spring-bean例子

1、已经在工程中定义了Spring配置文件beans.xml
2、定义类User，有方法say()输出"HelloWorld"
3、在beans.xml中配置了一个类User

     ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
        User user = (User) applicationContext.getBean("user");
        user.say();

spring加载bean

ClassPathXmlApplicationContext结构类图：

image.png

入口

代码new ClassPathXmlApplicationContext("beans.xml");使用了构造函数如下：

    public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)throws BeansException {
        //1.构造parent
        super(parent);
        //2.解析设置路径，解析占位符，创建StandardEnvironment
        setConfigLocations(configLocations);
       //3.刷新application
        if (refresh) {
            refresh();
        }
    }

refresh()

    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // 1.设置context属性，验证必要属性是否缺失
            prepareRefresh();

            // 2. 1.createBeanFactory 2.loadBeanDefinitions(beanFactory)
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // 3.设置beanfactory的一些属性
            prepareBeanFactory(beanFactory);

            try {
                // 4.由子类实现 BeanFactory 初始化后置处理
                postProcessBeanFactory(beanFactory);

                //5.注册并调用BeanFactoryPostProcessor
                invokeBeanFactoryPostProcessors(beanFactory);

                // 6.注册BeanPostProcessors
                registerBeanPostProcessors(beanFactory);

                // 7.Initialize message source for this context.
                initMessageSource();

                // 8.初始化上下文事件广播器
                initApplicationEventMulticaster();

                // 9.由子类实现初始化其他特殊的bean
                onRefresh();

                // 10.查找listener并注册为bean，然后注册到广播器中
                registerListeners();

                // 11.初始化剩下的非懒加载的bean
                finishBeanFactoryInitialization(beanFactory);

                // 12.发布响应事件
                finishRefresh();
            }

            catch (BeansException ex) {
                if (logger.isWarnEnabled()) {
                    logger.warn("Exception encountered during context initialization - " +
                            "cancelling refresh attempt: " + ex);
                }

                // Destroy already created singletons to avoid dangling resources.
                destroyBeans();

                // Reset 'active' flag.
                cancelRefresh(ex);

                // Propagate exception to caller.
                throw ex;
            }

            finally {
                // Reset common introspection caches in Spring's core, since we
                // might not ever need metadata for singleton beans anymore...
                resetCommonCaches();
            }
        }
    }

关键地方：
2.loadBeanDefinitions()加载所有的bean定义
5.PropertySourcesPlaceholderConfigurer 加载properties，解析占位符
11.getBean()(在之前的步骤中也执行过)
循环依赖
自定义BeanPostProcssor
InitializingBean
AutowiredAnnotationBeanPostProcessor 解析注解注入属性${}
FactoryBean
12.ApplicationListener