spring IOC 的BeanDefinition的注册

摘要：

上一篇博客IOC的载入与解析将xml文件通过io流加载成Document对象，再解析成BeanDefinition存放在BeanDefinitionHolder中。此时还不能在IOC中使用，需要IOC容器对Beandefinition数据进行注册。

本文简介

注册的过程就是把Beandefinition对象作为value，将beanName名或者别名作为key准出在map的过程。

详细分析

在载入解析BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele) 完成后，
启动注册：BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, this.getReaderContext().getRegistry());

    protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if (bdHolder != null) {
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);

            try {
                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, this.getReaderContext().getRegistry());
            } catch (BeanDefinitionStoreException var5) {
                this.getReaderContext().error("Failed to register bean definition with name '" + bdHolder.getBeanName() + "'", ele, var5);
            }

            this.getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
        }

    }

以在DefaultListableBeanFactory中为例，维护了一个Map属性。

    private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap(256);

在发生注册时，贴上源码 特地没挑代码最少的….

    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException {
        Assert.hasText(beanName, "Bean name must not be empty");
        Assert.notNull(beanDefinition, "BeanDefinition must not be null");
        if (beanDefinition instanceof AbstractBeanDefinition) {
            try {
                ((AbstractBeanDefinition)beanDefinition).validate();
            } catch (BeanDefinitionValidationException var9) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", var9);
            }
        }

        BeanDefinition oldBeanDefinition = (BeanDefinition)this.beanDefinitionMap.get(beanName);
        if (oldBeanDefinition != null) {
            if (!this.isAllowBeanDefinitionOverriding()) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName + "': There is already [" + oldBeanDefinition + "] bound.");
            }

            if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
                if (this.logger.isWarnEnabled()) {
                    this.logger.warn("Overriding user-defined bean definition for bean '" + beanName + "' with a framework-generated bean definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            } else if (!beanDefinition.equals(oldBeanDefinition)) {
                if (this.logger.isInfoEnabled()) {
                    this.logger.info("Overriding bean definition for bean '" + beanName + "' with a different definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            } else if (this.logger.isDebugEnabled()) {
                this.logger.debug("Overriding bean definition for bean '" + beanName + "' with an equivalent definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
            }

            this.beanDefinitionMap.put(beanName, beanDefinition);
        } else {
            if (this.hasBeanCreationStarted()) {
                Map var4 = this.beanDefinitionMap;
                synchronized(this.beanDefinitionMap) {
                    this.beanDefinitionMap.put(beanName, beanDefinition);
                    List<String> updatedDefinitions = new ArrayList(this.beanDefinitionNames.size() + 1);
                    updatedDefinitions.addAll(this.beanDefinitionNames);
                    updatedDefinitions.add(beanName);
                    this.beanDefinitionNames = updatedDefinitions;
                    if (this.manualSingletonNames.contains(beanName)) {
                        Set<String> updatedSingletons = new LinkedHashSet(this.manualSingletonNames);
                        updatedSingletons.remove(beanName);
                        this.manualSingletonNames = updatedSingletons;
                    }
                }
            } else {
                this.beanDefinitionMap.put(beanName, beanDefinition);
                this.beanDefinitionNames.add(beanName);
                this.manualSingletonNames.remove(beanName);
            }

            this.frozenBeanDefinitionNames = null;
        }

        if (oldBeanDefinition != null || this.containsSingleton(beanName)) {
            this.resetBeanDefinition(beanName);
        }

    }

BeanDefinition oldBeanDefinition = (BeanDefinition)this.beanDefinitionMap.get(beanName);根据beanName找到已经注册过的BeanDefinition。如果注册过并且设置为不允许重写的话，那就抛个异常。
没有重名的情况就将BeanDefinition作为value，beanName作为key，存放在spring容器的beanDefinitionMap中。

总结

到此为止，spring IOC 的初始化过程的主线任务结束。在spring容器中建立了Bean的配置信息。他们都被维护在beanDefinitionMap中。容器负责对map的控制和维护，这就是控制反转的基础，但是这些配置还只是空壳子，依赖注入还没有发生。
期待下节：依赖注入。