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day03-分析SpringBoot底层机制

2023-03-14 21:30:16 发布   22 浏览  
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分析SpringBoot底层机制

Tomcat启动分析,Spring容器初始化,Tomcat如何关联Spring容器?

1.创建SpringBoot环境

(1)创建Maven程序,创建SpringBoot环境

(2)pom.xml导入SpringBoot的父工程和依赖



    spring-boot-starter-parent
    org.springframework.boot
    2.5.3


    
    
        org.springframework.boot
        spring-boot-starter-web
    

(3)创建主程序MainApp.java

package com.li.springboot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

/**
 * @author 李
 * @version 1.0
 */
@SpringBootApplication//表示SpringBoot项目
public class MainApp {
    public static void main(String[] args) {
        //启动SpringBoot项目
        ConfigurableApplicationContext ioc =
                SpringApplication.run(MainApp.class, args);
    }
}

(4)启动项目,我们可以注意到Tomcat也随之启动了。

image-20230314175853668

问题一:当我们执行run方法时,为什么会启动我们内置的tomcat?它的底层是如何实现的?

2.Spring容器初始化(@Configuration+@Bean)

我们知道,如果在一个类上添加了注解@Configuration,那么这个类就会变成配置类;配置类中通过@Bean注解,可以将方法中 new 出来的Bean对象注入到容器中,该bean对象的id默认为方法名。

配置类本身也会作为bean注入到容器中

image-20230314183308566

容器初始化的底层机制仍然是我们之前分析的Spring容器的机制(IO/文件扫描+注解+反射+集合+映射)

对比:

  1. Spring通过@ComponentScan,指定要扫描的包;而SpringBoot默认从主程序所在的包开始扫描,同时也可以指定要扫描的包(scanBasePackages = {"xxx.xx"})。
  2. Spring通过xml或者注解,指定要注入的bean;SpringBoot通过扫描配置类(对应spring的xml)的@Bean或者注解,指定注入bean

3.SpringBoot怎样启动Tomcat,并能支持访问@Controller?

由前面的例子1中可以看到,当启动SpringBoot时,tomcat也会随之启动。那么问题来了:

  1. SpringBoot是怎么内嵌Tomcat,并启动Tomcat的?
  2. 而且底层是怎样让@Controller修饰的控制器也可以被访问的?

3.1源码分析SpringApplication.run()

SpringApplication.run()方法会完成两个重要任务:

  1. 创建容器
  2. 容器的刷新:包括参数的刷新+启动Tomcat

(1)创建一个控制器

package com.li.springboot.controller;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * @author 李
 * @version 1.0
 * HiController被标注后,作为一个控制器注入容器中
 */
@RestController//相当于@Controller+@ResponseBody
public class HiController {

    @RequestMapping("/hi")
    public String hi() {
        return "hi,HiController";
    }
}

(2)启动主程序MainApp.java,进行debug

image-20230314195800999

(3)首先进入SpringApplication.java的run方法

image-20230314201959442

(4)点击step into,进入如下方法

public ConfigurableApplicationContext run(String... args) {
    ...
    try {
        ...
        context = this.createApplicationContext();//严重分析,创建容器
        context.setApplicationStartup(this.applicationStartup);
        this.prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
        this.refreshContext(context);//刷新应用上下文,比如初始化默认设置/注入相关bean/启动Tomcat
        this.afterRefresh(context, applicationArguments);
        stopWatch.stop();
        ...

    } catch (Throwable var10) {...}
    ...
}

(5)分别对 **createApplicationContext() **和 refreshContext(context) 方法进行分析:

(5.1)step into 进入 **createApplicationContext() ** 方法中:

//springApplication.java
//容器类型很多,会根据你的this.webApplicationType创建对应的容器,默认this.webApplicationType
//的类型为SERVLET,也就是web容器(可以处理servlet)
protected ConfigurableApplicationContext createApplicationContext() {
    return this.applicationContextFactory.create(this.webApplicationType);
}
image-20230314203013719

(5.2)点击进入下一层

//接口 ApplicationContextFactory.java

//该方法根据webApplicationType创建不同的容器
ApplicationContextFactory DEFAULT = (webApplicationType) -> {
    try {
        switch(webApplicationType) {
        case SERVLET://默认进入这一分支,返回
                //AnnotationConfigServletWebServerApplicationContext容器
            return new AnnotationConfigServletWebServerApplicationContext();
        case REACTIVE:
            return new AnnotationConfigReactiveWebServerApplicationContext();
        default:
            return new AnnotationConfigApplicationContext();
        }
    } catch (Exception var2) {
        throw new IllegalStateException("Unable create a default ApplicationContext instance, you may need a custom ApplicationContextFactory", var2);
    }
};

总结:createApplicationContext()方法中创建了容器,但是还没有将bean注入到容器中。

(5.3)step into 进入 refreshContext(context) 方法中:

//springApplication.java
private void refreshContext(ConfigurableApplicationContext context) {
    if (this.registerShutdownHook) {
        shutdownHook.registerApplicationContext(context);
    }

    this.refresh(context);//核心,真正执行相关任务
}

(5.4)在this.refresh(context);这一步进入下一层:

//springApplication.java
protected void refresh(ConfigurableApplicationContext applicationContext) {
    applicationContext.refresh();
}

(5.5)继续进入下一层:

protected void refresh(ConfigurableApplicationContext applicationContext) {
    applicationContext.refresh();
}

(5.6)继续进入下一层:

//ServletWebServerApplicationContext.java
public final void refresh() throws BeansException, IllegalStateException {
    try {
        super.refresh();
    } catch (RuntimeException var3) {
        WebServer webServer = this.webServer;
        if (webServer != null) {
            webServer.stop();
        }

        throw var3;
    }
}

(5.7)在super.refresh();这一步进入下一层:

//AbstractApplicationContext.java

@Override
public void refresh() throws BeansException, IllegalStateException {
   synchronized (this.startupShutdownMonitor) {
      StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");
     ...
      try {
        ...
         // Initialize other special beans in specific context subclasses.
         //在上下文的子类初始化指定的bean
         onRefresh(); //当父类完成通用的工作后,再重新用动态绑定机制回到子类
        ...
      }

      catch (BeansException ex) {...}

      finally {...}
   }
}

(5.8)在onRefresh();这一步step into,会重新返回上一层:

//ServletWebServerApplicationContext.java
protected void onRefresh() {
    super.onRefresh();

    try {
        this.createWebServer();//创建一个webserver,可以理解成创建我们指定的web服务-Tomcat
    } catch (Throwable var2) {
        throw new ApplicationContextException("Unable to start web server", var2);
    }
}

(5.9)在this.createWebServer();这一步step into:

//ServletWebServerApplicationContext.java

private void createWebServer() {
    WebServer webServer = this.webServer;
    ServletContext servletContext = this.getServletContext();
    if (webServer == null && servletContext == null) {
        StartupStep createWebServer = this.getApplicationStartup().start("spring.boot.webserver.create");
        ServletWebServerFactory factory = this.getWebServerFactory();
        createWebServer.tag("factory", factory.getClass().toString());
        this.webServer = factory.getWebServer(new ServletContextInitializer[]{this.getSelfInitializer()});//使用TomcatServletWebServerFactory创建一个TomcatWebServer
        createWebServer.end();
        this.getBeanFactory().registerSingleton("webServerGracefulShutdown", new WebServerGracefulShutdownLifecycle(this.webServer));
        this.getBeanFactory().registerSingleton("webServerStartStop", new WebServerStartStopLifecycle(this, this.webServer));
    } else if (servletContext != null) {
        try {
            this.getSelfInitializer().onStartup(servletContext);
        } catch (ServletException var5) {
            throw new ApplicationContextException("Cannot initialize servlet context", var5);
        }
    }

    this.initPropertySources();
}
image-20230314205608658

(5.10)在this.webServer = factory.getWebServer(new ServletContextInitializer[]{this.getSelfInitializer()});这一步step into:

//TomcatServletWebServerFactory.java会创建Tomcat,并启动Tomcat

public WebServer getWebServer(ServletContextInitializer... initializers) {
    if (this.disableMBeanRegistry) {
        Registry.disableRegistry();
    }

    Tomcat tomcat = new Tomcat();//创建了Tomcat对象,下面是一系列的初始化任务
    File baseDir = this.baseDirectory != null ? this.baseDirectory : this.createTempDir("tomcat");
    tomcat.setBaseDir(baseDir.getAbsolutePath());
    Connector connector = new Connector(this.protocol);
    connector.setThrowOnFailure(true);
    tomcat.getService().addConnector(connector);
    this.customizeConnector(connector);
    tomcat.setConnector(connector);
    tomcat.getHost().setAutoDeploy(false);
    this.configureEngine(tomcat.getEngine());
    Iterator var5 = this.additionalTomcatConnectors.iterator();

    while(var5.hasNext()) {
        Connector additionalConnector = (Connector)var5.next();
        tomcat.getService().addConnector(additionalConnector);
    }

    this.prepareContext(tomcat.getHost(), initializers);
    return this.getTomcatWebServer(tomcat);
}

(5.11)在return this.getTomcatWebServer(tomcat);这一步step into:

//TomcatServletWebServerFactory.java

//这里做了端口校验,创建了TomcatWebServer
protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
    return new TomcatWebServer(tomcat, this.getPort() >= 0, this.getShutdown());
}

(5.12)继续step into进入下一层

//TomcatServletWebServerFactory.java

public TomcatWebServer(Tomcat tomcat, boolean autoStart, Shutdown shutdown) {
    this.monitor = new Object();
    this.serviceConnectors = new HashMap();
    Assert.notNull(tomcat, "Tomcat Server must not be null");
    this.tomcat = tomcat;
    this.autoStart = autoStart;
    this.gracefulShutdown = shutdown == Shutdown.GRACEFUL ? new GracefulShutdown(tomcat) : null;
    this.initialize();//进行初始化,并启动tomcat
}

(5.13)this.initialize();继续step into:

//TomcatServletWebServerFactory.java

private void initialize() throws WebServerException {
    logger.info("Tomcat initialized with port(s): " + this.getPortsDescription(false));
    synchronized(this.monitor) {
        try {
            this.addInstanceIdToEngineName();
            Context context = this.findContext();
            context.addLifecycleListener((event) -> {
                if (context.equals(event.getSource()) && "start".equals(event.getType())) {
                    this.removeServiceConnectors();
                }

            });
            this.tomcat.start();//启动Tomcat!
            this.rethrowDeferredStartupExceptions();

            try {
                ContextBindings.bindClassLoader(context, context.getNamingToken(), this.getClass().getClassLoader());
            } catch (NamingException var5) {
            }

            this.startDaemonAwaitThread();
        } catch (Exception var6) {
            this.stopSilently();
            this.destroySilently();
            throw new WebServerException("Unable to start embedded Tomcat", var6);
        }

    }
}

(6)一路返回上层,然后终于执行完refreshContext(context)方法,此时context为已经注入了bean

image-20230314211332259

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