@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication
@Import(BeanPostProcessorsRegistrar.class)
public class EmbeddedServletContainerAutoConfiguration {
/**
* Nested configuration if Tomcat is being used.
*/
@Configuration
//判斷是否引入了tomcat依賴
@ConditionalOnClass({ Servlet.class, Tomcat.class })
@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
//判斷目前容器中有沒有自己定義的EmbeddedServletContainerFactory(嵌入式servlet容器工廠)
//EmbeddedServletContainerFactory的作用:建立嵌入式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()
*/
//擷取嵌入式的servlet容器
EmbeddedServletContainer getEmbeddedServletContainer(
ServletContextInitializer... initializers);
}
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication
@Import(BeanPostProcessorsRegistrar.class)
//BeanPostProcessorsRegistrar是給容器導入一些元件的
//這裡是導入EmbeddedServletContainerCustomizerBeanPostProcessor：
//後置處理器：bean初始化前後（建立完對象，還沒指派指派）執行初始化工作
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為例
public class TomcatEmbeddedServletContainerFactory
extends AbstractEmbeddedServletContainerFactory implements ResourceLoaderAware {
@Override
public EmbeddedServletContainer getEmbeddedServletContainer(
ServletContextInitializer... initializers) {
//建立一個Tomcat
Tomcat tomcat = new Tomcat();
//開始配置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傳入進去，傳回一個EmbeddedServletContainer；
//并且啟動Tomcat伺服器
return getTomcatEmbeddedServletContainer(tomcat);
}
}
進入到getTomcatEmbeddedServletContainer()檢視
protected TomcatEmbeddedServletContainer getTomcatEmbeddedServletContainer(
Tomcat tomcat) {
return new TomcatEmbeddedServletContainer(tomcat, getPort() >= 0);
}
繼續跟蹤進去檢視,就是建立一個Tomcat嵌入式servlet容器,并且将Tomcat啟動
/**
* 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裡面有說明:
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）、伺服器啟動（web應用啟動）會建立目前web應用裡面
每一個jar包裡面ServletContainerInitializer執行個體：
2）、ServletContainerInitializer的實作放在jar包的META-INF/services檔案夾下，
有一個名為javax.servlet.ServletContainerInitializer的檔案，
内容就是ServletContainerInitializer的實作類的全類名
3）、還可以使用@HandlesTypes，在應用啟動的時候加載我們感興趣的類；
