外部Tomcat容器启动spring-flux

本文介绍: 外部To m cat容器中起一个Re actor Ne t t y的响应式服务

外部To m cat 容器 启动 spring-flux

springboot 启动类

首先继承Abs t rac tReactiveWebIni ti alizer类重写 createAp pli cat ionCon text和getCo nf i gClas s es 方法
配置Net t yReactiveWebSer verFactor y bean(这个是关键 )

public class DemoBootstrapApplication extends AbstractReactiveWebInitializer {

    public static void main(String[] args) {
       SpringApplication.run(DemoBootstrapApplication.class, args);
    }

    @Override
    protected ApplicationContext createApplicationContext() {
        SpringApplication springApplication = new SpringApplication(getConfigClasses());
       return springApplication.run();
    }

    @Override
    protected Class<?>[] getConfigClasses() {
        return new Class[]{DemoBootstrapApplication.class};
    }
    //这里是关键后面再提
    @Bean
    public NettyReactiveWebServerFactory nettyReactiveWebServerFactory() {
        return new NettyReactiveWebServerFactory();
    }
}

外置 tomcat 启动

tomcat 8启动 报错 如下：

提示找不到org.apache.tomcat.util.modeler.Registry.di sa bleRegistry()方法

Caused by: org.springframework.context.ApplicationContextException: Unable to start reactive web server; nested exception is java.lang.NoSuchMethodError: org.apache.tomcat.util.modeler.Registry.disableRegistry()V
		at org.springframework.boot.web.reactive.context.ReactiveWebServerApplicationContext.onRefresh(ReactiveWebServerApplicationContext.java:82)
		at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:577)
		at org.springframework.boot.web.reactive.context.ReactiveWebServerApplicationContext.refresh(ReactiveWebServerApplicationContext.java:64)
		at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:745)
		at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:420)
		at org.springframework.boot.SpringApplication.run(SpringApplication.java:307)
		at com.weibo.FizzBootstrapApplication.createApplicationContext(FizzBootstrapApplication.java:198)
		at org.springframework.web.server.adapter.AbstractReactiveWebInitializer.onStartup(AbstractReactiveWebInitializer.java:59)
		at org.springframework.web.SpringServletContainerInitializer.onStartup(SpringServletContainerInitializer.java:174)
		at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:4889)
		at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:171)
		... 10 more
	Caused by: java.lang.NoSuchMethodError: org.apache.tomcat.util.modeler.Registry.disableRegistry()V
		at org.springframework.boot.web.embedded.tomcat.TomcatReactiveWebServerFactory.getWebServer(TomcatReactiveWebServerFactory.java:119)
		at org.springframework.boot.web.reactive.context.WebServerManager.<init>(WebServerManager.java:50)
		at org.springframework.boot.web.reactive.context.ReactiveWebServerApplicationContext.createWebServer(ReactiveWebServerApplicationContext.java:94)
		at org.springframework.boot.web.reactive.context.ReactiveWebServerApplicationContext.onRefresh(ReactiveWebServerApplicationContext.java:79)
		... 20 more

主要原因是springboot2.x启动时会调用org.springframework.boot.web.embedded.tomcat.TomcatReactiveWebServerFactory类的getWebServer()方法，方法如下，是由于外置tomcat8加载是tomcat-coyote.jar中的Registry类（CATALINA_HOME/lib 目录下的jar包），而springboot2.x依赖的是tomcat-embed–core jar（version:9.X，可以理解为tomcat9）造成jar 冲突，这里可以尝试采用外置tomcat9.x启动，是不是可以解决 jar 冲突?，接下来尝试采用tomcat9.0启动

<dependency>
      <groupId>org.apache.tomcat.embed</groupId>
      <artifactId>tomcat-embed-core</artifactId>
      <version>9.0.68</version>
</dependency>

@Override
	public WebServer getWebServer(HttpHandler httpHandler) {
		if (this.disableMBeanRegistry) {
		    //这里报错，找不到disableRegistry方法
			Registry.disableRegistry();
		}
		Tomcat tomcat = new Tomcat();
		File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
		tomcat.setBaseDir(baseDir.getAbsolutePath());
		for (LifecycleListener listener : this.serverLifecycleListeners) {
			tomcat.getServer().addLifecycleListener(listener);
		}
		Connector connector = new Connector(this.protocol);
		connector.setThrowOnFailure(true);
		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);
		}
		TomcatHttpHandlerAdapter servlet = new TomcatHttpHandlerAdapter(httpHandler);
		prepareContext(tomcat.getHost(), servlet);
		return getTomcatWebServer(tomcat);
	}

tomcat 9启动：

报错如下：
- 找不到TomcatEmbeddedWebappClassLoa der类加载器

Caused by: java.lang.ClassNotFoundException: org.springframework.boot.web.embedded.tomcat.TomcatEmbeddedWebappClassLoader
		at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
		at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
		at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
		at java.lang.Class.forName0(Native Method)
		at java.lang.Class.forName(Class.java:264)
		at org.apache.catalina.loader.WebappLoader.createClassLoader(WebappLoader.java:515)
		at org.apache.catalina.loader.WebappLoader.startInternal(WebappLoader.java:389)
		... 79 more

问题原因
- 外置的Tomcat（WebappClassLoader类加载器）使得优先装配内嵌的tomcat（TomcatEmbeddedWebappClassLoader类加载器，下边会分析），可以看以下自动装配代码，会调用tomcatReactiveWebServerFactory()
  @ConditionalOnMissingBean(ReactiveWebServerFactory.class)
  @ConditionalOnClass({ org.apache.catalina.startup.Tomcat.class })
解决
- 我们自己注入一个 NettyReactiveWebServerFactory 来打破 @ConditionalOnMissingBean(ReactiveWebServerFactory.class) 这个条件, 自主选择使用Netty而非内嵌的tomcat，不走tomcatReactiveWebServerFactory就不会报错了。
- 自动装配包里的 ReactiveWebServerFactoryConfiguration 部分代码如下：
  - 自动注入NettyReactiveWebServerFactory而非TomcatReactiveWebServerFactory，自主选择使用Netty而非内嵌的tomcat

@Configuration
@ConditionalOnMissingBean(ReactiveWebServerFactory.class)
@ConditionalOnClass({ HttpServer.class })
static class EmbeddedNetty {

    @Bean
    public NettyReactiveWebServerFactory nettyReactiveWebServerFactory() {
        return new NettyReactiveWebServerFactory();
    }

}
     
@Configuration
@ConditionalOnMissingBean(ReactiveWebServerFactory.class)
@ConditionalOnClass({ org.apache.catalina.startup.Tomcat.class })
static class EmbeddedTomcat {

    @Bean
    public TomcatReactiveWebServerFactory tomcatReactiveWebServerFactory() {
        return new TomcatReactiveWebServerFactory();
    }

}

tomcat9启动失败主要原因

内嵌（embed）的tomcat的类加载器是 TomcatEmbeddedWebappClassLoader, 需要用此类加载器加载web应用的类, 而这个类加载器首先需要被 tomcat 的 WebappClassLoader 加载, 但是WebappClassLoader加载的是CATALINA_HOME/lib 目录下的类, 因此 TomcatEmbeddedWebappClassLoader 无法加载, 在加载WEB-INF下的类之前就会抛出ClassNotFound异常。