SpringBoot源码分析-启动过程经历了什么？
SpringBoot源码分析-启动过程经历了什么？
文章目录
- SpringBoot源码分析-启动过程经历了什么？
- 前言
- 启动概况
- 测试项目
- 项目主类分析
- 分析执行过程
- 1、SpringApplication.run 标识spring的初始执行
- 创建应用上下文
- 准备异常报告器
- 准备应用上下文
- 刷新应用上下文
前言
Spring Boot实战学习：1、Spring Boot介绍
Spring Boot是由Pivotal团队提供的全新框架，其设计目的是用来简化新Spring应用的初始搭建以及开发过程。该框架使用了特定的方式来进行配置，从而使开发人员不再需要定义样板化的配置。通过这种方式，Spring Boot致力于在蓬勃发展的快速应用开发领域(rapid application development)成为领导者。
有以下特点：
- 创建独立的Spring应用程序
- 嵌入的Tomcat，无需部署WAR文件
- 简化Maven配置
- 自动配置Spring
- 提供生产就绪型功能，如指标，健康检查和外部配置
下面我们从源码的级别来探究spring boot框架的启动原理，让我们从启动过程上去理解spring boot如何通过启动来获得强大的特性的。
启动概况
概述下主要的启动过程就是
- 初始化环境
- 初始化默认配置
- 初始化各类监听器、事件
- 创建上下文
- 在上下文中添加默认的bean
- 扫描文件、注解等各种类型的bean添加在上下文中
- 实例化各个bean
- 启动完毕
测试项目
测试项目maven配置
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0modelVersion>
<parent>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-starter-parentartifactId>
<version>2.1.5.RELEASEversion>
<relativePath/>
parent>
<groupId>com.examplegroupId>
<artifactId>demoartifactId>
<version>0.0.1-SNAPSHOTversion>
<name>demoname>
<description>Demo project for Spring Bootdescription>
<properties>
<java.version>1.8java.version>
properties>
<dependencies>
<dependency>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-starterartifactId>
dependency>
<dependency>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-starter-webartifactId>
dependency>
<dependency>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-configuration-processorartifactId>
<optional>trueoptional>
dependency>
<dependency>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-starter-testartifactId>
<scope>testscope>
dependency>
dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-maven-pluginartifactId>
plugin>
plugins>
build>
project>
项目主类分析
package com.example.demo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
}
大家知道springboot的工程是从一个main方法进行配置开发的，应用启动也是从这里进行，起始任何的java程序都是从main方法开发，只是有时方法被隐藏了，我们看不到内部实现。
这里我们从@SpringBootApplication注解开发：
@Target(ElementType.TYPE) // 注解的适用范围，其中TYPE用于描述类、接口（包括包注解类型）或enum声明
@Retention(RetentionPolicy.RUNTIME) // 注解的生命周期，保留到class文件中（三个生命周期）
@Documented // 表明这个注解应该被javadoc记录
@Inherited // 子类可以继承该注解
@SpringBootConfiguration // 继承了Configuration，表示当前是注解类
@EnableAutoConfiguration // 开启springboot的注解功能，springboot的四大神器之一，其借助@import的帮助
@ComponentScan(excludeFilters = { // 扫描路径设置（具体使用待确认）
@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
...
}
该注解是一个混合注解，可以标识main类的属性，在main方法启动后，进行相应class加载时候进行对应class文件注解扫描，当扫描到相应注解时候，判断注解属性让程序做一些特定的事情。
main方法中，只有一行执行代码 SpringApplication.run(DemoApplication.class, args);
那程序的初始化过程也应该在方法里面。
spring boot 启动日志
/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/bin/java -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:63595,suspend=y,server=n -XX:TieredStopAtLevel=1 -noverify -Dspring.output.ansi.enabled=always -Dcom.sun.management.jmxremote -Dspring.jmx.enabled=true -Dspring.liveBeansView.mbeanDomain -Dspring.application.admin.enabled=true -javaagent:/Users/public1/Library/Caches/IntelliJIdea2019.1/captureAgent/debugger-agent.jar -Dfile.encoding=UTF-8 -classpath "/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_211.jdk/Contents/Home/lib/tools.jar:/Users/public1/Documents/git/demo/target/classes:/Users/public1/.m2/repository/org/springframework/boot/spring-boot-starter/2.1.5.RELEASE/spring-boot-starter-2.1.5.RELEASE.jar:/Users/public1/.m2/repository/org/springframework/boot/spring-boot/2.1.5.RELEASE/spring-boot-2.1.5.RELEASE.jar:/Users/public1/.m2/repository/org/springframework/spring-context/5.1.7.RELEASE/spring-context-5.1.7.RELEASE.jar:/Users/public1/.m2/repository/org/springframework/boot/spring-boot-autoconfigure/2.1.5.RELEASE/spring-boot-autoconfigure-2.1.5.RELEASE.jar:/Users/public1/.m2/repository/org/springframework/boot/spring-boot-starter-logging/2.1.5.RELEASE/spring-boot-starter-logging-2.1.5.RELEASE.jar:/Users/public1/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar:/Users/public1/.m2/repository/ch/qos/logback/logback-core/1.2.3/logback-core-1.2.3.jar:/Users/public1/.m2/repository/org/apache/logging/log4j/log4j-to-slf4j/2.11.2/log4j-to-slf4j-2.11.2.jar:/Users/public1/.m2/repository/org/apache/logging/log4j/log4j-api/2.11.2/log4j-api-2.11.2.jar:/Users/public1/.m2/repository/org/slf4j/jul-to-slf4j/1.7.26/jul-to-slf4j-1.7.26.jar:/Users/public1/.m2/repository/javax/annotation/javax.annotation-api/1.3.2/javax.annotation-api-1.3.2.jar:/Users/public1/.m2/repository/org/springframework/spring-core/5.1.7.RELEASE/spring-core-5.1.7.RELEASE.jar:/Users/public1/.m2/repository/org/springframework/spring-jcl/5.1.7.RELEASE/spring-jcl-5.1.7.RELEASE.jar:/Users/public1/.m2/repository/org/yaml/snakeyaml/1.23/snakeyaml-1.23.jar:/Users/public1/.m2/repository/org/springframework/boot/spring-boot-starter-web/2.1.5.RELEASE/spring-boot-starter-web-2.1.5.RELEASE.jar:/Users/public1/.m2/repository/org/springframework/boot/spring-boot-starter-json/2.1.5.RELEASE/spring-boot-starter-json-2.1.5.RELEASE.jar:/Users/public1/.m2/repository/com/fasterxml/jackson/core/jackson-databind/2.9.8/jackson-databind-2.9.8.jar:/Users/public1/.m2/repository/com/fasterxml/jackson/core/jackson-annotations/2.9.0/jackson-annotations-2.9.0.jar:/Users/public1/.m2/repository/com/fasterxml/jackson/core/jackson-core/2.9.8/jackson-core-2.9.8.jar:/Users/public1/.m2/repository/com/fasterxml/jackson/datatype/jackson-datatype-jdk8/2.9.8/jackson-datatype-jdk8-2.9.8.jar:/Users/public1/.m2/repository/com/fasterxml/jackson/datatype/jackson-datatype-jsr310/2.9.8/jackson-datatype-jsr310-2.9.8.jar:/Users/public1/.m2/repository/com/fasterxml/jackson/module/jackson-module-parameter-names/2.9.8/jackson-module-parameter-names-2.9.8.jar:/Users/public1/.m2/repository/org/springframework/boot/spring-boot-starter-tomcat/2.1.5.RELEASE/spring-boot-starter-tomcat-2.1.5.RELEASE.jar:/Users/public1/.m2/repository/org/apache/tomcat/embed/tomcat-embed-core/9.0.19/tomcat-embed-core-9.0.19.jar:/Users/public1/.m2/repository/org/apache/tomcat/embed/tomcat-embed-el/9.0.19/tomcat-embed-el-9.0.19.jar:/Users/public1/.m2/repository/org/apache/tomcat/embed/tomcat-embed-websocket/9.0.19/tomcat-embed-websocket-9.0.19.jar:/Users/public1/.m2/repository/org/hibernate/validator/hibernate-validator/6.0.16.Final/hibernate-validator-6.0.16.Final.jar:/Users/public1/.m2/repository/javax/validation/validation-api/2.0.1.Final/validation-api-2.0.1.Final.jar:/Users/public1/.m2/repository/org/jboss/logging/jboss-logging/3.3.2.Final/jboss-logging-3.3.2.Final.jar:/Users/public1/.m2/repository/com/fasterxml/classmate/1.4.0/classmate-1.4.0.jar:/Users/public1/.m2/repository/org/springframework/spring-web/5.1.7.RELEASE/spring-web-5.1.7.RELEASE.jar:/Users/public1/.m2/repository/org/springframework/spring-beans/5.1.7.RELEASE/spring-beans-5.1.7.RELEASE.jar:/Users/public1/.m2/repository/org/springframework/spring-webmvc/5.1.7.RELEASE/spring-webmvc-5.1.7.RELEASE.jar:/Users/public1/.m2/repository/org/springframework/spring-aop/5.1.7.RELEASE/spring-aop-5.1.7.RELEASE.jar:/Users/public1/.m2/repository/org/springframework/spring-expression/5.1.7.RELEASE/spring-expression-5.1.7.RELEASE.jar:/Users/public1/.m2/repository/org/springframework/boot/spring-boot-configuration-processor/2.1.5.RELEASE/spring-boot-configuration-processor-2.1.5.RELEASE.jar:/Users/public1/.m2/repository/org/slf4j/slf4j-api/1.7.26/slf4j-api-1.7.26.jar:/Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar" com.example.demo.DemoApplication
Connected to the target VM, address: '127.0.0.1:63595', transport: 'socket'
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.1.5.RELEASE)
2019-06-19 17:20:37.736 INFO 2330 --- [ main] com.example.demo.DemoApplication : Starting DemoApplication on publics-MacBook-Pro.local with PID 2330 (/Users/public1/Documents/git/demo/target/classes started by public1 in /Users/public1/Documents/git/demo)
2019-06-19 17:20:37.740 INFO 2330 --- [ main] com.example.demo.DemoApplication : No active profile set, falling back to default profiles: default
2019-06-19 17:25:56.321 INFO 2330 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8082 (http)
2019-06-19 17:25:59.427 INFO 2330 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2019-06-19 17:25:59.428 INFO 2330 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.19]
2019-06-19 17:26:01.090 INFO 2330 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2019-06-19 17:26:01.090 INFO 2330 --- [ main] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 8274 ms
2019-06-19 17:26:01.266 INFO 2330 --- [ main] o.s.s.concurrent.ThreadPoolTaskExecutor : Initializing ExecutorService 'applicationTaskExecutor'
2019-06-19 17:26:01.414 INFO 2330 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8082 (http) with context path ''
2019-06-19 17:26:06.376 INFO 2330 --- [ main] com.example.demo.DemoApplication : Started DemoApplication in 1854.489 seconds (JVM running for 1936.518)
分析执行过程
1、SpringApplication.run 标识spring的初始执行
SpringApplication.java
/**
* Static helper that can be used to run a {@link SpringApplication} from the
* specified source using default settings.
* @param primarySource the primary source to load
* @param args the application arguments (usually passed from a Java main method)
* @return the running {@link ApplicationContext}
*/
public static ConfigurableApplicationContext run(Class<?> primarySource,
String... args) {
return run(new Class<?>[] { primarySource }, args);
}
上述过程调用了org.springframework.boot.SpringApplication类的run方法，返回一个ConfigurableApplicationContext对象。
接下来，执行内部的run方法：
/**
* Static helper that can be used to run a {@link SpringApplication} from the
* specified sources using default settings and user supplied arguments.
* @param primarySources the primary sources to load
* @param args the application arguments (usually passed from a Java main method)
* @return the running {@link ApplicationContext}
*/
public static ConfigurableApplicationContext run(Class<?>[] primarySources,
String[] args) {
return new SpringApplication(primarySources).run(args);
}
这里通过创建SpringApplication对象，去执行该对象run方法，并返回了一个ConfigurableApplicationContext对象。
SpringApplication类到底是干什么呢？
接着，进入到SpringApplication类后，该类class上有说明如下：
Class that can be used to bootstrap and launch a Spring application from a Java main method. By default class will perform the following steps to bootstrap your application
- 1、Create an appropriate {@link ApplicationContext} instance (depending on your classpath)
- 2、 Register a {@link CommandLinePropertySource} to expose command line arguments as Spring properties
- 3、Refresh the application context, loading all singleton beans
- 4、Trigger any {@link CommandLineRunner} beans
大意就是该类主要用main方法启动一个spring 应用，将会经历一下步骤去启动你的应用：
1、通过classpath创建一个合适的ApplicationContext实例（也就是spring 容器）
2、注册一个CommandLinePropertySource去执行命令行参数
3、刷新应用上下文，加载单例bean
4、触发所有的CommandLineRunner beans
ConfigurableApplicationContext类又是干什么呢？
我们查看了ConfigurableApplicationContext的类注释，还有它一些方法。
大概知道是spring 应用的一个上下文环境配置context
/**
* SPI interface to be implemented by most if not all application contexts.
* Provides facilities to configure an application context in addition
* to the application context client methods in the
* {@link org.springframework.context.ApplicationContext} interface.
*
* Configuration and lifecycle methods are encapsulated here to avoid
* making them obvious to ApplicationContext client code. The present
* methods should only be used by startup and shutdown code.
*
* @author Juergen Hoeller
* @author Chris Beams
* @since 03.11.2003
*/
public interface ConfigurableApplicationContext extends ApplicationContext, Lifecycle, Closeable {
接下来是SpringApplication的run方法，这个方法做了哪些事情呢？
SpringApplication的run方法：
/**
* Run the Spring application, creating and refreshing a new
* {@link ApplicationContext}.
* @param args the application arguments (usually passed from a Java main method)
* @return a running {@link ApplicationContext}
*/
public ConfigurableApplicationContext run(String... args) {
// 1、创建并启动计时监控类，用于启动耗时计算
StopWatch stopWatch = new StopWatch();
stopWatch.start();
// 2、初始化应用上下文和异常报告集合
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
// 3、设置系统属性 `java.awt.headless` 的值，默认值为：true
configureHeadlessProperty();
// 4、创建所有 Spring 运行监听器并发布应用启动事件
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
// 5、初始化默认应用参数类
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
// 6、根据运行监听器和应用参数来准备 Spring 环境
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
configureIgnoreBeanInfo(environment);
// 7、创建 Banner 打印类
Banner printedBanner = printBanner(environment);
// 8、创建应用上下文
context = createApplicationContext();
// 9、准备异常报告器
exceptionReporters = getSpringFactoriesInstances(
SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
// 10、准备应用上下文
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
// 11、刷新应用上下文，在这里会启动web容器如tomcat
refreshContext(context);
// 12、应用上下文刷新后置处理
afterRefresh(context, applicationArguments);
// 13、停止计时监控类，计算启动耗时。
stopWatch.stop();
// 14、输出日志记录执行主类名、时间信息
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
// 15、发布应用上下文启动完成事件
listeners.started(context);
// 16、执行所有 Runner 运行器 如如果有ApplicationRunner或者CommandLineRunner类型的bean，则触发run函数，启动任务。
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
}
try {
// 17、发布应用上下文就绪事件
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
// 18、返回应用上下文
return context;
}
下面重点介绍重要的方法执行过程：
创建应用上下文
context = createApplicationContext();
createApplicationContext的方法如下：
/**
* Strategy method used to create the {@link ApplicationContext}. By default this
* method will respect any explicitly set application context or application context
* class before falling back to a suitable default.
* @return the application context (not yet refreshed)
* @see #setApplicationContextClass(Class)
*/
protected ConfigurableApplicationContext createApplicationContext() {
Class<?> contextClass = this.applicationContextClass;
if (contextClass == null) {
try {
switch (this.webApplicationType) {
case SERVLET:
contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
break;
case REACTIVE:
contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
break;
default:
contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
}
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Unable create a default ApplicationContext, "
+ "please specify an ApplicationContextClass",
ex);
}
}
return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}
该方法内部相应的静态变量如下：
/**
* The class name of application context that will be used by default for non-web
* environments.
*/
public static final String DEFAULT_CONTEXT_CLASS = "org.springframework.context."
+ "annotation.AnnotationConfigApplicationContext";
/**
* The class name of application context that will be used by default for web
* environments.
*/
public static final String DEFAULT_SERVLET_WEB_CONTEXT_CLASS = "org.springframework.boot."
+ "web.servlet.context.AnnotationConfigServletWebServerApplicationContext";
/**
* The class name of application context that will be used by default for reactive web
* environments.
*/
public static final String DEFAULT_REACTIVE_WEB_CONTEXT_CLASS = "org.springframework."
+ "boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext";
通过执行过程可知道，通过判断webApplicationType的类型，是获得相应web容器实现类
可能会出现三种结果：
SERVLET 时候org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext
REACTIVE 会获得class org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext
default 会获得class：
org.springframework.context.annotation.AnnotationConfigApplicationContext
而AnnotationConfigServletWebServerApplicationContext的一个类关系图如下。
准备异常报告器
getSpringFactoriesInstances方法
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
return getSpringFactoriesInstances(type, new Class<?>[] {});
}
// 这里的入参type就是ApplicationContextInitializer.class
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
// 使用Set保存names来避免重复元素
Set<String> names = new LinkedHashSet<>(
SpringFactoriesLoader.loadFactoryNames(type, classLoader));
// 根据names来进行实例化
List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
classLoader, args, names);
// 对实例进行排序
AnnotationAwareOrderComparator.sort(instances);
return instances;
}
SpringFactoriesLoader.loadFactoryNames(type, classLoader)) 过程：
/**
* Load the fully qualified class names of factory implementations of the
* given type from {@value #FACTORIES_RESOURCE_LOCATION}, using the given
* class loader.
* @param factoryClass the interface or abstract class representing the factory
* @param classLoader the ClassLoader to use for loading resources; can be
* {@code null} to use the default
* @throws IllegalArgumentException if an error occurs while loading factory names
* @see #loadFactories
*/
public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
}
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
MultiValueMap<String, String> result = cache.get(classLoader);
if (result != null) {
return result;
}
try {
Enumeration<URL> urls = (classLoader != null ?
classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
result = new LinkedMultiValueMap<>();
while (urls.hasMoreElements()) {
URL url = urls.nextElement();
UrlResource resource = new UrlResource(url);
Properties properties = PropertiesLoaderUtils.loadProperties(resource);
for (Map.Entry<?, ?> entry : properties.entrySet()) {
String factoryClassName = ((String) entry.getKey()).trim();
for (String factoryName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {
result.add(factoryClassName, factoryName.trim());
}
}
}
cache.put(classLoader, result);
return result;
}
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load factories from location [" +
FACTORIES_RESOURCE_LOCATION + "]", ex);
}
}
//FACTORIES_RESOURCE_LOCATION
/**
* The location to look for factories.
* Can be present in multiple JAR files.
*/
public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
这个方法会尝试从类路径的META-INF/spring.factories处读取相应配置文件，然后进行遍历，读取配置文件中Key为：org.springframework.context.ApplicationContextInitializer的value。以spring-boot-autoconfigure这个包为例，它的META-INF/spring.factories部分定义如下所示：
META-INF/spring.factories内容：
# Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener
# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.autoconfigure.BackgroundPreinitializer
# Auto Configuration Import Listeners
org.springframework.boot.autoconfigure.AutoConfigurationImportListener=\
org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener
# Auto Configuration Import Filters
org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
org.springframework.boot.autoconfigure.condition.OnBeanCondition,\
org.springframework.boot.autoconfigure.condition.OnClassCondition,\
org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\
org.springframework.boot.autoconfigure.cloud.CloudServiceConnectorsAutoConfiguration,\
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\
org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\
org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\
org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration,\
org.springframework.boot.autoconfigure.elasticsearch.rest.RestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\
org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\
org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\
org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration,\
org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\
org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\
org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\
org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\
org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\
org.springframework.boot.autoconfigure.reactor.core.ReactorCoreAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityRequestMatcherProviderAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\
org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\
org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.ClientHttpConnectorAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration
# Failure analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\
org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer,\
org.springframework.boot.autoconfigure.session.NonUniqueSessionRepositoryFailureAnalyzer
# Template availability providers
org.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider=\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.mustache.MustacheTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.web.servlet.JspTemplateAvailabilityProvider
准备应用上下文
prepareContext(context,environment,listeners,applicationArguments,printedBanner);
prepareContext方法：
private void prepareContext(ConfigurableApplicationContext context,
ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments, Banner printedBanner) {
context.setEnvironment(environment);
postProcessApplicationContext(context);
applyInitializers(context);
listeners.contextPrepared(context);
if (this.logStartupInfo) {
logStartupInfo(context.getParent() == null);
logStartupProfileInfo(context);
}
// Add boot specific singleton beans
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
if (printedBanner != null) {
beanFactory.registerSingleton("springBootBanner", printedBanner);
}
if (beanFactory instanceof DefaultListableBeanFactory) {
((DefaultListableBeanFactory) beanFactory)
.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}
// Load the sources
Set<Object> sources = getAllSources();
Assert.notEmpty(sources, "Sources must not be empty");
load(context, sources.toArray(new Object[0]));
listeners.contextLoaded(context);
}
刷新应用上下文
这一步很重要，bean的注册，还有web容器都会在这里进行。
refreshContext(context);
refreshContext方法：
//这里会调用refresh（context）方法
private void refreshContext(ConfigurableApplicationContext context) {
refresh(context);
if (this.registerShutdownHook) {
try {
context.registerShutdownHook();
}
catch (AccessControlException ex) {
// Not allowed in some environments.
}
}
}
// refresh（context方法）
/**
* Refresh the underlying {@link ApplicationContext}.
* @param applicationContext the application context to refresh
*/
protected void refresh(ApplicationContext applicationContext) {
Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
((AbstractApplicationContext) applicationContext).refresh();
}
接着refresh方法会调用AbstractApplicationContext的子类AbstractApplicationContext的refresh方法，而AbstractApplicationContext是一个抽象类，refresh定义模板方法类，在该方法是空实现的，调用方法实际调用的是子类的方法。
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
比如onRefresh方法：
/**
* Template method which can be overridden to add context-specific refresh work.
* Called on initialization of special beans, before instantiation of singletons.
* This implementation is empty.
* @throws BeansException in case of errors
* @see #refresh()
*/
protected void onRefresh() throws BeansException {
// For subclasses: do nothing by default.
}
这里找到了其中一个抽象类实现ServletWebServerApplicationContext
ServletWebServerApplicationContext下实际的refresh方法是
@Override
protected void onRefresh() {
super.onRefresh();
try {
createWebServer();
}
catch (Throwable ex) {
throw new ApplicationContextException("Unable to start web server", ex);
}
}
private void createWebServer() {
WebServer webServer = this.webServer;
ServletContext servletContext = getServletContext();
if (webServer == null && servletContext == null) {
ServletWebServerFactory factory = getWebServerFactory();
this.webServer = factory.getWebServer(getSelfInitializer());
}
else if (servletContext != null) {
try {
getSelfInitializer().onStartup(servletContext);
}
catch (ServletException ex) {
throw new ApplicationContextException("Cannot initialize servlet context",
ex);
}
}
initPropertySources();
}
这里ServletWebServerFactory factory = getWebServerFactory(); 获得的是org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory 工厂类
接着通过工厂类TomcatServletWebServerFactory创建了WebServer
@Override
public WebServer getWebServer(ServletContextInitializer... initializers) {
Tomcat tomcat = new Tomcat();
File baseDir = (this.baseDirectory != null) ? this.baseDirectory
: createTempDir("tomcat");
tomcat.setBaseDir(baseDir.getAbsolutePath());
Connector connector = new Connector(this.protocol);
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);
}
prepareContext(tomcat.getHost(), initializers);
return getTomcatWebServer(tomcat);
}
/**
* Factory method called to create the {@link TomcatWebServer}. Subclasses can
* override this method to return a different {@link TomcatWebServer} or apply
* additional processing to the Tomcat server.
* @param tomcat the Tomcat server.
* @return a new {@link TomcatWebServer} instance
*/
protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
return new TomcatWebServer(tomcat, getPort() >= 0);
}
接下来，在创建TomcatWebServer的过程中，会对tomcat容器进行初始化，并启动servlet容器，开启web服务。
TomcatWebServer类是用来控制tomcat的，可以对web容器进行初始化。
/**
* {@link WebServer} that can be used to control a Tomcat web server. Usually this class
* should be created using the {@link TomcatReactiveWebServerFactory} of
* {@link TomcatServletWebServerFactory}, but not directly.
*
* @author Brian Clozel
* @author Kristine Jetzke
* @since 2.0.0
*/
public class TomcatWebServer implements WebServer {
private static final Log logger = LogFactory.getLog(TomcatWebServer.class);
private static final AtomicInteger containerCounter = new AtomicInteger(-1);
private final Object monitor = new Object();
private final Map<Service, Connector[]> serviceConnectors = new HashMap<>();
private final Tomcat tomcat;
private final boolean autoStart;
private volatile boolean started;
/**
* Create a new {@link TomcatWebServer} instance.
* @param tomcat the underlying Tomcat server
*/
public TomcatWebServer(Tomcat tomcat) {
this(tomcat, true);
}
/**
* Create a new {@link TomcatWebServer} instance.
* @param tomcat the underlying Tomcat server
* @param autoStart if the server should be started
*/
public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
Assert.notNull(tomcat, "Tomcat Server must not be null");
this.tomcat = tomcat;
this.autoStart = autoStart;
initialize();
}
private void initialize() throws WebServerException {
logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));
synchronized (this.monitor) {
try {
addInstanceIdToEngineName();
Context context = findContext();
context.addLifecycleListener((event) -> {
if (context.equals(event.getSource())
&& Lifecycle.START_EVENT.equals(event.getType())) {
// Remove service connectors so that protocol binding doesn't
// happen when the service is started.
removeServiceConnectors();
}
});
// Start the server to trigger initialization listeners
this.tomcat.start();
// We can re-throw failure exception directly in the main thread
rethrowDeferredStartupExceptions();
try {
ContextBindings.bindClassLoader(context, context.getNamingToken(),
getClass().getClassLoader());
}
catch (NamingException ex) {
// Naming is not enabled. Continue
}
// Unlike Jetty, all Tomcat threads are daemon threads. We create a
// blocking non-daemon to stop immediate shutdown
startDaemonAwaitThread();
}
catch (Exception ex) {
stopSilently();
throw new WebServerException("Unable to start embedded Tomcat", ex);
}
}
}
在上述的代码中创建TomcatWebServer的过程中会调用initialize();
在初始化的方法中，this.tomcat.start(); 对tomcat容易进行启动，这也就是spring boot实现web容器如tomcat嵌入到自己的服务。
/**
* Start the server.
*
* @throws LifecycleException Start error
*/
public void start() throws LifecycleException {
getServer();
server.start();
}
/**
* Get the server object. You can add listeners and few more
* customizations. JNDI is disabled by default.
* @return The Server
*/
public Server getServer() {
if (server != null) {
return server;
}
System.setProperty("catalina.useNaming", "false");
server = new StandardServer();
initBaseDir();
// Set configuration source
ConfigFileLoader.setSource(new CatalinaBaseConfigurationSource(new File(basedir), null));
server.setPort( -1 );
Service service = new StandardService();
service.setName("Tomcat");
server.addService(service);
return server;
}
然后在start的过程中会调用
public abstract class LifecycleBase implements Lifecycle
/**
* {@inheritDoc}
*/
@Override
public final synchronized void start() throws LifecycleException {
if (LifecycleState.STARTING_PREP.equals(state) || LifecycleState.STARTING.equals(state) ||
LifecycleState.STARTED.equals(state)) {
if (log.isDebugEnabled()) {
Exception e = new LifecycleException();
log.debug(sm.getString("lifecycleBase.alreadyStarted", toString()), e);
} else if (log.isInfoEnabled()) {
log.info(sm.getString("lifecycleBase.alreadyStarted", toString()));
}
return;
}
if (state.equals(LifecycleState.NEW)) {
init();
} else if (state.equals(LifecycleState.FAILED)) {
stop();
} else if (!state.equals(LifecycleState.INITIALIZED) &&
!state.equals(LifecycleState.STOPPED)) {
invalidTransition(Lifecycle.BEFORE_START_EVENT);
}
try {
setStateInternal(LifecycleState.STARTING_PREP, null, false);
startInternal();
if (state.equals(LifecycleState.FAILED)) {
// This is a 'controlled' failure. The component put itself into the
// FAILED state so call stop() to complete the clean-up.
stop();
} else if (!state.equals(LifecycleState.STARTING)) {
// Shouldn't be necessary but acts as a check that sub-classes are
// doing what they are supposed to.
invalidTransition(Lifecycle.AFTER_START_EVENT);
} else {
setStateInternal(LifecycleState.STARTED, null, false);
}
} catch (Throwable t) {
// This is an 'uncontrolled' failure so put the component into the
// FAILED state and throw an exception.
handleSubClassException(t, "lifecycleBase.startFail", toString());
}
}
在startInternal();方法中会调用实现类：
org.apache.catalina.core.StandardServer的startInternal()实现方法
在
@Override
protected void startInternal() throws LifecycleException {
fireLifecycleEvent(CONFIGURE_START_EVENT, null);
setState(LifecycleState.STARTING);
globalNamingResources.start();
// Start our defined Services
synchronized (servicesLock) {
for (int i = 0; i < services.length; i++) {
services[i].start();
}
}
if (periodicEventDelay > 0) {
monitorFuture = getUtilityExecutor().scheduleWithFixedDelay(
new Runnable() {
@Override
public void run() {
startPeriodicLifecycleEvent();
}
}, 0, 60, TimeUnit.SECONDS);
}
}
services[i].start(); 这里会对容器进行启动，调用start后回到lifeCycle方法，接着调用org.apache.catalina.core.StandardService的startInternal
org.apache.catalina.core.StandardService的startInternal
/**
* Start nested components ({@link Executor}s, {@link Connector}s and
* {@link Container}s) and implement the requirements of
* {@link org.apache.catalina.util.LifecycleBase#startInternal()}.
*
* @exception LifecycleException if this component detects a fatal error
* that prevents this component from being used
*/
@Override
protected void startInternal() throws LifecycleException {
if(log.isInfoEnabled())
log.info(sm.getString("standardService.start.name", this.name));
setState(LifecycleState.STARTING);
// Start our defined Container first
if (engine != null) {
synchronized (engine) {
engine.start();
}
}
synchronized (executors) {
for (Executor executor: executors) {
executor.start();
}
}
mapperListener.start();
// Start our defined Connectors second
synchronized (connectorsLock) {
for (Connector connector: connectors) {
// If it has already failed, don't try and start it
if (connector.getState() != LifecycleState.FAILED) {
connector.start();
}
}
}
}
接着调用 engine.start(); 这里会对容器进行启动，调用start后回到lifeCycle方法，接着调用org.apache.catalina.core.StandardEngined的startInternal
org.apache.catalina.core.StandardEngined的startInternal方法如下：
@Override
protected synchronized void startInternal() throws LifecycleException {
// Log our server identification information
if (log.isInfoEnabled()) {
log.info(sm.getString("standardEngine.start", ServerInfo.getServerInfo()));
}
// Standard container startup
super.startInternal();
}
最后调用tomcat内部的启动方法，开启socket监听服务，实现web容器的启动。
/**
* Start this component and implement the requirements
* of {@link org.apache.catalina.util.LifecycleBase#startInternal()}.
*
* @exception LifecycleException if this component detects a fatal error
* that prevents this component from being used
*/
@Override
protected synchronized void startInternal() throws LifecycleException {
// Start our subordinate components, if any
logger = null;
getLogger();
Cluster cluster = getClusterInternal();
if (cluster instanceof Lifecycle) {
((Lifecycle) cluster).start();
}
Realm realm = getRealmInternal();
if (realm instanceof Lifecycle) {
((Lifecycle) realm).start();
}
// Start our child containers, if any
Container children[] = findChildren();
List<Future<Void>> results = new ArrayList<>();
for (int i = 0; i < children.length; i++) {
results.add(startStopExecutor.submit(new StartChild(children[i])));
}
MultiThrowable multiThrowable = null;
for (Future<Void> result : results) {
try {
result.get();
} catch (Throwable e) {
log.error(sm.getString("containerBase.threadedStartFailed"), e);
if (multiThrowable == null) {
multiThrowable = new MultiThrowable();
}
multiThrowable.add(e);
}
}
if (multiThrowable != null) {
throw new LifecycleException(sm.getString("containerBase.threadedStartFailed"),
multiThrowable.getThrowable());
}
// Start the Valves in our pipeline (including the basic), if any
if (pipeline instanceof Lifecycle) {
((Lifecycle) pipeline).start();
}
setState(LifecycleState.STARTING);
// Start our thread
if (backgroundProcessorDelay > 0) {
monitorFuture = Container.getService(ContainerBase.this).getServer()
.getUtilityExecutor().scheduleWithFixedDelay(
new ContainerBackgroundProcessorMonitor(), 0, 60, TimeUnit.SECONDS);
}
}
到这里我们看到tomcat内部启动的方法
((Lifecycle) cluster).start();
通过这种方式启动内部web容器。