Add response_format to allow use of new JSON mode

api/src/main/java/com/theokanning/openai/completion/chat/ChatCompletionRequest.java

@@ -27,6 +27,14 @@ public class ChatCompletionRequest {
      */
     List<ChatMessage> messages;
 
+    /**
+     * Must be either 'text' or 'json_object'. <br>
+     * When specifying 'json_object' as the request format it's still necessary to instruct the model to return JSON.
+     * You may use {@link ChatResponseFormat.ResponseFormat} enum.
+     */
+    @JsonProperty("response_format")
+    ChatResponseFormat responseFormat;
+
     /**
      * What sampling temperature to use, between 0 and 2. Higher values like 0.8 will make the output more random, while lower
      * values like 0.2 will make it more focused and deterministic.<br>

api/src/main/java/com/theokanning/openai/completion/chat/ChatResponseFormat.java

@@ -0,0 +1,30 @@
+package com.theokanning.openai.completion.chat;
+
+import com.fasterxml.jackson.annotation.JsonValue;
+import lombok.Builder;
+import lombok.Data;
+
+/**
+ * see {@link ChatCompletionRequest} documentation.
+ */
+@Data
+@Builder
+public class ChatResponseFormat {
+    private ResponseFormat type;
+
+    public enum ResponseFormat {
+        TEXT("text"),
+        JSON("json_object");
+
+        private final String value;
+
+        ResponseFormat(final String value) {
+            this.value = value;
+        }
+
+        @JsonValue
+        public String value() {
+            return value;
+        }
+    }
+}

service/src/test/java/com/theokanning/openai/service/ChatCompletionTest.java

@@ -2,7 +2,9 @@
 
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.annotation.JsonPropertyDescription;
+import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.node.ObjectNode;
 import com.theokanning.openai.completion.chat.*;
 import org.junit.jupiter.api.Test;
@@ -84,6 +86,35 @@ void streamChatCompletion() {
         assertNotNull(chunks.get(0).getChoices().get(0));
     }
 
+    @Test
+    void createChatCompletionWithJsonMode() {
+        final List<ChatMessage> messages = new ArrayList<>();
+        final ChatMessage systemMessage = new ChatMessage(ChatMessageRole.SYSTEM.value(), "You will generate a random name and return it in JSON format.");
+        messages.add(systemMessage);
+
+        ChatCompletionRequest chatCompletionRequest = ChatCompletionRequest
+                .builder()
+                .model("gpt-3.5-turbo-1106")
+                .messages(messages)
+                .responseFormat(ChatResponseFormat.builder().type(ChatResponseFormat.ResponseFormat.JSON).build())
+                .maxTokens(50)
+                .logitBias(new HashMap<>())
+                .build();
+
+        ChatCompletionChoice choice = service.createChatCompletion(chatCompletionRequest).getChoices().get(0);
+        assertTrue(isValidJson(choice.getMessage().getContent()), "Response is not valid JSON");
+    }
+
+    private boolean isValidJson(String jsonString) {
+        ObjectMapper objectMapper = new ObjectMapper();
+        try {
+            objectMapper.readTree(jsonString);
+            return true;
+        } catch (JsonProcessingException e) {
+            return false;
+        }
+    }
+
     @Test
     void createChatCompletionWithFunctions() {
         final List<ChatFunction> functions = Collections.singletonList(ChatFunction.builder()