grpc/grpc-java · error · UnsupportedOperationException

Not implemented

Error message

Not implemented

What it means

LoadBalancer.createResolvingOobChannelBuilder(String) is a deprecated base-class stub in grpc-java that throws UnsupportedOperationException by default. Concrete LoadBalancer implementations are expected to override it; the base implementation exists only to preserve API compatibility. It is deprecated in favor of the credentials-aware overload, so calling the unoverridden default always fails.

Source

Thrown at api/src/main/java/io/grpc/LoadBalancer.java:1175

     * on {@link ManagedChannelBuilder#forTarget} for the format of a target string.
     *
     * <p>The target string will be resolved by a {@link NameResolver} created according to the
     * target string.
     *
     * <p>The returned oob-channel builder defaults to use the same authority and ChannelCredentials
     * (without bearer tokens) as the parent channel's for authentication. This is different from
     * {@link #createResolvingOobChannelBuilder(String, ChannelCredentials)}.
     *
     * <p>The LoadBalancer is responsible for closing unused OOB channels, and closing all OOB
     * channels within {@link #shutdown}.
     *
     * @deprecated Use {@link #createResolvingOobChannelBuilder(String, ChannelCredentials)}
     *     instead.
     * @since 1.31.0
     */
    @Deprecated
    public ManagedChannelBuilder<?> createResolvingOobChannelBuilder(String target) {
      throw new UnsupportedOperationException("Not implemented");
    }

    /**
     * Creates an out-of-band channel builder for LoadBalancer's own RPC needs, e.g., talking to an
     * external load-balancer service, that is specified by a target string and credentials.  See
     * the documentation on {@link Grpc#newChannelBuilder} for the format of a target string.
     *
     * <p>The target string will be resolved by a {@link NameResolver} created according to the
     * target string.
     *
     * <p>The LoadBalancer is responsible for closing unused OOB channels, and closing all OOB
     * channels within {@link #shutdown}.
     *
     * @since 1.35.0
     */
    public ManagedChannelBuilder<?> createResolvingOobChannelBuilder(
        String target, ChannelCredentials creds) {
      throw new UnsupportedOperationException();

View on GitHub (pinned to 64daddc1f3)

Solutions

  1. Switch to the non-deprecated overload createResolvingOobChannelBuilder(String target, ChannelCredentials creds), which concrete implementations override
  2. Use createOobChannel(ResolvedServerAddresses) / createResolvingOobChannel alternative entry points on the LoadBalancer.Helper if credentials handling is done elsewhere
  3. Upgrade or fix the LoadBalancer implementation so it overrides createResolvingOobChannelBuilder; never call the deprecated base stub directly
  4. Catch UnsupportedOperationException and fall back to a locally built channel via ManagedChannelBuilder.forTarget(target)

Example fix

// before
ManagedChannelBuilder<?> b = helper.createResolvingOobChannelBuilder(target);
// after
ManagedChannelBuilder<?> b = helper.createResolvingOobChannelBuilder(target, InsecureChannelCredentials.create());
Defensive patterns

Strategy: try-catch

Validate before calling

// Java: prefer the credentials overload outright
ManagedChannelBuilder<?> b = helper.createResolvingOobChannelBuilder(target, creds); // never the deprecated String-only stub

Try / catch

try {
  builder = helper.createResolvingOobChannelBuilder(target);
} catch (UnsupportedOperationException e) {
  builder = helper.createResolvingOobChannelBuilder(target, InsecureChannelCredentials.create());
}

Prevention

When it happens

Trigger: Calling the single-argument createResolvingOobChannelBuilder(target) on a LoadBalancer (or a third-party/custom LoadBalancer) that has not overridden it — the inherited base method throws immediately.

Common situations: Custom or third-party LoadBalancer implementations that predate the credentials-aware overload; code that still uses the deprecated String-target variant instead of createResolvingOobChannelBuilder(String, ChannelCredentials); library versions where implementers never overrode this stub.

Related errors

AI-assisted analysis of grpc/grpc-java@64daddc1f3 (2026-09-08). Data as JSON: /api/errors/0104844cb212519b. Report an issue: GitHub.