cleanup(gax-java): remove javax.annotation.Nonnull usage (#13959)

This PR removes all occurrences of legacy javax.annotation.Nonnull
annotations and imports across the gax-java codebase, removes the unused
jsr305 dependency, and corrects misplaced/incorrect nullability
annotations in the core modules (gax, gax-grpc, and gax-httpjson).
### Why this change is needed:
As part of the repository-wide migration to JSpecify annotations,
packages/classes are annotated with @NullMarked, making all unannotated
types non-nullable by default.

- The legacy javax.annotation.Nonnull annotations are redundant under
JSpecify semantics and can be safely removed.
- Resolving misplaced nullability signatures and aligning overridden
methods enables compilation checks under NullAway static analysis with
JSpecifyMode=true.

### JSR-305 (`jsr305`) Dependency Removal:
We removed the `com.google.code.findbugs:jsr305` dependency from the
`pom.xml` files. This is not a breaking change for the following
reasons:
* **Why it was removed**: Because we removed all references to the
`javax.annotation` package in the codebase, the Maven dependency
analyzer (`mvn dependency:analyze`) flagged `jsr305` as an **unused
declared dependency**. Since our verification fails on any warning
(`-DfailOnWarning=true`), the dependency had to be removed to pass
presubmit checks.
* **Why it's not a breaking change**: The dependency was declared with
`provided` scope, meaning it was only used during compilation and was
**never** distributed transitively to downstream users. Removing it has
no runtime impact on library consumers.
### Changes:
* Removed `import javax.annotation.Nonnull;` and `@Nonnull` from 30
files across `gax`, `gax-grpc`, and `gax-httpjson` (including test
files).
* Migrated remaining `javax.annotation.Nullable` usages in tests to
JSpecify's `@Nullable` type-use annotation.
* Removed the unused `jsr305` dependency from the `gax-java` module
POMs.
* Fixed type-use annotation placements and annotate missing annotations
* Formatted all modified files using `fmt-maven-plugin`.
* Verified that all compilation and dependency analysis stages pass
cleanly.

Author: nnicolee

sdk-platform-java/gax-java/gax-grpc/pom.xml

@@ -81,11 +81,7 @@
       <artifactId>grpc-googleapis</artifactId>
       <scope>runtime</scope>
     </dependency>
-    <dependency>
-      <groupId>com.google.code.findbugs</groupId>
-      <artifactId>jsr305</artifactId>
-      <scope>provided</scope>
-    </dependency>
+
     <dependency>
       <groupId>org.graalvm.sdk</groupId>
       <artifactId>nativeimage</artifactId>

sdk-platform-java/gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/GrpcCallContext.java

@@ -64,7 +64,6 @@
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
-import javax.annotation.Nonnull;
 import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
@@ -413,7 +412,7 @@ public GrpcCallContext withExtraHeaders(Map<String, List<String>> extraHeaders)
   }
 
   @Override
-  public RetrySettings getRetrySettings() {
+  public @Nullable RetrySettings getRetrySettings() {
     return retrySettings;
   }
 
@@ -436,7 +435,7 @@ public GrpcCallContext withRetrySettings(RetrySettings retrySettings) {
   }
 
   @Override
-  public Set<StatusCode.Code> getRetryableCodes() {
+  public @Nullable Set<StatusCode.Code> getRetryableCodes() {
     return retryableCodes;
   }
 
@@ -665,7 +664,6 @@ public GrpcCallContext withRequestParamsDynamicHeaderOption(String requestParams
 
   /** {@inheritDoc} */
   @Override
-  @Nonnull
   public ApiTracer getTracer() {
     ApiTracer tracer = callOptions.getOption(TRACER_KEY);
     if (tracer == null) {
@@ -676,7 +674,7 @@ public ApiTracer getTracer() {
 
   /** {@inheritDoc} */
   @Override
-  public GrpcCallContext withTracer(@Nonnull ApiTracer tracer) {
+  public GrpcCallContext withTracer(ApiTracer tracer) {
     Preconditions.checkNotNull(tracer);
     return withCallOptions(callOptions.withOption(TRACER_KEY, tracer));
   }

sdk-platform-java/gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/GrpcCallableFactory.java

@@ -60,7 +60,6 @@
 import com.google.longrunning.Operation;
 import com.google.longrunning.stub.OperationsStub;
 import io.grpc.MethodDescriptor;
-import javax.annotation.Nonnull;
 import org.jspecify.annotations.NullMarked;
 
 /** Class with utility methods to create grpc-based direct callables. */
@@ -330,7 +329,7 @@ ClientStreamingCallable<RequestT, ResponseT> createClientStreamingCallable(
   }
 
   @VisibleForTesting
-  static ApiTracerContext getApiTracerContext(@Nonnull MethodDescriptor<?, ?> methodDescriptor) {
+  static ApiTracerContext getApiTracerContext(MethodDescriptor<?, ?> methodDescriptor) {
     return ApiTracerContext.newBuilder()
         .setFullMethodName(methodDescriptor.getFullMethodName())
         .setTransport(ApiTracerContext.Transport.GRPC)

sdk-platform-java/gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/InstantiatingGrpcChannelProvider.java

@@ -266,9 +266,8 @@ public boolean needsExecutor() {
     return executor == null;
   }
 
-  @Nullable
   @Override
-  public Executor getExecutor() {
+  public @Nullable Executor getExecutor() {
     return executor;
   }
 
@@ -541,9 +540,9 @@ boolean canUseDirectPathWithUniverseDomain() {
     return endpoint.contains(Credentials.GOOGLE_DEFAULT_UNIVERSE);
   }
 
-  @Nullable
   @VisibleForTesting
-  ChannelCredentials createMtlsChannelCredentials() throws IOException, GeneralSecurityException {
+  @Nullable ChannelCredentials createMtlsChannelCredentials()
+      throws IOException, GeneralSecurityException {
     if (mtlsProvider == null) {
       return null;
     }
@@ -609,9 +608,8 @@ ChannelCredentials createMtlsChannelCredentials() throws IOException, GeneralSec
    * @return {@link ChannelCredentials} to use to create an mtls connection between client and S2A
    * @throws IOException on error
    */
-  @Nullable
   @VisibleForTesting
-  ChannelCredentials createMtlsToS2AChannelCredentials(
+  @Nullable ChannelCredentials createMtlsToS2AChannelCredentials(
       File trustBundle, File privateKey, File certChain) throws IOException {
     if (trustBundle == null || privateKey == null || certChain == null) {
       return null;

sdk-platform-java/gax-java/gax-grpc/src/test/java/com/google/api/gax/grpc/GrpcDirectStreamControllerTest.java

@@ -52,8 +52,7 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.TimeUnit;
-import javax.annotation.Nonnull;
-import javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.Timeout;
 
@@ -68,21 +67,19 @@ void testRetryNoRaceCondition() throws Exception {
         ManagedChannelBuilder.forAddress("localhost", 1234).usePlaintext().build();
     StreamResumptionStrategy<Color, Money> resumptionStrategy =
         new StreamResumptionStrategy<Color, Money>() {
-          @Nonnull
+
           @Override
           public StreamResumptionStrategy<Color, Money> createNew() {
             return this;
           }
 
-          @Nonnull
           @Override
           public Money processResponse(Money response) {
             return response;
           }
 
-          @Nullable
           @Override
-          public Color getResumeRequest(Color originalRequest) {
+          public @Nullable Color getResumeRequest(Color originalRequest) {
             return originalRequest;
           }
 

sdk-platform-java/gax-java/gax-grpc/src/test/java/com/google/api/gax/grpc/InstantiatingGrpcChannelProviderTest.java

@@ -81,7 +81,7 @@
 import java.util.logging.Level;
 import java.util.logging.LogRecord;
 import java.util.stream.Collectors;
-import javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.BeforeEach;
@@ -560,8 +560,7 @@ void testWithDefaultDirectPathServiceConfig() {
     assertThat(lbConfig.keySet()).containsExactly("pick_first");
   }
 
-  @Nullable
-  private static Map<String, ?> getAsObject(Map<String, ?> json, String key) {
+  private static @Nullable Map<String, ?> getAsObject(Map<String, ?> json, String key) {
     Object mapObject = json.get(key);
     if (mapObject == null) {
       return null;

sdk-platform-java/gax-java/gax-grpc/src/test/java/com/google/api/gax/grpc/MockClientCall.java

@@ -32,7 +32,7 @@
 import io.grpc.ClientCall;
 import io.grpc.Metadata;
 import io.grpc.Status;
-import javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 
 public class MockClientCall<RequestT, ResponseT> extends ClientCall<RequestT, ResponseT> {
 

sdk-platform-java/gax-java/gax-httpjson/pom.xml

@@ -72,11 +72,7 @@
       <groupId>com.google.protobuf</groupId>
       <artifactId>protobuf-java-util</artifactId>
     </dependency>
-    <dependency>
-      <groupId>com.google.code.findbugs</groupId>
-      <artifactId>jsr305</artifactId>
-      <scope>provided</scope>
-    </dependency>
+
     <dependency>
       <groupId>com.google.auto.value</groupId>
       <artifactId>auto-value-annotations</artifactId>

sdk-platform-java/gax-java/gax-httpjson/src/main/java/com/google/api/gax/httpjson/HttpJsonCallContext.java

@@ -55,7 +55,6 @@
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
-import javax.annotation.Nonnull;
 import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
@@ -510,7 +509,7 @@ public HttpJsonCallOptions getCallOptions() {
   }
 
   @Override
-  public RetrySettings getRetrySettings() {
+  public @Nullable RetrySettings getRetrySettings() {
     return retrySettings;
   }
 
@@ -531,7 +530,7 @@ public HttpJsonCallContext withRetrySettings(RetrySettings retrySettings) {
   }
 
   @Override
-  public Set<StatusCode.Code> getRetryableCodes() {
+  public @Nullable Set<StatusCode.Code> getRetryableCodes() {
     return retryableCodes;
   }
 
@@ -588,7 +587,6 @@ public HttpJsonCallContext withDeadline(org.threeten.bp.Instant newDeadline) {
     return withCallOptions(builder.setDeadline(newDeadline).build());
   }
 
-  @Nonnull
   @Override
   public ApiTracer getTracer() {
     if (tracer == null) {
@@ -599,7 +597,7 @@ public ApiTracer getTracer() {
 
   /** {@inheritDoc} */
   @Override
-  public HttpJsonCallContext withTracer(@Nonnull ApiTracer newTracer) {
+  public HttpJsonCallContext withTracer(ApiTracer newTracer) {
     Preconditions.checkNotNull(newTracer);
     HttpJsonCallOptions newCallOptions = callOptions.toBuilder().setTracer(newTracer).build();
 

sdk-platform-java/gax-java/gax-httpjson/src/main/java/com/google/api/gax/httpjson/HttpJsonCallableFactory.java

@@ -45,7 +45,6 @@
 import com.google.api.gax.rpc.UnaryCallable;
 import com.google.api.gax.tracing.ApiTracerContext;
 import com.google.api.gax.tracing.TracedUnaryCallable;
-import javax.annotation.Nonnull;
 import org.jspecify.annotations.NullMarked;
 
 /** Class with utility methods to create http/json-based direct callables. */
@@ -222,7 +221,7 @@ ServerStreamingCallable<RequestT, ResponseT> createServerStreamingCallable(
     return callable.withDefaultCallContext(clientContext.getDefaultCallContext());
   }
 
-  static ApiTracerContext getApiTracerContext(@Nonnull ApiMethodDescriptor<?, ?> methodDescriptor) {
+  static ApiTracerContext getApiTracerContext(ApiMethodDescriptor<?, ?> methodDescriptor) {
     return ApiTracerContext.newBuilder()
         .setFullMethodName(methodDescriptor.getFullMethodName())
         .setHttpMethod(methodDescriptor.getHttpMethod())