Netflix/Hystrix · error · java.lang.UnsupportedOperationException

Not implemented anymore. Will be implemented in a new class

Error message

Not implemented anymore.  Will be implemented in a new class shortly

What it means

SerialHystrixRequestEvents.toBytes(HystrixRequestEvents) is a deprecated stub that unconditionally throws UnsupportedOperationException. Hystrix request-event data (per-request command executions and emitted event counts, used by the request-log servlet and hystrix-request-servlet samples) moved to a JSON representation in 1.5.x, and the binary encoder was deleted. The implemented path in the same class is toJsonString(HystrixRequestEvents), which writes via a JsonGenerator.

Source

Thrown at hystrix-serialization/src/main/java/com/netflix/hystrix/serial/SerialHystrixRequestEvents.java:32

 * limitations under the License.
 */
package com.netflix.hystrix.serial;

import com.fasterxml.jackson.core.JsonGenerator;
import com.netflix.hystrix.ExecutionResult;
import com.netflix.hystrix.HystrixEventType;
import com.netflix.hystrix.metric.HystrixRequestEvents;

import java.io.IOException;
import java.io.StringWriter;
import java.util.List;
import java.util.Map;

public class SerialHystrixRequestEvents extends SerialHystrixMetric {

    @Deprecated
    public static byte[] toBytes(HystrixRequestEvents requestEvents) {
        throw new UnsupportedOperationException("Not implemented anymore.  Will be implemented in a new class shortly");
    }

    public static String toJsonString(HystrixRequestEvents requestEvents) {
        StringWriter jsonString = new StringWriter();

        try {
            JsonGenerator json = jsonFactory.createGenerator(jsonString);

            serializeRequestEvents(requestEvents, json);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }

        return jsonString.getBuffer().toString();
    }

    private static void serializeRequestEvents(HystrixRequestEvents requestEvents, JsonGenerator json) {
        try {

View on GitHub (pinned to 5ce3bc58c3)

Solutions

Switch to SerialHystrixRequestEvents.toJsonString(requestEvents) and store/transmit the JSON string.
If byte[] storage is required, encode the JSON string: toJsonString(requestEvents).getBytes(StandardCharsets.UTF_8).
Verify no other serial classes in the same call chain still use the removed binary API (grep for toBytes(/fromByteBuffer( against com.netflix.hystrix.serial).
Turn deprecation warnings into build errors so this class of latent runtime failure is caught at compile time.

Example fix

// before
byte[] blob = SerialHystrixRequestEvents.toBytes(requestEvents);

// after
byte[] blob = SerialHystrixRequestEvents.toJsonString(requestEvents)
        .getBytes(java.nio.charset.StandardCharsets.UTF_8);

Defensive patterns

Strategy: try-catch

Validate before calling

// Route request-event persistence through the implemented JSON API only.
static String persist(HystrixRequestEvents events) {
    return SerialHystrixRequestEvents.toJsonString(events); // never call toBytes()
}

Try / catch

try {
    blob = SerialHystrixRequestEvents.toBytes(requestEvents);
} catch (UnsupportedOperationException e) {
    blob = SerialHystrixRequestEvents.toJsonString(requestEvents)
            .getBytes(java.nio.charset.StandardCharsets.UTF_8);
}

Prevention

Use toJsonString for HystrixRequestEvents persistence; the byte[] overload is a guaranteed throw in 1.5.x.
Check the Hystrix release notes / migration guide (1.4 -> 1.5) before upgrading projects that serialize request logs.
Compile with deprecation-as-error so the @Deprecated stub cannot slip through.
Cover request-event persistence with a unit test that exercises the serialization call once — the stub fails on first invocation, so one test catches it.

When it happens

Trigger: Calling SerialHystrixRequestEvents.toBytes(requestEvents) — e.g. a request-log persistor or audit layer that stored per-request event blobs as byte arrays. Because the method signature still exists and compiles, the failure surfaces only at runtime on first call, for every request that reaches that code path.

Common situations: Porting a request-log/auditing extension from Hystrix 1.4 to 1.5+; following old documentation or blog examples that serialized HystrixRequestEvents to byte[] for storage in Redis/Kafka/files; teams adding request-event persistence for the first time and picking the byte-array overload from IDE suggestions without noticing @Deprecated.

Related errors

AI-assisted analysis of Netflix/Hystrix@5ce3bc58c3 (2026-08-14). Data as JSON: /api/errors/837958c46e2b9679. Report an issue: GitHub.