spring类型转换器(四)
在spring实例化和spring mvc中涉及到了大量的属性注入。这个过程中不可避免的就是类型转换，这章将会详细说明spring中类型转换器的使用和源码。
使用
PropertyEditor
首先来看下如何在spring中注册自定义的 PropertyEditor
public class CustomPropertyEditorRegistrar implements PropertyEditorRegistrar {
@Override
public void registerCustomEditors(PropertyEditorRegistry registry) {
registry.registerCustomEditor(Date.class,new DatePropertyEditor());
}
}
<bean class="org.springframework.beans.factory.config.CustomEditorConfigurer">
<property name="customEditors">
<map>
<entry key="java.util.Date.class" value="cn.zlz.editors.DatePropertyEditor"/>
</map>
</property>
<property name="propertyEditorRegistrars">
<list>
<ref bean="customPropertyEditorRegistrar"/>
</list>
</property>
</bean>
<bean id="customPropertyEditorRegistrar" class="cn.zlz.editors.CustomPropertyEditorRegistrar"/>
spring内部提供了一个 CustomEditorConfigurer 类，用于用户注册自定义类型转换器，可以通过customEditors注入自定义的PropertyEditor。也可以通过PropertyEditorRegistrar进行注册
PropertyEditor的注册是每个对象都创建一遍类型转换器，使用customEditors注册的是转换器的类型，然后每次都反射转换器对象。由于这样创建不够灵活，所以提供了PropertyEditorRegistrar接口，然后实现registerCustomEditors方法，通过这个方法可以灵活的注册自定义的类型转换器。
ConversionService
<bean id="conversionService"
class="org.springframework.context.support.ConversionServiceFactoryBean"/>
<bean id="conversionService"
class="org.springframework.context.support.ConversionServiceFactoryBean">
<property name="converters">
<set>
<bean class="example.MyCustomConverter"/>
</set>
</property>
</bean>
FormattingConversionService
<bean id="conversionService" class="org.springframework.format.support.FormattingConversionServiceFactoryBean"/>
源码
ConversionService类型转换实现
ConversionServiceFactoryBean实现了FactoryBean接口，主要就是创建了DefaultConversionService对象并注入的spring容器中
public class ConversionServiceFactoryBean implements FactoryBean<ConversionService>, InitializingBean {
private Set<?> converters;
private GenericConversionService conversionService;
@Override
public void afterPropertiesSet() {
this.conversionService = createConversionService();
//注册自定义类型转换器
ConversionServiceFactory.registerConverters(this.converters, this.conversionService);
}
protected GenericConversionService createConversionService() {
return new DefaultConversionService();
}
@Override
public ConversionService getObject() {
return this.conversionService;
}
}
FormattingConversionServiceFactoryBean同样实现了FactoryBean接口，创建了DefaultFormattingConversionService对象注册到spring容器中。
public class FormattingConversionServiceFactoryBean
implements FactoryBean<FormattingConversionService>, EmbeddedValueResolverAware, InitializingBean {
private Set<?> converters;
private Set<?> formatters;
private Set<FormatterRegistrar> formatterRegistrars;
private boolean registerDefaultFormatters = true;
private StringValueResolver embeddedValueResolver;
private FormattingConversionService conversionService;
@Override
public void afterPropertiesSet() {
//创建一个DefaultFormattingConversionService对象
this.conversionService = new DefaultFormattingConversionService(this.embeddedValueResolver, this.registerDefaultFormatters);
//注册自定义的converters
ConversionServiceFactory.registerConverters(this.converters, this.conversionService);
registerFormatters();//注册自定义的formatters
}
private void registerFormatters() {
if (this.formatters != null) {
for (Object formatter : this.formatters) {
if (formatter instanceof Formatter<?>) {
this.conversionService.addFormatter((Formatter<?>) formatter);
} else if (formatter instanceof AnnotationFormatterFactory<?>) {
this.conversionService.addFormatterForFieldAnnotation((AnnotationFormatterFactory<?>) formatter);
} else {
throw new IllegalArgumentException("");
}
}
}
if (this.formatterRegistrars != null) {
for (FormatterRegistrar registrar : this.formatterRegistrars) {
registrar.registerFormatters(this.conversionService);
}
}
}
}
通过 ConversionServiceFactoryBean或者FormattingConversionServiceFactoryBean都是向spring中注册一个id为conversionService的对象，那么是如何使用这个对象进行类型转换的呢？首先来看ApplicationContext的refresh方法
在refresh方法流程中有这么一段代码
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// String CONVERSION_SERVICE_BEAN_NAME = "conversionService";
if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
beanFactory.setConversionService(
beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
}
//....
}
可以看到，在ApplicationContext初始化的时候，会查询id为conversionService的ConversionService对象，然后调用BeanFactory的setConversionService方法，设置spring容器的类型转换器。BeanFactory只能配置一个ConversionService，通过上文我们知道DefaultFormattingConversionService是对DefaultConversionService的完全扩展，所以当需要格式化的时候直接使用FormattingConversionServiceFactoryBean就可以。
PropertyEditor实现
在使用ApplicationContext的时候，spring并没有暴露BeanFactory给我们，但是提供了一个BeanFactoryPostProcessor接口，spring实例化bean之前应用所有注册的BeanFactoryPostProcessor的实现类，调用每个的postProcessBeanFactory方法完成对spring容器的扩展。
来看CustomEditorConfigurer的源码，该类实现了BeanFactoryPostProcessor和Ordered接口。主要目的是在postProcessBeanFactory方法中向beanFactory中注册自定义的类型转换器
public class CustomEditorConfigurer implements BeanFactoryPostProcessor, Ordered {
private int order = Ordered.LOWEST_PRECEDENCE; // default: same as non-Ordered
private PropertyEditorRegistrar[] propertyEditorRegistrars;
private Map<Class<?>, Class<? extends PropertyEditor>> customEditors;
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
//向BeanFactory中注册propertyEditorRegistrars
if (this.propertyEditorRegistrars != null) {
for (PropertyEditorRegistrar propertyEditorRegistrar : this.propertyEditorRegistrars) {
beanFactory.addPropertyEditorRegistrar(propertyEditorRegistrar);
}
}//向BeanFactory中注册customEditors
if (this.customEditors != null) {
for (Map.Entry<Class<?>, Class<? extends PropertyEditor>> entry : this.customEditors.entrySet()) {
Class<?> requiredType = entry.getKey();
Class<? extends PropertyEditor> propertyEditorClass = entry.getValue();
beanFactory.registerCustomEditor(requiredType, propertyEditorClass);
}
}
}
}
在BeanFactory中注册全局的类型转换器，实例化每个bean的时候都会根据BeanFactory中注册的类型转换器在BeanWrapper中创建一份类型转换器。类型转换的过程是在getBean的时候，所以最好是在调用getBean即实例化Bean之前向BeanFactory中注册自定义的类型转换器。所以这里使用BeanFactoryPostProcessor实现了自定义类型转换器的注入
Bean实例化的属性注入
接下来我们来看一下bean实例化过程的属性注入是怎么实现的
调用BeanFactory的getBean方法会实例化Bean，第一步首先会反射创建一个目标对象，然后使用BeanWrapperImpll封装实例bean
//反射创建对象
Object beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
BeanWrapper bw = new BeanWrapperImpl(beanInstance);//使用BeanWrapper包装
this.beanFactory.initBeanWrapper(bw);//将BeanFactory中的类型转换器注册到BeanWrapper中
在initBeanWrapper方法将BeanFactory中定义的全局类型转换器注册到每个BeanWraper中，BeanWraper实现了PropertyEditorRegistry接口，本身带有注册转换器功能。
protected void initBeanWrapper(BeanWrapper bw) {
//将BeanFactory中的conversionService 添加到BeanWrapper中
bw.setConversionService(getConversionService());
registerCustomEditors(bw);
}
将BeanFactory中注册的 propertyEditorRegistrars和customEditors中的类型转换器添加BeanWrapper中。BeanWrapper实现了PropertyEditorRegistry接口
protected void registerCustomEditors(PropertyEditorRegistry registry) {
PropertyEditorRegistrySupport registrySupport =
(registry instanceof PropertyEditorRegistrySupport ? (PropertyEditorRegistrySupport) registry : null);
if (registrySupport != null) {
registrySupport.useConfigValueEditors();
}//注册 propertyEditorRegistrars 中注册的类型转换器
if (!this.propertyEditorRegistrars.isEmpty()) {
for (PropertyEditorRegistrar registrar : this.propertyEditorRegistrars) {
try {
registrar.registerCustomEditors(registry);
} catch (BeanCreationException ex) {
//...
}
}
}//注册 customEditors 添加的类型转换器
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));
}
}
}
创建完BeanWrapperImpl并完成类型转换器的注册后，接下来我们直接来看对Bean对象的属性赋值代码。在设置值的时候会首先获取类型转换器，如果没有设置TypeConverter，那么类型转化的功能就由BeanWrapper来实现。
protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
//.....
TypeConverter converter = getCustomTypeConverter();//获取BeanFactory中的 typeConverter
if (converter == null) {//如果没有配置 使用BeanWrapper作为类型转换器
converter = bw;
}
}
循环BeanDefinition中定义的属性值，然后将值转换为目标类型
BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);
for (PropertyValue pv : original) {
//....
String propertyName = pv.getName();
Object originalValue = pv.getValue();
//解析el表达式 beanExpressionResolver，如果指定了属性的type直接在这转换
Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
Object convertedValue = resolvedValue;
boolean convertible = bw.isWritableProperty(propertyName) &&
!PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
if (convertible) {//进行类型转换
convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
}
}
调用BeanWrapper中的convertForProperty将属性值的类型转换为bean中属性的类型，这里会使用到TypeConverter和ConverterService进行类型转换
private Object convertForProperty(Object value, String propertyName, BeanWrapper bw, TypeConverter converter) {
if (converter instanceof BeanWrapperImpl) {
return ((BeanWrapperImpl) converter).convertForProperty(value, propertyName);
} else { //如果有指定的的TyepConverter使用自定义的
PropertyDescriptor pd = bw.getPropertyDescriptor(propertyName);
MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd);
return converter.convertIfNecessary(value, pd.getPropertyType(), methodParam);
}
}
完成类型转换后，将属性值包装了MutablePropertyValues 类型，BeanWrapperImpl提供了属性的访问功能，调用BeanWrapperImpl的setPropertyValues对bean中的属性值进行设置,至此就完成了bean的属性注入
bw.setPropertyValues(new MutablePropertyValues(deepCopy));//在这个过程中也可进行类型转换
