SpringBoot（六）之內嵌容器

Spring Boot 提供了一種便捷的方式來創建獨立運行的 Spring 應用程序，內嵌容器（如 Tomcat、Jetty 或 Undertow）是其核心特性之一。這使得開發者不需要將應用程序部署到外部的應用服務器上，而是通過內嵌容器直接運行應用。這種方式簡化了部署流程，并且提高了開發和測試的效率。

內嵌容器的特點

1. 獨立性：應用程序包含了所有必要的依賴和服務器配置，能夠獨立運行，而不依賴外部的應用服務器。
2. 簡化部署：通過 Maven 或 Gradle 構建后，可以生成一個可執行的 JAR 文件，直接通過命令行運行。
3. 一致性：開發、測試和生產環境中的運行環境一致，減少了環境差異帶來的問題。

如何替換默認容器

1.pom形式

如何引入underTow作為內嵌servlet容器

• 在spring-boot-starter-web中排除掉tomcat的jar包
• 引入undertow的依賴

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId><exclusions><exclusion><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-tomcat</artifactId></exclusion></exclusions></dependency><!-- 使用 Undertow 替換掉 Tomcat --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-undertow</artifactId>
</dependency>

觀察console

2024-05-17 16:38:26.099  INFO 1108 --- [           main] io.undertow                              : starting server: Undertow - 2.2.16.Final
2024-05-17 16:38:26.102  INFO 1108 --- [           main] org.xnio                                 : XNIO version 3.8.6.Final
2024-05-17 16:38:26.105  INFO 1108 --- [           main] org.xnio.nio                             : XNIO NIO Implementation Version 3.8.6.Final
2024-05-17 16:38:26.125  INFO 1108 --- [           main] org.jboss.threads                        : JBoss Threads version 3.1.0.Final
2024-05-17 16:38:26.162  INFO 1108 --- [           main] o.s.b.w.e.undertow.UndertowWebServer     : Undertow started on port(s) 8080 (http)
2024-05-17 16:38:26.168  INFO 1108 --- [           main] c.a.s.SpringBootAnnotationApplication    : Started SpringBootAnnotationApplication in 1.179 seconds (JVM running for 1.914)

通過日志觀察，默認內嵌容器已經替換成underTow，同理jetty一樣

2.主動配置

由于SpringBoot在獲取servlet容器是通過ServletWebServerFactory類型來獲取。ServletWebServerFactory一共有三個實現類，分別為JettyServletWebServerFactory,UndertowServletWebServerFactory,TomcatServletWebServerFactory。分別對應jetty，underTow,tomcat。

SpringBoot在AbstractApplicationContext.refresh()方法的onRefresh()，通過 ServletWebServerApplicationContext重寫該方法創建webServer();

protected void onRefresh() {super.onRefresh();try {this.createWebServer();} catch (Throwable var2) {throw new ApplicationContextException("Unable to start web server", var2);}
}

在createWebServer()中有個獲取WebServerFactory方法獲取對應的實現類的方法getWebServerFactory();

protected ServletWebServerFactory getWebServerFactory() {String[] beanNames = this.getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class);if (beanNames.length == 0) {throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to missing ServletWebServerFactory bean.");} else if (beanNames.length > 1) {throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to multiple ServletWebServerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames));} else {return (ServletWebServerFactory)this.getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);}}

getWebServerFactory()，通過在Spring容器中獲取ServletWebServerFactory類型的bean，如果獲取不到和獲取多個都會拋出異常

所以我們可以通過手動配置ServletWebServerFactory對應的實現類，以此來切換不同的容器。

• 將tomcat，jetty，undertow的starter都引入到項目中
• 新建配置ServletServerConfig

@Configuration
public class ServletServerConfig {@Beanpublic ServletWebServerFactory underTowServletWebServerFactory(){UndertowServletWebServerFactory undertowServletWebServerFactory = new UndertowServletWebServerFactory();undertowServletWebServerFactory.setPort(8087);return undertowServletWebServerFactory;}//@Beanpublic ServletWebServerFactory tomcatServletWebServerFactory(){TomcatServletWebServerFactory tomcatServletWebServerFactory = new TomcatServletWebServerFactory();tomcatServletWebServerFactory.setPort(8081);return tomcatServletWebServerFactory;}//@Beanpublic ServletWebServerFactory jettyServletWebServerFactory(){JettyServletWebServerFactory jettyServletWebServerFactory = new JettyServletWebServerFactory();jettyServletWebServerFactory.setPort(8086);return jettyServletWebServerFactory;}
}

需要用哪個容器，就把其他兩個容器注釋掉。（不能創建多個ServletWebServerFactory，在getWebServerFactory()中會拋異常）

如何通過配置切換serlvet容器

在主動配置的基礎上,可以通過對config進行改造

1. 在application.yaml中配置servlet.server屬性 ，具體1,2,3代表tomcat還是jetty由自己定義
2. 利用SpringBoot注解@ConditionalOnProperty注解可以切換servlet容器

servlet:server: 2

@Configuration
public class ServletServerConfig {@Bean@ConditionalOnProperty(name = "servlet.server",havingValue = "1")public ServletWebServerFactory underTowServletWebServerFactory(){UndertowServletWebServerFactory undertowServletWebServerFactory = new UndertowServletWebServerFactory();undertowServletWebServerFactory.setPort(8087);return undertowServletWebServerFactory;}@Bean@ConditionalOnProperty(name = "servlet.server",havingValue = "2")public ServletWebServerFactory tomcatServletWebServerFactory(){TomcatServletWebServerFactory tomcatServletWebServerFactory = new TomcatServletWebServerFactory();tomcatServletWebServerFactory.setPort(8081);return tomcatServletWebServerFactory;}@Bean@ConditionalOnProperty(name = "servlet.server",havingValue = "3")public ServletWebServerFactory jettyServletWebServerFactory(){JettyServletWebServerFactory jettyServletWebServerFactory = new JettyServletWebServerFactory();jettyServletWebServerFactory.setPort(8086);return jettyServletWebServerFactory;}
}

ServletServerConfig中，1表示underTow，2表示tomdat，3,表示jetty。而application.yml中配置的2，則啟動項目,觀察console

2024-05-17 17:14:19.142  INFO 7500 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2024-05-17 17:14:19.148  INFO 7500 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]

將配置更改為3，再次啟動，觀察console

2024-05-17 17:15:01.473  INFO 5260 --- [           main] o.e.jetty.server.AbstractConnector       : Started ServerConnector@13579834{HTTP/1.1, (http/1.1)}{0.0.0.0:8080}
2024-05-17 17:15:01.473  INFO 5260 --- [           main] o.s.b.web.embedded.jetty.JettyWebServer  : Jetty started on port(s) 8080 (http/1.1) with context path '/'