嵌入式 Servlet 容器:应用打成可执行的jar包
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环境---应用以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)
详情参见:Spring Boot 创建Packaging为War包的应用并启动
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,最后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:
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感兴趣的类;
流程:
1,启动Tomcat
2,maven本地仓库下\org\springframework\spring-web\4.3.23.RELEASE\spring-web-4.3.23.RELEASE.jar!\META-INF\services\javax.servlet.ServletContainerInitializer:
Spring的web模块里面有这个文件:org.springframework.web.SpringServletContainerInitializer
3,SpringServletContainerInitializer 将 @HandlesTypes(WebApplicationInitializer.class) 标注的所有这个类型的类都传入到onStartup() 方法的 Set<Class<?>>;为这些 WebApplicationInitializer 类型的类创建实例;
4,每一个 WebApplicationInitializer 都调用自己的 onStartup();
5,相当于 SpringBootServletInitializer 的类会被创建对象,并执行onStartup()方法;
6,SpringBootServletInitializer 实例执行 onStartup() 的时候会调用 createRootApplicationContext 创建容器;
protected WebApplicationContext createRootApplicationContext(
ServletContext servletContext) {
//1、创建SpringApplicationBuilder
SpringApplicationBuilder builder = createSpringApplicationBuilder();
StandardServletEnvironment environment = new StandardServletEnvironment();
environment.initPropertySources(servletContext, null);
builder.environment(environment);
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(AnnotationConfigEmbeddedWebApplicationContext.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 = configure(builder);
//使用builder创建一个Spring应用
SpringApplication application = builder.build();
if (application.getSources().isEmpty() && AnnotationUtils
.findAnnotation(getClass(), Configuration.class) != null) {
application.getSources().add(getClass());
}
Assert.state(!application.getSources().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.getSources().add(ErrorPageFilterConfiguration.class);
}
//启动Spring应用
return run(application);
}
7,Spring的应用就启动了,并且创建IOC容器;
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
FailureAnalyzers analyzers = null;
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
Banner printedBanner = printBanner(environment);
context = createApplicationContext();
analyzers = new FailureAnalyzers(context);
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
//刷新IOC容器
refreshContext(context);
afterRefresh(context, applicationArguments);
listeners.finished(context, null);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
return context;
}
catch (Throwable ex) {
handleRunFailure(context, listeners, analyzers, ex);
throw new IllegalStateException(ex);
}
}
总结:先启动Servlet容器,再启动SpringBoot应用