探秘Spring的PropertyEditor

#探秘Spring的PropertyEditor 今天无心之中一位网友咨询一个问题让我有了深刻了解一下Spring的PropertyEditor机制的机会，虽然以前也大概知道些，可是都是知道它是什么，殊不知道在Spring整个机制中它是如何执行的。今天就趁着中午闲暇时间看了一下Spring这方面的源码。因此这里主要是经过分析Spring的源码来了解PropertyEditor。

其实PropertyEditor是JDK里面的java.beans下面的类，是提供AWT进行渲染用的。Spring经过利用该接口，来实现Bean的属性转换器。咱们在Spring的xml或者其余途径配置的bean属性都是字符串类型的值，可是对应到每一个具体的属性是各类类型的，Spring经过各类PropertyEditor来对各个属性进行类型转换，在Spring中的PropertyEditor并非直接实现PropertyEditor接口，是经过PropertyEditorSupport类屏蔽了一些Spring不须要的方法好比paintValue，从而对它们提供了默认的实现，因此Spring里面的PropertyEditor都是在PropertyEditorSupport的基础上实现的。那么先看看Spring到底提供了哪些PropertyEditor的实现，下面截取了经过IDE工具找到的实现类截图：

这里面基本涉及到了全部JDK提供的类型，知道spring提供哪些PropertyEditor以后，还得须要这些PropertyEditor是怎么嵌入Spring的。

##PropertyEditorRegistry 这个是Spring框架内部将PropertyEditor嵌入Spring的方式，其中BeanWrapperImpl就是一个例子。先看看BeanWrapperImpl的类图：

能够看到BeanWrapperImpl其实就是PropertyEditorRegistry的子类。其实PropertyEditorRegistry是一个接口，作具体事情的是PropertyEditorRegistrySupport。在PropertyEditorRegistrySupport中存在一个方法createDefaultEditors，这个方法就是初始化Spring中默认PropertyEditor。下面看看哪些是Spring默认的PropertyEditor： <!--lang:java--> 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());
	this.defaultEditors.put(Pattern.class, new PatternEditor());
	this.defaultEditors.put(Properties.class, new PropertiesEditor());
	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());

	// 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);
	}
}

执行完这个那么BeanWrapperImpl就具有上面类型的转换功能，可能上面可以转换的类型还不能知足咱们的需求，那么能够经过另外一种方式将PropertyEditor注入到Spring中。

##PropertyEditorRegistrar 该接口只有一个方法void registerCustomEditors(PropertyEditorRegistry registry),实现该方法就能够往传入的registry添加自定义的PropertyEditor，通常状况下传入的registry是BeanWrapperImpl的实体，因此就等于将自定义的PropertyEditor注入到BeanWrapperImpl里面。如今的问题是怎么将PropertyEditorRegistrar注入到Spring中，那么就能够将自定的PropertyEditor添加到Spring中。Spring提供了一个类专门用来将第三方的PropertyEditor注入到它里面，这个类就是CustomEditorConfigurer，先看看这个类的类图： 发现它是实现了BeanFactoryPostProcessor接口，那么将会在构造完BeanDefinition以后调用方法postProcessBeanFactory,只有整个方法是嵌入Spring的惟一途经，那么看看这个方法里面作了什么事情:

<!--lang:java-->
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
	if (this.propertyEditorRegistrars != null) {
		for (PropertyEditorRegistrar propertyEditorRegistrar : this.propertyEditorRegistrars) {
			beanFactory.addPropertyEditorRegistrar(propertyEditorRegistrar);
		}
	}

	if (this.customEditors != null) {
		for (Map.Entry<String, ?> entry : this.customEditors.entrySet()) {
			String key = entry.getKey();
			Object value = entry.getValue();
			Class requiredType = null;

			try {
				requiredType = ClassUtils.forName(key, this.beanClassLoader);
				if (value instanceof PropertyEditor) {
					if (logger.isWarnEnabled()) {
						logger.warn("Passing PropertyEditor instances into CustomEditorConfigurer is deprecated: " +
								"use PropertyEditorRegistrars or PropertyEditor class names instead. " +
								"Offending key [" + key + "; offending editor instance: " + value);
					}
					beanFactory.addPropertyEditorRegistrar(
							new SharedPropertyEditorRegistrar(requiredType, (PropertyEditor) value));
				}
				else if (value instanceof Class) {
					beanFactory.registerCustomEditor(requiredType, (Class) value);
				}
				else if (value instanceof String) {
					Class editorClass = ClassUtils.forName((String) value, this.beanClassLoader);
					Assert.isAssignable(PropertyEditor.class, editorClass);
					beanFactory.registerCustomEditor(requiredType, editorClass);
				}
				else {
					throw new IllegalArgumentException("Mapped value [" + value + "] for custom editor key [" +
							key + "] is not of required type [" + PropertyEditor.class.getName() +
							"] or a corresponding Class or String value indicating a PropertyEditor implementation");
				}
			}
			catch (ClassNotFoundException ex) {
				if (this.ignoreUnresolvableEditors) {
					logger.info("Skipping editor [" + value + "] for required type [" + key + "]: " +
							(requiredType != null ? "editor" : "required type") + " class not found.");
				}
				else {
					throw new FatalBeanException(
							(requiredType != null ? "Editor" : "Required type") + " class not found", ex);
				}
			}
		}
	}
}

发现它都调用了beanFactory的方法将配置的PropertyEditorRegistrar和customEditors注入到Spring的bean工厂里面。咱们只要往spring容器中注入一个CustomEditorConfigurerBean，而后设置propertyEditorRegistrars和customEditors属性就能够将自定义的PropertyEditor注入到Spring中了。固然你也能够不用CustomEditorConfigurer类，自定义一个类实现BeanFactoryPostProcessor接口，而后按照CustomEditorConfigurer相似的路径，也能够达到目的。下面给出一个自定义PropertyEditor大体流程：

<!--lang:java-->
public class CustomPropertyEditor extends PropertyEditorSupport {

@Override
public void setAsText(String text) throws IllegalArgumentException {
    super.setAsText(text);
}

@Override
public Object getValue() {
    return super.getValue();
}
}

上面是定义了一个自定义PropertyEditor,下面须要将这个PropertyEditor注入到Spring里面中：

<!--lang:xml-->
<bean class="org.springframework.beans.factory.config.CustomEditorConfigurer">
	<property name="customEditors">
		<map>
			<entry key="com.xx.foo.FooPojo" value="com.xx.foo.CustomPropertyEditor"/>
		</map>
	</property>
</bean>

Spring都会调用setAsText方法将该属性的字面值设置进来，而后须要根据你规定的规范转换成对应的属性对象。

下面再给出一个ClassEditor的实现，你们能够仿照这个来实现：

<!--lang:java-->
public class ClassEditor extends PropertyEditorSupport {

private final ClassLoader classLoader;


/**
 * Create a default ClassEditor, using the thread context ClassLoader.
 */
public ClassEditor() {
	this(null);
}

/**
 * Create a default ClassEditor, using the given ClassLoader.
 * @param classLoader the ClassLoader to use
 * (or {@code null} for the thread context ClassLoader)
 */
public ClassEditor(ClassLoader classLoader) {
	this.classLoader = (classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader());
}


@Override
public void setAsText(String text) throws IllegalArgumentException {
	if (StringUtils.hasText(text)) {
		setValue(ClassUtils.resolveClassName(text.trim(), this.classLoader));
	}
	else {
		setValue(null);
	}
}

@Override
public String getAsText() {
	Class clazz = (Class) getValue();
	if (clazz != null) {
		return ClassUtils.getQualifiedName(clazz);
	}
	else {
		return "";
	}
}

}