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fix(java): preserve LinkedHashMap access-order during serialization #4188

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fix(java): preserve LinkedHashMap access-order during serialization #4188

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8d48679
Fix LinkedHashMap access-order serialization
EthCas Oct 16, 2026
27ae67b
style(java): format LinkedHashMap access-order changes
EthCas Oct 16, 2026
bc94e23
test(java): strengthen LinkedHashMap access-order regression
EthCas Oct 16, 2026
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23 changes: 21 additions & 2 deletions java/fory-core/src/main/java/org/apache/fory/serializer/collection/MapSerializers.java
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Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,7 @@
import org.apache.fory.context.WriteContext;
import org.apache.fory.memory.MemoryBuffer;
import org.apache.fory.meta.TypeDef;
import org.apache.fory.reflect.FieldAccessor;
import org.apache.fory.reflect.ReflectionUtils;
import org.apache.fory.resolver.ClassResolver;
import org.apache.fory.resolver.TypeInfo;
Expand Down Expand Up @@ -107,23 +108,41 @@ public Map newMap(Map map) {
}

public static final class LinkedHashMapSerializer extends MapSerializer<LinkedHashMap> {
private static final class AccessOrderAccessor {
private static final FieldAccessor INSTANCE =
FieldAccessor.createAccessor(
ReflectionUtils.getDeclaredField(LinkedHashMap.class, "accessOrder"));
}

public LinkedHashMapSerializer(TypeResolver typeResolver) {
super(typeResolver, LinkedHashMap.class, true);
}

@Override
public Map onMapWrite(WriteContext writeContext, LinkedHashMap value) {
Map map = super.onMapWrite(writeContext, value);
if (!config.isXlang()) {
writeContext.getBuffer().writeBoolean(AccessOrderAccessor.INSTANCE.getBoolean(value));
}
return map;
}

@Override
public LinkedHashMap newMap(ReadContext readContext, boolean entryReadAlwaysAdvances) {
MemoryBuffer buffer = readContext.getBuffer();
int numElements = readMapSize(readContext, buffer, entryReadAlwaysAdvances);
setNumElements(numElements);
LinkedHashMap hashMap = new LinkedHashMap(numElements);

boolean accessOrder = !config.isXlang() && buffer.readBoolean();
LinkedHashMap hashMap = new LinkedHashMap(numElements, 0.75f, accessOrder);
readContext.reference(hashMap);
return hashMap;
}

@Override
public Map newMap(Map map) {
return new LinkedHashMap(map.size());
boolean accessOrder = !config.isXlang() && AccessOrderAccessor.INSTANCE.getBoolean(map);
return new LinkedHashMap(map.size(), 0.75f, accessOrder);
}
}

Expand Down
33 changes: 33 additions & 0 deletions java/fory-core/src/test/java/org/apache/fory/serializer/collection/MapSerializersTest.java
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Expand Up @@ -264,6 +264,39 @@ public void basicTestCaseWithMultiConfig(
serDeCheck(fory, obj1);
}

@Test
public void testLinkedHashMapAccessOrder() {
Fory fory = getJavaFory();

LinkedHashMap<Integer, Integer> original = new LinkedHashMap<>(16, 0.75f, true);
original.put(1, 1);
original.put(2, 2);
original.put(3, 3);
original.put(4, 4);

byte[] bytes = fory.serialize(original);
LinkedHashMap<Integer, Integer> deserialized =
(LinkedHashMap<Integer, Integer>) fory.deserialize(bytes);

original.get(2);
deserialized.get(2);

assertEquals(new ArrayList<>(original.keySet()), new ArrayList<>(deserialized.keySet()));
assertEquals(
new ArrayList<>(java.util.Arrays.asList(1, 3, 4, 2)),
new ArrayList<>(deserialized.keySet()));

original.get(4);
original.get(1);
original.get(3);

deserialized.get(4);
deserialized.get(1);
deserialized.get(3);

assertEquals(new ArrayList<>(original.keySet()), new ArrayList<>(deserialized.keySet()));
}

@Test(dataProvider = "referenceTrackingConfig")
public void testBasicMap(boolean referenceTrackingConfig) {
Fory fory =
Expand Down
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