Claude API in Java

Call the Anthropic Claude API from Java using the official SDK or the Java HttpClient. Complete examples for text generation, streaming, and tool use in Java 11+.

Anthropic ships official SDKs for Python, TypeScript, and Go. For Java, the cleanest path is the REST API via java.net.http.HttpClient (Java 11+). The examples below wrap this in a reusable utility class.

Dependencies (Maven)

<dependency>
  <groupId>com.google.code.gson</groupId>
  <artifactId>gson</artifactId>
  <version>2.10.1</version>
</dependency>

Basic message

import com.google.gson.*;
import java.net.URI;
import java.net.http.*;
import java.net.http.HttpResponse.BodyHandlers;

public class ClaudeClient {

    private static final String API_URL = "https://api.anthropic.com/v1/messages";
    private static final String API_KEY  = System.getenv("ANTHROPIC_API_KEY");
    private static final String MODEL    = "claude-sonnet-4-6-20251001";

    private final HttpClient http = HttpClient.newHttpClient();
    private final Gson gson = new Gson();

    public String chat(String userMessage) throws Exception {
        JsonObject body = new JsonObject();
        body.addProperty("model", MODEL);
        body.addProperty("max_tokens", 1024);

        JsonArray messages = new JsonArray();
        JsonObject msg = new JsonObject();
        msg.addProperty("role", "user");
        JsonArray content = new JsonArray();
        JsonObject textBlock = new JsonObject();
        textBlock.addProperty("type", "text");
        textBlock.addProperty("text", userMessage);
        content.add(textBlock);
        msg.add("content", content);
        messages.add(msg);
        body.add("messages", messages);

        HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create(API_URL))
            .header("Content-Type", "application/json")
            .header("x-api-key", API_KEY)
            .header("anthropic-version", "2023-06-01")
            .POST(HttpRequest.BodyPublishers.ofString(gson.toJson(body)))
            .build();

        HttpResponse<String> response = http.send(request, BodyHandlers.ofString());
        if (response.statusCode() != 200)
            throw new RuntimeException("API error " + response.statusCode() + ": " + response.body());

        JsonObject resp = JsonParser.parseString(response.body()).getAsJsonObject();
        return resp.getAsJsonArray("content")
                   .get(0).getAsJsonObject()
                   .get("text").getAsString();
    }

    public static void main(String[] args) throws Exception {
        ClaudeClient client = new ClaudeClient();
        System.out.println(client.chat("Explain Java virtual threads in two sentences."));
    }
}

Async call with CompletableFuture

public CompletableFuture<String> chatAsync(String userMessage) {
    JsonObject body = buildBody(userMessage);
    HttpRequest request = buildRequest(body);
    return http.sendAsync(request, BodyHandlers.ofString())
        .thenApply(response -> {
            if (response.statusCode() != 200)
                throw new RuntimeException("API error " + response.statusCode());
            return extractText(response.body());
        });
}

Error handling with exponential backoff

public String chatWithRetry(String userMessage, int maxRetries) throws Exception {
    int attempt = 0;
    while (true) {
        HttpResponse<String> response = http.send(buildRequest(buildBody(userMessage)), BodyHandlers.ofString());
        int status = response.statusCode();
        if (status == 200) return extractText(response.body());
        if ((status == 429 || status >= 500) && attempt++ < maxRetries) {
            Thread.sleep((long) Math.pow(2, attempt) * 1000L);
            continue;
        }
        throw new RuntimeException("Non-retryable error " + status);
    }
}

Model and pricing reference

Estimate costs for your Java workload at the Claude API Cost Calculator.

Frequently asked questions

Free tools

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