Spring源码-finishBeanFactoryInitialization方法

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// Initialize conversion service for this context.
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));
}

// Register a default embedded value resolver if no BeanFactoryPostProcessor
// (such as a PropertySourcesPlaceholderConfigurer bean) registered any before:
// at this point, primarily for resolution in annotation attribute values.
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}

// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}

// Stop using the temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(null);

// Allow for caching all bean definition metadata, not expecting further changes.
beanFactory.freezeConfiguration();

// Instantiate all remaining (non-lazy-init) singletons.
beanFactory.preInstantiateSingletons();
}

finishBeanFactoryInitialization方法设置ConversionService类型转换服务，还设置了EmbeddedValueResolver值处理器，用于解析value中存在的${}。初始化LoadTimeWeaverAware。冻结BeanDifinition信息。初始化非lazy的bean。

ConversionService接口的默认实现是DefaultConversionService，ConversionService里面主要保存了很多converter，由converter进行类型转换。

public static void addDefaultConverters(ConverterRegistry converterRegistry) {
addScalarConverters(converterRegistry);
addCollectionConverters(converterRegistry);

converterRegistry.addConverter(new ByteBufferConverter((ConversionService) converterRegistry));
converterRegistry.addConverter(new StringToTimeZoneConverter());
converterRegistry.addConverter(new ZoneIdToTimeZoneConverter());
converterRegistry.addConverter(new ZonedDateTimeToCalendarConverter());

converterRegistry.addConverter(new ObjectToObjectConverter());
converterRegistry.addConverter(new IdToEntityConverter((ConversionService) converterRegistry));
converterRegistry.addConverter(new FallbackObjectToStringConverter());
converterRegistry.addConverter(new ObjectToOptionalConverter((ConversionService) converterRegistry));
}

public static void addCollectionConverters(ConverterRegistry converterRegistry) {
ConversionService conversionService = (ConversionService) converterRegistry;

converterRegistry.addConverter(new ArrayToCollectionConverter(conversionService));
converterRegistry.addConverter(new CollectionToArrayConverter(conversionService));

converterRegistry.addConverter(new ArrayToArrayConverter(conversionService));
converterRegistry.addConverter(new CollectionToCollectionConverter(conversionService));
converterRegistry.addConverter(new MapToMapConverter(conversionService));

converterRegistry.addConverter(new ArrayToStringConverter(conversionService));
converterRegistry.addConverter(new StringToArrayConverter(conversionService));

converterRegistry.addConverter(new ArrayToObjectConverter(conversionService));
converterRegistry.addConverter(new ObjectToArrayConverter(conversionService));

converterRegistry.addConverter(new CollectionToStringConverter(conversionService));
converterRegistry.addConverter(new StringToCollectionConverter(conversionService));

converterRegistry.addConverter(new CollectionToObjectConverter(conversionService));
converterRegistry.addConverter(new ObjectToCollectionConverter(conversionService));

converterRegistry.addConverter(new StreamConverter(conversionService));
}

private static void addScalarConverters(ConverterRegistry converterRegistry) {
converterRegistry.addConverterFactory(new NumberToNumberConverterFactory());

converterRegistry.addConverterFactory(new StringToNumberConverterFactory());
converterRegistry.addConverter(Number.class, String.class, new ObjectToStringConverter());

converterRegistry.addConverter(new StringToCharacterConverter());
converterRegistry.addConverter(Character.class, String.class, new ObjectToStringConverter());

converterRegistry.addConverter(new NumberToCharacterConverter());
converterRegistry.addConverterFactory(new CharacterToNumberFactory());

converterRegistry.addConverter(new StringToBooleanConverter());
converterRegistry.addConverter(Boolean.class, String.class, new ObjectToStringConverter());

converterRegistry.addConverterFactory(new StringToEnumConverterFactory());
converterRegistry.addConverter(new EnumToStringConverter((ConversionService) converterRegistry));

converterRegistry.addConverterFactory(new IntegerToEnumConverterFactory());
converterRegistry.addConverter(new EnumToIntegerConverter((ConversionService) converterRegistry));

converterRegistry.addConverter(new StringToLocaleConverter());
converterRegistry.addConverter(Locale.class, String.class, new ObjectToStringConverter());

converterRegistry.addConverter(new StringToCharsetConverter());
converterRegistry.addConverter(Charset.class, String.class, new ObjectToStringConverter());

converterRegistry.addConverter(new StringToCurrencyConverter());
converterRegistry.addConverter(Currency.class, String.class, new ObjectToStringConverter());

converterRegistry.addConverter(new StringToPropertiesConverter());
converterRegistry.addConverter(new PropertiesToStringConverter());

converterRegistry.addConverter(new StringToUUIDConverter());
converterRegistry.addConverter(UUID.class, String.class, new ObjectToStringConverter());
}

converter有三类实现，分别是Converter<S, T>，GenericConverter，ConverterFactory<S, R>。

@FunctionalInterface
public interface Converter<S, T> {

/**
* Convert the source object of type {@code S} to target type {@code T}.
* @param source the source object to convert, which must be an instance of {@code S} (never {@code null})
* @return the converted object, which must be an instance of {@code T} (potentially {@code null})
* @throws IllegalArgumentException if the source cannot be converted to the desired target type
*/
@Nullable
T convert(S source);

/**
* Construct a composed {@link Converter} that first applies this {@link Converter}
* to its input, and then applies the {@code after} {@link Converter} to the
* result.
* @param after the {@link Converter} to apply after this {@link Converter}
* is applied
* @param the type of output of both the {@code after} {@link Converter}
* and the composed {@link Converter}
* @return a composed {@link Converter} that first applies this {@link Converter}
* and then applies the {@code after} {@link Converter}
* @since 5.3
*/
default Converter<S, U> andThen(Converter<? super T, ? extends U> after) {
Assert.notNull(after, "After Converter must not be null");
return (S s) -> {
T initialResult = convert(s);
return (initialResult != null ? after.convert(initialResult) : null);
};
}

}

Converter<S, T>由类型S转换成类型T。提供了一对一的转换服务。比如

class StringToTimeZoneConverter implements Converter<String, TimeZone> {

@Override
public TimeZone convert(String source) {
return StringUtils.parseTimeZoneString(source);
}

}

GenericConverter提供了两种或多种类型之间的转换。

public interface GenericConverter {

/**
* Return the source and target types that this converter can convert between.
*

Each entry is a convertible source-to-target type pair.
*

For {@link ConditionalConverter conditional converters} this method may return
* {@code null} to indicate all source-to-target pairs should be considered.
*/
@Nullable
Set getConvertibleTypes();

/**
* Convert the source object to the targetType described by the {@code TypeDescriptor}.
* @param source the source object to convert (may be {@code null})
* @param sourceType the type descriptor of the field we are converting from
* @param targetType the type descriptor of the field we are converting to
* @return the converted object
*/
@Nullable
Object convert(@Nullable Object source, TypeDescriptor sourceType, TypeDescriptor targetType);

/**
* Holder for a source-to-target class pair.
*/
final class ConvertiblePair {

private final Class<?> sourceType;

private final Class<?> targetType;

/**
* Create a new source-to-target pair.
* @param sourceType the source type
* @param targetType the target type
*/
public ConvertiblePair(Class sourceType, Class targetType) {
Assert.notNull(sourceType, "Source type must not be null");
Assert.notNull(targetType, "Target type must not be null");
this.sourceType = sourceType;
this.targetType = targetType;
}

public Class<?> getSourceType() {
return this.sourceType;
}

public Class<?> getTargetType() {
return this.targetType;
}

@Override
public boolean equals(@Nullable Object other) {
if (this == other) {
return true;
}
if (other == null || other.getClass() != ConvertiblePair.class) {
return false;
}
ConvertiblePair otherPair = (ConvertiblePair) other;
return (this.sourceType == otherPair.sourceType && this.targetType == otherPair.targetType);
}

@Override
public int hashCode() {
return (this.sourceType.hashCode() * 31 + this.targetType.hashCode());
}

@Override
public String toString() {
return (this.sourceType.getName() + " -> " + this.targetType.getName());
}
}

}

比如：

final class ArrayToCollectionConverter implements ConditionalGenericConverter {

private final ConversionService conversionService;

public ArrayToCollectionConverter(ConversionService conversionService) {
this.conversionService = conversionService;
}

@Override
public Set getConvertibleTypes() {
return Collections.singleton(new ConvertiblePair(Object[].class, Collection.class));
}

@Override
public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
return ConversionUtils.canConvertElements(
sourceType.getElementTypeDescriptor(), targetType.getElementTypeDescriptor(), this.conversionService);
}

@Override
@Nullable
public Object convert(@Nullable Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
if (source == null) {
return null;
}

int length = Array.getLength(source);
TypeDescriptor elementDesc = targetType.getElementTypeDescriptor();
Collection