springbootHelloWorld深入研究笔记二

xiaoxiao2025-01-17 9

首先我们先从pox.xml中的springboot的父项目开始研究

<parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>1.5.9.RELEASE</version> </parent>

上面这个父项目是所有springboot启动器的父项目。然后我们点击这个父项目的spring-boot-starter-parent。发现父项目还依赖了一个父项目

<parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-dependencies</artifactId> <version>1.5.9.RELEASE</version> <relativePath>../../spring-boot-dependencies</relativePath> </parent>

然后我们再次点击spring-boot-dependencies查看里面有什么。当我们点进去以后，发现了这个：

<properties>  <activemq.version>5.14.5</activemq.version> <antlr2.version>2.7.7</antlr2.version> <appengine-sdk.version>1.9.59</appengine-sdk.version> <artemis.version>1.5.5</artemis.version> <aspectj.version>1.8.13</aspectj.version> <assertj.version>2.6.0</assertj.version> <atomikos.version>3.9.3</atomikos.version> <bitronix.version>2.1.4</bitronix.version> <caffeine.version>2.3.5</caffeine.version> <cassandra-driver.version>3.1.4</cassandra-driver.version> <classmate.version>1.3.4</classmate.version> <commons-beanutils.version>1.9.3</commons-beanutils.version> <commons-collections.version>3.2.2</commons-collections.version> <commons-codec.version>1.10</commons-codec.version> <commons-dbcp.version>1.4</commons-dbcp.version> <commons-dbcp2.version>2.1.1</commons-dbcp2.version> <commons-digester.version>2.1</commons-digester.version> <commons-pool.version>1.6</commons-pool.version> <commons-pool2.version>2.4.3</commons-pool2.version> <couchbase-client.version>2.3.7</couchbase-client.version> <couchbase-cache-client.version>2.1.0</couchbase-cache-client.version> <crashub.version>1.3.2</crashub.version> <derby.version>10.13.1.1</derby.version> <dom4j.version>1.6.1</dom4j.version> <dropwizard-metrics.version>3.1.5</dropwizard-metrics.version> <ehcache.version>2.10.4</ehcache.version> <ehcache3.version>3.2.3</ehcache3.version> <embedded-mongo.version>1.50.5</embedded-mongo.version> <flyway.version>3.2.1</flyway.version> <freemarker.version>2.3.27-incubating</freemarker.version> <elasticsearch.version>2.4.6</elasticsearch.version> <gemfire.version>8.2.7</gemfire.version> <glassfish-el.version>3.0.0</glassfish-el.version> <gradle.version>2.9</gradle.version> <groovy.version>2.4.13</groovy.version> <gson.version>2.8.2</gson.version> <h2.version>1.4.196</h2.version> <hamcrest.version>1.3</hamcrest.version> <hazelcast.version>3.7.8</hazelcast.version> <hazelcast-hibernate4.version>3.7.1</hazelcast-hibernate4.version> <hazelcast-hibernate5.version>1.1.3</hazelcast-hibernate5.version> <hibernate.version>5.0.12.Final</hibernate.version> <hibernate-validator.version>5.3.6.Final</hibernate-validator.version> <hikaricp.version>2.5.1</hikaricp.version> <hikaricp-java6.version>2.3.13</hikaricp-java6.version> <hikaricp-java7.version>2.4.13</hikaricp-java7.version> <hsqldb.version>2.3.5</hsqldb.version> <htmlunit.version>2.21</htmlunit.version> <httpasyncclient.version>4.1.3</httpasyncclient.version> <httpclient.version>4.5.3</httpclient.version> <httpcore.version>4.4.8</httpcore.version> <infinispan.version>8.2.8.Final</infinispan.version> <jackson.version>2.8.10</jackson.version> <janino.version>2.7.8</janino.version> <javassist.version>3.21.0-GA</javassist.version>  <javax-cache.version>1.0.0</javax-cache.version> <javax-mail.version>1.5.6</javax-mail.version> <javax-transaction.version>1.2</javax-transaction.version> <javax-validation.version>1.1.0.Final</javax-validation.version> <jaxen.version>1.1.6</jaxen.version> <jaybird.version>2.2.13</jaybird.version> <jboss-logging.version>3.3.1.Final</jboss-logging.version> <jboss-transaction-spi.version>7.6.0.Final</jboss-transaction-spi.version> <jdom2.version>2.0.6</jdom2.version> <jedis.version>2.9.0</jedis.version> <jersey.version>2.25.1</jersey.version> <jest.version>2.0.4</jest.version> <jetty.version>9.4.7.v20170914</jetty.version> <jetty-jsp.version>2.2.0.v201112011158</jetty-jsp.version> <jetty-el.version>8.0.33</jetty-el.version> <jms-api.version>1.1-rev-1</jms-api.version> <jmustache.version>1.13</jmustache.version> <jna.version>4.2.2</jna.version> <joda-time.version>2.9.9</joda-time.version> <jolokia.version>1.3.7</jolokia.version> <jooq.version>3.9.6</jooq.version> <json.version>20140107</json.version> <jsonassert.version>1.4.0</jsonassert.version> <json-path.version>2.2.0</json-path.version> <jstl.version>1.2</jstl.version> <jtds.version>1.3.1</jtds.version> <junit.version>4.12</junit.version> <liquibase.version>3.5.3</liquibase.version> <log4j2.version>2.7</log4j2.version> <logback.version>1.1.11</logback.version> <lombok.version>1.16.18</lombok.version> <mariadb.version>1.5.9</mariadb.version> <mssql-jdbc.version>6.1.0.jre7</mssql-jdbc.version> <mockito.version>1.10.19</mockito.version> <mongodb.version>3.4.3</mongodb.version> <mysql.version>5.1.44</mysql.version> <narayana.version>5.5.30.Final</narayana.version> <nekohtml.version>1.9.22</nekohtml.version> <neo4j-ogm.version>2.1.5</neo4j-ogm.version> <postgresql.version>9.4.1212.jre7</postgresql.version> <querydsl.version>4.1.4</querydsl.version> <reactor.version>2.0.8.RELEASE</reactor.version> <reactor-spring.version>2.0.7.RELEASE</reactor-spring.version> <selenium.version>2.53.1</selenium.version> <selenium-htmlunit.version>2.21</selenium-htmlunit.version> <sendgrid.version>2.2.2</sendgrid.version> <servlet-api.version>3.1.0</servlet-api.version> <simple-json.version>1.1.1</simple-json.version> <slf4j.version>1.7.25</slf4j.version> <snakeyaml.version>1.17</snakeyaml.version> <solr.version>5.5.5</solr.version> <spock.version>1.0-groovy-2.4</spock.version> <spring.version>4.3.13.RELEASE</spring.version> <spring-amqp.version>1.7.4.RELEASE</spring-amqp.version> <spring-cloud-connectors.version>1.2.5.RELEASE</spring-cloud-connectors.version> <spring-batch.version>3.0.8.RELEASE</spring-batch.version> <spring-data-releasetrain.version>Ingalls-SR9</spring-data-releasetrain.version> <spring-hateoas.version>0.23.0.RELEASE</spring-hateoas.version> <spring-integration.version>4.3.12.RELEASE</spring-integration.version> <spring-integration-java-dsl.version>1.2.3.RELEASE</spring-integration-java-dsl.version> <spring-kafka.version>1.1.7.RELEASE</spring-kafka.version> <spring-ldap.version>2.3.2.RELEASE</spring-ldap.version> <spring-loaded.version>1.2.8.RELEASE</spring-loaded.version> <spring-mobile.version>1.1.5.RELEASE</spring-mobile.version> <spring-plugin.version>1.2.0.RELEASE</spring-plugin.version> <spring-restdocs.version>1.1.3.RELEASE</spring-restdocs.version> <spring-retry.version>1.2.1.RELEASE</spring-retry.version> <spring-security.version>4.2.3.RELEASE</spring-security.version> <spring-security-jwt.version>1.0.8.RELEASE</spring-security-jwt.version> <spring-security-oauth.version>2.0.14.RELEASE</spring-security-oauth.version> <spring-session.version>1.3.1.RELEASE</spring-session.version> <spring-social.version>1.1.4.RELEASE</spring-social.version> <spring-social-facebook.version>2.0.3.RELEASE</spring-social-facebook.version> <spring-social-linkedin.version>1.0.2.RELEASE</spring-social-linkedin.version> <spring-social-twitter.version>1.1.2.RELEASE</spring-social-twitter.version> <spring-ws.version>2.4.2.RELEASE</spring-ws.version> <sqlite-jdbc.version>3.15.1</sqlite-jdbc.version> <statsd-client.version>3.1.0</statsd-client.version> <sun-mail.version>${javax-mail.version}</sun-mail.version> <thymeleaf.version>2.1.6.RELEASE</thymeleaf.version> <thymeleaf-extras-springsecurity4.version>2.1.3.RELEASE</thymeleaf-extras-springsecurity4.version> <thymeleaf-extras-conditionalcomments.version>2.1.2.RELEASE</thymeleaf-extras-conditionalcomments.version> <thymeleaf-layout-dialect.version>1.4.0</thymeleaf-layout-dialect.version> <thymeleaf-extras-data-attribute.version>1.3</thymeleaf-extras-data-attribute.version> <thymeleaf-extras-java8time.version>2.1.0.RELEASE</thymeleaf-extras-java8time.version> <tomcat.version>8.5.23</tomcat.version> <undertow.version>1.4.21.Final</undertow.version> <unboundid-ldapsdk.version>3.2.1</unboundid-ldapsdk.version> <webjars-hal-browser.version>9f96c74</webjars-hal-browser.version> <webjars-locator.version>0.32-1</webjars-locator.version> <wsdl4j.version>1.6.3</wsdl4j.version> <xml-apis.version>1.4.01</xml-apis.version>  <build-helper-maven-plugin.version>1.10</build-helper-maven-plugin.version> <exec-maven-plugin.version>1.5.0</exec-maven-plugin.version> <git-commit-id-plugin.version>2.2.3</git-commit-id-plugin.version> <maven-antrun-plugin.version>1.8</maven-antrun-plugin.version> <maven-assembly-plugin.version>2.6</maven-assembly-plugin.version> <maven-clean-plugin.version>2.6.1</maven-clean-plugin.version> <maven-compiler-plugin.version>3.1</maven-compiler-plugin.version> <maven-dependency-plugin.version>2.10</maven-dependency-plugin.version> <maven-deploy-plugin.version>2.8.2</maven-deploy-plugin.version> <maven-eclipse-plugin.version>2.10</maven-eclipse-plugin.version> <maven-enforcer-plugin.version>1.4</maven-enforcer-plugin.version> <maven-failsafe-plugin.version>2.18.1</maven-failsafe-plugin.version> <maven-install-plugin.version>2.5.2</maven-install-plugin.version> <maven-invoker-plugin.version>1.10</maven-invoker-plugin.version> <maven-help-plugin.version>2.2</maven-help-plugin.version> <maven-jar-plugin.version>2.6</maven-jar-plugin.version> <maven-javadoc-plugin.version>2.10.4</maven-javadoc-plugin.version> <maven-resources-plugin.version>2.7</maven-resources-plugin.version> <maven-shade-plugin.version>2.4.3</maven-shade-plugin.version> <maven-site-plugin.version>3.5.1</maven-site-plugin.version> <maven-source-plugin.version>2.4</maven-source-plugin.version> <maven-surefire-plugin.version>2.18.1</maven-surefire-plugin.version> <maven-war-plugin.version>2.6</maven-war-plugin.version> <versions-maven-plugin.version>2.2</versions-maven-plugin.version> </properties>

上面的长篇大论就是我们在pom.xml中引入starter启动器的时候默认的依赖版本，也就是说我们不需要指定版本号，springboot已经帮我们做了，说白了就是springboot 1.5.9对应的所有依赖的jar包的默认版本都已经配置好了，它是版本仲裁中心。但是引入了没有在这个仲裁中心管理的jar包，就一定要标明版本号。

然后研究我们在pom文件中导入的springboot依赖。

<dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> </dependencies>

上面我们就没有写版本号，因为仲裁中心已经帮我们自动依赖了相应的版本号。看名字spring-boot-starter-web其中spring-boot-starter是springboot的场景启动器，web是指定springboot的哪个启动器模块。我们点进去这个启动器，看看里面都有什么。

<dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-tomcat</artifactId> </dependency> <dependency> <groupId>org.hibernate</groupId> <artifactId>hibernate-validator</artifactId> </dependency> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-web</artifactId> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> </dependency> </dependencies>

可以看到，我们的spring-boot-starter-web引入了这些依赖，其中有我们基本的springboot启动器，tomcat，hibernate数据校验，web和webmvc，也就是帮我们导入了web模块所需要的jar包，当然版本都受仲裁中心的版本管理。

主程序、主入口类

/** * @SpringBootApplication 来标注一个主程序类，说明这是一个SpringBoot应用 */ @SpringBootApplication public class HelloWorldMainApplication { public static void main(String[] args){ //spring应用启动起来 SpringApplication.run(HelloWorldMainApplication.class,args); } }

上面这个类就是我们springboot应用的主入口类，首先介绍一下@SpringBootApplication注解吧 @SpringBootApplication：SpringBoot应用标注再某个类上说明这个类是SpringBoot的主配置类，SpringBoot就应该运行这个类的main方法来启动SpringBoot应用。然后我们点这个注解，看看这个注解里面都有什么。

@Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @SpringBootConfiguration @EnableAutoConfiguration @ComponentScan( excludeFilters = {@Filter( type = FilterType.CUSTOM, classes = {TypeExcludeFilter.class} ), @Filter( type = FilterType.CUSTOM, classes = {AutoConfigurationExcludeFilter.class} )} )

@SpringBootConfiguration：spring Boot的配置类标注在某个类上，表示这个springboot的配置类这个注解里面包含一个@Configuration注解，这个注解就是我们spring底层用到的配置类注解。我们在点击@Configuration注解里面有一个@Component注解，这个注解就是我们spring里的容器组件，所以Configuration就是一个组件。

@EnableAutoConfiguration：开启自动配置功能；以前我们需要配置的东西，SpringBoot帮我们自动配置；@EnableAutoConfiguration告诉SpringBoot开启自动配置功能；这样自动配置功能才能生效。我们进入@EnableAutoConfiguration看看里面有什么

@AutoConfigurationPackage @Import({EnableAutoConfigurationImportSelector.class}) public @interface EnableAutoConfiguration {

@AutoConfigurationPackage自动配置包 @Import(AutoConfigurationPackages.Registrar)这个注解是自动配置包内部的，这个注解是spring的底层注解。表示给容器导入一个组件；导入的组件Registrar.class，我们点进去，看看里面都有什么。

@Order(-2147483648) static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports { Registrar() { } public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) { AutoConfigurationPackages.register(registry, (new AutoConfigurationPackages.PackageImport(metadata)).getPackageName()); } public Set<Object> determineImports(AnnotationMetadata metadata) { return Collections.singleton(new AutoConfigurationPackages.PackageImport(metadata)); } }

上面就是register内部类，里面有一个registerBeanDefinitions方法，曾格格方法属于spring定义的，就是上面@Import注解的过滤逻辑。也是ImportBeanDefinitionRegistrar接口定义的方法。参数传了一个Annotation的注解源信息，我们打个断点运行一下，看看发生了什么。我们捕捉到了SpringBootApplication注解。并且这个注解标在了HelloWorldMainApplication类上。然后我们计算了一下报名，看上面的截图显示，这个包名就是我们的com.meng，所以这就可以断定AutoConfigurationPackage注解就是将我们标注的主配置类，也就是SpringBootApplication这个注解下所有包中的组件都会扫描一遍，注入到spring容器中。

EnableAutoConfiguration 注解中的 @Import({EnableAutoConfigurationImportSelector.class})注解，表示给容器中导入组件 EnableAutoConfigurationImportSelector：导入哪些组件的选择器。我点进去查看一下。经过查看，类锁定到AutoConfigurationImportSelector中的selectImport方法上。

public String[] selectImports(AnnotationMetadata annotationMetadata) { if (!this.isEnabled(annotationMetadata)) { return NO_IMPORTS; } else { try { AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader); AnnotationAttributes attributes = this.getAttributes(annotationMetadata); List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes); configurations = this.removeDuplicates(configurations); configurations = this.sort(configurations, autoConfigurationMetadata); .......

这个方法是spring底层的一些方法，是批量导入spring组件的一种方式，这里的组件其实指的就是自动配置类。我们打个断点运行一下。上面的批量注入组件源代码很可疑，所以我们查看debug的configurations属性可以看到这个属性就是包含了所有模块需要的自动配置文件，在启动springboot的时候就直接全部的导入到spring容器里面了。有了自动配置类，就免去手动配置的繁琐过程了。那么我们再次探究这些自动配置类都是从哪里加载起来的。

我们再次看selectImport方法箭头所指向的方法我们点进去。然后我们继续在点击箭头指向的loadFactoryNames方法。上面的代码就是获取自动配置类的主要来源了，我来解析一下，首先参数是EnableAutoConfiguration类的实例，第二个是类加载器，首先获取EnableAutoConfiguration类的名称，然后用类加载器获取配置文件的内容，但是他是一个集合，然后遍历这个集合，用配置文件处理类加载配置文件中的每一个配置，然后放入集合中，那么来源在哪里，在META-INF/spring.factories中。上图就是配置文件中定义的哪些自动配置类的类路径。

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