claude-code-system-prompts/system-prompts/data-claude-api-reference-java.md
2026-03-19 14:56:37 -06:00

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<!--
name: 'Data: Claude API reference — Java'
description: Java SDK reference including installation, client initialization, basic requests, streaming, and beta tool use
ccVersion: 2.1.78
-->
# 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
<dependency>
<groupId>com.anthropic</groupId>
<artifactId>anthropic-java</artifactId>
<version>2.16.1</version>
</dependency>
```
Gradle:
```groovy
implementation("com.anthropic:anthropic-java:2.16.1")
```
## 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(16000L)
.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(64000L)
.addUserMessage("Write a haiku")
.build();
try (StreamResponse<RawMessageStreamEvent> 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()));
}
```
---
## Thinking
**Adaptive thinking is the recommended mode for Claude 4.6+ models.** Claude decides dynamically when and how much to think. The builder has a direct `.thinking(ThinkingConfigAdaptive)` overload — no manual union wrapping.
```java
import com.anthropic.models.messages.ContentBlock;
import com.anthropic.models.messages.MessageCreateParams;
import com.anthropic.models.messages.Model;
import com.anthropic.models.messages.ThinkingConfigAdaptive;
MessageCreateParams params = MessageCreateParams.builder()
.model(Model.CLAUDE_SONNET_4_6)
.maxTokens(16000L)
.thinking(ThinkingConfigAdaptive.builder().build())
.addUserMessage("Solve this step by step: 27 * 453")
.build();
for (ContentBlock block : client.messages().create(params).content()) {
block.thinking().ifPresent(t -> System.out.println("[thinking] " + t.thinking()));
block.text().ifPresent(t -> System.out.println(t.text()));
}
```
> **Deprecated:** `ThinkingConfigEnabled.builder().budgetTokens(N)` (and the `.enabledThinking(N)` shortcut) still works on Claude 4.6 but is deprecated. Use adaptive thinking above.
`ContentBlock` narrowing: `.thinking()` / `.text()` return `Optional<T>` — use `.ifPresent(...)` or `.stream().flatMap(...)`. Alternative: `isThinking()` / `asThinking()` boolean+unwrap pairs (throws on wrong variant).
---
## Tool Use (Beta)
The Java SDK supports beta tool use with annotated classes. Tool classes implement `Supplier<String>` 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<String> {
@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("{{OPUS_ID}}")
.maxTokens(16000L)
.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);
}
```
### Memory Tool
The Java SDK provides `BetaMemoryToolHandler` for implementing the memory tool backend. You supply a handler that manages file storage, and the `BetaToolRunner` handles memory tool calls automatically.
```java
import com.anthropic.helpers.BetaMemoryToolHandler;
import com.anthropic.helpers.BetaToolRunner;
import com.anthropic.models.beta.messages.BetaMemoryTool20250818;
import com.anthropic.models.beta.messages.BetaMessage;
import com.anthropic.models.beta.messages.MessageCreateParams;
import com.anthropic.models.beta.messages.ToolRunnerCreateParams;
// Implement BetaMemoryToolHandler with your storage backend (e.g., filesystem)
BetaMemoryToolHandler memoryHandler = new FileSystemMemoryToolHandler(sandboxRoot);
MessageCreateParams createParams = MessageCreateParams.builder()
.model("{{OPUS_ID}}")
.maxTokens(4096L)
.addTool(BetaMemoryTool20250818.builder().build())
.addUserMessage("Remember that my favorite color is blue")
.build();
BetaToolRunner toolRunner = client.beta().messages().toolRunner(
ToolRunnerCreateParams.builder()
.betaMemoryToolHandler(memoryHandler)
.initialMessageParams(createParams)
.build());
for (BetaMessage message : toolRunner) {
System.out.println(message);
}
```
See the [shared memory tool concepts](../shared/tool-use-concepts.md) for more details on the memory tool.
### Non-Beta Tool Declaration (manual JSON schema)
`Tool.InputSchema.Properties` is a freeform `Map<String, JsonValue>` wrapper — build property schemas via `putAdditionalProperty`. `type: "object"` is the default. The builder has a direct `.addTool(Tool)` overload that wraps in `ToolUnion` automatically.
```java
import com.anthropic.core.JsonValue;
import com.anthropic.models.messages.Tool;
Tool tool = Tool.builder()
.name("get_weather")
.description("Get the current weather in a given location")
.inputSchema(Tool.InputSchema.builder()
.properties(Tool.InputSchema.Properties.builder()
.putAdditionalProperty("location", JsonValue.from(Map.of("type", "string")))
.build())
.required(List.of("location"))
.build())
.build();
MessageCreateParams params = MessageCreateParams.builder()
.model(Model.CLAUDE_SONNET_4_6)
.maxTokens(16000L)
.addTool(tool)
.addUserMessage("Weather in Paris?")
.build();
```
For manual tool loops, handle `tool_use` blocks in the response, send `tool_result` back, loop until `stop_reason` is `"end_turn"`. See [shared tool use concepts](../shared/tool-use-concepts.md).
### Building `MessageParam` with Content Blocks (Tool Result Round-Trip)
`MessageParam.Content` is an inner union class (string | list). Use the builder's `.contentOfBlockParams(List<ContentBlockParam>)` alias — there is NO separate `MessageParamContent` class with a static `ofBlockParams`:
```java
import com.anthropic.models.messages.MessageParam;
import com.anthropic.models.messages.ContentBlockParam;
import com.anthropic.models.messages.ToolResultBlockParam;
List<ContentBlockParam> results = List.of(
ContentBlockParam.ofToolResult(ToolResultBlockParam.builder()
.toolUseId(toolUseBlock.id())
.content(yourResultString)
.build())
);
MessageParam toolResultMsg = MessageParam.builder()
.role(MessageParam.Role.USER)
.contentOfBlockParams(results) // builder alias for Content.ofBlockParams(...)
.build();
```
---
## Effort Parameter
Effort is nested inside `OutputConfig` — there is NO `.effort()` directly on `MessageCreateParams.Builder`.
```java
import com.anthropic.models.messages.OutputConfig;
.outputConfig(OutputConfig.builder()
.effort(OutputConfig.Effort.HIGH) // or LOW, MEDIUM, MAX
.build())
```
Combine with `Thinking = ThinkingConfigAdaptive` for cost-quality control.
---
## Prompt Caching
System message as a list of `TextBlockParam` with `CacheControlEphemeral`. Use `.systemOfTextBlockParams(...)` — the plain `.system(String)` overload can't carry cache control.
```java
import com.anthropic.models.messages.TextBlockParam;
import com.anthropic.models.messages.CacheControlEphemeral;
.systemOfTextBlockParams(List.of(
TextBlockParam.builder()
.text(longSystemPrompt)
.cacheControl(CacheControlEphemeral.builder()
.ttl(CacheControlEphemeral.Ttl.TTL_1H) // optional; also TTL_5M
.build())
.build()))
```
There's also a top-level `.cacheControl(CacheControlEphemeral)` on `MessageCreateParams.Builder` and on `Tool.builder()`.
---
## Token Counting
```java
import com.anthropic.models.messages.MessageCountTokensParams;
long tokens = client.messages().countTokens(
MessageCountTokensParams.builder()
.model(Model.CLAUDE_SONNET_4_6)
.addUserMessage("Hello")
.build()
).inputTokens();
```
---
## Structured Output
The class-based overload auto-derives the JSON schema from your POJO and gives you a typed `.text()` return — no manual schema, no manual parsing.
```java
import com.anthropic.models.messages.StructuredMessageCreateParams;
record Book(String title, String author) {}
record BookList(List<Book> books) {}
StructuredMessageCreateParams<BookList> params = MessageCreateParams.builder()
.model(Model.CLAUDE_SONNET_4_6)
.maxTokens(16000L)
.outputConfig(BookList.class) // returns a typed builder
.addUserMessage("List 3 classic novels")
.build();
client.messages().create(params).content().stream()
.flatMap(cb -> cb.text().stream())
.forEach(typed -> {
// typed.text() returns BookList, not String
for (Book b : typed.text().books()) System.out.println(b.title());
});
```
Supports Jackson annotations: `@JsonPropertyDescription`, `@JsonIgnore`, `@ArraySchema(minItems=...)`. Manual schema path: `OutputConfig.builder().format(JsonOutputFormat.builder().schema(...).build())`.
---
## PDF / Document Input
`DocumentBlockParam` builder has source shortcuts. Wrap in `ContentBlockParam.ofDocument()` and pass via `.addUserMessageOfBlockParams()`.
```java
import com.anthropic.models.messages.DocumentBlockParam;
import com.anthropic.models.messages.ContentBlockParam;
import com.anthropic.models.messages.TextBlockParam;
DocumentBlockParam doc = DocumentBlockParam.builder()
.base64Source(base64String) // or .urlSource("https://...") or .textSource("...")
.title("My Document") // optional
.build();
.addUserMessageOfBlockParams(List.of(
ContentBlockParam.ofDocument(doc),
ContentBlockParam.ofText(TextBlockParam.builder().text("Summarize this").build())))
```
---
## Server-Side Tools
Version-suffixed types; `name`/`type` auto-set by builder. Direct `.addTool()` overloads exist for every type — no manual `ToolUnion` wrapping.
```java
import com.anthropic.models.messages.WebSearchTool20260209;
import com.anthropic.models.messages.ToolBash20250124;
import com.anthropic.models.messages.ToolTextEditor20250728;
import com.anthropic.models.messages.CodeExecutionTool20260120;
.addTool(WebSearchTool20260209.builder()
.maxUses(5L) // optional
.allowedDomains(List.of("example.com")) // optional
.build())
.addTool(ToolBash20250124.builder().build())
.addTool(ToolTextEditor20250728.builder().build())
.addTool(CodeExecutionTool20260120.builder().build())
```
Also available: `WebFetchTool20260209`, `MemoryTool20250818`, `ToolSearchToolBm25_20251119`.
### Beta namespace (MCP, compaction)
For beta-only features use `com.anthropic.models.beta.messages.*` — class names have a `Beta` prefix AND live in the beta package. The beta `MessageCreateParams.Builder` has direct `.addTool(BetaToolBash20250124)` overloads AND `.addMcpServer()`:
```java
import com.anthropic.models.beta.messages.MessageCreateParams;
import com.anthropic.models.beta.messages.BetaToolBash20250124;
import com.anthropic.models.beta.messages.BetaCodeExecutionTool20260120;
import com.anthropic.models.beta.messages.BetaRequestMcpServerUrlDefinition;
MessageCreateParams params = MessageCreateParams.builder()
.model(Model.CLAUDE_OPUS_4_6)
.maxTokens(16000L)
.addBeta("mcp-client-2025-11-20")
.addTool(BetaToolBash20250124.builder().build())
.addTool(BetaCodeExecutionTool20260120.builder().build())
.addMcpServer(BetaRequestMcpServerUrlDefinition.builder()
.name("my-server")
.url("https://example.com/mcp")
.build())
.addUserMessage("...")
.build();
client.beta().messages().create(params);
```
`BetaTool*` types are NOT interchangeable with non-beta `Tool*` — pick one namespace per request.
**Reading server-tool blocks in the response:** `ServerToolUseBlock` has `.id()`, `.name()` (enum), and `._input()` returning raw `JsonValue` — there is NO typed `.input()`. For code execution results, unwrap two levels:
```java
for (ContentBlock block : response.content()) {
block.serverToolUse().ifPresent(stu -> {
System.out.println("tool: " + stu.name() + " input: " + stu._input());
});
block.codeExecutionToolResult().ifPresent(r -> {
r.content().resultBlock().ifPresent(result -> {
System.out.println("stdout: " + result.stdout());
System.out.println("stderr: " + result.stderr());
System.out.println("exit: " + result.returnCode());
});
});
}
```
---
## Files API (Beta)
Under `client.beta().files()`. File references in messages need the beta message types (non-beta `DocumentBlockParam.Source` has no file-ID variant).
```java
import com.anthropic.models.beta.files.FileUploadParams;
import com.anthropic.models.beta.files.FileMetadata;
import com.anthropic.models.beta.messages.BetaRequestDocumentBlock;
import java.nio.file.Paths;
FileMetadata meta = client.beta().files().upload(
FileUploadParams.builder()
.file(Paths.get("/path/to/doc.pdf")) // or .file(InputStream) or .file(byte[])
.build());
// Reference in a beta message:
BetaRequestDocumentBlock doc = BetaRequestDocumentBlock.builder()
.fileSource(meta.id())
.build();
```
Other methods: `.list()`, `.delete(String fileId)`, `.download(String fileId)`, `.retrieveMetadata(String fileId)`.