Spring源码解析-PropertyEditor

PropertyEditor最早用于Swing编程中，在Spring中主要被用于xml内value的转换和mvc中参数值得转换。

Spring容器在applyPropertyValues通过TypeConverter对value进行值得转换,具体的调用栈如下

createBean->doCreateBean->populateBean->applyPropertyValues

具体的转换代码如下

private Object convertForProperty(Object value, String propertyName, BeanWrapper bw, TypeConverter converter) {if (converter instanceof BeanWrapperImpl) {return ((BeanWrapperImpl) converter).convertForProperty(value, propertyName);}else {PropertyDescriptor pd = bw.getPropertyDescriptor(propertyName);MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd);return converter.convertIfNecessary(value, pd.getPropertyType(), methodParam);}}

从源码可以看出当customTypeConverter为空是，将会使用BeanWrapper进行转换，因为BeanWrapper实现了PropertyEditorRegistry接口。

现在讲讲如何配置自定义的PropertyEditor, 通过配置CustomEditorConfigurer代码如下

<bean class="org.springframework.beans.factory.config.CustomEditorConfigurer">        <property name="customEditors">            <map>                <entry key="com.spring.User"                       value="com.spring.UserEditor"/>            </map>        </property></bean>

CustomEditorConfigurer本质上是一个BeanFactoryPostProcessor, 所以在初始化容器之后，会通过ConfigurableListableBeanFactory的addPropertyEditorRegistrar和registerCustomEditor, 将其自身配置的propertyEditorRegistrars和customEditors添加到容器中。那么就到了下一步，如果使用这些最后都变成PropertyEditor并且用于转换value为对应类型的object。
首先要知道AbstractBeanFactory中有以下变量,

customEditors, propertyEditorRegistrars, typeConverter, conversionService

typeConverter内部结合了conversionService和PropertyEditor来转换值，

conversionService是spring3.0新加的用于转换的接口和PropertyEditor属于一个性质的东西。

之前说到BeanWrapper是一个实现了PropertyEditorRegistry的接口，其内部有很多的PropertyEditor，这些editor则是通过beanFactory的initBeanWrapper注册到beanwrapper当中的，代码如下：

/** * Initialize the given BeanWrapper with the custom editors registered * with this factory. To be called for BeanWrappers that will create * and populate bean instances. * <p>The default implementation delegates to {@link #registerCustomEditors}. * Can be overridden in subclasses. * @param bw the BeanWrapper to initialize */protected void initBeanWrapper(BeanWrapper bw) {bw.setConversionService(getConversionService());registerCustomEditors(bw);}

/** * Initialize the given PropertyEditorRegistry with the custom editors * that have been registered with this BeanFactory. * <p>To be called for BeanWrappers that will create and populate bean * instances, and for SimpleTypeConverter used for constructor argument * and factory method type conversion. * @param registry the PropertyEditorRegistry to initialize */protected void registerCustomEditors(PropertyEditorRegistry registry) {PropertyEditorRegistrySupport registrySupport =(registry instanceof PropertyEditorRegistrySupport ? (PropertyEditorRegistrySupport) registry : null);if (registrySupport != null) {registrySupport.useConfigValueEditors();}if (!this.propertyEditorRegistrars.isEmpty()) {for (PropertyEditorRegistrar registrar : this.propertyEditorRegistrars) {try {registrar.registerCustomEditors(registry);}catch (BeanCreationException ex) {Throwable rootCause = ex.getMostSpecificCause();if (rootCause instanceof BeanCurrentlyInCreationException) {BeanCreationException bce = (BeanCreationException) rootCause;if (isCurrentlyInCreation(bce.getBeanName())) {if (logger.isDebugEnabled()) {logger.debug("PropertyEditorRegistrar [" + registrar.getClass().getName() +"] failed because it tried to obtain currently created bean '" +ex.getBeanName() + "': " + ex.getMessage());}onSuppressedException(ex);continue;}}throw ex;}}}if (!this.customEditors.isEmpty()) {for (Map.Entry<Class<?>, Class<? extends PropertyEditor>> entry : this.customEditors.entrySet()) {Class<?> requiredType = entry.getKey();Class<? extends PropertyEditor> editorClass = entry.getValue();registry.registerCustomEditor(requiredType, BeanUtils.instantiateClass(editorClass));}}}

所以每一个BeanWrapper相当于都从BeanFactory中获取PropertyEditor,最终用于值转换,

对于BeanFactory而言，则在AbstractApplicationContext的prepareBeanFactory中添加一个ResourceEditorRegistrar。代码如下

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {// Tell the internal bean factory to use the context's class loader etc.beanFactory.setBeanClassLoader(getClassLoader());beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));// Configure the bean factory with context callbacks.beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));beanFactory.ignoreDependencyInterface(EnvironmentAware.class);beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);beanFactory.ignoreDependencyInterface(MessageSourceAware.class);beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);// BeanFactory interface not registered as resolvable type in a plain factory.// MessageSource registered (and found for autowiring) as a bean.beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);beanFactory.registerResolvableDependency(ResourceLoader.class, this);beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);beanFactory.registerResolvableDependency(ApplicationContext.class, this);// Register early post-processor for detecting inner beans as ApplicationListeners.beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));// Detect a LoadTimeWeaver and prepare for weaving, if found.if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));// Set a temporary ClassLoader for type matching.beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));}// Register default environment beans.if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());}if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());}if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());}}