Spring源码(二)-Context的创建核心逻辑(上)

043d96008c2e11e9a1f1b3cbe472f1b9
202 阅读3分钟

我们前一章介绍了spring的整体架构以及模块划分，也已经将代码导入ide中，那么接下来就要开始让人心动的Spring源码之旅了。

1、默认的Spring启动器

@SpringBootApplication
@ComponentScan(basePackages = {"com"})
public class SpringSourceApplication {
    public static void main(String[] args) {
        ApplicationContext ctx = SpringApplication.run(SpringSourceApplication.class, args);
    }
}

该方法是Springboot的启动类

2、进入SpringApplication.java

public static ConfigurableApplicationContext run(Object source, String... args) {
    return run(new Object[] { source }, args);
}
public static ConfigurableApplicationContext run(Object[] sources, String[] args) {
    return new SpringApplication(sources).run(args);
}

这里创建了一个SpringApplication方法，执行run方法，返回一个ConfigurableApplicationContext,这只是一个接口而已，根据名称来看，这是一个可配置的应用程序上下文。

3、进入RUN方法

SpringApplication(sources)这个类的初始化就先不看，这里面调用了initialize()方法，主要完成了当前的运行环境，以及设置了ApplicationListener相关的东西，这里我们先不做分析，直接进入run方法。

public ConfigurableApplicationContext run(String... args) {
    //记录程序运行时间
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    ConfigurableApplicationContext context = null;
    FailureAnalyzers analyzers = null;
    /**
     * 设置headless模式
     * 在我们的例子中该属性会被设置为true，因为我们开发的是服务器程序，
     * 一般运行在没有显示器和键盘的环境。关于java中的headless模式
     */
    configureHeadlessProperty();
    SpringApplicationRunListeners listeners = getRunListeners(args);
    listeners.starting();
    try {
        ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                args);
        ConfigurableEnvironment environment = prepareEnvironment(listeners,
                applicationArguments);
        configureIgnoreBeanInfo(environment);
        bindToSpringApplication(environment);
        Banner printedBanner = printBanner(environment);
        /**
         * 它创建出来的是ConfigurableApplicationContext类的实例对象
         *AnnotationConfigEmbeddedWebApplicationContext
         */
        context = createApplicationContext();
        analyzers = new FailureAnalyzers(context);
        /**
         *     该方法对context进行了预设置，设置了ResourceLoader和ClassLoader，
         *  并向bean工厂中添加了一个beanNameGenerator
         */
        prepareContext(context, environment, listeners, applicationArguments,
                printedBanner);
        /**
         * prepareContext()已经做好了refresh上下文的基础准备工作
         * spring对ApplicationContext进行了向下转型，
         * 转型后的类型为：AbstractApplicationContex，并调用了它的refresh()方法
         * 详见方法内部实现
         */
        refreshContext(context);
        afterRefresh(context, applicationArguments);
        listeners.finished(context, null);
        stopWatch.stop();
        if (this.logStartupInfo) {
            new StartupInfoLogger(this.mainApplicationClass)
                    .logStarted(getApplicationLog(), stopWatch);
        }
        return context;
    }
    catch (Throwable ex) {
        handleRunFailure(context, listeners, analyzers, ex);
        throw new IllegalStateException(ex);
    }
}

try代码块中是我们最核心的功能，代码中也添加了一部分的注释。我们先看context的创建过程即进入到createApplicationContext()方法。

protected ConfigurableApplicationContext createApplicationContext() {
    Class<?> contextClass = this.applicationContextClass;
    if (contextClass == null) {
        try {
            switch (this.webApplicationType) {
                case SERVLET:
                    //此处采用反射获取WebApplicationContext
                    contextClass = Class.forName(DEFAULT_WEB_CONTEXT_CLASS);
                    break;
                case REACTIVE:
                    contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
                    break;
                default:
                    contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
            }
        }
        catch (ClassNotFoundException ex) {
            throw new IllegalStateException(
                    "Unable create a default ApplicationContext, "
                            + "please specify an ApplicationContextClass",
                    ex);
        }
    }
    return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}

DEFAULT_WEB_CONTEXT_CLASS —>AnnotationConfigEmbeddedWebApplicationContext
接下来执行AnnotationConfigEmbeddedWebApplicationContext的构造方法

public AnnotationConfigEmbeddedWebApplicationContext() {  
        this.reader = new AnnotatedBeanDefinitionReader(this);  
        this.scanner = new ClassPathBeanDefinitionScanner(this);  
}

上面实例化了AnnotatedBeanDefinitionReader以及ClassPathBeanDefinitionScanner
实例化AnnotatedBeanDefinitionReader

public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {  
    this(registry, getOrCreateEnvironment(registry));  
}

接下来是调用

public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {  
        Assert.notNull(registry, "BeanDefinitionRegistry must not be null");  
        Assert.notNull(environment, "Environment must not be null");  
        this.registry = registry;  
        this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);  
        AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);  
    }

实例化 ConditionEvaluator，将其属性ConditionContextImpl赋值

AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);

具体实现如下:

public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
        BeanDefinitionRegistry registry, @Nullable Object source) {
    //获取beanfactory信息,Spring IOC的核心
    DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry)
    if (beanFactory != null) {
        if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
            beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
        }
        if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
            beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
        }
    }

    Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(4);

    if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
    }

    if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
    }

    if (!registry.containsBeanDefinition(REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition(RequiredAnnotationBeanPostProcessor.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
    }

    // Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
    if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
    }

    // Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
    if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition();
        try {
            def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
                    AnnotationConfigUtils.class.getClassLoader()));
        }
        catch (ClassNotFoundException ex) {
            throw new IllegalStateException(
                    "Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
        }
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
    }

    if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
    }
    if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
    }

    return beanDefs;
}

上面代码比较长，我们来分开解析

  • 1、DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);

    由wrap就可以看出此处使用的是装饰器模式，registry包裹成一个指定的beanFactory

    private static DefaultListableBeanFactory unwrapDefaultListableBeanFactory(BeanDefinitionRegistry registry) {
    if (registry instanceof DefaultListableBeanFactory) {
        return (DefaultListableBeanFactory) registry;
    }
    else if (registry instanceof GenericApplicationContext) {
        //此处 GenericApplicationContext构造函数初始化beanFactory为DefaultListableBeanFactory
        return ((GenericApplicationContext) registry).getDefaultListableBeanFactory();
    }
    else {
        return null;
    }
}

代码执行到registry instanceof GenericApplicationContext(通过类继承结构可得到)，随后调用GenericApplicationContext#getDefaultListableBeanFactory()方法，GenericApplicationContext在构造方法中实例化了属性beanFactory的值为DefaultListableBeanFactory:

public GenericApplicationContext() {  
        this.beanFactory = new DefaultListableBeanFactory();  
    }

其构造优先于AnnotationConfigEmbeddedWebApplicationContext构造方法执行。
以上获得了BeanFactory信息

代码的构建请参考 github
该地址有相应代码的注释


原文链接：http://www.spring4all.com/article/15046


avatar
文章
阅读
粉丝