Using the SDK

Configurable client options ship in v1.3.0. See the Changelog before upgrading.

Initialize the client

Your Blnk client is the single entry point to everything: ledgers, balances, transactions, webhooks, and more. Configure it once when your app starts, then use it everywhere.

BlnkClient.java

import com.blnkfinance.blnk.Blnk;
import com.blnkfinance.blnk.BlnkClientOptions;

public final class BlnkClient {
  private static final String apiKey = System.getenv().getOrDefault("BLNK_API_KEY", "");
  private static final String baseUrl = System.getenv().getOrDefault(
      "BLNK_BASE_URL",
      "http://localhost:5001"
  );

  public static final Blnk BLNK = Blnk.init(
      apiKey,
      BlnkClientOptions.builder()
          .baseUrl(baseUrl)
          .build());
}

That’s it. One import, one call, one client. From here you can create ledgers, move money, reconcile transactions, and manage your entire financial infrastructure.

CreateLedgerExample.java

import com.blnkfinance.blnk.types.ApiResponse;
import com.blnkfinance.blnk.types.CreateLedger;
import com.fasterxml.jackson.databind.JsonNode;

import java.util.Map;

ApiResponse<JsonNode> response = BlnkClient.BLNK.ledgers().create(
    CreateLedger.create()
        .name("Customer Savings Account")
        .metaData(Map.of("project_owner", "YOUR_APP_NAME")));

System.out.println("Ledger Created: " + response.data());

Services are accessed through methods on the client: ledgers(), ledgerBalances(), transactions(), balanceMonitor(), reconciliation(), identity(), metadata(), hooks(), search(), apiKeys(), and system().

Builders and wire fields

Request bodies are built with fluent types in com.blnkfinance.blnk.types. Builder methods use camelCase (for example metaData(), skipQueue(), preciseAmount()). Blnk Core receives snake_case JSON on the wire (for example meta_data, skip_queue, precise_amount). On method pages, request field tables list the wire field name because it matches the HTTP API and response JSON. Map it to the Java builder in your code:

Wire field (table)	Java builder
`meta_data`	`.metaData()`
`skip_queue`	`.skipQueue()`
`precise_amount`	`.preciseAmount()`
`allow_overdraft`	`.allowOverdraft()`
`identity_type`	`.identityType()`
`expires_at`	`.expiresAt()`

When prose refers to an SDK method, it uses Java names: createBulk, updateStatus, blnk.transactions().create. JSON examples and metadata keys may still use snake_case (for example a custom metadata key named update_status).

Response bodies

Every method returns ApiResponse<JsonNode>. Treat response.data() as parsed JSON:

Object responses: response.data().get("ledger_id").asText()
Array responses: check response.data().isArray(), then read response.data().get(i).get("field")
Nested arrays: response.data().get("results").get(i).get("status").asText()
No body (204): response.data() is null; branch on response.status() only

Field tables on method pages use wire JSON names because they match the HTTP API. Read those fields from the JsonNode returned in response.data().

Authentication

Blnk.init takes two arguments: an API key and a BlnkClientOptions object. The options object must include baseUrl, the root URL of your Blnk Core instance. The SDK sends the API key on every request in the X-Blnk-Key header. How you set the API key depends on whether Core runs in secure mode:

Secure mode
Auth disabled

When server.secure is enabled, pass your API key as the first argument. Set baseUrl to the URL where Core is reachable.

String apiKey = System.getenv().getOrDefault("BLNK_API_KEY", "");
String baseUrl = System.getenv().getOrDefault(
    "BLNK_BASE_URL",
    "http://localhost:5001"
);

Blnk blnk = Blnk.init(
    apiKey,
    BlnkClientOptions.builder()
        .baseUrl(baseUrl)
        .build());

When secure mode is off, pass an empty string as the first argument.

Blnk blnk = Blnk.init(
    "",
    BlnkClientOptions.builder()
        .baseUrl("http://localhost:5001")
        .build());

Secure Blnk

Secure mode, master key, and server hardening.

Scoped API keys

Owner-scoped keys and permission limits.

Timeouts and retries

When connections fail, Core restarts, or requests hang, the SDK handles it without blocking your app. Pass these parameters on BlnkClientOptions.builder():

Blnk blnk = Blnk.init(
    apiKey,
    BlnkClientOptions.builder()
        .baseUrl("http://localhost:5001")
        .timeout(30000)
        .retryCount(3)
        .retryDelayMs(2000)
        .build());

Option	Type	Default	What it does for you
`timeout`	`int`	`10000`	Milliseconds to wait before giving up on a request. Bump this for slow operations like bulk reconciliations.
`retryCount`	`int`	`1`	Total attempts including the first. `1` means one attempt, no retries. `3` means try up to 3 times.
`retryDelayMs`	`int`	`2000`	Milliseconds between retries. Uses linear backoff.

When to tune these:

Keep defaults if you’re making fast, local calls and want to fail fast.
Increase timeout if you’re running large batch requests that may take a while to complete synchronously.
Increase retryCount if you’re reading data across an unreliable network.

Retries apply to GET requests only. Timeouts return a synthetic 408 response and are never retried.

Custom logger

By default, the SDK logs internal events through a built-in logger that writes to the console with INFO: and ERROR: prefixes. Pass a custom BlnkLogger to route these messages to your own logging system instead of the console.

import com.blnkfinance.blnk.BlnkLogger;

public final class AppLogger implements BlnkLogger {
  @Override
  public void info(String message, Object... meta) {
    appLogger.info(message);
  }

  @Override
  public void error(String message, Object... meta) {
    appLogger.error(message);
  }
}

Blnk blnk = Blnk.init(
    apiKey,
    BlnkClientOptions.builder()
        .baseUrl("http://localhost:5001")
        .logger(new AppLogger())
        .build());

Metadata passed to the logger is redacted. The SDK strips values for keys such as api_key, authorization, token, and secret before logging.

Level	When the SDK calls it
`info`	Before a retry, or when a retryable `GET` failure will be retried
`error`	When a request times out, returns a non-retryable HTTP error, or fails with a network error

Example logs

INFO: Retrying request to transactions/txn_f482a1b3-6c2d-4e89-a17b-3d5e8f2a1c94 { attempt: 2, maxAttempts: 3, delayMs: 2000 }

ERROR: Request timed out { endpoint: 'transactions/txn_f482a1b3-6c2d-4e89-a17b-3d5e8f2a1c94', timeoutMs: 30000 }

ERROR: Request to transactions/txn_f482a1b3-6c2d-4e89-a17b-3d5e8f2a1c94 failed with status 404.

Quick start

Install the SDK and create your first transaction.

Error handling

ApiResponse checks and Core error bodies.

Changelog

Java SDK releases and version history.

Need help?

We are very happy to help you make the most of Blnk, regardless of whether it is your first time or you are switching from another tool. To ask questions or discuss issues, please contact us or join our Discord community.

Start Here

Ledgers

Ledger balances

Transactions

Reconciliation

Identities

Metadata

Hooks

Search

API keys

System

Initialize the client

Builders and wire fields

Response bodies

Authentication

Secure Blnk

Scoped API keys

Timeouts and retries

Custom logger

Quick start

Error handling

Changelog

Need help?

​Initialize the client

​Builders and wire fields

​Response bodies

​Authentication

Secure Blnk

Scoped API keys

​Timeouts and retries

​Custom logger

​Related docs

Quick start

Error handling

Changelog

​Need help?

Initialize the client

Builders and wire fields

Response bodies

Authentication

Timeouts and retries

Custom logger

Related docs

Need help?