day03-分析SpringBoot底层机制

Posted liyuelian

tags:

篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了day03-分析SpringBoot底层机制相关的知识,希望对你有一定的参考价值。

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

<!--导入SpringBoot父工程-规定写法-->
<parent>
    <artifactId>spring-boot-starter-parent</artifactId>
    <groupId>org.springframework.boot</groupId>
    <version>2.5.3</version>
</parent>
<dependencies>
    <!--导入web项目场景启动器:会自动导入和web开发相关的所有依赖[jar包]-->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>

(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。

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

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

(3)首先进入SpringApplication.java的run方法

(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);

(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();

(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

以上是关于day03-分析SpringBoot底层机制的主要内容,如果未能解决你的问题,请参考以下文章

day02-自己实现Mybatis底层机制-01

SpringBoot项目SpringBoot项目-瑞吉外卖day03分类管理

springboot官方为何不支持mybatis,而选择底层为hibernate的JPA?

反射机制知识点总结

java并发day03 JMM可见性 有序性 volatile底层原理 happens-before

java并发day03 JMM可见性 有序性 volatile底层原理 happens-before