SpringBoot（六）之内嵌容器

Spring Boot 提供了一种便捷的方式来创建独立运行的 Spring 应用程序，内嵌容器（如 Tomcat、Jetty 或 Undertow）是其核心特性之一。这使得开发者不需要将应用程序部署到外部的应用服务器上，而是通过内嵌容器直接运行应用。这种方式简化了部署流程，并且提高了开发和测试的效率。

内嵌容器的特点

1. 独立性：应用程序包含了所有必要的依赖和服务器配置，能够独立运行，而不依赖外部的应用服务器。
2. 简化部署：通过 Maven 或 Gradle 构建后，可以生成一个可执行的 JAR 文件，直接通过命令行运行。
3. 一致性：开发、测试和生产环境中的运行环境一致，减少了环境差异带来的问题。

如何替换默认容器

1.pom形式

如何引入underTow作为内嵌servlet容器

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

<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 替换掉 Tomcat --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-undertow</artifactId>
</dependency>

观察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)

通过日志观察，默认内嵌容器已经替换成underTow，同理jetty一样

2.主动配置

由于SpringBoot在获取servlet容器是通过ServletWebServerFactory类型来获取。ServletWebServerFactory一共有三个实现类，分别为JettyServletWebServerFactory,UndertowServletWebServerFactory,TomcatServletWebServerFactory。分别对应jetty，underTow,tomcat。

SpringBoot在AbstractApplicationContext.refresh()方法的onRefresh()，通过 ServletWebServerApplicationContext重写该方法创建webServer();

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

在createWebServer()中有个获取WebServerFactory方法获取对应的实现类的方法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()，通过在Spring容器中获取ServletWebServerFactory类型的bean，如果获取不到和获取多个都会抛出异常

所以我们可以通过手动配置ServletWebServerFactory对应的实现类，以此来切换不同的容器。

• 将tomcat，jetty，undertow的starter都引入到项目中
• 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;}
}

需要用哪个容器，就把其他两个容器注释掉。（不能创建多个ServletWebServerFactory，在getWebServerFactory()中会抛异常）

如何通过配置切换serlvet容器

在主动配置的基础上,可以通过对config进行改造

1. 在application.yaml中配置servlet.server属性 ，具体1,2,3代表tomcat还是jetty由自己定义
2. 利用SpringBoot注解@ConditionalOnProperty注解可以切换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，则启动项目,观察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]

将配置更改为3，再次启动，观察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 '/'