[学习交流] 【广州校区】+【原创】Spring boot 核心功能

SpringBoot

SpringBoot基于约定优于配置的思想,可以让开发人员不必在配置与逻辑业务之间进行思维的切换
全身心的投入到逻辑业务的代码编写中，从而大大提高了开发的效率

SpringBoot的特点

为基于Spring的开发提供更快的入门体验
开箱即用，没有代码生成，也无需XML配置。同时也可以修改默认值来满足特定的需求
提供了一些大型项目中常见的非功能性特性，如嵌入式服务器、安全、指标，健康检测、外部配置等
SpringBoot不是对Spring功能上的增强，而是提供了一种快速使用Spring的方式

SpringBoot的核心功能

起步依赖
- 起步依赖本质上是一个Maven项目对象模型(POM),定义了对其他库的传递依赖,这些东西加在一起即支持某项功能
- 简单的说，起步依赖就是将具备某种功能的坐标打包到一起，并提供一些默认的功能
自动配置
- Spring Boot的自动配置是一个运行时的过程,考虑了众多因素,才决定Spring配置应该用哪个，不该用哪个
- 该过程是Spring自动完成的

SpringBoot快速入门

创建maven工程(jar)
添加SpringBoot的起步依赖
- SpringBoot要求，项目要继承SpringBoot的起步依赖spring-boot-starter-parent
- SpringBoot要集成SpringMVC进行Controller的开发，所以项目要导入web的启动依赖

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<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.0.1.RELEASE</version>
</parent>
<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>

编写SpringBoot引导类

要通过SpringBoot提供的引导类起步SpringBoot才可以进行访问

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

@SpringBootApplication
public class MySpringBootApplication {
    public static void main(String[] args) {
        SpringApplication.run(MySpringBootApplication.class);
    }
}

编写Controller

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@RestController
public class QuickStartController {
    @RequestMapping("/quick")
    public String quick() {
        return "springboot 访问成功!";
    }
}

快速入门解析

SpringBoot代码解析
- @SpringBootApplication
  - 标注SpringBoot的启动类
- SpringApplication.run(MySpringBootApplication.class) 代表运行SpringBoot的启动类
  - SpringBoot启动类的字节码对象
SpringBoot工程热部署
- 我们在开发中反复修改类、页面等资源，每次修改后都是需要重新启动才生效,这样很浪费时间
- 我们可以在修改代码后不重启就能生效
- 在 pom.xml 中添加如下配置就可以实现这样的功能，我们称之为热部署
- 注意：IDEA进行SpringBoot热部署失败原因
  - 出现这种情况，并不是热部署配置问题
  - 其根本原因是因为Intellij IEDA默认情况下不会自动编译
  - settint-->compiler-->build project automatically
  - 然后按快捷键： Shift+Ctrl+Alt+/，选择Registry
    - 选中register
    - 勾选compiler.automake.allow.when.app.running

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<!--热部署配置-->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
</dependency>

SpringBoot原理分析分析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

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<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-dependencies</artifactId>
    <version>2.0.1.RELEASE</version>
    <relativePath>../../spring-boot-dependencies</relativePath>
</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

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<properties>
    <activemq.version>5.15.3</activemq.version>
    <antlr2.version>2.7.7</antlr2.version>
    <appengine-sdk.version>1.9.63</appengine-sdk.version>
    <artemis.version>2.4.0</artemis.version>
    <aspectj.version>1.8.13</aspectj.version>
    <assertj.version>3.9.1</assertj.version>
    <atomikos.version>4.0.6</atomikos.version>
    <bitronix.version>2.1.4</bitronix.version>
    <build-helper-maven-plugin.version>3.0.0</build-helper-maven-plugin.version>
    ……
</properties>
<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot</artifactId>
            <version>2.0.1.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-test</artifactId>
            <version>2.0.1.RELEASE</version>
        </dependency>
        ……
</dependencies>
</dependencyManagement>
<build>
    <pluginManagement>
        <plugins>
            <plugin>
                <groupId>org.jetbrains.kotlin</groupId>
                <artifactId>kotlin-maven-plugin</artifactId>
                <version>${kotlin.version}</version>
            </plugin>
            <plugin>
                <groupId>org.jooq</groupId>
                <artifactId>jooq-codegen-maven</artifactId>
                <version>${jooq.version}</version>
            </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

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

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<?xml version="1.0" encoding="UTF-8"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starters</artifactId>
    <version>2.0.1.RELEASE</version>
  </parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
  <version>2.0.1.RELEASE</version>
  <name>Spring Boot Web Starter</name>
<dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter</artifactId>
      <version>2.0.1.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-json</artifactId>
      <version>2.0.1.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-tomcat</artifactId>
      <version>2.0.1.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.hibernate.validator</groupId>
      <artifactId>hibernate-validator</artifactId>
      <version>6.0.9.Final</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-web</artifactId>
      <version>5.0.5.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>5.0.5.RELEASE</version>
      <scope>compile</scope>
    </dependency>
  </dependencies>
</project>

从上面的spring-boot-starter-web的pom.xml中我们可以发现，spring-boot-starter-web就是将web开发要使用的spring-web、spring-webmvc等坐标进行了“打包”
这样我们的工程只要引入spring-boot-starter-web起步依赖的坐标就可以进行web开发了，同样体现了依赖传递的作用

自动配置原理解析

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

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@SpringBootApplication
public class MySpringBootApplication {
    public static void main(String[] args) {
        SpringApplication.run(MySpringBootApplication.class);
    }
}

注解@SpringBootApplication的源码

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@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 {};

   ……
}

@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

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@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
    ………[mw_shl_code=java,true]@Override
public String[] selectImports(AnnotationMetadata annotationMetadata) {
   if (!isEnabled(annotationMetadata)) {
      return NO_IMPORTS;
   }
   AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
         .loadMetadata(this.beanClassLoader);
   AnnotationAttributes attributes = getAttributes(annotationMetadata);
   "List<String> configurations = getCandidateConfigurations(annotationMetadata,attributes);"
   configurations = removeDuplicates(configurations);
   Set<String> exclusions = getExclusions(annotationMetadata, attributes);
   checkExcludedClasses(configurations, exclusions);
   configurations.removeAll(exclusions);
   configurations = filter(configurations, autoConfigurationMetadata);
   fireAutoConfigurationImportEvents(configurations, exclusions);
   return StringUtils.toStringArray(configurations);
}

}[/mw_shl_code]

其中，@Import(AutoConfigurationImportSelector.class) 导入了AutoConfigurationImportSelector类
按住Ctrl点击查看AutoConfigurationImportSelector源码

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@Override
public String[] selectImports(AnnotationMetadata annotationMetadata) {
   if (!isEnabled(annotationMetadata)) {
      return NO_IMPORTS;
   }
   AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
         .loadMetadata(this.beanClassLoader);
   AnnotationAttributes attributes = getAttributes(annotationMetadata);
   "List<String> configurations = getCandidateConfigurations(annotationMetadata,attributes);"
   configurations = removeDuplicates(configurations);
   Set<String> exclusions = getExclusions(annotationMetadata, attributes);
   checkExcludedClasses(configurations, exclusions);
   configurations.removeAll(exclusions);
   configurations = filter(configurations, autoConfigurationMetadata);
   fireAutoConfigurationImportEvents(configurations, exclusions);
   return StringUtils.toStringArray(configurations);
}

protected List<String> "getCandidateConfigurations"(AnnotationMetadata metadata,
      AnnotationAttributes attributes) {
   List<String> 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

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……
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.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

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@Configuration
@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

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@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;
   … … …
}

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[学习交流] 【广州校区】+【原创】Spring boot 核心功能

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