属性编辑器PropertyEditorSupport在spring中的应用

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本文介绍在Spring框架中如何解决Date类型属性从XML配置文件注入的问题，包括自定义属性编辑器的方法及配置。

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当我们通过xml定义bean的时候，如果bean中的有的属性是Date类型，而我们在xml中给这个属性赋值，然后实例化这个bean时，却会报类型转换错误，如下

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'propertyEditorBean' defined in class path resource [mybeans.xml]: Initialization of bean failed; nested exception is org.springframework.beans.ConversionNotSupportedException: Failed to convert property value of type 'java.lang.String' to required type 'java.util.Date' for property 'myDate'; nested exception is java.lang.IllegalStateException: Cannot convert value of type 'java.lang.String' to required type 'java.util.Date' for property 'myDate': no matching editors or conversion strategy found
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:564)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483)
	at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:761)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543)
	at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
	at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
	at com.shux.springsource.App.testPropertyEditor(App.java:130)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:483)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
	at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
	at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: org.springframework.beans.ConversionNotSupportedException: Failed to convert property value of type 'java.lang.String' to required type 'java.util.Date' for property 'myDate'; nested exception is java.lang.IllegalStateException: Cannot convert value of type 'java.lang.String' to required type 'java.util.Date' for property 'myDate': no matching editors or conversion strategy found
	at org.springframework.beans.AbstractNestablePropertyAccessor.convertIfNecessary(AbstractNestablePropertyAccessor.java:603)
	at org.springframework.beans.AbstractNestablePropertyAccessor.convertForProperty(AbstractNestablePropertyAccessor.java:615)
	at org.springframework.beans.BeanWrapperImpl.convertForProperty(BeanWrapperImpl.java:216)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.convertForProperty(AbstractAutowireCapableBeanFactory.java:1577)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1536)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1276)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:553)
	... 34 more
Caused by: java.lang.IllegalStateException: Cannot convert value of type 'java.lang.String' to required type 'java.util.Date' for property 'myDate': no matching editors or conversion strategy found
	at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:306)
	at org.springframework.beans.AbstractNestablePropertyAccessor.convertIfNecessary(AbstractNestablePropertyAccessor.java:588)
	... 40 more

例子如下

先定义bean

package com.shux.springsource.bean;

import java.util.Date;

/**
 * 描述：
 * 
 * <pre>HISTORY
 * ****************************************************************************
 *  ID   DATE           PERSON          REASON
 *  1    2018年2月1日      Simba.Hua         Create
 * ****************************************************************************
 * </pre>
 * @author Simba.Hua
 */
public class PropertyEditorBean {
	private Date myDate;

	public Date getMyDate() {
		return myDate;
	}

	public void setMyDate(Date myDate) {
		this.myDate = myDate;
	}
	@Override
	public String toString() {
		return "myDate:" + myDate;
	}
}

在XML中定义bean

<bean id="propertyEditorBean" class="com.shux.springsource.bean.PropertyEditorBean" >
		<property name="myDate" >
			<value>2018-02-01</value>
		</property>
	</bean>

测试代码

@Test
    public void testPropertyEditor() {
    	ApplicationContext context = new ClassPathXmlApplicationContext("mybeans.xml");
    	PropertyEditorBean propertyEditorBean = context.getBean("propertyEditorBean", PropertyEditorBean.class);
    	System.out.println(propertyEditorBean);
    }

测试后报以上错误，报以上错的主要原因是Spring在实例化的属性填充阶段没有对String转换为Date做处理，但为什么其他的如Integer，File又能够自动识别呢？

我们看spring源码会发现，在属性填充阶段，类AbstractAutowireCapableBeanFactory的applyBeanPropertiesValues方法

	@Override
	public void applyBeanPropertyValues(Object existingBean, String beanName) throws BeansException {
		markBeanAsCreated(beanName);
		BeanDefinition bd = getMergedBeanDefinition(beanName);
		BeanWrapper bw = new BeanWrapperImpl(existingBean);
		initBeanWrapper(bw);
		applyPropertyValues(beanName, bd, bw, bd.getPropertyValues());
	}

BeanWrapperImpl除了实现BeanWrapper接口，还继承了PropertyEditorRegistrySupport，而在PropertyEditorRegistrySupport中有一个createDefaultEditors方法，里面加入了常用的属性编辑器，类TypeConverterDelegate的convertIfNecessary方法会调用此方法，如下所示

convertIfNecessary(String propertyName, Object oldValue, Object newValue,
Class<T> requiredType, TypeDescriptor typeDescriptor)方法

/**
	 * Convert the value to the required type (if necessary from a String),
	 * for the specified property.
	 * @param propertyName name of the property
	 * @param oldValue the previous value, if available (may be {@code null})
	 * @param newValue the proposed new value
	 * @param requiredType the type we must convert to
	 * (or {@code null} if not known, for example in case of a collection element)
	 * @param typeDescriptor the descriptor for the target property or field
	 * @return the new value, possibly the result of type conversion
	 * @throws IllegalArgumentException if type conversion failed
	 */
	@SuppressWarnings("unchecked")
	public <T> T convertIfNecessary(String propertyName, Object oldValue, Object newValue,
			Class<T> requiredType, TypeDescriptor typeDescriptor) throws IllegalArgumentException {

		// Custom editor for this type?获取自定义的属性编辑器PropertyEditor，如果不存在将会获取默认的属性编辑器
		PropertyEditor editor = this.propertyEditorRegistry.findCustomEditor(requiredType, propertyName);

		ConversionFailedException conversionAttemptEx = null;

		// No custom editor but custom ConversionService specified?
		ConversionService conversionService = this.propertyEditorRegistry.getConversionService();
		if (editor == null && conversionService != null && newValue != null && typeDescriptor != null) {
			TypeDescriptor sourceTypeDesc = TypeDescriptor.forObject(newValue);
			if (conversionService.canConvert(sourceTypeDesc, typeDescriptor)) {
				try {
					return (T) conversionService.convert(newValue, sourceTypeDesc, typeDescriptor);
				}
				catch (ConversionFailedException ex) {
					// fallback to default conversion logic below
					conversionAttemptEx = ex;
				}
			}
		}

		Object convertedValue = newValue;

		// Value not of required type?如果自定义的属性编辑器存在，则使用自定义的属性编辑器转换属性值
		if (editor != null || (requiredType != null && !ClassUtils.isAssignableValue(requiredType, convertedValue))) {
			if (typeDescriptor != null && requiredType != null && Collection.class.isAssignableFrom(requiredType) &&
					convertedValue instanceof String) {
				TypeDescriptor elementTypeDesc = typeDescriptor.getElementTypeDescriptor();
				if (elementTypeDesc != null) {
					Class<?> elementType = elementTypeDesc.getType();
					if (Class.class == elementType || Enum.class.isAssignableFrom(elementType)) {
						convertedValue = StringUtils.commaDelimitedListToStringArray((String) convertedValue);
					}
				}
			}
			if (editor == null) {//如果自定义属性编辑器为空，则使用默认的属性编辑器，里面定义了常用的属性编辑器，但不含date的属性编辑器
				editor = findDefaultEditor(requiredType);
			}
			convertedValue = doConvertValue(oldValue, convertedValue, requiredType, editor);
		}

		boolean standardConversion = false;

		if (requiredType != null) {
			// Try to apply some standard type conversion rules if appropriate.

			if (convertedValue != null) {
				if (Object.class == requiredType) {
					return (T) convertedValue;
				}
				else if (requiredType.isArray()) {
					// Array required -> apply appropriate conversion of elements.
					if (convertedValue instanceof String && Enum.class.isAssignableFrom(requiredType.getComponentType())) {
						convertedValue = StringUtils.commaDelimitedListToStringArray((String) convertedValue);
					}
					return (T) convertToTypedArray(convertedValue, propertyName, requiredType.getComponentType());
				}
				else if (convertedValue instanceof Collection) {
					// Convert elements to target type, if determined.
					convertedValue = convertToTypedCollection(
							(Collection<?>) convertedValue, propertyName, requiredType, typeDescriptor);
					standardConversion = true;
				}
				else if (convertedValue instanceof Map) {
					// Convert keys and values to respective target type, if determined.
					convertedValue = convertToTypedMap(
							(Map<?, ?>) convertedValue, propertyName, requiredType, typeDescriptor);
					standardConversion = true;
				}
				if (convertedValue.getClass().isArray() && Array.getLength(convertedValue) == 1) {
					convertedValue = Array.get(convertedValue, 0);
					standardConversion = true;
				}
				if (String.class == requiredType && ClassUtils.isPrimitiveOrWrapper(convertedValue.getClass())) {
					// We can stringify any primitive value...
					return (T) convertedValue.toString();
				}
				else if (convertedValue instanceof String && !requiredType.isInstance(convertedValue)) {
					if (conversionAttemptEx == null && !requiredType.isInterface() && !requiredType.isEnum()) {
						try {
							Constructor<T> strCtor = requiredType.getConstructor(String.class);
							return BeanUtils.instantiateClass(strCtor, convertedValue);
						}
						catch (NoSuchMethodException ex) {
							// proceed with field lookup
							if (logger.isTraceEnabled()) {
								logger.trace("No String constructor found on type [" + requiredType.getName() + "]", ex);
							}
						}
						catch (Exception ex) {
							if (logger.isDebugEnabled()) {
								logger.debug("Construction via String failed for type [" + requiredType.getName() + "]", ex);
							}
						}
					}
					String trimmedValue = ((String) convertedValue).trim();
					if (requiredType.isEnum() && "".equals(trimmedValue)) {
						// It's an empty enum identifier: reset the enum value to null.
						return null;
					}
					convertedValue = attemptToConvertStringToEnum(requiredType, trimmedValue, convertedValue);
					standardConversion = true;
				}
				else if (convertedValue instanceof Number && Number.class.isAssignableFrom(requiredType)) {
					convertedValue = NumberUtils.convertNumberToTargetClass(
							(Number) convertedValue, (Class<Number>) requiredType);
					standardConversion = true;
				}
			}
			else {
				// convertedValue == null
				if (javaUtilOptionalEmpty != null && requiredType == javaUtilOptionalEmpty.getClass()) {
					convertedValue = javaUtilOptionalEmpty;
				}
			}

			if (!ClassUtils.isAssignableValue(requiredType, convertedValue)) {
				if (conversionAttemptEx != null) {
					// Original exception from former ConversionService call above...
					throw conversionAttemptEx;
				}
				else if (conversionService != null) {
					// ConversionService not tried before, probably custom editor found
					// but editor couldn't produce the required type...
					TypeDescriptor sourceTypeDesc = TypeDescriptor.forObject(newValue);
					if (conversionService.canConvert(sourceTypeDesc, typeDescriptor)) {
						return (T) conversionService.convert(newValue, sourceTypeDesc, typeDescriptor);
					}
				}

				// Definitely doesn't match: throw IllegalArgumentException/IllegalStateException
				StringBuilder msg = new StringBuilder();
				msg.append("Cannot convert value of type '").append(ClassUtils.getDescriptiveType(newValue));
				msg.append("' to required type '").append(ClassUtils.getQualifiedName(requiredType)).append("'");
				if (propertyName != null) {
					msg.append(" for property '").append(propertyName).append("'");
				}
				if (editor != null) {
					msg.append(": PropertyEditor [").append(editor.getClass().getName()).append(
							"] returned inappropriate value of type '").append(
							ClassUtils.getDescriptiveType(convertedValue)).append("'");
					throw new IllegalArgumentException(msg.toString());
				}
				else {
					msg.append(": no matching editors or conversion strategy found");
					throw new IllegalStateException(msg.toString());
				}
			}
		}

		if (conversionAttemptEx != null) {
			if (editor == null && !standardConversion && requiredType != null && Object.class != requiredType) {
				throw conversionAttemptEx;
			}
			logger.debug("Original ConversionService attempt failed - ignored since " +
					"PropertyEditor based conversion eventually succeeded", conversionAttemptEx);
		}

		return (T) convertedValue;
	}

createDefaultEditors默认属性编辑器，定义了常用的属性编辑器，但不存在date的属性编辑器，所以如果要使用把string转换成date，则需要自己写自定义属性编辑器

private void createDefaultEditors() {
		this.defaultEditors = new HashMap<Class<?>, PropertyEditor>(64);

		// Simple editors, without parameterization capabilities.
		// The JDK does not contain a default editor for any of these target types.
		this.defaultEditors.put(Charset.class, new CharsetEditor());
		this.defaultEditors.put(Class.class, new ClassEditor());
		this.defaultEditors.put(Class[].class, new ClassArrayEditor());
		this.defaultEditors.put(Currency.class, new CurrencyEditor());
		this.defaultEditors.put(File.class, new FileEditor());
		this.defaultEditors.put(InputStream.class, new InputStreamEditor());
		this.defaultEditors.put(InputSource.class, new InputSourceEditor());
		this.defaultEditors.put(Locale.class, new LocaleEditor());
		if (pathClass != null) {
			this.defaultEditors.put(pathClass, new PathEditor());
		}
		this.defaultEditors.put(Pattern.class, new PatternEditor());
		this.defaultEditors.put(Properties.class, new PropertiesEditor());
		this.defaultEditors.put(Reader.class, new ReaderEditor());
		this.defaultEditors.put(Resource[].class, new ResourceArrayPropertyEditor());
		this.defaultEditors.put(TimeZone.class, new TimeZoneEditor());
		this.defaultEditors.put(URI.class, new URIEditor());
		this.defaultEditors.put(URL.class, new URLEditor());
		this.defaultEditors.put(UUID.class, new UUIDEditor());
		if (zoneIdClass != null) {
			this.defaultEditors.put(zoneIdClass, new ZoneIdEditor());
		}

		// Default instances of collection editors.
		// Can be overridden by registering custom instances of those as custom editors.
		this.defaultEditors.put(Collection.class, new CustomCollectionEditor(Collection.class));
		this.defaultEditors.put(Set.class, new CustomCollectionEditor(Set.class));
		this.defaultEditors.put(SortedSet.class, new CustomCollectionEditor(SortedSet.class));
		this.defaultEditors.put(List.class, new CustomCollectionEditor(List.class));
		this.defaultEditors.put(SortedMap.class, new CustomMapEditor(SortedMap.class));

		// Default editors for primitive arrays.
		this.defaultEditors.put(byte[].class, new ByteArrayPropertyEditor());
		this.defaultEditors.put(char[].class, new CharArrayPropertyEditor());

		// The JDK does not contain a default editor for char!
		this.defaultEditors.put(char.class, new CharacterEditor(false));
		this.defaultEditors.put(Character.class, new CharacterEditor(true));

		// Spring's CustomBooleanEditor accepts more flag values than the JDK's default editor.
		this.defaultEditors.put(boolean.class, new CustomBooleanEditor(false));
		this.defaultEditors.put(Boolean.class, new CustomBooleanEditor(true));

		// The JDK does not contain default editors for number wrapper types!
		// Override JDK primitive number editors with our own CustomNumberEditor.
		this.defaultEditors.put(byte.class, new CustomNumberEditor(Byte.class, false));
		this.defaultEditors.put(Byte.class, new CustomNumberEditor(Byte.class, true));
		this.defaultEditors.put(short.class, new CustomNumberEditor(Short.class, false));
		this.defaultEditors.put(Short.class, new CustomNumberEditor(Short.class, true));
		this.defaultEditors.put(int.class, new CustomNumberEditor(Integer.class, false));
		this.defaultEditors.put(Integer.class, new CustomNumberEditor(Integer.class, true));
		this.defaultEditors.put(long.class, new CustomNumberEditor(Long.class, false));
		this.defaultEditors.put(Long.class, new CustomNumberEditor(Long.class, true));
		this.defaultEditors.put(float.class, new CustomNumberEditor(Float.class, false));
		this.defaultEditors.put(Float.class, new CustomNumberEditor(Float.class, true));
		this.defaultEditors.put(double.class, new CustomNumberEditor(Double.class, false));
		this.defaultEditors.put(Double.class, new CustomNumberEditor(Double.class, true));
		this.defaultEditors.put(BigDecimal.class, new CustomNumberEditor(BigDecimal.class, true));
		this.defaultEditors.put(BigInteger.class, new CustomNumberEditor(BigInteger.class, true));

		// Only register config value editors if explicitly requested.
		if (this.configValueEditorsActive) {
			StringArrayPropertyEditor sae = new StringArrayPropertyEditor();
			this.defaultEditors.put(String[].class, sae);
			this.defaultEditors.put(short[].class, sae);
			this.defaultEditors.put(int[].class, sae);
			this.defaultEditors.put(long[].class, sae);
		}
	}

而这个方法中却没有Date的属性编辑器，如果要支持，需要自定义一个PropertyEditorSupport，如下所示

import java.beans.PropertyEditorSupport;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * 描述：
 * 
 * <pre>HISTORY
 * ****************************************************************************
 *  ID   DATE           PERSON          REASON
 *  1    2018年2月1日      Simba.Hua         Create
 * ****************************************************************************
 * </pre>
 * @author Simba.Hua
 */
public class DatePropertyEditor extends PropertyEditorSupport{
	private String format = "yyyy-MM-dd";

	public void setFormat(String format) {
		this.format = format;
	}
	@Override
	public void setAsText(String arg0) throws IllegalArgumentException {
		SimpleDateFormat sdf = new SimpleDateFormat(format);
		try {
			Date date = sdf.parse(arg0);
			this.setValue(date);
		} catch (ParseException e) {
			e.printStackTrace();
		}
	}
}

重写setAsText方法，在类TypeConverterDelegate的doConvertTextValue(Object oldValue, String newTextValue, PropertyEditor editor)方法会执行setAsText，然后进行转换。需要在xml中配置这个属性编辑器，如下所示

<bean class="org.springframework.beans.factory.config.CustomEditorConfigurer">
		<property name="customEditors">
			<map>
				<entry key="java.util.Date" value="com.shux.springsource.property.editor.DatePropertyEditor">
				</entry>
			</map>
		</property>
	</bean>

注意，这里不能写成以下形式，否则会报以下错误

<bean class="org.springframework.beans.factory.config.CustomEditorConfigurer">
		<property name="customEditors">
			<map>
				<entry key="java.util.Date" >
				<bean class="com.shux.springsource.property.editor.DatePropertyEditor">
					<property name="format" value="yyyy-MM-dd"></property>
				</bean>
				</entry>
			</map>
		</property>
	</bean>

Initialization of bean failed; nested exception is org.springframework.beans.TypeMismatchException: Failed to convert property value of type 'java.util.LinkedHashMap' to required type 'java.util.Map' for property 'customEditors'; nested exception is java.lang.IllegalArgumentException: Cannot convert value of type [org.xjs.exec.DatePropertyEditor] to required type [java.lang.Class] for property 'customEditors[java.util.Date]': PropertyEditor [org.springframework.beans.propertyeditors.ClassEditor] returned inappropriate value of type [com.shux.springsource.property.editor.DatePropertyEditor]

主要原因是org.springframework.beans.factory.config.CustomEditorConfigurer里的Map<Class<?>, Class<? extends PropertyEditor>> customEditors是Class类型的，而如果按照以上写法实际上生成的是Bean实例，会导致类型不一致。

最后正确执行
myDate:Thu Feb 01 00:00:00 CST 2018