探秘Spring的PropertyEditor

java.beans.PropertyEditor是JDK自带的类，是提供给AWT。

Spring利用该接口来实现Bean的属性转换器。

Spring xml配置的bean属性都是字符串类型的值，但是对应到的每个具体的属性是各种类型的，Spring通过各种PropertyEditor来对各个属性进行类型转换。

Spring并不是直接实现PropertyEditor接口，而是继承PropertyEditorSupport类。

`PropertyEditorRegistry`

BeanWrapperImpl是PropertyEditorRegistrySupport的子类。
PropertyEditorRegistry是一个接口，PropertyEditorRegistrySupport是它的实现类。
PropertyEditorRegistrySupport中的方法createDefaultEditors，该方法初始化Spring中默认PropertyEditor。

/**
 * Actually register the default editors for this registry instance.
 */
private void createDefaultEditors() {
    this.defaultEditors = new HashMap<>(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(Path.class, 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());
    this.defaultEditors.put(ZoneId.class, 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);
    }
}

可能上面能够转换的类型还不能满足需求，那么可以通过另一种方式将PropertyEditor注入到Spring中。

`PropertyEditorRegistrar`

该接口只有一个方法:

1	void registerCustomEditors(PropertyEditorRegistry registry)

实现该方法就可以往传入的registry添加自定义的PropertyEditor，一般情况下传入的registry是BeanWrapperImpl的实例，即将自定义的PropertyEditor注入到BeanWrapperImpl。

`CustomEditorConfigurer`

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

把PropertyEditorRegistrar添加到BeanFactory。

它是实现了BeanFactoryPostProcessor接口，即在构造完BeanDefinition之后会调用方法postProcessBeanFactory。

注入一个CustomEditorConfigurerBean(设置propertyEditorRegistrars和customEditors属性)就可以将自定义的PropertyEditor注入到Spring中了。

例子

自定义`PropertyEditor`

public class CustomPropertyEditor extends PropertyEditorSupport {
    @Override
    public void setAsText(String text) throws IllegalArgumentException {
        super.setAsText(text);
    }
    @Override
    public Object getValue() {
        return super.getValue();
    }
}

将这个`PropertyEditor`注入到Spring里面中

<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>

`ClassEditor`的实现

public class ClassEditor extends PropertyEditorSupport {
    private final ClassLoader classLoader;
    public ClassEditor() {
        this(null);
    }
    public ClassEditor(ClassLoader classLoader) {
        this.classLoader = (classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader());
    }
    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 "";
        }
    }
}

PropertyEditorRegistry

PropertyEditorRegistrar

CustomEditorConfigurer

例子

自定义PropertyEditor

将这个PropertyEditor注入到Spring里面中

ClassEditor的实现