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Integrate with OpenAI(ChatGPT) Completion API in Java using WebClient


By now you all would have heard about OpenAI and played with its famous product ChatGPT. OpenAI also provides APIs which can be used to integrate features like text completion, code generation, image generation and chat completion in your applications.

In this post I will show you how to make use of the Text completion API in Java application. For this we will be using Spring Framework’s WebClient to invoke the APIs.

Before you start the development work you need to have OpenAI API’s secret key which you can obtain from after creating an account on OpenAI.

Text Completion API

The text completion API can be invoked by sending a POST request to the URL with the following parameters:

There are other options which can be used to tweak the behavior of the model like:

We will create some Java classes to capture the response of the API

public class CompletionResponse {
String id;
String object;
Long createdOn;
String model;
List<CompletionResponseChoice> choices;
CompletionResponseUsage usage;

CompletionResponse will hold the response retrieved from the API.

public class CompletionResponseChoice{
String text;
Integer index;
String finishReason;
String logProbs;

CompletionResponseChoice will hold the choices returned by the API. This will contain the required information we are looking for.

public class CompletionResponseUsage{
Integer promptTokens;
Integer completionTokens;
Integer totalTokens;

CompletionResponseUsage will have the token usage information.

Token is a very important concept in the API. A token approximately corresponds to 4 characters and 3/4th of the word. So 100 tokens ~= 75 words. This page shows how the tokenization works.

Lets now integrate with the API

WebClient webClient = WebClient.create();
Map<String, Object> requestBody = new HashMap<>();
requestBody.put("model", "text-davinci-003");
requestBody.put("prompt", "10 tips for time management for married working professional with kids");
requestBody.put("max_tokens", 500);
requestBody.put("temperature", 0.5);

In the code snippet above the model specified is taken from the models listed here. The completion API doesnt support the newer models: gpt-3.5-turbo and gpt-3.5-turbo-0301. These newer models are supported in the new Chat Completion API which I will illustrate in my next post.

The below code uses WebClient to make the API request. It handles the error scenarios as well by printing the error response to the console.

String url = "";
ObjectMapper objectMapper = new ObjectMapper();
Mono<CompletionResponse> completionResponseMono =
        .headers(httpHeaders -> {
        .exchangeToMono(clientResponse -> {
            HttpStatusCode httpStatus = clientResponse.statusCode();
            if (httpStatus.is2xxSuccessful()) {
                return clientResponse.bodyToMono(CompletionResponse.class);
            } else {
                Mono<String> stringMono = clientResponse.bodyToMono(String.class);
                stringMono.subscribe(s -> {
                    System.err.println("Response from Open AI API " + s);
                System.err.println("Error occurred while invoking Open AI API");
                return Mono.error(new Exception(
                        "Error occurred while generating wordage"));

CompletionResponse completionResponse = completionResponseMono.block();

List<CompletionResponseChoice> choices = completionResponse.getChoices();


Note: The variable secret will hold the secret which you had generated initially.

The output will be:

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