Claude API — Java

Note: The Java SDK supports the Claude API and beta tool use with annotated classes. Agent SDK is not yet available for Java.

Installation

Maven:

```xml com.anthropic anthropic-java 2.14.0 ```

Gradle:

```groovy implementation("com.anthropic:anthropic-java:2.14.0") ```

Client Initialization

```java import com.anthropic.client.AnthropicClient; import com.anthropic.client.okhttp.AnthropicOkHttpClient;

// Default (reads ANTHROPIC_API_KEY from environment) AnthropicClient client = AnthropicOkHttpClient.fromEnv();

// Explicit API key AnthropicClient client = AnthropicOkHttpClient.builder() .apiKey("your-api-key") .build(); ```

Basic Message Request

```java import com.anthropic.models.messages.MessageCreateParams; import com.anthropic.models.messages.Message; import com.anthropic.models.messages.Model;

MessageCreateParams params = MessageCreateParams.builder() .model(Model.CLAUDE_OPUS_4_6) .maxTokens(1024L) .addUserMessage("What is the capital of France?") .build();

Message response = client.messages().create(params); response.content().stream() .flatMap(block -> block.text().stream()) .forEach(textBlock -> System.out.println(textBlock.text())); ```

Streaming

```java import com.anthropic.core.http.StreamResponse; import com.anthropic.models.messages.RawMessageStreamEvent;

MessageCreateParams params = MessageCreateParams.builder() .model(Model.CLAUDE_OPUS_4_6) .maxTokens(1024L) .addUserMessage("Write a haiku") .build();

try (StreamResponse streamResponse = client.messages().createStreaming(params)) { streamResponse.stream() .flatMap(event -> event.contentBlockDelta().stream()) .flatMap(deltaEvent -> deltaEvent.delta().text().stream()) .forEach(textDelta -> System.out.print(textDelta.text())); } ```

Tool Use (Beta)

The Java SDK supports beta tool use with annotated classes. Tool classes implement `Supplier` for automatic execution via `BetaToolRunner`.

Tool Runner (automatic loop)

```java import com.anthropic.models.beta.messages.MessageCreateParams; import com.anthropic.models.beta.messages.BetaMessage; import com.anthropic.helpers.BetaToolRunner; import com.fasterxml.jackson.annotation.JsonClassDescription; import com.fasterxml.jackson.annotation.JsonPropertyDescription; import java.util.function.Supplier;

@JsonClassDescription("Get the weather in a given location") static class GetWeather implements Supplier { @JsonPropertyDescription("The city and state, e.g. San Francisco, CA") public String location;

@Override
public String get() {
    return "The weather in " + location + " is sunny and 72°F";
}

}

BetaToolRunner toolRunner = client.beta().messages().toolRunner( MessageCreateParams.builder() .model("claude-opus-4-6") .maxTokens(1024L) .putAdditionalHeader("anthropic-beta", "structured-outputs-2025-11-13") .addTool(GetWeather.class) .addUserMessage("What's the weather in San Francisco?") .build());

for (BetaMessage message : toolRunner) { System.out.println(message); } ```

Non-Beta Tool Use

Tool use is also available through the non-beta `com.anthropic.models.messages.MessageCreateParams` with `addTool(Tool)` for manually defined JSON schemas, without needing the beta namespace. The beta namespace is only needed for the class-annotation convenience layer (`@JsonClassDescription`, `BetaToolRunner`).

Manual Loop

For manual tool loops, define tools as JSON schema in the request, handle `tool_use` blocks in the response, send `tool_result` back, and loop until `stop_reason` is `"end_turn"`. See the shared tool use concepts for the agentic loop pattern.

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