Generating custom subsegments with the X-Ray SDK for Java - Amazon X-Ray
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Generating custom subsegments with the X-Ray SDK for Java

Subsegments extend a trace's segment with details about work done in order to serve a request. Each time you make a call with an instrumented client, the X-Ray SDK records the information generated in a subsegment. You can create additional subsegments to group other subsegments, to measure the performance of a section of code, or to record annotations and metadata.

To manage subsegments, use the beginSubsegment and endSubsegment methods.

Example - custom subsegment
import com.amazonaws.xray.AWSXRay; ... public void saveGame(Game game) throws SessionNotFoundException { // wrap in subsegment Subsegment subsegment = AWSXRay.beginSubsegment("Save Game"); try { // check session String sessionId = game.getSession(); if (sessionModel.loadSession(sessionId) == null ) { throw new SessionNotFoundException(sessionId); }; } catch (Exception e) { subsegment.addException(e); throw e; } finally { AWSXRay.endSubsegment(); } }

In this example, the code within the subsegment loads the game's session from DynamoDB with a method on the session model, and uses the Amazon SDK for Java's DynamoDB mapper to save the game. Wrapping this code in a subsegment makes the calls DynamoDB children of the Save Game subsegment in the trace view in the console.

If the code in your subsegment throws checked exceptions, wrap it in a try block and call AWSXRay.endSubsegment() in a finally block to ensure that the subsegment is always closed. If a subsegment is not closed, the parent segment cannot be completed and won't be sent to X-Ray.

For code that doesn't throw checked exceptions, you can pass the code to AWSXRay.CreateSubsegment as a Lambda function.

Example Subsegment Lambda function
import com.amazonaws.xray.AWSXRay; AWSXRay.createSubsegment("getMovies", (subsegment) -> { // function code });

When you create a subsegment within a segment or another subsegment, the X-Ray SDK for Java generates an ID for it and records the start time and end time.

Example Subsegment with metadata
"subsegments": [{ "id": "6f1605cd8a07cb70", "start_time": 1.480305974194E9, "end_time": 1.4803059742E9, "name": "Custom subsegment for UserModel.saveUser function", "metadata": { "debug": { "test": "Metadata string from UserModel.saveUser" } },

For asynchronous and multi-threaded programming, you must manually pass the subsegment to the endSubsegment() method to ensure it is closed correctly because the X-Ray context may be modified during async execution. If an asynchronous subsegment is closed after its parent segment is closed, this method will automatically stream the entire segment to the X-Ray daemon.

Example Asynchronous Subsegment
@GetMapping("/api") public ResponseEntity<?> api() { CompletableFuture.runAsync(() -> { Subsegment subsegment = AWSXRay.beginSubsegment("Async Work"); try { Thread.sleep(3000); } catch (InterruptedException e) { subsegment.addException(e); throw e; } finally { AWSXRay.endSubsegment(subsegment); } }); return ResponseEntity.ok().build(); }