[Enhancement #68] Cache type map for deserialization to prevent repea…

…ted classpath scanning.

src/main/java/cz/cvut/kbss/jsonld/ConfigParam.java

@@ -39,9 +39,9 @@ public enum ConfigParam {
     /**
      * Whether to require an identifier when serializing an object.
      * <p>
-     * If set to {@code true} and no identifier is found (either there is no identifier field or its value is {@code
-     * null}), an exception will be thrown. If configured to {@code false}, a blank node identifier is generated if no
-     * id is present.
+     * If set to {@code true} and no identifier is found (either there is no identifier field or its value is
+     * {@code null}), an exception will be thrown. If configured to {@code false}, a blank node identifier is generated
+     * if no id is present.
      */
     REQUIRE_ID("requireId"),
 
@@ -59,8 +59,8 @@ public enum ConfigParam {
      * Enables optimistic target type resolution.
      * <p>
      * This means that when a an ambiguous target type is encountered during deserialization of an object (i.e.,
-     * multiple concrete classes match the data type), instead of throwing an {@link
-     * cz.cvut.kbss.jsonld.exception.AmbiguousTargetTypeException}, one of the classes will be selected for
+     * multiple concrete classes match the data type), instead of throwing an
+     * {@link cz.cvut.kbss.jsonld.exception.AmbiguousTargetTypeException}, one of the classes will be selected for
      * instantiation.
      * <p>
      * Note that enabling this behavior should probably be done together with setting {@link #IGNORE_UNKNOWN_PROPERTIES}
@@ -98,19 +98,34 @@ public enum ConfigParam {
     /**
      * Format string used to serialize and deserialize datetime values.
      * <p>
-     * Note that if {@link #SERIALIZE_DATETIME_AS_MILLIS} is enabled, this parameter has no effect on serialization of datetime.
+     * Note that if {@link #SERIALIZE_DATETIME_AS_MILLIS} is enabled, this parameter has no effect on serialization of
+     * datetime.
      * <p>
-     * Also note that this format applies only to full datetime values. Date or time values have to be formatted per-attribute.
+     * Also note that this format applies only to full datetime values. Date or time values have to be formatted
+     * per-attribute.
      */
     DATE_TIME_FORMAT("datetimeFormat"),
 
     /**
      * Whether to serialize individuals using expanded term definition in context.
-     *
+     * <p>
      * This basically means that the individual's identifier is provided directly as a string and an expanded term
-     * definition (consisting of a {@literal @id} and {@literal @type}) is added into the context, specifying that the string is an identifier.
+     * definition (consisting of a {@literal @id} and {@literal @type}) is added into the context, specifying that the
+     * string is an identifier.
+     */
+    SERIALIZE_INDIVIDUALS_USING_EXPANDED_DEFINITION("serializeIndividualsUsingExpandedDefinition"),
+
+    /**
+     * Whether to disable the type map cache.
+     * <p>
+     * Type map is used to map JSON-LD types to Java classes for deserialization. Since this map is built by scanning
+     * the classpath (see the {@link #SCAN_PACKAGE} parameter), it is cached by default to avoid repeated scanning of
+     * the classpath.
+     * <p>
+     * If every deserializer instance should get a fresh type map based on the current configuration, disable this
+     * cache.
      */
-    SERIALIZE_INDIVIDUALS_USING_EXPANDED_DEFINITION("serializeIndividualsUsingExpandedDefinition");
+    DISABLE_TYPE_MAP_CACHE("disableTypeMapCache");
 
     private final String name;
 

src/main/java/cz/cvut/kbss/jsonld/deserialization/JsonLdDeserializer.java

@@ -36,6 +36,8 @@
  */
 public abstract class JsonLdDeserializer implements Configured {
 
+    private static final TypeMap TYPE_MAP = new TypeMap();
+
     private final Configuration configuration;
 
     protected final TargetClassResolver classResolver;
@@ -53,19 +55,33 @@ protected JsonLdDeserializer(Configuration configuration) {
     }
 
     private TargetClassResolver initializeTargetClassResolver() {
-        final TypeMap typeMap = new TypeMap();
         final String scanPath = configuration.get(ConfigParam.SCAN_PACKAGE, "");
+        final TypeMap typeMap = discoverAvailableTypes(scanPath, configuration.is(ConfigParam.DISABLE_TYPE_MAP_CACHE));
+        return new TargetClassResolver(typeMap,
+                                       new TargetClassResolverConfig(
+                                               configuration.is(ConfigParam.ASSUME_TARGET_TYPE),
+                                               configuration().is(ConfigParam.ENABLE_OPTIMISTIC_TARGET_TYPE_RESOLUTION),
+                                               configuration().is(ConfigParam.PREFER_SUPERCLASS)));
+    }
+
+    /**
+     * Finds potential deserialization target types on the classpath.
+     *
+     * @param scanPath Path to scan on classpath
+     * @return Map of types to Java classes
+     */
+    private static TypeMap discoverAvailableTypes(String scanPath, boolean disableCache) {
+        final TypeMap map = disableCache ? new TypeMap() : TYPE_MAP;
+        if (!map.isEmpty()) {
+            return map;
+        }
         new ClasspathScanner(c -> {
             final OWLClass ann = c.getDeclaredAnnotation(OWLClass.class);
             if (ann != null) {
-                typeMap.register(BeanAnnotationProcessor.expandIriIfNecessary(ann.iri(), c), c);
+                map.register(BeanAnnotationProcessor.expandIriIfNecessary(ann.iri(), c), c);
             }
         }).processClasses(scanPath);
-        return new TargetClassResolver(typeMap,
-                new TargetClassResolverConfig(
-                        configuration.is(ConfigParam.ASSUME_TARGET_TYPE),
-                        configuration().is(ConfigParam.ENABLE_OPTIMISTIC_TARGET_TYPE_RESOLUTION),
-                        configuration().is(ConfigParam.PREFER_SUPERCLASS)));
+        return map;
     }
 
     @Override
@@ -78,9 +94,9 @@ public Configuration configuration() {
      * <p>
      * If a deserializer already existed for the type, it is replaced by the new one.
      *
-     * @param type       Target type to register the deserializer for
+     * @param type         Target type to register the deserializer for
      * @param deserializer Deserializer to register
-     * @param <T>        Target type
+     * @param <T>          Target type
      */
     public <T> void registerDeserializer(Class<T> type, ValueDeserializer<T> deserializer) {
         Objects.requireNonNull(type);

src/main/java/cz/cvut/kbss/jsonld/deserialization/util/TypeMap.java

@@ -17,14 +17,19 @@
  */
 package cz.cvut.kbss.jsonld.deserialization.util;
 
-import java.util.*;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
 
 /**
  * Represents a map of type IRIs to their mapped Java classes.
  * <p>
  * Used by the deserialization when determining target class from JSON-LD object types.
  * <p>
- * This class is not synchronized, as it is expected that types will be registered by one thread once and then only queried.
+ * Read access is not synchronized, as it is expected that types will be registered by one thread once and then only
+ * queried.
  */
 public class TypeMap {
 
@@ -41,4 +46,8 @@ public synchronized void register(String type, Class<?> cls) {
     public Set<Class<?>> get(String type) {
         return typeMap.getOrDefault(type, Collections.emptySet());
     }
+
+    public synchronized boolean isEmpty() {
+        return typeMap.isEmpty();
+    }
 }

src/test/java/cz/cvut/kbss/jsonld/deserialization/JsonLdDeserializerTest.java

@@ -35,6 +35,7 @@
 import static cz.cvut.kbss.jsonld.environment.TestUtil.readAndExpand;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.hasItem;
+import static org.hamcrest.Matchers.not;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -45,6 +46,7 @@ class JsonLdDeserializerTest {
     void constructionScansClasspathAndBuildsTypeMap() throws Exception {
         final Configuration config = new Configuration();
         config.set(ConfigParam.SCAN_PACKAGE, "cz.cvut.kbss.jsonld");
+        config.set(ConfigParam.DISABLE_TYPE_MAP_CACHE, "true");
         final JsonLdDeserializer deserializer = JsonLdDeserializer.createExpandedDeserializer(config);
         assertFalse(typeMap(deserializer).get(Vocabulary.STUDY).isEmpty());
         assertTrue(typeMap(deserializer).get(Vocabulary.STUDY).contains(Study.class));
@@ -60,6 +62,7 @@ private TypeMap typeMap(JsonLdDeserializer deserializer) throws Exception {
     void constructionScansClasspathWithSpecifiedPackageAndBuildsTypeMap() throws Exception {
         final Configuration config = new Configuration();
         config.set(ConfigParam.SCAN_PACKAGE, "cz.cvut.kbss.jsonld.deserialization");
+        config.set(ConfigParam.DISABLE_TYPE_MAP_CACHE, "true");
         final JsonLdDeserializer deserializer = JsonLdDeserializer.createExpandedDeserializer(config);
         assertTrue(typeMap(deserializer).get(Vocabulary.GENERIC_MEMBER).isEmpty());
         assertTrue(typeMap(deserializer).get(Vocabulary.AGENT).contains(TestClass.class));
@@ -82,8 +85,38 @@ void deserializationThrowsJsonLdDeserializationExceptionWhenInputIsNotValidJsonL
     void constructionExpandsCompactIrisWhenBuildingTypeMap() throws Exception {
         final Configuration config = new Configuration();
         config.set(ConfigParam.SCAN_PACKAGE, "cz.cvut.kbss.jsonld.environment.model");
+        config.set(ConfigParam.DISABLE_TYPE_MAP_CACHE, "true");
         final JsonLdDeserializer deserializer = JsonLdDeserializer.createExpandedDeserializer(config);
         assertFalse(typeMap(deserializer).get(Vocabulary.STUDY).isEmpty());
         assertThat(typeMap(deserializer).get(Vocabulary.STUDY), hasItem(StudyWithNamespaces.class));
     }
+
+    @Test
+    void constructionCachesTypeMapByDefault() throws Exception {
+        final Configuration config = new Configuration();
+        config.set(ConfigParam.SCAN_PACKAGE, "cz.cvut.kbss.jsonld");
+        final JsonLdDeserializer deserializerOne = JsonLdDeserializer.createExpandedDeserializer(config);
+        final TypeMap typeMapOne = typeMap(deserializerOne);
+        assertThat(typeMapOne.get(Vocabulary.STUDY), hasItem(Study.class));
+        config.set(ConfigParam.SCAN_PACKAGE, "cz.cvut.kbss.jsonld.deserialization");
+        final JsonLdDeserializer deserializerTwo = JsonLdDeserializer.createExpandedDeserializer(config);
+        final TypeMap typeMapTwo = typeMap(deserializerTwo);
+        // If classpath scanning occurred again, the updated scan package would be too specific for Study
+        assertThat(typeMapTwo.get(Vocabulary.STUDY), hasItem(Study.class));
+    }
+
+    @Test
+    void constructionBuildsFreshTypeMapWhenTypeMapCacheIsDisabled() throws Exception {
+        final Configuration config = new Configuration();
+        config.set(ConfigParam.SCAN_PACKAGE, "cz.cvut.kbss.jsonld");
+        final JsonLdDeserializer deserializerOne = JsonLdDeserializer.createExpandedDeserializer(config);
+        final TypeMap typeMapOne = typeMap(deserializerOne);
+        assertThat(typeMapOne.get(Vocabulary.STUDY), hasItem(Study.class));
+        config.set(ConfigParam.SCAN_PACKAGE, "cz.cvut.kbss.jsonld.deserialization");
+        config.set(ConfigParam.DISABLE_TYPE_MAP_CACHE, "true");
+        final JsonLdDeserializer deserializerTwo = JsonLdDeserializer.createExpandedDeserializer(config);
+        final TypeMap typeMapTwo = typeMap(deserializerTwo);
+        // If classpath scanning occurred again, the updated scan package would be too specific for Study
+        assertThat(typeMapTwo.get(Vocabulary.STUDY), not(hasItem(Study.class)));
+    }
 }

src/test/java/cz/cvut/kbss/jsonld/deserialization/expanded/ExpandedJsonLdDeserializerTest.java

@@ -108,6 +108,7 @@ private static Map<URI, User> initUsers() {
     void setUp() {
         final Configuration config = new Configuration();
         config.set(ConfigParam.SCAN_PACKAGE, "cz.cvut.kbss.jsonld");
+        config.set(ConfigParam.DISABLE_TYPE_MAP_CACHE, "true");
         this.sut = JsonLdDeserializer.createExpandedDeserializer(config);
     }