Spring框架系列(7) - Spring IOC实现原理详解之IOC初始化流程-优快云博客

本文链接：https://blog.youkuaiyun.com/sudadaipeng1/article/details/125495331

上文，我们看了IOC设计要点和设计结构；紧接着这篇，我们可以看下源码的实现了：Spring如何实现将资源配置（以xml配置为例）通过加载，解析，生成BeanDefination并注册到IoC容器中的。@pdai

Spring框架系列(7) - Spring IOC实现原理详解之IOC初始化流程

引入

上文，我们看了IOC设计要点和设计结构；紧接着这篇，我们可以看下源码的实现了：Spring如何实现将资源配置（以xml配置为例）通过加载，解析，生成BeanDefination并注册到IoC容器中的（就是我们圈出来的部分）

如何将Bean从XML配置中解析后放到IoC容器中的？

本文的目标就是分析Spring如何实现将资源配置（以xml配置为例）通过加载，解析，生成BeanDefination并注册到IoC容器中的。

初始化的入口

对于xml配置的Spring应用，在main()方法中实例化ClasspathXmlApplicationContext即可创建一个IoC容器。我们可以从这个构造方法开始，探究一下IoC容器的初始化过程。

 // create and configure beans
ApplicationContext context = new ClassPathXmlApplicationContext("aspects.xml", "daos.xml", "services.xml");

public ClassPathXmlApplicationContext(String... configLocations) throws BeansException {
   
    this(configLocations, true, (ApplicationContext)null);
}

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, @Nullable ApplicationContext parent) throws BeansException {
   
    // 设置Bean资源加载器
    super(parent);

    // 设置配置路径
    this.setConfigLocations(configLocations);

    // 初始化容器
    if (refresh) {
   
        this.refresh();
    }
}

设置资源解析器和环境

调用父类容器AbstractApplicationContext的构造方法(super(parent)方法)为容器设置好Bean资源加载器

public AbstractApplicationContext(@Nullable ApplicationContext parent) {
   
    // 默认构造函数初始化容器id, name, 状态 以及 资源解析器
    this();

    // 将父容器的Environment合并到当前容器
    this.setParent(parent);
}

通过AbstractApplicationContext默认构造函数初始化容器id, name, 状态以及资源解析器

public AbstractApplicationContext() {
   
    this.logger = LogFactory.getLog(this.getClass());
    this.id = ObjectUtils.identityToString(this);
    this.displayName = ObjectUtils.identityToString(this);
    this.beanFactoryPostProcessors = new ArrayList();
    this.active = new AtomicBoolean();
    this.closed = new AtomicBoolean();
    this.startupShutdownMonitor = new Object();
    this.applicationStartup = ApplicationStartup.DEFAULT;
    this.applicationListeners = new LinkedHashSet();
    this.resourcePatternResolver = this.getResourcePatternResolver();
}
// Spring资源加载器
protected ResourcePatternResolver getResourcePatternResolver() {
   
    return new PathMatchingResourcePatternResolver(this);
}

通过AbstractApplicationContext的setParent(parent)方法将父容器的Environment合并到当前容器

public void setParent(@Nullable ApplicationContext parent) {
   
    this.parent = parent;
    if (parent != null) {
   
        Environment parentEnvironment = parent.getEnvironment();
        if (parentEnvironment instanceof ConfigurableEnvironment) {
   
            this.getEnvironment().merge((ConfigurableEnvironment)parentEnvironment);
        }
    }
}

设置配置路径

在设置容器的资源加载器之后，接下来FileSystemXmlApplicationContet执行setConfigLocations方法通过调用其父类AbstractRefreshableConfigApplicationContext的方法进行对Bean定义资源文件的定位

public void setConfigLocations(@Nullable String... locations) {
   
    if (locations != null) {
   
        Assert.noNullElements(locations, "Config locations must not be null");
        this.configLocations = new String[locations.length];

        for(int i = 0; i < locations.length; ++i) {
   
            // 解析配置路径
            this.configLocations[i] = this.resolvePath(locations[i]).trim();
        }
    } else {
   
        this.configLocations = null;
    }
}
protected String resolvePath(String path) {
   
    // 从上一步Environment中解析
    return this.getEnvironment().resolveRequiredPlaceholders(path);
}

初始化的主体流程

Spring IoC容器对Bean定义资源的载入是从refresh()函数开始的，refresh()是一个模板方法，refresh()方法的作用是：在创建IoC容器前，如果已经有容器存在，则需要把已有的容器销毁和关闭，以保证在refresh之后使用的是新建立起来的IoC容器。refresh的作用类似于对IoC容器的重启，在新建立好的容器中对容器进行初始化，对Bean定义资源进行载入。

@Override
public void refresh() throws BeansException, IllegalStateException {
   
    synchronized (this.startupShutdownMonitor) {
   
        StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");

        // Prepare this context for refreshing.
        prepareRefresh();

        // Tell the subclass to refresh the internal bean factory.
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

        // Prepare the bean factory for use in this context.
        prepareBeanFactory(beanFactory);

        try {
   
            // Allows post-processing of the bean factory in context subclasses.
            postProcessBeanFactory(beanFactory);

            StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
            // Invoke factory processors registered as beans in the context.
            invokeBeanFactoryPostProcessors(beanFactory);

            // Register bean processors that intercept bean creation.
            registerBeanPostProcessors(beanFactory);
            beanPostProcess.end();

            // Initialize message source for this context.
            initMessageSource();

            // Initialize event multicaster for this context.