org.bbottema.javareflection.valueconverter.ValueConversionHelper Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of java-reflection Show documentation
Show all versions of java-reflection Show documentation
Java Reflection provides a small package with nifty reflection features that will help with finding constructors, methods and value conversions
package org.bbottema.javareflection.valueconverter;
import lombok.experimental.UtilityClass;
import org.bbottema.javareflection.TypeUtils;
import org.bbottema.javareflection.util.graph.GraphHelper;
import org.bbottema.javareflection.util.graph.Node;
import org.bbottema.javareflection.valueconverter.converters.BooleanConverters;
import org.bbottema.javareflection.valueconverter.converters.CharacterConverters;
import org.bbottema.javareflection.valueconverter.converters.NumberConverters;
import org.bbottema.javareflection.valueconverter.converters.StringConverters;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import static java.util.Arrays.asList;
/**
* This reflection utility class predicts (and converts) which types a specified value can be converted into. It can only do conversions of
* known 'common' types, which include:
*
* - Any {@link Number} type (Integer, Character, Double, byte, etc.)
* StringBooleanCharacter
* In addition enums can be converted as well.
*
* @see IncompatibleTypeException
*/
@UtilityClass
public final class ValueConversionHelper {
/**
* A list of all primitive number types.
*/
private static final List> PRIMITIVE_NUMBER_TYPES = asList(new Class[] { byte.class, short.class, int.class, long.class,
float.class, double.class });
/**
* Contains all user-provided converters. User converters also act as intermediate converters, ie. if a user converter can go to int,
* double is automatically supported as well as common conversion.
*/
private static final Map, Map, ValueFunction>> valueConverters = new HashMap<>();
/**
* Graph of from-to type conversions so we can calculate shortes conversion path between two types.
*/
private static final Map, Node>> converterGraph = new HashMap<>();
private static final int LOW_CONVERTER_PRIORITY = 10; // higher edge weight, heavier in cost
private static final int HIGH_CONVERTER_PRIORITY = 1; // lower edge weight, lighter in cost
static {
resetDefaultConverters();
}
public static void resetDefaultConverters() {
valueConverters.clear();
final Collection> defaultConverters = new HashSet<>();
defaultConverters.addAll(NumberConverters.NUMBER_CONVERTERS);
defaultConverters.addAll(BooleanConverters.BOOLEAN_CONVERTERS);
defaultConverters.addAll(CharacterConverters.CHARACTER_CONVERTERS);
defaultConverters.addAll(StringConverters.STRING_CONVERTERS);
for (ValueFunction numberConverter : defaultConverters) {
registerValueConverter(numberConverter);
}
}
/**
* Registers a user-provided converter. User converters also act as intermediate converters, ie. if a user converter can go to int,
* double is automatically supported as well as common conversion.
*/
@SuppressWarnings({"unchecked", "unused", "WeakerAccess"})
public static void registerValueConverter(final ValueFunction userConverter) {
if (!valueConverters.containsKey(userConverter.getFromType())) {
valueConverters.put(userConverter.getFromType(), new HashMap, ValueFunction>());
}
valueConverters.get(userConverter.getFromType()).put(userConverter.getTargetType(), (ValueFunction) userConverter);
updateTypeGraph();
TypeUtils.clearCaches();
}
private static void updateTypeGraph() {
converterGraph.clear();
// add nodes and edges
for (Map.Entry, Map, ValueFunction>> convertersForFromType : valueConverters.entrySet()) {
Class fromType = convertersForFromType.getKey();
Node> fromNode = converterGraph.containsKey(fromType) ? converterGraph.get(fromType) : new Node>(fromType);
converterGraph.put(fromType, fromNode);
for (Class toType : convertersForFromType.getValue().keySet()) {
Node> toNode = converterGraph.containsKey(toType) ? converterGraph.get(toType) : new Node>(toType);
converterGraph.put(toType, toNode);
ValueFunction converter = convertersForFromType.getValue().get(toType);
fromNode.getToNodes().put(toNode, determineConversionCost(converter)); // edge
}
}
}
private static Integer determineConversionCost(ValueFunction converter) {
if (converter.getFromType() == converter.getTargetType()) {
return 0;
} else {
String converterPackage = ValueConversionHelper.class.getPackage().toString();
boolean isSystemConverter = converter.getClass().getPackage().toString().contains(converterPackage);
return isSystemConverter ? LOW_CONVERTER_PRIORITY : HIGH_CONVERTER_PRIORITY;
}
}
@SuppressWarnings("WeakerAccess")
public static boolean isCommonType(final Class c) {
Map, ValueFunction> classValueFunctionMap = valueConverters.get(c);
return valueConverters.containsKey(c) &&
(classValueFunctionMap.keySet().size() > 1 ||
!classValueFunctionMap.keySet().contains(String.class));
}
/**
* Determines to which types the specified value (its type) can be converted to. Most common types can be converted to most other common
* types and all types can be converted into a String using {@link Object#toString()}.
*
* @param fromType The input type to find compatible conversion output types for
* @return The list with compatible conversion output types.
*/
@SuppressWarnings("WeakerAccess")
@NotNull
public static Set> collectRegisteredCompatibleTargetTypes(final Class fromType) {
Set> compatibleTypes = new HashSet<>(Collections.>singleton(fromType));
if (converterGraph.containsKey(fromType)) {
for (Node> reachableNode : GraphHelper.findReachableNodes(converterGraph.get(fromType))) {
compatibleTypes.add(reachableNode.getType());
}
}
return compatibleTypes;
}
/**
* @return Whether targetType can be derived from fromType.
*/
@SuppressWarnings("unused")
public static boolean typesCompatible(final Class fromType, final Class targetType) {
if (targetType.isAssignableFrom(fromType)) {
return true;
} else {
for (Class registeredCompatibleTargetType : collectCompatibleTargetTypes(fromType)) {
if (targetType.isAssignableFrom(registeredCompatibleTargetType)) {
return true;
}
}
}
return false;
}
public static Set> collectCompatibleTargetTypes(Class fromType) {
checkForAndRegisterToStringConverter(fromType);
Set> compatibleTargetTypes = new HashSet<>();
Node> fromNode = converterGraph.get(fromType);
for (Map, ValueFunction> convertersForFromTypes : valueConverters.values()) {
for (Class targetType : convertersForFromTypes.keySet()) {
if (isCompatibleTargetType(fromNode, targetType)) {
compatibleTargetTypes.add(targetType);
}
}
}
return compatibleTargetTypes;
}
private static boolean isCompatibleTargetType(Node> fromNode, Class targetType) {
for (Node> toNode : collectTypeCompatibleNodes(targetType)) {
if (GraphHelper.isPathPossible(fromNode, toNode)) {
return true;
}
}
return false;
}
/**
* Converts a list of values to their converted form, as indicated by the specified targetTypes.
*
* @param args The list with value to convert.
* @param targetTypes The output types the specified values should be converted into.
* @param useOriginalValueWhenIncompatible Indicates whether an exception should be thrown for inconvertible values or that the original
* value should be used instead. Basically change mode to "convert what you can".
* @return Array containing converted values where convertible or the original value otherwise.
* @throws IncompatibleTypeException Thrown when unable to convert and not use the original value.
*/
@NotNull
public static Object[] convert(final Object[] args, final Class[] targetTypes, boolean useOriginalValueWhenIncompatible)
throws IncompatibleTypeException {
if (args.length != targetTypes.length) {
throw new IllegalStateException("number of target types should match the number of arguments");
}
final Object[] convertedValues = new Object[args.length];
for (int i = 0; i < targetTypes.length; i++) {
try {
convertedValues[i] = convert(args[i], targetTypes[i]);
} catch (IncompatibleTypeException e) {
if (useOriginalValueWhenIncompatible) {
// simply take over the original value and keep converting where possible
convertedValues[i] = args[i];
} else {
throw e;
}
}
}
return convertedValues;
}
/**
* Converts a single value into a target output datatype. Only input/output pairs should be passed in here according to the possible
* conversions as determined by {@link #collectRegisteredCompatibleTargetTypes(Class)}.
*
* First checks if the input and output types aren't the same. Then the conversions are checked for and done in the following order:
*
* - conversion to
String (value.toString())
*
*
* @param fromValue The value to convert.
* @param targetType The target data type the value should be converted into.
* @return The converted value according the specified target data type.
* @throws IncompatibleTypeException Thrown by the various convert() methods used.
*/
@SuppressWarnings("unchecked")
@Nullable
public static T convert(@Nullable final Object fromValue, final Class targetType)
throws IncompatibleTypeException {
if (fromValue == null) {
return null;
} else if (targetType.isAssignableFrom(fromValue.getClass())) {
return (T) fromValue;
} else {
checkForAndRegisterEnumConverter(targetType);
checkForAndRegisterToStringConverter(fromValue.getClass());
return convertWithConversionGraph(fromValue, targetType);
}
}
@NotNull
private static T convertWithConversionGraph(@NotNull Object fromValue, @NotNull Class targetType) {
final Node> fromNode = converterGraph.get(fromValue.getClass());
if (fromNode != null) {
for (Node> toNode : collectTypeCompatibleNodes(targetType)) {
for (List>> conversionPathAscending : GraphHelper.findAllPathsAscending(fromNode, toNode)) {
try {
Object evolvingValueToConvert = fromValue;
for (Node> nodeInConversionPath : conversionPathAscending) {
Class currentFromType = evolvingValueToConvert.getClass();
Class currentToType = nodeInConversionPath.getType();
evolvingValueToConvert = valueConverters.get(currentFromType).get(currentToType).convertValue(evolvingValueToConvert);
}
//noinspection unchecked
return (T) evolvingValueToConvert;
} catch (IncompatibleTypeException e) {
// keep trying conversion paths...
}
}
}
}
// conversion paths exhausted.
throw new IncompatibleTypeException(fromValue, fromValue.getClass(), targetType);
}
@SuppressWarnings("unchecked")
private static > void checkForAndRegisterEnumConverter(Class targetType) {
if (Enum.class.isAssignableFrom(targetType)) {
if (!valueConverters.get(String.class).containsKey(targetType)) {
registerValueConverter(StringConverters.produceStringToEnumConverter((Class) targetType));
}
}
}
private static void checkForAndRegisterToStringConverter(Class fromType) {
if (!valueConverters.containsKey(fromType) || !valueConverters.get(fromType).containsKey(String.class)) {
registerValueConverter(StringConverters.produceTypeToStringConverter(fromType));
}
}
static Set>> collectTypeCompatibleNodes(Class targetType) {
final Set>> typeCompatibleNodes = new HashSet<>();
for (Map.Entry, Node>> converterNodeEntry : converterGraph.entrySet()) {
if (targetType.isAssignableFrom(converterNodeEntry.getKey())) {
typeCompatibleNodes.add(converterNodeEntry.getValue());
}
}
return typeCompatibleNodes;
}
/**
* Returns whether a {@link Class} is a primitive number.
*
* @param targetType The class to check whether it's a number.
* @return Whether specified class is a primitive number.
*/
@SuppressWarnings("WeakerAccess")
public static boolean isPrimitiveNumber(final Class targetType) {
return PRIMITIVE_NUMBER_TYPES.contains(targetType);
}
}