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ObjectGraphTraverser.java
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ObjectGraphTraverser.java
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/**
* Copyright (C) 2020 Czech Technical University in Prague
*
* 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.
*
* 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.jsonld.serialization.traversal;
import cz.cvut.kbss.jsonld.common.BeanAnnotationProcessor;
import cz.cvut.kbss.jsonld.common.BeanClassProcessor;
import cz.cvut.kbss.jsonld.common.IdentifierUtil;
import cz.cvut.kbss.jsonld.exception.JsonLdSerializationException;
import cz.cvut.kbss.jsonld.exception.MissingIdentifierException;
import java.lang.reflect.Field;
import java.util.*;
public class ObjectGraphTraverser implements InstanceVisitor {
private final Set<InstanceVisitor> visitors = new HashSet<>(4);
private final InstanceTypeResolver typeResolver = new InstanceTypeResolver();
private boolean requireId = false;
private Map<Object, String> knownInstances;
public void addVisitor(InstanceVisitor visitor) {
Objects.requireNonNull(visitor);
visitors.add(visitor);
}
public void removeVisitor(InstanceVisitor visitor) {
visitors.remove(visitor);
}
private void resetKnownInstances() {
this.knownInstances = new IdentityHashMap<>();
}
public void traverse(Object instance) {
Objects.requireNonNull(instance);
resetKnownInstances();
try {
if (instance instanceof Collection) {
traverseCollection((Collection<?>) instance);
} else {
traverseImpl(instance);
}
} catch (IllegalAccessException e) {
throw new JsonLdSerializationException("Unable to extract field value.", e);
}
}
private void traverseCollection(Collection<?> col) throws IllegalAccessException {
openCollection(col);
for (Object item : col) {
traverseImpl(item);
}
closeCollection(col);
}
private void traverseImpl(Object instance) throws IllegalAccessException {
if (instance == null) {
return;
}
if (knownInstances.containsKey(instance)) {
visitKnownInstance(knownInstances.get(instance), instance);
return;
}
openInstance(instance);
visitIdentifier(null, instance);
if (!BeanClassProcessor.isIdentifierType(instance.getClass())) {
visitTypes(null, instance);
serializeFields(instance);
}
closeInstance(instance);
}
private void serializeFields(Object instance) throws IllegalAccessException {
final List<Field> fieldsToSerialize =
orderAttributesForSerialization(BeanAnnotationProcessor.getSerializableFields(instance),
BeanAnnotationProcessor.getAttributeOrder(instance.getClass()));
for (Field f : fieldsToSerialize) {
if (BeanAnnotationProcessor.isInstanceIdentifier(f)) {
continue;
}
Object value = BeanClassProcessor.getFieldValue(f, instance);
visitField(f, value);
if (value != null && BeanAnnotationProcessor.isObjectProperty(f)) {
traverseObjectPropertyValue(value);
}
}
}
private List<Field> orderAttributesForSerialization(List<Field> fields, String[] ordering) {
final List<Field> result = new ArrayList<>(fields.size());
for (String item : ordering) {
final Iterator<Field> it = fields.iterator();
while (it.hasNext()) {
final Field f = it.next();
if (f.getName().equals(item)) {
it.remove();
result.add(f);
break;
}
}
}
result.addAll(fields);
return result;
}
private void traverseObjectPropertyValue(Object value) throws IllegalAccessException {
if (value instanceof Collection) {
final Collection<?> col = (Collection<?>) value;
openCollection(col);
for (Object elem : col) {
traverseImpl(elem);
}
closeCollection(col);
} else if (value.getClass().isArray()) {
throw new JsonLdSerializationException("Arrays are not supported, yet.");
} else {
traverseImpl(value);
}
}
@Override
public void openInstance(Object instance) {
if (!BeanClassProcessor.isIdentifierType(instance.getClass())) {
final Optional<Object> identifier = BeanAnnotationProcessor.getInstanceIdentifier(instance);
knownInstances.put(instance, identifier.orElse(IdentifierUtil.generateBlankNodeId()).toString());
}
visitors.forEach(v -> v.openInstance(instance));
}
@Override
public void closeInstance(Object instance) {
visitors.forEach(v -> v.closeInstance(instance));
}
@Override
public void visitKnownInstance(String id, Object instance) {
visitors.forEach(v -> v.visitKnownInstance(id, instance));
}
@Override
public void visitIdentifier(String identifier, Object instance) {
final String id;
if (BeanClassProcessor.isIdentifierType(instance.getClass())) {
id = instance.toString();
} else {
final Optional<Object> extractedId = BeanAnnotationProcessor.getInstanceIdentifier(instance);
if (!extractedId.isPresent() && requireId) {
throw MissingIdentifierException.create(instance);
}
id = extractedId.orElse(IdentifierUtil.generateBlankNodeId()).toString();
knownInstances.put(instance, id);
}
visitors.forEach(v -> v.visitIdentifier(id, instance));
}
@Override
public void visitTypes(Collection<String> types, Object instance) {
final Set<String> resolvedTypes = typeResolver.resolveTypes(instance);
assert !resolvedTypes.isEmpty();
visitors.forEach(v -> v.visitTypes(resolvedTypes, instance));
}
@Override
public void visitField(Field field, Object value) {
visitors.forEach(v -> v.visitField(field, value));
}
@Override
public void openCollection(Collection<?> collection) {
visitors.forEach(v -> v.openCollection(collection));
}
@Override
public void closeCollection(Collection<?> collection) {
visitors.forEach(v -> v.closeCollection(collection));
}
public void setRequireId(boolean requireId) {
this.requireId = requireId;
}
}