Spring源码追踪1——doGetBean（为什么org.springframework.data.redis.core.RedisTemplate的实例可以注入为ListOperations）

类org.springframework.beans.factory.support.AbstractBeanFactory
方法T doGetBean(final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)

这里requiredType是获取的实例要转换成的类型，转换通过org.springframework.beans.TypeConverter进行。

if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
    try {
        return getTypeConverter().convertIfNecessary(bean, requiredType);
    }
    catch (TypeMismatchException ex) {
        if (logger.isDebugEnabled()) {
            logger.debug("Failed to convert bean '" + name + "' to required type [" +
                    ClassUtils.getQualifiedName(requiredType) + "]", ex);
        }
        throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
    }
}

类org.springframework.beans.TypeConverterDelegate

TypeConverter调用java.beans.PropertyEditor。

public <T> T convertIfNecessary(String propertyName, Object oldValue, Object newValue,
        Class<T> requiredType, TypeDescriptor typeDescriptor) throws IllegalArgumentException {

    Object convertedValue = newValue;

    // Custom editor for this type?
    PropertyEditor editor = this.propertyEditorRegistry.findCustomEditor(requiredType, propertyName);

    ConversionFailedException firstAttemptEx = null;

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

    // Value not of required type?
    if (editor != null || (requiredType != null && !ClassUtils.isAssignableValue(requiredType, convertedValue))) {
        if (requiredType != null && Collection.class.isAssignableFrom(requiredType) && convertedValue instanceof String) {
            TypeDescriptor elementType = typeDescriptor.getElementTypeDescriptor();
            if (elementType != null && Enum.class.isAssignableFrom(elementType.getType())) {
                convertedValue = StringUtils.commaDelimitedListToStringArray((String) convertedValue);
            }
        }
        if (editor == null) {
            editor = findDefaultEditor(requiredType); // redis进入的是此分支路径
        }
        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.equals(requiredType)) {
                return (T) convertedValue;
            }
            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.equals(requiredType) && ClassUtils.isPrimitiveOrWrapper(convertedValue.getClass())) {
                // We can stringify any primitive value...
                return (T) convertedValue.toString();
            }
            else if (convertedValue instanceof String && !requiredType.isInstance(convertedValue)) {
                if (firstAttemptEx == 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;
            }
        }

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

    return (T) convertedValue;
}

类org.springframework.beans.BeanUtils
方法PropertyEditor findEditorByConvention(Class<?> targetType)

spring会自动获取type对应的editor

String editorName = targetType.getName() + "Editor";
try {
    Class<?> editorClass = cl.loadClass(editorName);
    if (!PropertyEditor.class.isAssignableFrom(editorClass)) {
        if (logger.isWarnEnabled()) {
            logger.warn("Editor class [" + editorName +
                    "] does not implement [java.beans.PropertyEditor] interface");
        }
        unknownEditorTypes.put(targetType, Boolean.TRUE);
        return null;
    }
    return (PropertyEditor) instantiateClass(editorClass);
}

例如对org.springframework.data.redis.core.ListOperations则有org.springframework.data.redis.core.ListOperationsEditor

class ListOperationsEditor extends PropertyEditorSupport {

    public void setValue(Object value) {
        if (value instanceof RedisOperations) {
            super.setValue(((RedisOperations) value).opsForList());
        } else {
            throw new java.lang.IllegalArgumentException("Editor supports only conversion of type " + RedisOperations.class);
        }
    }
}