(三)关于SpringBoot的启动配置原理

一、启动流程

  1. 创建SpringApplication对象

public class SpringApplication {
public SpringApplication(Class... primarySources) {
this((ResourceLoader)null, primarySources);
}
public SpringApplication(ResourceLoader resourceLoader, Class... primarySources) {
this.sources = new LinkedHashSet();
this.bannerMode = Mode.CONSOLE;
this.logStartupInfo = true;
this.addCommandLineProperties = true;
this.addConversionService = true;
this.headless = true;
this.registerShutdownHook = true;
this.additionalProfiles = new HashSet();
this.isCustomEnvironment = false;
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
// 保存主配置类
this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));
// 判断当前是否一个web应用
this.webApplicationType = WebApplicationType.deduceFromClasspath();
// 从类路径下找到META-INF/spring.factories配置的所有ApplicationContextInitializer;然后保存起来。
this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
// 从类路径下找到META-INF/spring.factories配置的所有ApplicationListener
this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
//从多个配置类中找到有main方法的主配置类
this.mainApplicationClass = this.deduceMainApplicationClass();
}
  1. 运行run方法

public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
this.configureHeadlessProperty();
// 获取SpringApplicationRunListener; 从类路径下META-INF/spring.factories获取
SpringApplicationRunListeners listeners = this.getRunListeners(args);
// 回调所有的获取SpringApplicationRunListener.starting()方法
listeners.starting();
Collection exceptionReporters;
try {
// 封装命令行参数
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
// 准备环境
ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
this.configureIgnoreBeanInfo(environment);
// 创建环境完成后回调SpringApplicationRunListener.environmentPrepared();表示环境准备完成
Banner printedBanner = this.printBanner(environment);
// 创建ApplicationContext;决定创建web的IOC还是普通的IOC
context = this.createApplicationContext();
exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
// 准备上下文环境;将environment保存到IOC中,而且applyInitializers();
// 而且applyInitializers():回调之前保存的所有ApplicationContextInitializer的initialize方法
// 回调所有的SpringApplicationRunListener的contextPrepared();
this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
// prepareContext运行完成以后回调所有的SpringApplicationRunListener的contextLoaded();
// 扫描容器;IOC容器初始化(如果是web应用还会创建嵌入的Tomcat);
// 扫描,创建,加载所有组件的地方(配置类,组件,自动配置)
this.refreshContext(context);
// 从IOC容器中获取所有的ApplicationRunner和CommandLineRunner进行回调
// ApplicationRunner先回调,CommandLineRunner再回调
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);
// 整个SpringBoot应用启动完成以后返回启动的IOC容器
return context;
} catch (Throwable var9) {
this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null);
throw new IllegalStateException(var9);
}
}
  1. 事件监听机制

    需要配置在META-INF/spring.factories中的事件监听器。

    ApplicationContextInitializer

public class CustomApplicationContextInitializer implements
ApplicationContextInitializer<ConfigurableApplicationContext> {
@Override
public void initialize(ConfigurableApplicationContext configurableApplicationContext) {
System.out.println("ApplicationContextInitializer.....initialize");
}
}

SpringApplicationRunListener

public class CustomSrpingApplicationRunListener implements SpringApplicationRunListener {
// 必须有的构造器
public CustomSrpingApplicationRunListener(SpringApplication application,String[] args){
}
@Override
public void starting() {
System.out.println("SpringApplicationRunListener...starting....");
}
@Override
public void environmentPrepared(ConfigurableEnvironment environment) {
Object o = environment.getSystemEnvironment().get("os.name");
System.out.println("SpringApplicationRunListener...environmentPrepared...."+o);
}
@Override
public void contextPrepared(ConfigurableApplicationContext context) {
System.out.println("SpringApplicationRunListener..contextPrepared");
}
@Override
public void contextLoaded(ConfigurableApplicationContext context) {
System.out.println("SpringApplicationRunListener..contextLoaded");
}
@Override
public void started(ConfigurableApplicationContext context) {
System.out.println("SpringApplicationRunListener..started");
}
@Override
public void running(ConfigurableApplicationContext context) {
System.out.println("SpringApplicationRunListener..running");
}
@Override
public void failed(ConfigurableApplicationContext context, Throwable exception) {
System.out.println("SpringApplicationRunListener..failed");
}
}

配置(META-INF/spring.factories)

org.springframework.context.ApplicationContextInitializer=com.desperado.demo.CustomApplicationContextInitializer
org.springframework.boot.SpringApplicationRunListener=com.desperado.demo.CustomSrpingApplicationRunListener

只需要放在IOC容器中的监听器。 ApplicationRunner

@Component
public class CustomApplicationRunner implements ApplicationRunner {
@Override
public void run(ApplicationArguments args) {
System.out.println("ApplicationRunner ... run....");
}
}

CommandLineRunner

@Component
public class CustomCommandLineRunner implements CommandLineRunner {
@Override
public void run(String... args) {
System.out.println("commandLineRunner ... run ...");
}
}

二、自定义starter

  1. 要使用到的注解 @Configuration 指定类是一个配置类 @ConditionalOnXXX 在指定条件成立的情况下自动配置生效、 @AutoConfigureAfter 在特定自动装配class之后(指定自动配置类的顺序) @AutoConfigureBefore 在特定自动装配class之前(指定自动配置类的顺序) @AutoConfigureOrder 指定顺序 @Bean 给容器中添加组件 @ConfigurationPropertie 结合相关xxxProperties类来绑定相关的配置。 @EnableConfigurationProperties 让xxxProperties生效加入到容器中。

  2. 加载方式 自动配置类要能加载,将需要启动就加载的自动配置类,配置在META-INF/spring.factories文件中。

  3. 启动器模式 启动器只用来做依赖导入,专门写一个自动配置模块。启动器依赖自动配置,使用时只需要引入启动器(starter)。

  4. 启动器规则 启动器就是个空jar文件,仅提供辅助性依赖管理,这些依赖可能用于自动装配或者其他库。

命名规范:

  • 推荐使用以下命名规范

  • 官方命名空间

    &emsp;- 前缀:spring-boot-starter-
    &emsp;- 模式:spring-boot-starter-模块名
  • 自定义命名空间

      - 后缀:-spring-boot-starter

      - 模式:模块名-spring-boot-starter

  1. 编写一个启动器模块

    1). 启动器模块

<?xml version="1.0" encoding="UTF-8"?>
<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>4.0.0</modelVersion>
<groupId>com.desperado.starter</groupId>
<artifactId>desperado-spring-boot-starter</artifactId>
<version>0.0.1-SNAPSHOT</version>
<!-- 启动器 -->
<dependencies>
<!-- 引入自动配置模块 -->
<dependency>
<groupId>com.desperado.starter</groupId>
<artifactId>desperado-spring-boot-starter-autoconfigurer</artifactId>
<version>0.0.1-SNAPSHOT</version>
</dependency>
</dependencies>
</project>

2). 自动配置模块

<?xml version="1.0" encoding="UTF-8"?>
<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>4.0.0</modelVersion>
<groupId>com.desperado.starter</groupId>
<artifactId>desperado-spring-boot-starter-autoconfigurer</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.5.RELEASE</version>
<relativePath/>
</parent>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
</properties>
<!-- 引入spring-boot-starter;所有starter的基本配置 -->
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
</dependency>
</dependencies>
</project>

3). 编写配置文件类

@ConfigurationProperties(prefix = "desperado.custom")
public class CustomProperties {
private String prefix;
private String suffix;
public String getPrefix() {
return prefix;
}
public void setPrefix(String prefix) {
this.prefix = prefix;
}
public String getSuffix() {
return suffix;
}
public void setSuffix(String suffix) {
this.suffix = suffix;
}
}

4). 进行配置文件的处理

public class CustomService {
CustomProperties customProperties;
public CustomProperties getCustomProperties(){
return customProperties;
}
public void setCustomProperties(CustomProperties customProperties){
this.customProperties = customProperties;
}
public String sayHello(String name){
return customProperties.getPrefix()+"-"+name+customProperties.getSuffix();
}
}

5). 编写自动配置类

@ConditionalOnWebApplication
@EnableConfigurationProperties(CustomProperties.class)
public class CustomServiceAutoConfiguration {
@Autowired
CustomProperties customProperties;
@Bean
public CustomService customService(){
CustomService customService = new CustomService();
customService.setCustomProperties(customProperties);
return customService;
}
}