added example and created new annotation for instantiating server interceptors as beans rather than directly via GRpcServerRunner

Author: James Smith

grpc-spring-boot-starter-demo/src/main/java/org/lognet/springboot/grpc/demo/DemoInterceptor.java

@@ -0,0 +1,23 @@
+package org.lognet.springboot.grpc.demo;
+
+import io.grpc.Metadata;
+import io.grpc.ServerCall;
+import io.grpc.ServerCallHandler;
+import io.grpc.ServerInterceptor;
+import lombok.extern.slf4j.Slf4j;
+import org.lognet.springboot.grpc.GRpcInterceptor;
+
+/**
+ * Created by jamessmith on 9/7/16.
+ */
+@Slf4j
+@GRpcInterceptor
+public class DemoInterceptor implements ServerInterceptor {
+
+    @Override
+    public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(ServerCall<ReqT, RespT> call, Metadata headers,
+                                                                 ServerCallHandler<ReqT, RespT> next) {
+        log.info("Demo interceptor invoked!");
+        return next.startCall(call, headers);
+    }
+}

grpc-spring-boot-starter-demo/src/main/java/org/lognet/springboot/grpc/demo/GreeterApp.java

@@ -17,7 +17,7 @@
 @SpringBootApplication
 public class GreeterApp {
 
-    @GRpcService
+    @GRpcService(interceptors = { DemoInterceptor.class })
     public static class GreeterService extends GreeterGrpc.GreeterImplBase {
         @Override
         public void sayHello(GreeterOuterClass.HelloRequest request, StreamObserver<GreeterOuterClass.HelloReply> responseObserver) {
@@ -32,4 +32,3 @@ public static void main(String[] args) {
     }
 
 }
-

grpc-spring-boot-starter/src/main/java/org/lognet/springboot/grpc/GRpcInterceptor.java

@@ -0,0 +1,19 @@
+package org.lognet.springboot.grpc;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.springframework.stereotype.Service;
+
+/**
+ * Created by jamessmith on 9/7/16.
+ */
+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+@Service
+public @interface GRpcInterceptor {
+}

grpc-spring-boot-starter/src/main/java/org/lognet/springboot/grpc/GRpcServerRunner.java

@@ -75,11 +75,7 @@ private List<ServerInterceptor> buildInterceptors(Class<? extends ServerIntercep
         List<ServerInterceptor> interceptors = new ArrayList<>();
 
         for(Class<? extends ServerInterceptor> clazz : classes) {
-            try {
-                interceptors.add(clazz.newInstance());
-            } catch (InstantiationException | IllegalAccessException e) {
-                log.error("Unable to instantiate ServerInterceptor from class {}", clazz, e);
-            }
+            interceptors.add(applicationContext.getBean(clazz));
         }
 
         return interceptors;