springBoot--原理分析

起步依赖分析

分析spring-boot-starter-parent

按住Ctrl点击pom.xml中的spring-boot-starter-parent，跳转到了spring-boot-starter-parent的pom.xml，xml配置如下（只摘抄了部分重点配置）：

<parent>
  <groupId>org.springframework.bootgroupId>
  <artifactId>spring-boot-dependenciesartifactId>
  <version>2.2.5.RELEASEversion>
  <relativePath>../../spring-boot-dependenciesrelativePath>
parent>

按住Ctrl点击pom.xml中的spring-boot-starter-dependencies，跳转到了spring-boot-starter-dependencies的pom.xml，xml配置如下（只摘抄了部分重点配置）：

<properties>
  <activemq.version>5.15.11activemq.version>
  <antlr2.version>2.7.7antlr2.version>
  <appengine-sdk.version>1.9.78appengine-sdk.version>
  <artemis.version>2.10.1artemis.version>
  <aspectj.version>1.9.5aspectj.version>
  <assertj.version>3.13.2assertj.version>
  <atomikos.version>4.0.6atomikos.version>
  <awaitility.version>4.0.2awaitility.version>
  <bitronix.version>2.1.4bitronix.version>
  <build-helper-maven-plugin.version>3.0.0build-helper-maven-plugin.version>
  <byte-buddy.version>1.10.8byte-buddy.version>
  ...  ....  ...
  
  <dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>org.springframework.bootgroupId>
      <artifactId>spring-bootartifactId>
      <version>2.2.5.RELEASEversion>
    dependency>
    <dependency>
      <groupId>org.springframework.bootgroupId>
      <artifactId>spring-boot-testartifactId>
      <version>2.2.5.RELEASEversion>
    dependency>
    ... ... ...
    dependencies>
dependencyManagement>
<build>
  <pluginManagement>
    <plugins>
      <plugin>
        <groupId>org.apache.johnzongroupId>
        <artifactId>johnzon-maven-pluginartifactId>
        <version>${johnzon.version}version>
      plugin>
      <plugin>
        <groupId>org.jetbrains.kotlingroupId>
        <artifactId>kotlin-maven-pluginartifactId>
        <version>${kotlin.version}version>
      plugin>
      <plugin>
        <groupId>org.jooqgroupId>
        <artifactId>jooq-codegen-mavenartifactId>
        <version>${jooq.version}version>
      plugin>
      <plugin>
        <groupId>org.springframework.bootgroupId>
        <artifactId>spring-boot-maven-pluginartifactId>
        <version>2.2.5.RELEASEversion>
      plugin>
            ... ... ...
        plugins>
      pluginManagement>
build>

从上面的spring-boot-starter-dependencies的pom.xml中我们可以发现，一部分坐标的版本、依赖管理、插件管理已经定义好，所以我们的SpringBoot工程继承spring-boot-starter-parent后已经具备版本锁定等配置了。所以起步依赖的作用就是进行依赖的传递。

分析spring-boot-starter-web

按住Ctrl点击pom.xml中的spring-boot-starter-web，跳转到了spring-boot-starter-web的pom.xml，xml配置如下（只摘抄了部分重点配置）：

<parent>
  <groupId>org.springframework.bootgroupId>
  <artifactId>spring-boot-startersartifactId>
  <version>2.2.5.RELEASEversion>
parent>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-starter-webartifactId>
<version>2.2.5.RELEASEversion>
<name>Spring Boot Web Startername>
 <dependencies>
    <dependency>
      <groupId>org.springframework.bootgroupId>
      <artifactId>spring-boot-starterartifactId>
      <version>2.2.5.RELEASEversion>
      <scope>compilescope>
    dependency>
    <dependency>
      <groupId>org.springframework.bootgroupId>
      <artifactId>spring-boot-starter-jsonartifactId>
      <version>2.2.5.RELEASEversion>
      <scope>compilescope>
    dependency>
    <dependency>
      <groupId>org.springframework.bootgroupId>
      <artifactId>spring-boot-starter-tomcatartifactId>
      <version>2.2.5.RELEASEversion>
      <scope>compilescope>
    dependency>
    <dependency>
      <groupId>org.springframework.bootgroupId>
      <artifactId>spring-boot-starter-validationartifactId>
      <version>2.2.5.RELEASEversion>
      <scope>compilescope>
      <exclusions>
        <exclusion>
          <artifactId>tomcat-embed-elartifactId>
          <groupId>org.apache.tomcat.embedgroupId>
        exclusion>
      exclusions>
    dependency>
    <dependency>
      <groupId>org.springframeworkgroupId>
      <artifactId>spring-webartifactId>
      <version>5.2.4.RELEASEversion>
      <scope>compilescope>
    dependency>
    <dependency>
      <groupId>org.springframeworkgroupId>
      <artifactId>spring-webmvcartifactId>
      <version>5.2.4.RELEASEversion>
      <scope>compilescope>
    dependency>
  dependencies>
project>

自动配置原理解析

按住Ctrl点击查看启动类MySpringBootApplication上的注解@SpringBootApplication

package xyz.ytfs;

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

@SpringBootApplication
public class SpringbootQuick2Application {

    public static void main(String[] args) {
        SpringApplication.run(SpringbootQuick2Application.class, args);
    }

}

/*
 * Copyright 2012-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.boot.autoconfigure;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.boot.SpringBootConfiguration;
import org.springframework.boot.context.TypeExcludeFilter;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.ComponentScan.Filter;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.core.annotation.AliasFor;
import org.springframework.data.repository.Repository;

/**
 * Indicates a {@link Configuration configuration} class that declares one or more
 * {@link Bean @Bean} methods and also triggers {@link EnableAutoConfiguration
 * auto-configuration} and {@link ComponentScan component scanning}. This is a convenience
 * annotation that is equivalent to declaring {@code @Configuration},
 * {@code @EnableAutoConfiguration} and {@code @ComponentScan}.
 *
 * @author Phillip Webb
 * @author Stephane Nicoll
 * @author Andy Wilkinson
 * @since 1.2.0
 */
@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) })
public @interface SpringBootApplication {

   /**
    * Exclude specific auto-configuration classes such that they will never be applied.
    * @return the classes to exclude
    */
   @AliasFor(annotation = EnableAutoConfiguration.class)
   Class<?>[] exclude() default {};

   /**
    * Exclude specific auto-configuration class names such that they will never be
    * applied.
    * @return the class names to exclude
    * @since 1.3.0
    */
   @AliasFor(annotation = EnableAutoConfiguration.class)
   String[] excludeName() default {};
       ... ... ...

}

其中，

@SpringBootConfiguration：等同与@Configuration，既标注该类是Spring的一个配置类

@EnableAutoConfiguration：SpringBoot自动配置功能开启

按住Ctrl点击查看注解@EnableAutoConfiguration

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
    ... ... ...
}

其中，@Import(AutoConfigurationImportSelector.class) 导入了AutoConfigurationImportSelector类

按住Ctrl点击查看AutoConfigurationImportSelector源码

public String[] selectImports(AnnotationMetadata annotationMetadata) {
   if (!isEnabled(annotationMetadata)) {
      return NO_IMPORTS;
   }
   AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
         .loadMetadata(this.beanClassLoader);
   AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(autoConfigurationMetadata,
         annotationMetadata);
   return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
}

protected List getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
   List configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),
         getBeanClassLoader());
   Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you "
         + "are using a custom packaging, make sure that file is correct.");
   return configurations;
}

其中，SpringFactoriesLoader.loadFactoryNames 方法的作用就是从META-INF/spring.factories文件中读取指定类对应的类名称列表

spring.factories 文件中有关自动配置的配置信息如下：

... ... ...

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,\

... ... ...

上面配置文件存在大量的以Configuration为结尾的类名称，这些类就是存有自动配置信息的类，而SpringApplication在获取这些类名后再加载

我们以ServletWebServerFactoryAutoConfiguration为例来分析源码：

@Configuration(proxyBeanMethods = false)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@ConditionalOnClass(ServletRequest.class)
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(ServerProperties.class)
@Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
      ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
      ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
      ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })
public class ServletWebServerFactoryAutoConfiguration {
    ... ... ...
    }

其中，

@EnableConfigurationProperties(ServerProperties.class) 代表加载ServerProperties服务器配置属性类

进入ServerProperties.class源码如下：

@ConfigurationProperties(prefix = "server", ignoreUnknownFields = true)
public class ServerProperties {

   /**
    * Server HTTP port.
    */
   private Integer port;

   /**
    * Network address to which the server should bind.
    */
   private InetAddress address;;
  
      ... ... ...
  
}

其中，

prefix = "server" 表示SpringBoot配置文件中的前缀，SpringBoot会将配置文件中以server开始的属性映射到该类的字段中。映射关系如下

springboot

springBoot--原理分析

起步依赖分析

分析spring-boot-starter-parent

分析spring-boot-starter-web

自动配置原理解析

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