checkstyle change:

1. Adds <property name="separateLineBetweenGroups" value="true"/> to CustomImportOrder to enfore blank line between imports groups.
2. Uses checkstyle 6.5, which fixed a bug of "CustomImportOrder checks import sorting according to ASCII order instead of case-insensitive alphabetical order".

benchmarks/src/main/java/io/grpc/benchmarks/qps/QpsClient.java

@@ -61,8 +61,8 @@ import java.util.List;
 import java.util.concurrent.CancellationException;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
-import java.util.concurrent.TimeoutException;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
 import java.util.logging.Logger;
 
 /**

build.gradle

@@ -90,7 +90,7 @@ subprojects {
 
     checkstyle {
         configFile = file("$rootDir/checkstyle.xml")
-        toolVersion = "6.2"
+        toolVersion = "6.5"
         ignoreFailures = true
         if (rootProject.hasProperty("checkstyle.ignoreFailures")) {
             ignoreFailures = rootProject.properties["checkstyle.ignoreFailures"].toBoolean()

checkstyle.xml

@@ -165,6 +165,7 @@
             <property name="specialImportsRegExp" value="com.google"/>
             <property name="sortImportsInGroupAlphabetically" value="true"/>
             <property name="customImportOrderRules" value="STATIC###SPECIAL_IMPORTS###THIRD_PARTY_PACKAGE###STANDARD_JAVA_PACKAGE"/>
+            <property name="separateLineBetweenGroups" value="true"/>
         </module>
         <module name="MethodParamPad"/>
         <module name="OperatorWrap">

core/src/main/java/io/grpc/AbstractChannelBuilder.java

@@ -37,8 +37,8 @@ import com.google.common.util.concurrent.ThreadFactoryBuilder;
 import io.grpc.SharedResourceHolder.Resource;
 import io.grpc.transport.ClientTransportFactory;
 
-import java.util.concurrent.Executors;
 import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 
 import javax.annotation.Nullable;
 

core/src/main/java/io/grpc/ChannelImpl.java

@@ -39,8 +39,8 @@ import io.grpc.transport.ClientStreamListener;
 import io.grpc.transport.ClientTransport;
 import io.grpc.transport.ClientTransportFactory;
 
-import java.io.InputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.concurrent.ExecutorService;

core/src/main/java/io/grpc/DeferredInputStream.java

@@ -31,8 +31,8 @@
 
 package io.grpc;
 
-import java.io.InputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.io.OutputStream;
 
 import javax.annotation.Nullable;

core/src/main/java/io/grpc/ServerImpl.java

@@ -41,8 +41,8 @@ import io.grpc.transport.ServerStream;
 import io.grpc.transport.ServerStreamListener;
 import io.grpc.transport.ServerTransportListener;
 
-import java.io.InputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.util.Collection;
 import java.util.HashSet;
 import java.util.concurrent.Executor;

core/src/main/java/io/grpc/transport/MessageDeframer.java

@@ -36,8 +36,8 @@ import com.google.common.base.Preconditions;
 import io.grpc.Status;
 
 import java.io.Closeable;
-import java.io.InputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.util.zip.GZIPInputStream;
 
 import javax.annotation.concurrent.NotThreadSafe;

core/src/main/java/io/grpc/transport/MessageFramer.java

@@ -40,8 +40,8 @@ import io.grpc.DeferredInputStream;
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
-import java.io.InputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.io.OutputStream;
 import java.nio.ByteBuffer;
 import java.util.zip.GZIPOutputStream;

core/src/main/java/io/grpc/transport/ReadableBuffers.java

@@ -35,8 +35,8 @@ import static com.google.common.base.Charsets.UTF_8;
 
 import com.google.common.base.Preconditions;
 
-import java.io.InputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.io.OutputStream;
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;

core/src/test/java/io/grpc/ServerImplTest.java

@@ -64,13 +64,13 @@ import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 
 import java.io.ByteArrayInputStream;
-import java.io.InputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.util.concurrent.BrokenBarrierException;
 import java.util.concurrent.CyclicBarrier;
 import java.util.concurrent.Executor;
-import java.util.concurrent.Executors;
 import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
 

core/src/test/java/io/grpc/transport/MessageDeframerTest.java

@@ -51,8 +51,8 @@ import org.junit.runners.JUnit4;
 import org.mockito.ArgumentCaptor;
 
 import java.io.ByteArrayOutputStream;
-import java.io.InputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.util.List;
 import java.util.zip.GZIPOutputStream;
 

examples/src/main/java/io/grpc/examples/routeguide/RouteGuideUtil.java

@@ -31,8 +31,8 @@
 
 package io.grpc.examples.routeguide;
 
-import java.io.InputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.net.URL;
 import java.util.ArrayList;
 import java.util.List;

integration-testing/src/main/java/io/grpc/testing/integration/TestServiceImpl.java

@@ -45,8 +45,8 @@ import io.grpc.testing.integration.Messages.StreamingInputCallResponse;
 import io.grpc.testing.integration.Messages.StreamingOutputCallRequest;
 import io.grpc.testing.integration.Messages.StreamingOutputCallResponse;
 
-import java.io.InputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.util.LinkedList;
 import java.util.Queue;
 import java.util.Random;

integration-testing/src/main/java/io/grpc/testing/integration/Util.java

@@ -41,8 +41,8 @@ import org.junit.Assert;
 import java.io.BufferedWriter;
 import java.io.File;
 import java.io.FileWriter;
-import java.io.InputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.net.ServerSocket;
 import java.util.List;
 

nano/src/main/java/io/grpc/nano/NanoUtils.java

@@ -38,8 +38,8 @@ import com.google.protobuf.nano.MessageNano;
 import io.grpc.Marshaller;
 import io.grpc.Status;
 
-import java.io.InputStream;
 import java.io.IOException;
+import java.io.InputStream;
 
 /**
  * Utility methods for using nano proto with grpc.

netty/src/main/java/io/grpc/transport/netty/Utils.java

@@ -50,8 +50,8 @@ import io.netty.util.concurrent.GenericFutureListener;
 
 import java.nio.ByteBuffer;
 import java.util.Map;
-import java.util.concurrent.Executors;
 import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.concurrent.ThreadFactory;
 
 /**

netty/src/test/java/io/grpc/transport/netty/NettyClientHandlerTest.java

@@ -34,8 +34,8 @@ package io.grpc.transport.netty;
 import static com.google.common.base.Charsets.UTF_8;
 import static io.grpc.transport.netty.Utils.CONTENT_TYPE_GRPC;
 import static io.grpc.transport.netty.Utils.CONTENT_TYPE_HEADER;
-import static io.grpc.transport.netty.Utils.HTTP_METHOD;
 import static io.grpc.transport.netty.Utils.HTTPS;
+import static io.grpc.transport.netty.Utils.HTTP_METHOD;
 import static io.grpc.transport.netty.Utils.STATUS_OK;
 import static io.grpc.transport.netty.Utils.TE_HEADER;
 import static io.grpc.transport.netty.Utils.TE_TRAILERS;

okhttp/src/main/java/io/grpc/transport/okhttp/OkHttpChannelBuilder.java

@@ -40,8 +40,8 @@ import io.grpc.SharedResourceHolder.Resource;
 import io.grpc.transport.ClientTransportFactory;
 
 import java.net.InetSocketAddress;
-import java.util.concurrent.Executors;
 import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 
 import javax.net.ssl.SSLSocketFactory;
 

okhttp/src/test/java/io/grpc/transport/okhttp/OkHttpClientTransportTest.java

@@ -73,17 +73,17 @@ import org.mockito.MockitoAnnotations;
 
 import java.io.BufferedReader;
 import java.io.ByteArrayInputStream;
+import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
-import java.io.IOException;
 import java.net.Socket;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.CountDownLatch;
-import java.util.concurrent.Executors;
 import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
 
 /**