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JSON Patch implementation in Java
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/*
* Copyright (c) 2014, Francis Galiegue ([email protected])
*
* This software is dual-licensed under:
*
* - the Lesser General Public License (LGPL) version 3.0 or, at your option, any
* later version;
* - the Apache Software License (ASL) version 2.0.
*
* The text of this file and of both licenses is available at the root of this
* project or, if you have the jar distribution, in directory META-INF/, under
* the names LGPL-3.0.txt and ASL-2.0.txt respectively.
*
* Direct link to the sources:
*
* - LGPL 3.0: https://www.gnu.org/licenses/lgpl-3.0.txt
* - ASL 2.0: http://www.apache.org/licenses/LICENSE-2.0.txt
*/
package com.github.fge.jsonpatch.diff;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.databind.node.ObjectNode;
import com.github.fge.jackson.JacksonUtils;
import com.github.fge.jackson.JsonNumEquals;
import com.github.fge.jackson.NodeType;
import com.github.fge.jackson.jsonpointer.JsonPointer;
import com.github.fge.jsonpatch.JsonPatch;
import com.github.fge.jsonpatch.JsonPatchMessages;
import com.github.fge.msgsimple.bundle.MessageBundle;
import com.github.fge.msgsimple.load.MessageBundles;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Equivalence;
import com.google.common.collect.Maps;
import com.google.common.collect.Sets;
import javax.annotation.ParametersAreNonnullByDefault;
import java.io.IOException;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
/**
* JSON "diff" implementation
*
* This class generates a JSON Patch (as in, an RFC 6902 JSON Patch) given
* two JSON values as inputs. The patch can be obtained directly as a {@link
* JsonPatch} or as a {@link JsonNode}.
*
* Note: there is no guarantee about the usability of the generated
* patch for any other source/target combination than the one used to generate
* the patch.
*
* This class always performs operations in the following order: removals,
* additions and replacements. It then factors removal/addition pairs into
* move operations, or copy operations if a common element exists, at the same
* {@link JsonPointer pointer}, in both the source and destination.
*
* You can obtain a diff either as a {@link JsonPatch} directly or, for
* backwards compatibility, as a {@link JsonNode}.
*
* @since 1.2
*/
@ParametersAreNonnullByDefault
public final class JsonDiff
{
private static final MessageBundle BUNDLE
= MessageBundles.getBundle(JsonPatchMessages.class);
private static final ObjectMapper MAPPER = JacksonUtils.newMapper();
private static final Equivalence EQUIVALENCE
= JsonNumEquals.getInstance();
private JsonDiff()
{
}
/**
* Generate a JSON patch for transforming the source node into the target
* node
*
* @param source the node to be patched
* @param target the expected result after applying the patch
* @return the patch as a {@link JsonPatch}
*
* @since 1.9
*/
public static JsonPatch asJsonPatch(final JsonNode source,
final JsonNode target)
{
BUNDLE.checkNotNull(source, "common.nullArgument");
BUNDLE.checkNotNull(target, "common.nullArgument");
final Map unchanged
= getUnchangedValues(source, target);
final DiffProcessor processor = new DiffProcessor(unchanged);
generateDiffs(processor, JsonPointer.empty(), source, target);
return processor.getPatch();
}
/**
* Generate a JSON patch for transforming the source node into the target
* node
*
* @param source the node to be patched
* @param target the expected result after applying the patch
* @return the patch as a {@link JsonNode}
*/
public static JsonNode asJson(final JsonNode source, final JsonNode target)
{
final String s;
try {
s = MAPPER.writeValueAsString(asJsonPatch(source, target));
return MAPPER.readTree(s);
} catch (IOException e) {
throw new RuntimeException("cannot generate JSON diff", e);
}
}
private static void generateDiffs(final DiffProcessor processor,
final JsonPointer pointer, final JsonNode source, final JsonNode target)
{
if (EQUIVALENCE.equivalent(source, target))
return;
final NodeType firstType = NodeType.getNodeType(source);
final NodeType secondType = NodeType.getNodeType(target);
/*
* Node types differ: generate a replacement operation.
*/
if (firstType != secondType) {
processor.valueReplaced(pointer, source, target);
return;
}
/*
* If we reach this point, it means that both nodes are the same type,
* but are not equivalent.
*
* If this is not a container, generate a replace operation.
*/
if (!source.isContainerNode()) {
processor.valueReplaced(pointer, source, target);
return;
}
/*
* If we reach this point, both nodes are either objects or arrays;
* delegate.
*/
if (firstType == NodeType.OBJECT)
generateObjectDiffs(processor, pointer, (ObjectNode) source,
(ObjectNode) target);
else // array
generateArrayDiffs(processor, pointer, (ArrayNode) source,
(ArrayNode) target);
}
private static void generateObjectDiffs(final DiffProcessor processor,
final JsonPointer pointer, final ObjectNode source,
final ObjectNode target)
{
final Set firstFields
= Sets.newTreeSet(Sets.newHashSet(source.fieldNames()));
final Set secondFields
= Sets.newTreeSet(Sets.newHashSet(target.fieldNames()));
for (final String field: Sets.difference(firstFields, secondFields))
processor.valueRemoved(pointer.append(field), source.get(field));
for (final String field: Sets.difference(secondFields, firstFields))
processor.valueAdded(pointer.append(field), target.get(field));
for (final String field: Sets.intersection(firstFields, secondFields))
generateDiffs(processor, pointer.append(field), source.get(field),
target.get(field));
}
private static void generateArrayDiffs(final DiffProcessor processor,
final JsonPointer pointer, final ArrayNode source,
final ArrayNode target)
{
final int firstSize = source.size();
final int secondSize = target.size();
final int size = Math.min(firstSize, secondSize);
/*
* Source array is larger; in this case, elements are removed from the
* target; the index of removal is always the original arrays's length.
*/
for (int index = size; index < firstSize; index++)
processor.valueRemoved(pointer.append(size), source.get(index));
for (int index = 0; index < size; index++)
generateDiffs(processor, pointer.append(index), source.get(index),
target.get(index));
// Deal with the destination array being larger...
for (int index = size; index < secondSize; index++)
processor.valueAdded(pointer.append("-"), target.get(index));
}
@VisibleForTesting
static Map getUnchangedValues(final JsonNode source,
final JsonNode target)
{
final Map ret = Maps.newHashMap();
computeUnchanged(ret, JsonPointer.empty(), source, target);
return ret;
}
private static void computeUnchanged(final Map ret,
final JsonPointer pointer, final JsonNode first, final JsonNode second)
{
if (EQUIVALENCE.equivalent(first, second)) {
ret.put(pointer, second);
return;
}
final NodeType firstType = NodeType.getNodeType(first);
final NodeType secondType = NodeType.getNodeType(second);
if (firstType != secondType)
return; // nothing in common
// We know they are both the same type, so...
switch (firstType) {
case OBJECT:
computeObject(ret, pointer, first, second);
break;
case ARRAY:
computeArray(ret, pointer, first, second);
default:
/* nothing */
}
}
private static void computeObject(final Map ret,
final JsonPointer pointer, final JsonNode source,
final JsonNode target)
{
final Iterator firstFields = source.fieldNames();
String name;
while (firstFields.hasNext()) {
name = firstFields.next();
if (!target.has(name))
continue;
computeUnchanged(ret, pointer.append(name), source.get(name),
target.get(name));
}
}
private static void computeArray(final Map ret,
final JsonPointer pointer, final JsonNode source, final JsonNode target)
{
final int size = Math.min(source.size(), target.size());
for (int i = 0; i < size; i++)
computeUnchanged(ret, pointer.append(i), source.get(i),
target.get(i));
}
}