HeaderClientInterceptor.java

package example.grpc.clients.testing_service;
 
import io.grpc.CallOptions;
import io.grpc.Channel;
import io.grpc.ClientCall;
import io.grpc.ClientInterceptor;
import io.grpc.ForwardingClientCall.SimpleForwardingClientCall;
import io.grpc.ForwardingClientCallListener.SimpleForwardingClientCallListener;
import io.grpc.Metadata;
import io.grpc.MethodDescriptor;
 
public class HeaderClientInterceptor implements ClientInterceptor {
 @Override
 public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(MethodDescriptor<ReqT, RespT> method,
   CallOptions callOptions, Channel next) {
  return new SimpleForwardingClientCall<ReqT, RespT>(next.newCall(method, callOptions)) {
   @Override
   public void start(Listener<RespT> responseListener, Metadata headers) {
    if (headers != null) {
     Metadata fixedHeaders = new Metadata();
     Metadata.Key<String> key = Metadata.Key.of("header", Metadata.ASCII_STRING_MARSHALLER);
     fixedHeaders.put(key, "hiiii");
     headers.merge(fixedHeaders);
    }
    super.start(new SimpleForwardingClientCallListener<RespT>(responseListener) {
     @Override
     public void onHeaders(Metadata headers) {
      super.onHeaders(headers);
     }
    }, headers);
   }
  };
 }
}