Java 9: cannot find symbol javax.annotation.Generated

[fcnn]

/root/grpc-kotlin-hello/proto/src/main/java/io/grpc/examples/helloworld/GreeterGrpc.java:23: error: cannot find symbol
@javax.annotation.Generated(
^
symbol: class Generated
location: package javax.annotation
1 error

FAILURE: Build failed with an exception.

[ejona86]

That class exists in Java 9: https://docs.oracle.com/javase/8/docs/api/javax/annotation/Generated.html . It seems like the problem is with an example that isn't maintained here.

[ejona86]

Okay... I've now run into this as well for our example after #3637.

[ejona86]

For gRPC's build, after #3633 I don't see a problem with @Generated for :compileJava. But I do see it for :javadoc. But in the example @Generated is broken in :compileJava, even if depending on a grpc dep that built fine (e.g., grpc-testing-proto, but installed using Java 8). :-/

[ejona86]

@onesea, I'd suggest adding a dependency on javax.annotation:javax.annotation-api for the moment. It's possible to pass --add-modules java.xml.ws.annotation, but it seems it might cause more problems than it solves.

[davido]

I run into the same problem while working on Bazel build with Java 9: bazelbuild/bazel#4709.

[davido]

The way it was fixed in other java based libraries, like auto-common, auto-value and dagger, is to dynamically select the right annotation to use:

• Java 9: javax.annotation.processing.Generated
• Java 8: javax.annotation.Generated

See e.g.: google/auto@f04406c, google/dagger#882.

[ejona86]

@davido, dynamic selection doesn't really seem to be a solution except for annotation processors.

[davido]

@ejona86 The other two options would be to detect the Java runtime or pass explicit option to gRpc compiler, a lá: --release 9 or similar?

[davido]

I was able to patch gRpc compiler in Bazel tree, with this one liner:

diff --git a/third_party/grpc/compiler/src/java_plugin/cpp/java_generator.cpp b/third_party/grpc/compiler/src/java_plugin/cpp/java_generator.cpp
index 7cb01238ac..3264f15ecf 100644
--- a/third_party/grpc/compiler/src/java_plugin/cpp/java_generator.cpp
+++ b/third_party/grpc/compiler/src/java_plugin/cpp/java_generator.cpp
@@ -1203,7 +1203,7 @@ void GenerateService(const ServiceDescriptor* service,
   vars["NanoUtils"] = "io.grpc.protobuf.nano.NanoUtils";
   vars["StreamObserver"] = "io.grpc.stub.StreamObserver";
   vars["Iterator"] = "java.util.Iterator";
-  vars["Generated"] = "javax.annotation.Generated";
+  vars["Generated"] = "javax.annotation.processing.Generated";
   vars["ListenableFuture"] =
       "com.google.common.util.concurrent.ListenableFuture";
   vars["ExperimentalApi"] = "io.grpc.ExperimentalApi";

With this, the generated source is:

/**
 */
@javax.annotation.processing.Generated(
    value = "by gRPC proto compiler",
    comments = "Source: src/main/protobuf/command_server.proto")
public final class CommandServerGrpc {

  private CommandServerGrpc() {}
[...]

And the Bazel build on Java 9 just works:

  $ bazel --host_javabase=/usr/lib64/jvm/java-9-openjdk build --javacopt='--release 9' --java_toolchain=@bazel_tools//tools/jdk:toolchain_jdk9 src:bazel
[...]
INFO: From Compiling Java headers src/main/java/com/google/devtools/build/lib/worker/libworker-hjar.jar (16 files):
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by com.google.protobuf.UnsafeUtil (file:/home/davido/.cache/bazel/_bazel_davido/install/5906941a530f40a3f4749e5cfd148312/_embedded_binaries/embedded_tools/tools/jdk/turbine_deploy.jar) to field java.nio.Buffer.address
WARNING: Please consider reporting this to the maintainers of com.google.protobuf.UnsafeUtil
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
INFO: From Building src/main/java/com/google/devtools/build/lib/libbazel-main-class.jar (4 source files) and running annotation processors (OptionProcessor):
warning: Supported source version 'RELEASE_8' from annotation processor 'com.google.devtools.common.options.processor.OptionProcessor' less than -source '1.9'
Target //src:bazel up-to-date:
  bazel-bin/src/bazel
INFO: Elapsed time: 149.130s, Critical Path: 111.80s
INFO: Build completed successfully, 1986 total actions