Spring Boot笔记启动配置原理

2020-09-02 21:35

2435

#以debug来理解
在Spring Boot项目，主配置类的run()方法处打断点，以debug模式运行，可以看到如下代码，留意两个流程：
1、创建SpringApplication对象
2、运行run()方法。

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public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
    return (new SpringApplication(primarySources)).run(args);
}

创建SpringApplication对象

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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.lazyInitialization = false;
    this.resourceLoader = resourceLoader;
    Assert.notNull(primarySources, "PrimarySources must not be null");
    this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));
    // 调用deduceFromClasspath()方法判断当前Web应用的类型：NONE,SERVLET,REACTIVE
    this.webApplicationType = WebApplicationType.deduceFromClasspath();
    // 调用getSpringFactoriesInstances()方法从类路径下找到META-INF/spring.factories配置的ApplicationContextInitializer类，保存起来
    this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
    // 调用getSpringFactoriesInstances()方法从类路径下找到META-INF/spring.factories配置的ApplicationListener类，保存起来
    this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
    // 从多个配置类中查找主配置类
    this.mainApplicationClass = this.deduceMainApplicationClass();
}
 
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
    return this.getSpringFactoriesInstances(type, new Class[0]);
}
 
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
    ClassLoader classLoader = this.getClassLoader();
    // 调用loadFactoryNames()方法从META-INF/spring.factories下找类名
    Set<String> names = new LinkedHashSet(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
    // 根据类名，通过反射创建实体放入instances中
    List<T> instances = this.createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
    AnnotationAwareOrderComparator.sort(instances);
    return instances;
}
 
public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {
    String factoryTypeName = factoryType.getName();
    return (List)loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList());
}
 
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
    MultiValueMap<String, String> result = (MultiValueMap)cache.get(classLoader);
    if (result != null) {
        return result;
    } else {
        try {
            // 从META-INF/spring.factories位置找类名
            // 此处可以看一下org/springframework/boot/spring-boot-autoconfigure/2.2.6.RELEASE/spring-boot-autoconfigure-2.2.6.RELEASE.jar!/META-INF/spring.factories里的内容
            Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources(
            LinkedMultiValueMap result = new LinkedMultiValueMap();
            while(urls.hasMoreElements()) {
                URL url = (URL)urls.nextElement();
                UrlResource resource = new UrlResource(url);
                Properties properties = PropertiesLoaderUtils.loadProperties(resource);
                Iterator var6 = properties.entrySet().iterator();
                while(var6.hasNext()) {
                    Entry<?, ?> entry = (Entry)var6.next();
                    String factoryTypeName = ((String)entry.getKey()).trim();
                    String[] var9 = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());
                    int var10 = var9.length;
                    for(int var11 = 0; var11 < var10; ++var11) {
                        String factoryImplementationName = var9[var11];
                        result.add(factoryTypeName, factoryImplementationName.trim());
                    }
                }
            }
            cache.put(classLoader, result);
            return result;
        } catch (IOException var13) {
            throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var13);
        }
    }
}
 
private Class<?> deduceMainApplicationClass() {
    try {
        StackTraceElement[] stackTrace = (new RuntimeException()).getStackTrace();
        StackTraceElement[] var2 = stackTrace;
        int var3 = stackTrace.length;
        for(int var4 = 0; var4 < var3; ++var4) {
            StackTraceElement stackTraceElement = var2[var4];
            // 从多个配置类中查找方法名是main的确定主配置类
            if ("main".equals(stackTraceElement.getMethodName())) {
                return Class.forName(stackTraceElement.getClassName());
            }
        }
    } catch (ClassNotFoundException var6) {
    }
    return null;
}

2.运行run()方法

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public ConfigurableApplicationContext run(String... args) {
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    ConfigurableApplicationContext context = null;
    Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
    this.configureHeadlessProperty();
    // 获取SpringApplicationRunListeners，也是调用getSpringFactoriesInstances()方法从META-INF/spring.factories获取的
    SpringApplicationRunListeners listeners = this.getRunListeners(args);
    // 将这些监听器启动
    listeners.starting();
    Collection exceptionReporters;
    try {
        // 将命令行参数做一个封装
        ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
        // 准备环境
        ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
        this.configureIgnoreBeanInfo(environment);
        // 打印Banner图标
        Banner printedBanner = this.printBanner(environment);
        // 创建IOC容器
        context = this.createApplicationContext();
        // 获取一个处理异常的实例，当出现异常的时候，用来处理异常报告，在catch里面会用到这个对象
        exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
        // 准备上下文环境
        this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
        // 刷新IOC容器，扫描注解，加载里面的所有组件，如果是Web环境，创建Tomcat容器
        this.refreshContext(context);
        this.afterRefresh(context, applicationArguments);
        stopWatch.stop();
        if (this.logStartupInfo) {
            (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
        }
        // 所有的SpringApplicationRunListener回调started()方法
        listeners.started(context);
        // 从IOC容器中获取所有的ApplicationRunner和CommandLineRunner进行回调，先回调ApplicationRunner，后回调CommandLineRunner
        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);
    }
}
 
private SpringApplicationRunListeners getRunListeners(String[] args) {
    Class<?>[] types = new Class[]{SpringApplication.class, String[].class};
    return new SpringApplicationRunListeners(logger, this.getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));
}
 
private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) {
    // 获取或创建环境
    ConfigurableEnvironment environment = this.getOrCreateEnvironment();
    this.configureEnvironment((ConfigurableEnvironment)environment, applicationArguments.getSourceArgs());
    ConfigurationPropertySources.attach((Environment)environment);
    // 回调SpringApplicationRunListener.environmentPrepared()方法表示环境准备完成
    listeners.environmentPrepared((ConfigurableEnvironment)environment);
    this.bindToSpringApplication((ConfigurableEnvironment)environment);
    if (!this.isCustomEnvironment) {
        environment = (new EnvironmentConverter(this.getClassLoader())).convertEnvironmentIfNecessary((ConfigurableEnvironment)environment, this.deduceEnvironmentClass());
    }
    ConfigurationPropertySources.attach((Environment)environment);
    return (ConfigurableEnvironment)environment;
}
 
protected ConfigurableApplicationContext createApplicationContext() {
    Class<?> contextClass = this.applicationContextClass;
    if (contextClass == null) {
        try {
            // 根据webApplicationType的类型，得到类名，通过反射方式，创建对应的IOC容器
            switch(this.webApplicationType) {
            case SERVLET:
                contextClass = Class.forName("org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext");
                break;
            case REACTIVE:
                contextClass = Class.forName("org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext");
                break;
            default:
                contextClass = Class.forName("org.springframework.context.annotation.AnnotationConfigApplicationContext");
            }
        } catch (ClassNotFoundException var3) {
            throw new IllegalStateException("Unable create a default ApplicationContext, please specify an ApplicationContextClass", var3);
        }
    }
    return (ConfigurableApplicationContext)BeanUtils.instantiateClass(contextClass);
}
 
private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
    // 将刚才创建的IOC环境设置进来
    context.setEnvironment(environment);
    this.postProcessApplicationContext(context);
    // 在创建SpringApplication的时候设置了一些initializer，获取这些initializer，调用initialize()方法
    this.applyInitializers(context);
    // 在创建SpringApplication的时候设置了一些listener，获取这些listener，调用contextPrepared()方法
    listeners.contextPrepared(context);
    if (this.logStartupInfo) {
        this.logStartupInfo(context.getParent() == null);
        this.logStartupProfileInfo(context);
    }
    ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
    beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
    if (printedBanner != null) {
        beanFactory.registerSingleton("springBootBanner", printedBanner);
    }
    if (beanFactory instanceof DefaultListableBeanFactory) {
        ((DefaultListableBeanFactory)beanFactory).setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
    }
    if (this.lazyInitialization) {
        context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
    }
    Set<Object> sources = this.getAllSources();
    Assert.notEmpty(sources, "Sources must not be empty");
    this.load(context, sources.toArray(new Object[0]));
    // 回调所有listener的contextLoaded()方法
    listeners.contextLoaded(context);
}
 
protected void applyInitializers(ConfigurableApplicationContext context) {
    Iterator var2 = this.getInitializers().iterator();
    while(var2.hasNext()) {
        ApplicationContextInitializer initializer = (ApplicationContextInitializer)var2.next();
        Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(initializer.getClass(), ApplicationContextInitializer.class);
        Assert.isInstanceOf(requiredType, context, "Unable to call initializer.");
        // 获取SpringApplication中所有的initializer，调用initialize()方法
        initializer.initialize(context);
    }
}
 
void contextPrepared(ConfigurableApplicationContext context) {
    Iterator var2 = this.listeners.iterator();
    while(var2.hasNext()) {
        SpringApplicationRunListener listener = (SpringApplicationRunListener)var2.next();
        // 获取SpringApplication中所有的listener，调用contextPrepared()方法
        listener.contextPrepared(context);
    }
}

##3.事件监听机制
ApplicationContextInitializer和SpringApplicationRunListener需要配置在META-INF/spring.factories中。

ApplicationRunner和CommandLineRunner只需要放在IOC容器中。

ApplicationContextInitializer

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package com.atguigu.springboot.listener;
 
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;
 
// ConfigurableApplicationContext是用来监听IOC容器的，当IOC容器初始化的时候，执行initialize()方法
public class HelloApplicationContextInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {
    @Override
    public void initialize(ConfigurableApplicationContext configurableApplicationContext) {
        System.out.println("ApplicationContextInitializer...initialize..." + configurableApplicationContext);
    }
}

SpringApplicationRunListener.java

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package com.atguigu.springboot.listener;
 
import org.springframework.boot.SpringApplication;
import org.springframework.boot.SpringApplicationRunListener;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.env.ConfigurableEnvironment;
 
public class HelloSpringApplicationRunListener implements SpringApplicationRunListener {
    // 构造器，否则会报错
    public HelloSpringApplicationRunListener(SpringApplication application, String[] args) {
    }
 
    @Override
    public void starting() {
        System.out.println("HelloSpringApplicationRunListener.starting");
    }
 
    @Override
    public void environmentPrepared(ConfigurableEnvironment environment) {
        Object name = environment.getSystemProperties().get("os.name");
        System.out.println("HelloSpringApplicationRunListener.environmentPrepared：" + name);
    }
 
    @Override
    public void contextPrepared(ConfigurableApplicationContext context) {
        System.out.println("HelloSpringApplicationRunListener.contextPrepared");
    }
 
    @Override
    public void contextLoaded(ConfigurableApplicationContext context) {
        System.out.println("HelloSpringApplicationRunListener.contextLoaded");
    }
 
    @Override
    public void running(ConfigurableApplicationContext context) {
        System.out.println("HelloSpringApplicationRunListener.running");
    }
 
    @Override
    public void failed(ConfigurableApplicationContext context, Throwable exception) {
        System.out.println("HelloSpringApplicationRunListener.failed");
    }
}

HelloApplicationRunner.java

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package com.atguigu.springboot.listener;
 
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
 
@Component
public class HelloApplicationRunner implements ApplicationRunner {
    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("HelloApplicationRunner.run");
    }
}

HelloCommandLineRunner.java

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package com.atguigu.springboot.listener;
 
import org.springframework.boot.CommandLineRunner;
 
import java.util.Arrays;
 
@Component
public class HelloCommandLineRunner implements CommandLineRunner {
    @Override
    public void run(String... args) throws Exception {
        System.out.println("HelloCommandLineRunner.run..." + Arrays.asList(args));
    }
}

因为ApplicationRunner和CommandLineRunner需要放在IOC容器中，所以我们给HelloApplicationRunner和HelloCommandLineRunner的类添加@Component注解。

因为ApplicationContextInitializer和SpringApplicationRunListener需要配置在META-INF/spring.factories中，所以我们在resources目录下，添加META-INF/spring.factories文件，内容如下。

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org.springframework.context.ApplicationContextInitializer=\
com.atguigu.springboot.listener.HelloApplicationContextInitializer
org.springframework.boot.SpringApplicationRunListener=\
com.atguigu.springboot.listener.HelloSpringApplicationRunListener

启动项目，可以在控制台根据打印的log查看启动顺序。

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