Fix a enum serialization issue leading to stackoverflow when creating schemas from classes (#1450)

- **Fixes #1447 Make vector embedding calculation in batch mode to speed
up the calculation of all embeddings for each label.**
- **Remove unneeded import**
- **[Gemini] Fix enum schema handling**

langchain4j-vertex-ai-gemini/src/main/java/dev/langchain4j/model/vertexai/SchemaHelper.java

@@ -76,6 +76,14 @@ public class SchemaHelper {
         } else if (Collection.class.isAssignableFrom(theClass)) {
             // Because of type erasure, we can't easily know the type of the items in the collection
             return Schema.newBuilder().setType(Type.ARRAY).build();
+        } else if (theClass.isEnum()) {
+            List<String> enumConstantNames = Arrays.stream(theClass.getEnumConstants())
+                .map(Object::toString)
+                .collect(Collectors.toList());
+            return Schema.newBuilder()
+                .setType(Type.STRING)
+                .addAllEnum(enumConstantNames)
+                .build();
         } else {
             // This is some kind of object, let's go through its fields
             Schema.Builder schemaBuilder = Schema.newBuilder().setType(Type.OBJECT);

langchain4j-vertex-ai-gemini/src/test/java/dev/langchain4j/model/vertexai/SchemaHelperTest.java

@@ -2,8 +2,14 @@ package dev.langchain4j.model.vertexai;
 
 import com.google.cloud.vertexai.api.Schema;
 import com.google.cloud.vertexai.api.Type;
+import lombok.Data;
+import lombok.Getter;
 import org.junit.jupiter.api.Test;
 
+import java.util.Arrays;
+import java.util.Collections;
+
+import static dev.langchain4j.model.vertexai.SchemaHelper.fromClass;
 import static org.assertj.core.api.Assertions.assertThat;
 
 public class SchemaHelperTest {
@@ -17,10 +23,10 @@ public class SchemaHelperTest {
             public int age;
             public boolean isStudent;
             public String[] friends;
-        };
+        }
 
         // when
-        Schema schema = SchemaHelper.fromClass(Person.class);
+        Schema schema = fromClass(Person.class);
         System.out.println("schema = " + schema);
 
         // then
@@ -78,6 +84,38 @@ public class SchemaHelperTest {
         assertThat(schema.getPropertiesMap().get("artist-adult").getType()).isEqualTo(Type.BOOLEAN);
         assertThat(schema.getPropertiesMap().get("artist-pets").getType()).isEqualTo(Type.ARRAY);
         assertThat(schema.getPropertiesMap().get("artist-pets").getItems().getType()).isEqualTo(Type.STRING);
+    }
 
+    @Getter
+    enum Sentiment {
+        POSITIVE(1.0), NEUTRAL(0.0), NEGATIVE(-1.0);
+        private final double value;
+        Sentiment(double val) {
+            this.value = val;
+        }
+    }
+
+    @Data
+    static class SentimentClassification {
+        private Sentiment sentiment;
+    }
+
+    @Test
+    void should_support_enum_schema_without_stackoverflow() {
+
+        // given
+        Schema schemaFromEnum = fromClass(SentimentClassification.class);
+
+        Schema expectedSchema = Schema.newBuilder()
+            .setType(Type.OBJECT)
+            .putProperties("sentiment", Schema.newBuilder()
+                .setType(Type.STRING)
+                .addAllEnum(Arrays.asList("POSITIVE", "NEUTRAL", "NEGATIVE"))
+                .build())
+            .addAllRequired(Collections.singletonList("sentiment"))
+            .build();
+
+        // then
+        assertThat(schemaFromEnum).isEqualTo(expectedSchema);
     }
 }