SpringBoot原理分析

Spring简介

Spring是一个开源框架，2003兴起的，是轻量级的Java开发框架；

Spring目的就是为了解决企业开发的复杂性问题；

Spring简化Java开发的方式

• JavaBean
• IOC思想
• AOP切面编程
• 模板引擎使用，简化开发

程序的发展

Servlet+JSP+Tomcat+MySQL=> 配置服务器、编写web.xml，注册一堆Servlet、Filter...

在这个时候，存在大量的与业务无关的工作！

SSH：Spring+Struts+Hibernate

SSM：Spring+SpringMVC+MyBatis

框架之后，大大的简了化开发，我们只需要简单的配置！但是现在已经经历了17年！

Spring变成了配置地狱，大量的积累和粘合，导致整个Spring生态越来越臃肿，配置十分的麻烦！

Spring Boot：启动器

所有的技术发展路线：复杂的场景>衍生出来一些规范>配置完成代码==>配置变多，希望自动配置(轻量级)

SpringBoot原理分析

快速构建一个SpringBoot项目

我们可以看到，有:

• pom.xml;
• 主启动类SpringbootApplication;
• 一个配置文件application.properties;
• 一个测试类SpringbootApplicationTests。

分析 pom.xml文件

1、父依赖spring-boot-starter-parent 本质也是一个启动器；

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.1.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

点进源码分析；

父依赖的作用：

• 作用1：管理插件和资源过滤

发现过滤资源的文件除了properties还有别的

<!--Spring Boot推荐使用yaml-->
<include>**/application*.yml</include>
<include>**/application*.yaml</include>
<include>**/application*.properties</include>

• 作用2：帮助我们自动配置所有常用的依赖环境，版本控制！ spring-boot-dependencies
  • 帮我们解决了版本的问题，如果SpringBoot中存在这个依赖，我们不需要编写版本号，如果没有再编写；

2、启动器spring-boot-starter-xxx

<!--一组对应场景的启动项依赖-->
<dependency>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-starter-web</artifactId>
</dependency>

并且我们还可以自定义场景启动项！

分析主启动类

@SpringBootApplication
public class SpringbootApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringbootApplication.class, args);
    }

}

这个主启动类有：

• 一个注解@SpringBootApplication
• 一个类SpringApplication；
• 一个run方法。

首先分析注解@SpringBootApplication

点进源码：

可以看到除了元注解，其主要的注解有三个：

1、@SpringBootConfiguration

产看注解的源码：

一个注解@Configuration

Spring中传统的配置文件applicationContext.xml

<beans>
    <bean id=""></bean>
    <import .. />
    <context: componment-scan="" />
</beans>

Spring4以后推荐使用javaConfig编写配置！

@Configuration //代表这是一个配置文件
@Import(otherConfig.class) //导入其他的配置类
@ComponentScan("")
class config(){

    @Bean
    public User user(){
        return New User();
    }
}

在SpringBoot中看不到配置文件，都是使用JavaConfig；

所以主启动类也是一个配置类；

产看注解@Configuration的源码

注解@Component，表示这个应该组件；

所以主启动类也是Spring容器中的组件；

2、@EnableAutoConfiguration

产看源码：

两个注解：

• @AutoConfigurationPackage

表示自动怕配置包，但是配置哪些包呢？

查看源码：

导入一个静态内部类Registrar

查看源码：

这个类重写了方法，获得注解下所在的包名！

结合@ComponentScan注解；

主启动类能够扫描当前的包，获取其中的配置

• @Import(AutoConfigurationImportSelector.class)

这个注解表示导入一个自动导入选择器的类，那导入哪些选择器呢？查看源码：

该方法表示获得自动配置的实体！那这个是怎么配置的呢？查看源码：

使用这个方法获取候选配置，查看方法的源码：

发现了一个断言：META-INF/spring.factories

查看loadFactoryNames的源码：

继续看源码：

这里无论怎么判断都指定有：META-INF/spring.factories

该方法最后得到一个Propeties

我们来全局搜索与一下：META-INF/spring.factories

选择spring-boot-autoconfigure-2.2.1.RELEASE.jar包下的文件

查看这个文件：

# 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.elasticsearch.ReactiveElasticsearchRepositoriesAutoConfiguration,
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveRestClientAutoConfiguration,
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.rsocket.RSocketMessagingAutoConfiguration,
org.springframework.boot.autoconfigure.rsocket.RSocketRequesterAutoConfiguration,
org.springframework.boot.autoconfigure.rsocket.RSocketServerAutoConfiguration,
org.springframework.boot.autoconfigure.rsocket.RSocketStrategiesAutoConfiguration,
org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,
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.security.rsocket.RSocketSecurityAutoConfiguration,
org.springframework.boot.autoconfigure.security.saml2.Saml2RelyingPartyAutoConfiguration,
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.flyway.FlywayMigrationScriptMissingFailureAnalyzer,
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

监听器和过滤器：
# Initializers
# Application Listeners
# Auto Configuration Import Listeners
# Auto Configuration Import Filters

大量的自动配置文件：
# Auto Configure

3、@ComponentScan

也是JavaConfig中的扫描包的注解

我们再来分析SpringApplication类

查看该类的源码：

构造器中有四个字段：

this.webApplicationType = WebApplicationType.deduceFromClasspath();//判断这个是不是一个web应用
this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));//设置初始化内容
this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));//监听器
this.mainApplicationClass = this.deduceMainApplicationClass();推断是否是main方法

这些字段就对应配置文件中的配置

我们可以点进某一个配置，比如webmvc的自动配置

可以看到里面有很多对应的bean和方法(视图解析，国际化解析等等)

那么这些bean从哪里来呢？

就是由对应的一组场景启动项的依赖支持，如果删掉依赖就会爆红失效！

但是没有的依赖的配置怎么处理呢？

依靠@ConditionalON注解

虽然我们有大量的自动配置文件，但是我们并未让他生效，如果要生效则一定要导入对应的场景启动器

分析run方法

public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
        this.configureHeadlessProperty();
        SpringApplicationRunListeners listeners = this.getRunListeners(args);
        listeners.starting();

        Collection exceptionReporters;
        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
            this.configureIgnoreBeanInfo(environment);
            Banner printedBanner = this.printBanner(environment);
            context = this.createApplicationContext();
            exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
            this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
            this.refreshContext(context);
            this.afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
            }

            listeners.started(context);
            this.callRunners(context, applicationArguments);
        } catch (Throwable var10) {
            this.handleRunFailure(context, var10, exceptionReporters, listeners);
            throw new IllegalStateException(var10);
        }

        try {
            listeners.running(context);
            return context;
        } catch (Throwable var9) {
            this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null);
            throw new IllegalStateException(var9);
        }
    }

run方法的流程图：

注解分析图：

分析配置文件

https://www.cnblogs.com/lmx-181028/p/12411104.html