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()); } }