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# 嵌入式servlet服务器

# 原理描述

官方描述

Under the hood, Spring Boot uses a different type of ApplicationContext for embedded servlet container support. The ServletWebServerApplicationContext is a special type of WebApplicationContext that bootstraps itself by searching for a single ServletWebServerFactory bean. Usually a TomcatServletWebServerFactory, JettyServletWebServerFactory, or UndertowServletWebServerFactory has been auto-configured.

  1. spring boot启动，发现是一个web项目（因为导入web的start），导入tomcat

  2. servlet的web服务器ServletWebServerFactoryAutoConfiguration在启动的时候，会导入ServletWebServerFactoryConfiguration，此ServletWebServerFactoryConfiguration中，有多个bean，都是不同服务器的WebServerFactory

@Bean
TomcatServletWebServerFactory tomcatServletWebServerFactory(){}

@Bean
JettyServletWebServerFactory JettyServletWebServerFactory()

@Bean
UndertowServletWebServerFactory undertowServletWebServerFactory()
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  1. ServletWebServerApplicationContext启动的时候，会寻找ServletWebServerFactory

    在ServletWebServerFactoryConfiguration中内置了三个ServletWebServerFactory，TomcatServletWebServerFactory, JettyServletWebServerFactory, or UndertowServletWebServerFactory

  2. 因为springboot在启动的时候，会自动导入xxAutoConfiguration中的配置，导入ServletWebServerFactoryAutoConfiguration中的配置，还会导入ServletWebServerFactoryConfiguration配置，ServletWebServerFactoryConfiguration会动态的判断导入的是哪个WebServletFactory，因为导入的是web-start，所以默认是tomcat--->TomcatServletWebServerFactory

  3. TomcatServletWebServerFactory会创建tomcat服务器，并会启动

    ServletWebServerApplicationContext容器在启动的时候，会有一个

    public final void refresh() throws BeansException, IllegalStateException {
    try {
        super.refresh();
    }
    catch (RuntimeException ex) {
        ////////////////////重要
        WebServer webServer = this.webServer;
        if (webServer != null) {
            webServer.stop();
        }
        throw ex;
    }
}

//如果发生异常的话，就会停止，否则会createWebServer();
@Override
protected void onRefresh() {
    super.onRefresh();
    try {
        createWebServer();
    }
    catch (Throwable ex) {
        throw new ApplicationContextException("Unable to start web server", ex);
    }
}
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    下面方法是寻找webServletFactory，在一个应用中，只能有一个web服务器

    protected ServletWebServerFactory getWebServerFactory() {
    // Use bean names so that we don't consider the hierarchy
    String[] beanNames = getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class);
    if (beanNames.length == 0) {
        throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to missing "
                                              + "ServletWebServerFactory bean.");
    }
    if (beanNames.length > 1) {
        throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to multiple "
                                              + "ServletWebServerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames));
    }
    return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
}
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    在WebServer中，可以看到webServer的实现，对于tomcat

    public WebServer getWebServer(ServletContextInitializer... initializers) {
    if (this.disableMBeanRegistry) {
        Registry.disableRegistry();
    }
    Tomcat tomcat = new Tomcat();
    ............
    for (Connector additionalConnector : this.additionalTomcatConnectors) {
        tomcat.getService().addConnector(additionalConnector);
    }
    prepareContext(tomcat.getHost(), initializers);
    return getTomcatWebServer(tomcat);
}
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    在这里直接new了一个tomcat，Tomcat tomcat = new Tomcat()，此方法调用之后，会返回一个TomcatWebServer，在这个类中，存在一个start()方法，这个就是启动tomcat

# 选择servlet服务器

因为默认使用的是tomcat服务器，但是我们可以选择其他的

因为默认的是tomcat，我们如果想要使用其他的服务器的话，就需要将tomcat进行移除，因为只能有一个服务器

<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>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-undertow</artifactId>
</dependency>
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# 定制化servlet容器

官方文档https://docs.spring.io/spring-boot/docs/current/reference/html/features.html##features.developing-web-applications.embedded-container.customizing

  • 实现 WebServerFactoryCu**stomizer<ConfigurableServletWebServerFactory>

  • 把配置文件的值和**ServletWebServerFactory 进行绑定**

  • 修改配置文件 server.xxx

  • 直接自定义 ConfigurableServletWebServerFactory

xxxxxCustomizer：定制化器，可以改变xxxx的默认规则

import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.boot.web.servlet.server.ConfigurableServletWebServerFactory;
import org.springframework.stereotype.Component;

@Component
public class CustomizationBean implements WebServerFactoryCustomizer<ConfigurableServletWebServerFactory> {

    @Override
    public void customize(ConfigurableServletWebServerFactory server) {
        server.setPort(9000);
    }
}
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