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ConverterResolver.java
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ConverterResolver.java
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/**
* Copyright (C) 2022 Czech Technical University in Prague
* <p>
* This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public
* License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later
* version.
* <p>
* This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
* warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
* details. You should have received a copy of the GNU General Public License along with this program. If not, see
* <http://www.gnu.org/licenses/>.
*/
package cz.cvut.kbss.jopa.model.metamodel;
import cz.cvut.kbss.jopa.exception.InvalidConverterException;
import cz.cvut.kbss.jopa.exception.InvalidFieldMappingException;
import cz.cvut.kbss.jopa.model.AttributeConverter;
import cz.cvut.kbss.jopa.model.annotations.Convert;
import cz.cvut.kbss.jopa.oom.converter.*;
import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.util.Arrays;
import java.util.Optional;
/**
* Determines potential converters which may be used on a field.
* <p>
* Currently, only built-in converters for data and annotation property attributes are supported, but in the future,
* custom converters should be also supported.
*/
class ConverterResolver {
private final Converters converters;
ConverterResolver(Converters converters) {
this.converters = converters;
}
/**
* Determines converter which should be used for transformation of values to and from the specified field.
* <p>
* Besides custom converters, the system supports a number of built-in converters, which ensure that e.g. widening
* conversion or mapping to Java 8 Date/Time API is supported.
*
* @param field The field for which converter should be determined
* @param config Mapping configuration extracted during metamodel building
* @return Possible converter instance to be used for transformation of values of the specified field. Returns empty
* {@code Optional} if no suitable converter is found (or needed)
*/
public Optional<ConverterWrapper<?, ?>> resolveConverter(Field field, PropertyAttributes config) {
if (config.getPersistentAttributeType() == Attribute.PersistentAttributeType.OBJECT) {
return Optional.empty();
}
final Class<?> attValueType = config.getType().getJavaType();
if (attValueType.isEnum()) {
return Optional.of(new EnumConverter(attValueType));
}
final Optional<ConverterWrapper<?, ?>> customConverter = resolveCustomConverter(field);
if (customConverter.isPresent()) {
return customConverter;
}
if (config.hasDatatype()) {
verifyTypeIsString(field, attValueType);
return Optional.of(new ToRdfLiteralConverter(config.getDatatype()));
}
if (config.isLexicalForm()) {
return Optional.of(new ToLexicalFormConverter());
}
return converters.getConverter(attValueType);
}
private static void verifyTypeIsString(Field field, Class<?> attValueType) {
if (!attValueType.equals(String.class)) {
throw new InvalidFieldMappingException(
"Attributes with explicit datatype identifier must have values of type String. " +
"The provided attribute " + field + " has type " + attValueType);
}
}
private static Optional<ConverterWrapper<?, ?>> resolveCustomConverter(Field field) {
final Convert convertAnn = field.getAnnotation(Convert.class);
if (convertAnn == null || convertAnn.disableConversion()) {
return Optional.empty();
}
final Class converterType = convertAnn.converter();
try {
return Optional.of(new CustomConverterWrapper((AttributeConverter<?, ?>) converterType.newInstance(),
resolveConverterAxiomType(
(Class<? extends AttributeConverter<?, ?>>) converterType)));
} catch (InstantiationException | IllegalAccessException e) {
throw new InvalidConverterException(
"Converter type " + converterType + " must have a public no-arg constructor to be used.", e);
}
}
private static Class<?> resolveConverterAxiomType(Class<?> converterType) {
final ParameterizedType typeSpec = (ParameterizedType) Arrays.stream(converterType.getGenericInterfaces())
.filter(t -> t instanceof ParameterizedType && ((ParameterizedType) t).getRawType()
.equals(AttributeConverter.class))
.findAny().orElseThrow(
() -> new InvalidConverterException(
"Type specified in @Convert annotation does not implement " + AttributeConverter.class.getSimpleName()));
return (Class<?>) typeSpec.getActualTypeArguments()[1];
}
/**
* Alternative method for resolving converter. Can be used when the persistent attribute type is not relevant and/or
* the class {@link PropertyAttributes} is not used for attribute configuration, e.g. for attributes defined by a
* query.
* <p>
* Determines converter which should be used for transformation of values to and from the specified type of field.
* <p>
* Beside custom converters, the system supports a number of built-in converters, which ensure that e.g. widening
* conversion or mapping to Java 8 Date/Time API is supported.
*
* @param type attribute type as defined in {@link cz.cvut.kbss.jopa.model.metamodel.Type} (not to be confused with
* {@link java.lang.reflect.Type})
* @return Possible converter instance to be used for transformation of values of the specified field. Returns empty
* {@code Optional} if no suitable converter is found (or needed)
* @see cz.cvut.kbss.jopa.model.metamodel.QueryAttribute
*/
public Optional<ConverterWrapper<?, ?>> resolveConverter(Type<?> type) {
final Class<?> attValueType = type.getJavaType();
if (attValueType.isEnum()) {
return Optional.of(new EnumConverter(attValueType));
}
return converters.getConverter(attValueType);
}
}