrorPageFilter) {
application.getSources().add(ErrorPageFilterConfiguration.class);
}
//啓動spring應用
return this.run(application);
}
protected SpringApplicationBuilder createSpringApplicationBuilder() {
return new SpringApplicationBuilder(new Object[0]);
}
【6】啓動spring應用,並創建IOC容器
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
FailureAnalyzers analyzers = null;
this.configureHeadlessProperty();
SpringApplicationRunListeners listeners = this.getRunListeners(args);
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
Banner printedBanner = this.printBanner(environment);
context = this.createApplicationContext();
new FailureAnalyzers(context);
this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
//刷新IOC容器
this.refreshContext(context);
this.afterRefresh(context, applicationArguments);
listeners.finished(context, (Throwable)null);
stopWatch.stop();
if (this.logStartupInfo) {
(new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
}
return context;
} catch (Throwable var9) {
this.handleRunFailure(context, listeners, (FailureAnalyzers)analyzers, var9);
throw new IllegalStateException(var9);
}
}
一句話總結:先啓動Servlet容器,啓動spring應用,再創建IOC容器。