@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication
@Import(BeanPostProcessorsRegistrar.class)
public class EmbeddedServletContainerAutoConfiguration {
/**
* Nested configuration if Tomcat is being used.
*/
@Configuration
//判断是否引入了tomcat依赖
@ConditionalOnClass({ Servlet.class, Tomcat.class })
@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
//判断当前容器中有没有自己定义的EmbeddedServletContainerFactory(嵌入式servlet容器工厂)
//EmbeddedServletContainerFactory的作用:创建嵌入式servlet容器
public static class EmbeddedTomcat {
@Bean
public TomcatEmbeddedServletContainerFactory tomcatEmbeddedServletContainerFactory() {
return new TomcatEmbeddedServletContainerFactory();
}
}
EmbeddedServletContainerFactory
public interface EmbeddedServletContainerFactory {
/**
* Gets a new fully configured but paused {@link EmbeddedServletContainer} instance.
* Clients should not be able to connect to the returned server until
* {@link EmbeddedServletContainer#start()} is called (which happens when the
* {@link ApplicationContext} has been fully refreshed).
* @param initializers {@link ServletContextInitializer}s that should be applied as
* the container starts
* @return a fully configured and started {@link EmbeddedServletContainer}
* @see EmbeddedServletContainer#stop()
*/
//获取嵌入式的servlet容器
EmbeddedServletContainer getEmbeddedServletContainer(
ServletContextInitializer... initializers);
}
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication
@Import(BeanPostProcessorsRegistrar.class)
//BeanPostProcessorsRegistrar是给容器导入一些组件的
//这里是导入EmbeddedServletContainerCustomizerBeanPostProcessor：
//后置处理器：bean初始化前后（创建完对象，还没赋值赋值）执行初始化工作
public class EmbeddedServletContainerAutoConfiguration {
/**
* Nested configuration if Tomcat is being used.
*/
@Configuration
@ConditionalOnClass({ Servlet.class, Tomcat.class })
@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedTomcat {
@Bean
public TomcatEmbeddedServletContainerFactory tomcatEmbeddedServletContainerFactory() {
return new TomcatEmbeddedServletContainerFactory();
}
}
/**
* Nested configuration if Jetty is being used.
*/
@Configuration
@ConditionalOnClass({ Servlet.class, Server.class, Loader.class,
WebAppContext.class })
@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedJetty {
@Bean
public JettyEmbeddedServletContainerFactory jettyEmbeddedServletContainerFactory() {
return new JettyEmbeddedServletContainerFactory();
}
}
/**
* Nested configuration if Undertow is being used.
*/
@Configuration
@ConditionalOnClass({ Servlet.class, Undertow.class, SslClientAuthMode.class })
@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedUndertow {
@Bean
public UndertowEmbeddedServletContainerFactory undertowEmbeddedServletContainerFactory() {
return new UndertowEmbeddedServletContainerFactory();
}
}
以TomcatEmbeddedServletContainerFactory为例
public class TomcatEmbeddedServletContainerFactory
extends AbstractEmbeddedServletContainerFactory implements ResourceLoaderAware {
@Override
public EmbeddedServletContainer getEmbeddedServletContainer(
ServletContextInitializer... initializers) {
//创建一个Tomcat
Tomcat tomcat = new Tomcat();
//开始配置tomcat
File baseDir = (this.baseDirectory != null ? this.baseDirectory
: createTempDir("tomcat"));
tomcat.setBaseDir(baseDir.getAbsolutePath());
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);
//将配置好的Tomcat传入进去，返回一个EmbeddedServletContainer；
//并且启动Tomcat服务器
return getTomcatEmbeddedServletContainer(tomcat);
}
}
进入到getTomcatEmbeddedServletContainer()查看
protected TomcatEmbeddedServletContainer getTomcatEmbeddedServletContainer(
Tomcat tomcat) {
return new TomcatEmbeddedServletContainer(tomcat, getPort() >= 0);
}
继续跟踪进去查看,就是创建一个Tomcat嵌入式servlet容器,并且将Tomcat启动
/**
* Create a new {@link TomcatEmbeddedServletContainer} instance.
* @param tomcat the underlying Tomcat server
* @param autoStart if the server should be started
*/
public TomcatEmbeddedServletContainer(Tomcat tomcat, boolean autoStart) {
Assert.notNull(tomcat, "Tomcat Server must not be null");
this.tomcat = tomcat;
this.autoStart = autoStart;
initialize();
}
private void initialize() throws EmbeddedServletContainerException {
TomcatEmbeddedServletContainer.logger
.info("Tomcat initialized with port(s): " + getPortsDescription(false));
synchronized (this.monitor) {
try {
addInstanceIdToEngineName();
try {
// Remove service connectors to that protocol binding doesn't happen
// yet
removeServiceConnectors();
// Start the server to trigger initialization listeners
this.tomcat.start();
// We can re-throw failure exception directly in the main thread
rethrowDeferredStartupExceptions();
Context context = findContext();
try {
ContextBindings.bindClassLoader(context, getNamingToken(context),
getClass().getClassLoader());
}
catch (NamingException ex) {
// Naming is not enabled. Continue
}
// Unlike Jetty, all Tomcat threads are daemon threads. We create a
// blocking non-daemon to stop immediate shutdown
startDaemonAwaitThread();
}
catch (Exception ex) {
containerCounter.decrementAndGet();
throw ex;
}
}
catch (Exception ex) {
throw new EmbeddedServletContainerException(
"Unable to start embedded Tomcat", ex);
}
}
}
原因:
在servlet3.0的8.2.4 Shared libraries / runtimes pluggability里面有说明:
The ServletContainerInitializer class is looked up via the jar services API.
For each application, an instance of the ServletContainerInitializer is
created by the container at application startup time. The framework providing an
implementation of the ServletContainerInitializer MUST bundle in the
META-INF/services directory of the jar file a file called
javax.servlet.ServletContainerInitializer, as per the jar services API,
that points to the implementation class of the ServletContainerInitializer.
In addition to the ServletContainerInitializer we also have an annotation -
HandlesTypes. The HandlesTypes annotation on the implementation of the
ServletContainerInitializer is used to express interest in classes that may
have annotations (type, method or field level annotations) specified in the value of
the HandlesTypes or if it extends / implements one those classes anywhere in the
class’ super types. The HandlesTypes annotation is applied irrespective of the
setting of metadata-complete.
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；
