[Feature] Add Serialization Optimization for Primitive Collection Types

changelog/@unreleased/pr-2386.v2.yml

@@ -0,0 +1,5 @@
+type: improvement
+improvement:
+  description: '[FR] Add Serialization Optimization for Primitive Collection Types'
+  links:
+  - https://github.com/palantir/conjure-java/pull/2386

conjure-java-core/src/test/java/com/palantir/conjure/java/NonNullCollectionsTest.java

@@ -22,15 +22,19 @@
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.exc.InvalidNullException;
+import com.palantir.conjure.java.lib.SafeLong;
 import com.palantir.conjure.java.serialization.ObjectMappers;
 import com.palantir.product.CovariantListExample;
 import com.palantir.product.ListExample;
+import com.palantir.product.PrimitiveExample;
 import java.util.Collections;
+import java.util.List;
 import java.util.Optional;
 import org.junit.jupiter.api.Test;
 
 public class NonNullCollectionsTest {
-    private static final ObjectMapper objectMapper = ObjectMappers.newClientObjectMapper();
+    private static final ObjectMapper clientMapper = ObjectMappers.newClientObjectMapper();
+    private static final ObjectMapper serverMapper = ObjectMappers.newServerJsonMapper();
 
     @Test
     public void throwsNpe() {
@@ -55,7 +59,7 @@ public void testOptionalSerialization() throws JsonProcessingException {
                 .optionalItems(Collections.singleton(Optional.empty()))
                 .build();
 
-        assertThat(objectMapper.readValue(objectMapper.writeValueAsString(listExample), ListExample.class))
+        assertThat(clientMapper.readValue(clientMapper.writeValueAsString(listExample), ListExample.class))
                 .isEqualTo(listExample);
 
         // non-null collections will add "contentNulls = Nulls.FAIL" to the JsonSetter annotation. This will cause deser
@@ -64,12 +68,31 @@ public void testOptionalSerialization() throws JsonProcessingException {
                 .addAllItems(Collections.singleton(Optional.empty()))
                 .build();
         assertThatExceptionOfType(InvalidNullException.class)
-                .isThrownBy(() -> objectMapper.readValue(
-                        objectMapper.writeValueAsString(covariantListExample), CovariantListExample.class));
+                .isThrownBy(() -> clientMapper.readValue(
+                        clientMapper.writeValueAsString(covariantListExample), CovariantListExample.class));
 
         // Similarly, setting a null in the builder also breaks
         assertThatExceptionOfType(NullPointerException.class).isThrownBy(() -> CovariantListExample.builder()
                 .addAllItems(Collections.singleton(null))
                 .build());
     }
+
+    @Test
+    public void testSerDeOptimizationRespectsConjureEmptyCollections() throws JsonProcessingException {
+        PrimitiveExample expected = PrimitiveExample.builder().build();
+        assertThat(clientMapper.writeValueAsString(expected))
+                .describedAs("Does not serialize any empty collections, even when optimizing for primitives")
+                .isEqualTo("{}");
+    }
+
+    @Test
+    public void testSerializationRoundtrip() throws JsonProcessingException {
+        PrimitiveExample expected = PrimitiveExample.builder()
+                .ints(List.of(1, 2, 3))
+                .doubles(List.of(1.1, 2.2, 3.3))
+                .longs(List.of(SafeLong.of(1L), SafeLong.of(2L)))
+                .build();
+        String serialized = serverMapper.writeValueAsString(expected);
+        assertThat(expected).isEqualTo(clientMapper.readValue(serialized, PrimitiveExample.class));
+    }
 }

conjure-java-core/src/test/java/com/palantir/conjure/java/types/ObjectGeneratorTests.java

@@ -168,6 +168,21 @@ public void testObjectGenerator_excludeEmptyCollections() throws IOException {
         assertThatFilesAreTheSame(files, REFERENCE_FILES_FOLDER);
     }
 
+    @Test
+    public void testObjectGenerator_primitiveCollections() throws IOException {
+        ConjureDefinition def =
+                Conjure.parse(ImmutableList.of(new File("src/test/resources/primitive-collections.yml")));
+        List<Path> files = new GenerationCoordinator(
+                        MoreExecutors.directExecutor(),
+                        ImmutableSet.of(new ObjectGenerator(Options.builder()
+                                .excludeEmptyCollections(true)
+                                .nonNullCollections(true)
+                                .build())))
+                .emit(def, tempDir);
+
+        assertThatFilesAreTheSame(files, REFERENCE_FILES_FOLDER);
+    }
+
     @Test
     public void testConjureImports() throws IOException {
         ConjureDefinition conjure = Conjure.parse(ImmutableList.of(

conjure-java-core/src/test/resources/primitive-collections.yml

@@ -0,0 +1,9 @@
+types:
+  definitions:
+    default-package: com.palantir.product
+    objects:
+      PrimitiveExample:
+        fields:
+          ints: list<integer>
+          doubles: list<double>
+          longs: list<safelong>

conjure-lib/src/main/java/com/palantir/conjure/java/lib/internal/ConjureCollections.java

@@ -38,8 +38,33 @@ private ConjureCollections() {
         // cannot instantiate
     }
 
+    /*
+     * This is bizarre. Allow me to explain...
+     *
+     * We do _not_ want to expose the Conjure*List types externally
+     * but we also want the optimizations they provide to make it thru
+     * to jackson for serialization. So the runtime type needs to be
+     * preserved while also not exposing the type :phew:.
+     *
+     * To achieve this we have to do some gymnastics surrounding the type
+     * system. We need this to return the type of the list given, but also
+     * return specific Conjure types when detected. This requires that we
+     * erase the type info, but we know this is safe because we are directly
+     * returning the same type which is by definition the identity function.
+     * Therefore the input List<T> is the same types as the output List<T>.
+     */
     public static <T> List<T> unmodifiableList(List<T> list) {
-        return Collections.unmodifiableList(list);
+        // Return the unmodifiable version of the Eclipse types
+        if (list instanceof ConjureIntegerList) {
+            return (List<T>) ((ConjureIntegerList) list).asUnmodifiable();
+        } else if (list instanceof ConjureDoubleList) {
+            return (List<T>) ((ConjureDoubleList) list).asUnmodifiable();
+        } else if (list instanceof ConjureSafeLongList) {
+            return (List<T>) ((ConjureSafeLongList) list).asUnmodifiable();
+        } else {
+            // Otherwise use the JDK types
+            return Collections.unmodifiableList(list);
+        }
     }
 
     @SuppressWarnings("unchecked")

conjure-lib/src/main/java/com/palantir/conjure/java/lib/internal/ConjureDoubleList.java

@@ -16,20 +16,21 @@
 
 package com.palantir.conjure.java.lib.internal;
 
+import com.fasterxml.jackson.annotation.JsonValue;
 import java.util.AbstractList;
 import java.util.Collection;
 import java.util.RandomAccess;
-import org.eclipse.collections.impl.list.mutable.primitive.DoubleArrayList;
+import org.eclipse.collections.api.list.primitive.MutableDoubleList;
 import org.eclipse.collections.impl.utility.Iterate;
 
 /**
  * ConjureDoubleList is a boxed list wrapper for the eclipse-collections DoubleArrayList. In eclipse-collections 12,
  * a BoxedMutableDoubleList will be released. Once available, ConjureDoubleList should be replaced with that.
  */
 final class ConjureDoubleList extends AbstractList<Double> implements RandomAccess {
-    private final DoubleArrayList delegate;
+    private final MutableDoubleList delegate;
 
-    ConjureDoubleList(DoubleArrayList delegate) {
+    ConjureDoubleList(MutableDoubleList delegate) {
         this.delegate = delegate;
     }
 
@@ -69,4 +70,15 @@ public void clear() {
     public Double set(int index, Double element) {
         return delegate.set(index, element);
     }
+
+    public ConjureDoubleList asUnmodifiable() {
+        return new ConjureDoubleList(delegate.asUnmodifiable());
+    }
+
+    // Cannot be named 'toArray' as that conflicts with the #toArray in AbstractList
+    // This is a serialization optimization that avoids boxing, but does copy
+    @JsonValue
+    double[] jacksonSerialize() {
+        return delegate.toArray();
+    }
 }