Implementation:Datahub project Datahub RestEmitter

Knowledge Sources	Datahub_project_Datahub
Domains	Java_SDK, Metadata_Management
Last Updated	2026-02-10 00:00 GMT

Overview

RestEmitter is a thread-safe HTTP client wrapper that provides non-blocking emission of metadata change proposals (MCPs) to the DataHub GMS backend over REST.

Description

The RestEmitter class is a thin wrapper on top of the Apache HttpClient 5 async library. It handles the details of JSON serialization of metadata aspects, authentication via bearer tokens, retry strategies, SSL configuration, and both the legacy RestLI ingest endpoint (/aspects?action=ingestProposal) and the OpenAPI entities endpoint (/openapi/entities/v1/). All HTTP calls are non-blocking, returning Future<MetadataWriteResponse> to allow asynchronous metadata emission.

Key responsibilities:

• Serialization: Converts MetadataChangeProposal and MetadataChangeProposalWrapper objects to JSON payloads using Jackson and JacksonDataTemplateCodec.
• Authentication: Supports bearer token authentication via the Authorization header, along with custom extra headers.
• SSL: Supports optional SSL verification disablement for development environments via TrustAllStrategy and NoopHostnameVerifier.
• Retry: Uses a configurable DatahubHttpRequestRetryStrategy with max retries and retry interval.
• Connection test: Provides a testConnection() method that GETs the /config endpoint to verify connectivity.
• OpenAPI support: Supports batch upserts via List<UpsertAspectRequest> on the OpenAPI endpoint.

The class implements the Emitter interface and is annotated @ThreadSafe.

Usage

Use RestEmitter when you need to programmatically emit metadata to a DataHub instance from a Java application. It is the primary transport mechanism used by the Java SDK V2 EntityClient to send entity data to the server. Users can construct it via the fluent builder factory method or obtain it indirectly through DataHubClientV2.

Code Reference

Source Location

• Repository: Datahub_project_Datahub
• File: metadata-integration/java/datahub-client/src/main/java/datahub/client/rest/RestEmitter.java

Signature

@ThreadSafe
@Slf4j
public class RestEmitter implements Emitter {

    // Factory methods
    public static RestEmitter create(Consumer<RestEmitterConfig.RestEmitterConfigBuilder> builderSupplier);
    public static RestEmitter createWithDefaults();

    // Constructor
    public RestEmitter(RestEmitterConfig config);

    // Emit methods
    public Future<MetadataWriteResponse> emit(MetadataChangeProposalWrapper mcpw, Callback callback) throws IOException;
    public Future<MetadataWriteResponse> emit(MetadataChangeProposal mcp, Callback callback) throws IOException;
    public Future<MetadataWriteResponse> emit(List<UpsertAspectRequest> request, Callback callback) throws IOException;

    // Utility methods
    public boolean testConnection() throws IOException, ExecutionException, InterruptedException;
    public RestEmitterConfig getConfig();
    public Future<MetadataWriteResponse> get(String urlStr) throws IOException;
    public void close() throws IOException;
}

Import

import datahub.client.rest.RestEmitter;

I/O Contract

Inputs

Parameter	Type	Description
config	RestEmitterConfig	Configuration including server URL, token, timeout, SSL settings, extra headers, retry policy, and async ingest flag
mcpw	MetadataChangeProposalWrapper	Wrapped metadata change proposal for emission via RestLI endpoint
mcp	MetadataChangeProposal	Raw metadata change proposal for emission via RestLI endpoint
request	List<UpsertAspectRequest>	Batch of aspect upsert requests for emission via OpenAPI endpoint
callback	Callback	Optional callback invoked on completion or failure

Outputs

Return Type	Description
Future<MetadataWriteResponse>	Asynchronous response indicating success/failure, HTTP status, and response body content
boolean	Connection test result (from testConnection())

Usage Examples

// Create with fluent builder
RestEmitter emitter = RestEmitter.create(b -> b
    .server("http://localhost:8080")
    .token("your-access-token")
);

// Test connection
boolean connected = emitter.testConnection();

// Emit a MetadataChangeProposalWrapper
MetadataChangeProposalWrapper mcp = MetadataChangeProposalWrapper.builder()
    .entityType("dataset")
    .entityUrn(datasetUrn)
    .upsert()
    .aspect(ownership)
    .build();
Future<MetadataWriteResponse> future = emitter.emit(mcp, null);
MetadataWriteResponse response = future.get();

// Create with default settings
RestEmitter defaultEmitter = RestEmitter.createWithDefaults();

// Close when done
emitter.close();

Related Pages

• Environment:Datahub_project_Datahub_Java_17_Backend_Environment