From 80d1c06dc04937a47e0853309e0add63903023b8 Mon Sep 17 00:00:00 2001
From: Aljoscha Krettek <aljoscha.krettek@gmail.com>
Date: Fri, 17 Mar 2017 15:32:23 +0100
Subject: [PATCH] [FLINK-6107] Custom checkstyle for flink-streaming-java

This is based on the Apache Beam checkstyle with some custom
modifications for making it fit the exisiting Flink code base. The most
notable change is that Flink uses Tabs for indentation while Beam uses
spaces.

This adds a lot of checks that are commented out because they require
non-trivial changes to the code base.

There are some trivial code changes for good practices checkstyle rules
that where only broken in very few places.
---
 flink-streaming-java/pom.xml                  |  35 ++
 .../collector/selector/OutputSelector.java    |   2 +-
 .../streaming/api/datastream/DataStream.java  |   2 +-
 .../source/ContinuousFileReaderOperator.java  |   2 +-
 .../MessageAcknowledgingSourceBase.java       |   4 +-
 .../windowing/delta/DeltaFunction.java        |   2 +-
 .../windowing/delta/extractor/Extractor.java  |   2 +-
 .../flink/streaming/api/graph/StreamEdge.java |   8 +-
 .../api/graph/StreamGraphGenerator.java       |   2 +-
 .../flink/streaming/api/graph/StreamNode.java |   2 +-
 .../api/operators/StreamSourceContexts.java   |   2 +-
 .../streaming/api/operators/Triggerable.java  |   2 +-
 .../runtime/operators/windowing/KeyMap.java   |   4 +-
 .../operators/windowing/WindowOperator.java   |   2 +-
 .../runtime/tasks/ProcessingTimeCallback.java |   2 +-
 .../util/typeutils/FieldAccessor.java         |   4 +-
 .../util/typeutils/FieldAccessorFactory.java  |   6 +-
 tools/maven/strict-checkstyle.xml             | 550 ++++++++++++++++++
 18 files changed, 609 insertions(+), 24 deletions(-)
 create mode 100644 tools/maven/strict-checkstyle.xml

diff --git a/flink-streaming-java/pom.xml b/flink-streaming-java/pom.xml
index 950c923fc4d..72c2133722a 100644
--- a/flink-streaming-java/pom.xml
+++ b/flink-streaming-java/pom.xml
@@ -123,6 +123,41 @@ under the License.
 					</execution>
 				</executions>
 			</plugin>
+
+			<!-- We have more strict checkstyle rules than the rest of the project -->
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-checkstyle-plugin</artifactId>
+				<version>2.17</version>
+				<dependencies>
+					<dependency>
+						<groupId>com.puppycrawl.tools</groupId>
+						<artifactId>checkstyle</artifactId>
+						<version>6.19</version>
+					</dependency>
+				</dependencies>
+				<configuration>
+					<configLocation>../tools/maven/strict-checkstyle.xml</configLocation>
+					<suppressionsLocation>../tools/maven/suppressions.xml</suppressionsLocation>
+					<logViolationsToConsole>true</logViolationsToConsole>
+					<failOnViolation>true</failOnViolation>
+				</configuration>
+				<executions>
+					<!--
+					Execute checkstyle after compilation but before tests.
+
+					This ensures that any parsing or type checking errors are from
+					javac, so they look as expected. Beyond that, we want to
+					fail as early as possible.
+					-->
+					<execution>
+						<phase>test-compile</phase>
+						<goals>
+							<goal>check</goal>
+						</goals>
+					</execution>
+				</executions>
+			</plugin>
 		</plugins>
 	</build>
 
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/collector/selector/OutputSelector.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/collector/selector/OutputSelector.java
index 6632da48a12..126effef275 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/collector/selector/OutputSelector.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/collector/selector/OutputSelector.java
@@ -42,5 +42,5 @@ public interface OutputSelector<OUT> extends Serializable {
 	 * @param value
 	 *            Output object for which the output selection should be made.
 	 */
-	public Iterable<String> select(OUT value);
+	Iterable<String> select(OUT value);
 }
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/datastream/DataStream.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/datastream/DataStream.java
index 71ef048d6ef..fc70416e7d9 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/datastream/DataStream.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/datastream/DataStream.java
@@ -1147,7 +1147,7 @@ public class DataStream<T> {
 
 		// configure the type if needed
 		if (sinkFunction instanceof InputTypeConfigurable) {
-			((InputTypeConfigurable) sinkFunction).setInputType(getType(), getExecutionConfig() );
+			((InputTypeConfigurable) sinkFunction).setInputType(getType(), getExecutionConfig());
 		}
 
 		StreamSink<T> sinkOperator = new StreamSink<>(clean(sinkFunction));
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/ContinuousFileReaderOperator.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/ContinuousFileReaderOperator.java
index b86d97c476a..6e8d01d3212 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/ContinuousFileReaderOperator.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/ContinuousFileReaderOperator.java
@@ -367,7 +367,7 @@ public class ContinuousFileReaderOperator<OUT> extends AbstractStreamOperator<OU
 
 		private List<TimestampedFileInputSplit> getReaderState() throws IOException {
 			List<TimestampedFileInputSplit> snapshot = new ArrayList<>(this.pendingSplits.size());
-			if (currentSplit != null ) {
+			if (currentSplit != null) {
 				if (this.format instanceof CheckpointableInputFormat && this.isSplitOpen) {
 					Serializable formatState =
 						((CheckpointableInputFormat<TimestampedFileInputSplit, Serializable>) this.format).getCurrentState();
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/MessageAcknowledgingSourceBase.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/MessageAcknowledgingSourceBase.java
index 035b7ddd1c9..e835070d0fd 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/MessageAcknowledgingSourceBase.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/MessageAcknowledgingSourceBase.java
@@ -178,9 +178,9 @@ public abstract class MessageAcknowledgingSourceBase<Type, UId>
 
 	/**
 	 * This method must be implemented to acknowledge the given set of IDs back to the message queue.
-	 * @param UIds The list od IDs to acknowledge.
+	 * @param uIds The list od IDs to acknowledge.
 	 */
-	protected abstract void acknowledgeIDs(long checkpointId, List<UId> UIds);
+	protected abstract void acknowledgeIDs(long checkpointId, List<UId> uIds);
 
 	/**
 	 * Adds an ID to be stored with the current checkpoint.
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/windowing/delta/DeltaFunction.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/windowing/delta/DeltaFunction.java
index b94e453c07c..d9295c42a72 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/windowing/delta/DeltaFunction.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/windowing/delta/DeltaFunction.java
@@ -42,6 +42,6 @@ public interface DeltaFunction<DATA> extends Serializable {
 	 *            the new data point.
 	 * @return the delta between the two given points.
 	 */
-	public double getDelta(DATA oldDataPoint, DATA newDataPoint);
+	double getDelta(DATA oldDataPoint, DATA newDataPoint);
 
 }
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/windowing/delta/extractor/Extractor.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/windowing/delta/extractor/Extractor.java
index a94f09a2fc8..0b7e4da0005 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/windowing/delta/extractor/Extractor.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/windowing/delta/extractor/Extractor.java
@@ -41,6 +41,6 @@ public interface Extractor<FROM, TO> extends Serializable {
 	 *            the input data
 	 * @return the extracted/converted data
 	 */
-	public TO extract(FROM in);
+	TO extract(FROM in);
 
 }
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/graph/StreamEdge.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/graph/StreamEdge.java
index 8e1c36165ca..94e624ff4e9 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/graph/StreamEdge.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/graph/StreamEdge.java
@@ -34,15 +34,15 @@ public class StreamEdge implements Serializable {
 
 	private static final long serialVersionUID = 1L;
 
-	final private String edgeId;
+	private final String edgeId;
 
-	final private StreamNode sourceVertex;
-	final private StreamNode targetVertex;
+	private final StreamNode sourceVertex;
+	private final StreamNode targetVertex;
 
 	/**
 	 * The type number of the input for co-tasks.
 	 */
-	final private int typeNumber;
+	private final int typeNumber;
 
 	/**
 	 * A list of output names that the target vertex listens to (if there is
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/graph/StreamGraphGenerator.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/graph/StreamGraphGenerator.java
index f9eec4f10ca..3b9a506cfb4 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/graph/StreamGraphGenerator.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/graph/StreamGraphGenerator.java
@@ -369,7 +369,7 @@ public class StreamGraphGenerator {
 			iterate.getParallelism(),
 			iterate.getMaxParallelism(),
 			iterate.getMinResources(),
-			iterate.getPreferredResources()	);
+			iterate.getPreferredResources());
 
 		StreamNode itSource = itSourceAndSink.f0;
 		StreamNode itSink = itSourceAndSink.f1;
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/graph/StreamNode.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/graph/StreamNode.java
index e4164bad65e..71f2a4a4e1b 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/graph/StreamNode.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/graph/StreamNode.java
@@ -40,7 +40,7 @@ public class StreamNode implements Serializable {
 
 	private static final long serialVersionUID = 1L;
 
-	transient private StreamExecutionEnvironment env;
+	private transient StreamExecutionEnvironment env;
 
 	private final int id;
 	private Integer parallelism = null;
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/StreamSourceContexts.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/StreamSourceContexts.java
index e4d051c01f0..36d10d3c980 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/StreamSourceContexts.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/StreamSourceContexts.java
@@ -336,7 +336,7 @@ public class StreamSourceContexts {
 	 * toggles the status. ACTIVE status resumes as soon as some record or watermark is collected
 	 * again.
 	 */
-	private static abstract class WatermarkContext<T> implements SourceFunction.SourceContext<T> {
+	private abstract static class WatermarkContext<T> implements SourceFunction.SourceContext<T> {
 
 		protected final ProcessingTimeService timeService;
 		protected final Object checkpointLock;
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/Triggerable.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/Triggerable.java
index 36e9ad19524..48b18b33057 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/Triggerable.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/Triggerable.java
@@ -36,5 +36,5 @@ public interface Triggerable<K, N> {
 	/**
 	 * Invoked when a processing-time timer fires.
 	 */
-	void onProcessingTime(InternalTimer<K, N> timer) throws Exception ;
+	void onProcessingTime(InternalTimer<K, N> timer) throws Exception;
 }
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/KeyMap.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/KeyMap.java
index 52c321c731a..b0f4f46949b 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/KeyMap.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/KeyMap.java
@@ -606,7 +606,7 @@ public class KeyMap<K, V> implements Iterable<KeyMap.Entry<K, V>> {
 	 *
 	 * @param <V> The type created by the factory.
 	 */
-	public static interface LazyFactory<V> {
+	public interface LazyFactory<V> {
 
 		/**
 		 * The factory method; creates the value.
@@ -625,7 +625,7 @@ public class KeyMap<K, V> implements Iterable<KeyMap.Entry<K, V>> {
 	 * @param <K> The type of the key.
 	 * @param <V> The type of the value.
 	 */
-	public static interface TraversalEvaluator<K, V> {
+	public interface TraversalEvaluator<K, V> {
 
 		/**
 		 * Called whenever the traversal starts with a new key.
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/WindowOperator.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/WindowOperator.java
index 3d407167b5c..70692517960 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/WindowOperator.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/WindowOperator.java
@@ -310,7 +310,7 @@ public class WindowOperator<K, IN, ACC, OUT, W extends Window>
 
 			final TupleSerializer<Tuple2<W, W>> tupleSerializer = new TupleSerializer<>(
 					typedTuple,
-					new TypeSerializer[] {windowSerializer, windowSerializer} );
+					new TypeSerializer[] {windowSerializer, windowSerializer});
 
 			final ListStateDescriptor<Tuple2<W, W>> mergingSetsStateDescriptor =
 					new ListStateDescriptor<>("merging-window-set", tupleSerializer);
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/ProcessingTimeCallback.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/ProcessingTimeCallback.java
index 035939f7b3b..7588c3d54c9 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/ProcessingTimeCallback.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/ProcessingTimeCallback.java
@@ -36,5 +36,5 @@ public interface ProcessingTimeCallback {
 	 * 
 	 * @param timestamp The timestamp for which the trigger event was scheduled.
 	 */
-	void onProcessingTime(long timestamp) throws Exception ;
+	void onProcessingTime(long timestamp) throws Exception;
 }
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/util/typeutils/FieldAccessor.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/util/typeutils/FieldAccessor.java
index 2828308589c..21f477ae2ce 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/util/typeutils/FieldAccessor.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/util/typeutils/FieldAccessor.java
@@ -92,7 +92,7 @@ public abstract class FieldAccessor<T, F> implements Serializable {
 	 * This is when the entire record is considered as a single field. (eg. field 0 of a basic type, or a
 	 * field of a POJO that is itself some composite type but is not further decomposed)
 	 */
-	final static class SimpleFieldAccessor<T> extends FieldAccessor<T, T> {
+	static final class SimpleFieldAccessor<T> extends FieldAccessor<T, T> {
 
 		private static final long serialVersionUID = 1L;
 
@@ -113,7 +113,7 @@ public abstract class FieldAccessor<T, F> implements Serializable {
 		}
 	}
 
-	final static class ArrayFieldAccessor<T, F> extends FieldAccessor<T, F> {
+	static final class ArrayFieldAccessor<T, F> extends FieldAccessor<T, F> {
 
 		private static final long serialVersionUID = 1L;
 
diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/util/typeutils/FieldAccessorFactory.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/util/typeutils/FieldAccessorFactory.java
index 6dbeedd6ab4..1bfce5ba546 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/util/typeutils/FieldAccessorFactory.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/util/typeutils/FieldAccessorFactory.java
@@ -198,9 +198,9 @@ public class FieldAccessorFactory implements Serializable {
 
 	// --------------------------------------------------------------------------------------------------
 
-	private final static String REGEX_FIELD = "[\\p{L}\\p{Digit}_\\$]*"; // This can start with a digit (because of Tuples)
-	private final static String REGEX_NESTED_FIELDS = "("+REGEX_FIELD+")(\\.(.+))?";
-	private final static String REGEX_NESTED_FIELDS_WILDCARD = REGEX_NESTED_FIELDS
+	private  static final String REGEX_FIELD = "[\\p{L}\\p{Digit}_\\$]*"; // This can start with a digit (because of Tuples)
+	private static final String REGEX_NESTED_FIELDS = "("+REGEX_FIELD+")(\\.(.+))?";
+	private static final String REGEX_NESTED_FIELDS_WILDCARD = REGEX_NESTED_FIELDS
 		+"|\\"+ Keys.ExpressionKeys.SELECT_ALL_CHAR
 		+"|\\"+ Keys.ExpressionKeys.SELECT_ALL_CHAR_SCALA;
 
diff --git a/tools/maven/strict-checkstyle.xml b/tools/maven/strict-checkstyle.xml
new file mode 100644
index 00000000000..ba2f4be6efe
--- /dev/null
+++ b/tools/maven/strict-checkstyle.xml
@@ -0,0 +1,550 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+<!DOCTYPE module PUBLIC
+    "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
+    "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
+
+<!--
+This is a checkstyle configuration file. For descriptions of
+what the following rules do, please see the checkstyle configuration
+page at http://checkstyle.sourceforge.net/config.html.
+
+This file is based on the checkstyle file of Apache Beam.
+-->
+
+<module name="Checker">
+
+  <!--<module name="FileTabCharacter">-->
+    <!--&lt;!&ndash; Checks that there are no tab characters in the file. &ndash;&gt;-->
+  <!--</module>-->
+
+  <!--<module name="NewlineAtEndOfFile">-->
+    <!--&lt;!&ndash; windows can use \n\r vs \n, so enforce the most used one ie UNIx style &ndash;&gt;-->
+    <!--<property name="lineSeparator" value="lf" />-->
+  <!--</module>-->
+
+  <module name="RegexpSingleline">
+    <!-- Checks that TODOs don't have stuff in parenthesis, e.g., username. -->
+    <property name="format" value="((//.*)|(\*.*))TODO\(" />
+    <property name="message" value="TODO comments must not include usernames." />
+    <property name="severity" value="error" />
+  </module>
+
+  <!--<module name="RegexpSingleline">-->
+    <!--<property name="format" value="\s+$"/>-->
+    <!--<property name="message" value="Trailing whitespace"/>-->
+    <!--<property name="severity" value="error"/>-->
+  <!--</module>-->
+
+  <module name="RegexpSingleline">
+    <property name="format" value="Throwables.propagate\("/>
+    <property name="message" value="Throwables.propagate is deprecated"/>
+    <property name="severity" value="error"/>
+  </module>
+
+  <!-- Prevent *Tests.java as tools may not pick them up -->
+  <!--<module name="RegexpOnFilename">-->
+    <!--<property name="fileNamePattern" value=".*Tests\.java$" />-->
+  <!--</module>-->
+
+  <!-- Allow use of comment to suppress javadocstyle -->
+  <module name="SuppressionCommentFilter">
+    <property name="offCommentFormat" value="CHECKSTYLE.OFF\: ([\w\|]+)"/>
+    <property name="onCommentFormat" value="CHECKSTYLE.ON\: ([\w\|]+)"/>
+    <property name="checkFormat" value="$1"/>
+  </module>
+  <module name="SuppressionFilter">
+    <property name="file" value="${checkstyle.suppressions.file}" default="suppressions.xml" />
+  </module>
+
+  <!-- Check that every module has a package-info.java -->
+  <!--<module name="JavadocPackage"/>-->
+
+  <!--
+
+  FLINK CUSTOM CHECKS
+
+  -->
+
+  <module name="FileLength">
+    <property name="max" value="2500"/>
+  </module>
+
+  <!-- All Java AST specific tests live under TreeWalker module. -->
+  <module name="TreeWalker">
+
+    <!--
+
+    FLINK CUSTOM CHECKS
+
+    -->
+
+    <module name="RegexpSinglelineJava">
+      <property name="format" value="^\t* +\t*\S" />
+      <property name="message"
+                value="Line has leading space characters; indentation should be performed with tabs only." />
+      <property name="ignoreComments" value="true" />
+    </module>
+
+    <!-- Prohibit T.getT() methods for standard boxed types -->
+    <module name="Regexp">
+      <property name="format" value="Boolean\.getBoolean"/>
+      <property name="illegalPattern" value="true"/>
+      <property name="message" value="Use System.getProperties() to get system properties."/>
+    </module>
+
+    <module name="Regexp">
+      <property name="format" value="Integer\.getInteger"/>
+      <property name="illegalPattern" value="true"/>
+      <property name="message" value="Use System.getProperties() to get system properties."/>
+    </module>
+
+    <module name="Regexp">
+      <property name="format" value="Long\.getLong"/>
+      <property name="illegalPattern" value="true"/>
+      <property name="message" value="Use System.getProperties() to get system properties."/>
+    </module>
+
+    <!--
+
+    IllegalImport cannot blacklist classes so we have to fall back to Regexp.
+
+    -->
+
+    <!-- forbid use of commons lang validate -->
+    <module name="Regexp">
+      <property name="format" value="org\.apache\.commons\.lang3\.Validate"/>
+      <property name="illegalPattern" value="true"/>
+      <property name="message" value="Use Guava Checks instead of Commons Validate. Please refer to the coding guidelines."/>
+    </module>
+    <!-- forbid the use of google.common.base.Preconditions -->
+    <module name="Regexp">
+      <property name="format" value="import com\.google\.common\.base\.Preconditions"/>
+      <property name="illegalPattern" value="true"/>
+      <property name="message" value="Use Flink's Preconditions instead of Guava's Preconditions"/>
+    </module>
+    <!-- forbid the use of com.google.common.annotations.VisibleForTesting -->
+    <module name="Regexp">
+      <property name="format" value="import com\.google\.common\.annotations\.VisibleForTesting"/>
+      <property name="illegalPattern" value="true"/>
+      <property name="message" value="Use Flink's VisibleForTesting instead of Guava's VisibleForTesting"/>
+    </module>
+    <module name="Regexp">
+      <property name="format" value="import static com\.google\.common\.base\.Preconditions"/>
+      <property name="illegalPattern" value="true"/>
+      <property name="message" value="Use Flink's Preconditions instead of Guava's Preconditions"/>
+    </module>
+    <!-- forbid the use of org.apache.commons.lang.SerializationUtils -->
+    <module name="Regexp">
+      <property name="format" value="org\.apache\.commons\.lang\.SerializationUtils"/>
+      <property name="illegalPattern" value="true"/>
+      <property name="message" value="Use Flink's InstantiationUtil instead of common's SerializationUtils"/>
+    </module>
+    <module name="Regexp">
+      <property name="format" value="org\.apache\.commons\.lang3\.SerializationUtils"/>
+      <property name="illegalPattern" value="true"/>
+      <property name="message" value="Use Flink's InstantiationUtil instead of common's SerializationUtils"/>
+    </module>
+    <module name="Regexp">
+      <property name="format" value="org\.apache\.commons\.lang\."/>
+      <property name="illegalPattern" value="true"/>
+      <property name="message" value="Use commons-lang3 instead of commons-lang."/>
+    </module>
+    <module name="Regexp">
+      <property name="format" value="org\.codehaus\.jettison"/>
+      <property name="illegalPattern" value="true"/>
+      <property name="message" value="Use com.fasterxml.jackson instead of jettison."/>
+    </module>
+
+    <!-- Enforce Java-style array declarations -->
+    <module name="ArrayTypeStyle" />
+
+    <module name="TodoComment">
+      <!-- Checks that disallowed strings are not used in comments.  -->
+      <property name="format" value="(FIXME)|(XXX)|(@author)" />
+    </module>
+
+    <!--
+
+    IMPORT CHECKS
+
+    -->
+
+    <module name="RedundantImport">
+      <!-- Checks for redundant import statements. -->
+      <property name="severity" value="error"/>
+      <message key="import.redundancy"
+               value="Redundant import {0}."/>
+    </module>
+
+    <!--<module name="ImportOrder">-->
+      <!--&lt;!&ndash; Checks for out of order import statements. &ndash;&gt;-->
+      <!--<property name="severity" value="error"/>-->
+      <!--&lt;!&ndash; This ensures that static imports go first. &ndash;&gt;-->
+      <!--<property name="option" value="top"/>-->
+      <!--<property name="sortStaticImportsAlphabetically" value="true"/>-->
+      <!--<property name="tokens" value="STATIC_IMPORT, IMPORT"/>-->
+      <!--<message key="import.ordering"-->
+               <!--value="Import {0} appears after other imports that it should precede"/>-->
+    <!--</module>-->
+
+    <module name="AvoidStarImport">
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="IllegalImport">
+      <property name="illegalPkgs" value="org.apache.flink.shaded, autovalue.shaded, avro.shaded, com.google.api.client.repackaged, com.google.appengine.repackaged, io.netty.util.internal"/>
+    </module>
+
+    <module name="RedundantModifier">
+      <!-- Checks for redundant modifiers on various symbol definitions.
+        See: http://checkstyle.sourceforge.net/config_modifier.html#RedundantModifier
+      -->
+      <property name="tokens" value="METHOD_DEF, VARIABLE_DEF, ANNOTATION_FIELD_DEF, INTERFACE_DEF, CLASS_DEF, ENUM_DEF"/>
+    </module>
+
+    <!--
+        IllegalImport cannot blacklist classes, and c.g.api.client.util is used for some shaded
+        code and some useful code. So we need to fall back to Regexp.
+    -->
+    <!--<module name="RegexpSinglelineJava">-->
+      <!--<property name="format" value="com\.google\.api\.client\.util\.(ByteStreams|Charsets|Collections2|Joiner|Lists|Maps|Objects|Preconditions|Sets|Strings|Throwables)"/>-->
+    <!--</module>-->
+
+    <!--
+         Require static importing from Preconditions.
+    -->
+    <module name="RegexpSinglelineJava">
+      <property name="format" value="^import com.google.common.base.Preconditions;$"/>
+      <property name="message" value="Static import functions from Guava Preconditions"/>
+    </module>
+
+    <module name="UnusedImports">
+      <property name="severity" value="error"/>
+      <property name="processJavadoc" value="true"/>
+      <message key="import.unused"
+               value="Unused import: {0}."/>
+    </module>
+
+    <!--
+
+    JAVADOC CHECKS
+
+    -->
+
+    <!-- Checks for Javadoc comments.                     -->
+    <!-- See http://checkstyle.sf.net/config_javadoc.html -->
+    <!--<module name="JavadocMethod">-->
+      <!--<property name="scope" value="protected"/>-->
+      <!--<property name="severity" value="error"/>-->
+      <!--<property name="allowMissingJavadoc" value="true"/>-->
+      <!--<property name="allowMissingParamTags" value="true"/>-->
+      <!--<property name="allowMissingReturnTag" value="true"/>-->
+      <!--<property name="allowMissingThrowsTags" value="true"/>-->
+      <!--<property name="allowThrowsTagsForSubclasses" value="true"/>-->
+      <!--<property name="allowUndeclaredRTE" value="true"/>-->
+    <!--</module>-->
+
+    <!--&lt;!&ndash; Check that paragraph tags are used correctly in Javadoc. &ndash;&gt;-->
+    <!--<module name="JavadocParagraph"/>-->
+
+    <!--<module name="JavadocType">-->
+      <!--<property name="scope" value="protected"/>-->
+      <!--<property name="severity" value="error"/>-->
+      <!--<property name="allowMissingParamTags" value="true"/>-->
+    <!--</module>-->
+
+    <!--<module name="JavadocStyle">-->
+      <!--<property name="severity" value="error"/>-->
+      <!--<property name="checkHtml" value="true"/>-->
+    <!--</module>-->
+
+    <!--
+
+    NAMING CHECKS
+
+    -->
+
+    <!-- Item 38 - Adhere to generally accepted naming conventions -->
+
+    <module name="PackageName">
+      <!-- Validates identifiers for package names against the
+        supplied expression. -->
+      <!-- Here the default checkstyle rule restricts package name parts to
+        seven characters, this is not in line with common practice at Google.
+      -->
+      <property name="format" value="^[a-z]+(\.[a-z][a-z0-9]{1,})*$"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="TypeNameCheck">
+      <!-- Validates static, final fields against the
+      expression "^[A-Z][a-zA-Z0-9]*$". -->
+      <metadata name="altname" value="TypeName"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="ConstantNameCheck">
+      <!-- Validates non-private, static, final fields against the supplied
+      public/package final fields "^[A-Z][A-Z0-9]*(_[A-Z0-9]+)*$". -->
+      <metadata name="altname" value="ConstantName"/>
+      <property name="applyToPublic" value="true"/>
+      <property name="applyToProtected" value="true"/>
+      <property name="applyToPackage" value="true"/>
+      <property name="applyToPrivate" value="false"/>
+      <property name="format" value="^([A-Z][A-Z0-9]*(_[A-Z0-9]+)*|FLAG_.*)$"/>
+      <message key="name.invalidPattern"
+               value="Variable ''{0}'' should be in ALL_CAPS (if it is a constant) or be private (otherwise)."/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <!--<module name="StaticVariableNameCheck">-->
+      <!--&lt;!&ndash; Validates static, non-final fields against the supplied-->
+      <!--expression "^[a-z][a-zA-Z0-9]*_?$". &ndash;&gt;-->
+      <!--<metadata name="altname" value="StaticVariableName"/>-->
+      <!--<property name="applyToPublic" value="true"/>-->
+      <!--<property name="applyToProtected" value="true"/>-->
+      <!--<property name="applyToPackage" value="true"/>-->
+      <!--<property name="applyToPrivate" value="true"/>-->
+      <!--<property name="format" value="^[a-z][a-zA-Z0-9]*_?$"/>-->
+      <!--<property name="severity" value="error"/>-->
+    <!--</module>-->
+
+    <!--<module name="MemberNameCheck">-->
+      <!--&lt;!&ndash; Validates non-static members against the supplied expression. &ndash;&gt;-->
+      <!--<metadata name="altname" value="MemberName"/>-->
+      <!--<property name="applyToPublic" value="true"/>-->
+      <!--<property name="applyToProtected" value="true"/>-->
+      <!--<property name="applyToPackage" value="true"/>-->
+      <!--<property name="applyToPrivate" value="true"/>-->
+      <!--<property name="format" value="^[a-z][a-zA-Z0-9]*$"/>-->
+      <!--<property name="severity" value="error"/>-->
+    <!--</module>-->
+
+    <module name="MethodNameCheck">
+      <!-- Validates identifiers for method names. -->
+      <metadata name="altname" value="MethodName"/>
+      <property name="format" value="^[a-z][a-zA-Z0-9]*(_[a-zA-Z0-9]+)*$"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="ParameterName">
+      <!-- Validates identifiers for method parameters against the
+        expression "^[a-z][a-zA-Z0-9]*$". -->
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="LocalFinalVariableName">
+      <!-- Validates identifiers for local final variables against the
+        expression "^[a-z][a-zA-Z0-9]*$". -->
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="LocalVariableName">
+      <!-- Validates identifiers for local variables against the
+        expression "^[a-z][a-zA-Z0-9]*$". -->
+      <property name="severity" value="error"/>
+    </module>
+
+    <!-- Type parameters must be either one of the four blessed letters
+    T, K, V, W, X or else be capital-case terminated with a T,
+    such as MyGenericParameterT -->
+    <!--<module name="ClassTypeParameterName">-->
+      <!--<property name="format" value="^(((T|K|V|W|X)[0-9]*)|([A-Z][a-z][a-zA-Z]*T))$"/>-->
+      <!--<property name="severity" value="error"/>-->
+    <!--</module>-->
+
+    <!--<module name="MethodTypeParameterName">-->
+      <!--<property name="format" value="^(((T|K|V|W|X)[0-9]*)|([A-Z][a-z][a-zA-Z]*T))$"/>-->
+      <!--<property name="severity" value="error"/>-->
+    <!--</module>-->
+
+    <!--<module name="InterfaceTypeParameterName">-->
+      <!--<property name="format" value="^(((T|K|V|W|X)[0-9]*)|([A-Z][a-z][a-zA-Z]*T))$"/>-->
+      <!--<property name="severity" value="error"/>-->
+    <!--</module>-->
+
+    <!--
+
+    LENGTH and CODING CHECKS
+
+    -->
+
+    <!--<module name="LineLength">-->
+      <!--&lt;!&ndash; Checks if a line is too long. &ndash;&gt;-->
+      <!--<property name="max" value="100"/>-->
+      <!--<property name="severity" value="error"/>-->
+
+      <!--&lt;!&ndash;-->
+        <!--The default ignore pattern exempts the following elements:-->
+          <!-- - import statements-->
+          <!-- - long URLs inside comments-->
+      <!--&ndash;&gt;-->
+
+      <!--<property name="ignorePattern"-->
+          <!--value="^(package .*;\s*)|(import .*;\s*)|( *\* .*https?://.*)$"/>-->
+    <!--</module>-->
+
+    <!--<module name="LeftCurly">-->
+      <!--&lt;!&ndash; Checks for placement of the left curly brace ('{'). &ndash;&gt;-->
+      <!--<property name="severity" value="error"/>-->
+    <!--</module>-->
+
+    <!--<module name="RightCurly">-->
+      <!--&lt;!&ndash; Checks right curlies on CATCH, ELSE, and TRY blocks are on-->
+      <!--the same line. e.g., the following example is fine:-->
+      <!--<pre>-->
+        <!--if {-->
+          <!--...-->
+        <!--} else-->
+      <!--</pre>-->
+      <!--&ndash;&gt;-->
+      <!--&lt;!&ndash; This next example is not fine:-->
+      <!--<pre>-->
+        <!--if {-->
+          <!--...-->
+        <!--}-->
+        <!--else-->
+      <!--</pre>-->
+      <!--&ndash;&gt;-->
+      <!--<property name="option" value="same"/>-->
+      <!--<property name="severity" value="error"/>-->
+    <!--</module>-->
+
+    <!-- Checks for braces around if and else blocks -->
+    <module name="NeedBraces">
+      <property name="severity" value="error"/>
+      <property name="tokens" value="LITERAL_IF, LITERAL_ELSE, LITERAL_FOR, LITERAL_WHILE, LITERAL_DO"/>
+    </module>
+
+    <module name="UpperEll">
+      <!-- Checks that long constants are defined with an upper ell.-->
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="FallThrough">
+      <!-- Warn about falling through to the next case statement.  Similar to
+      javac -Xlint:fallthrough, but the check is suppressed if a single-line comment
+      on the last non-blank line preceding the fallen-into case contains 'fall through' (or
+      some other variants that we don't publicized to promote consistency).
+      -->
+      <property name="reliefPattern"
+       value="fall through|Fall through|fallthru|Fallthru|falls through|Falls through|fallthrough|Fallthrough|No break|NO break|no break|continue on"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <!-- Checks for over-complicated boolean expressions. -->
+    <module name="SimplifyBooleanExpression"/>
+
+    <!-- Detects empty statements (standalone ";" semicolon). -->
+    <module name="EmptyStatement"/>
+
+    <!--
+
+    MODIFIERS CHECKS
+
+    -->
+
+    <module name="ModifierOrder">
+      <!-- Warn if modifier order is inconsistent with JLS3 8.1.1, 8.3.1, and
+           8.4.3.  The prescribed order is:
+           public, protected, private, abstract, static, final, transient, volatile,
+           synchronized, native, strictfp
+        -->
+      <property name="severity" value="error"/>
+    </module>
+
+
+    <!--
+
+    WHITESPACE CHECKS
+
+    -->
+
+    <!--<module name="WhitespaceAround">-->
+      <!--&lt;!&ndash; Checks that various tokens are surrounded by whitespace.-->
+           <!--This includes most binary operators and keywords followed-->
+           <!--by regular or curly braces.-->
+      <!--&ndash;&gt;-->
+      <!--<property name="tokens" value="ASSIGN, BAND, BAND_ASSIGN, BOR,-->
+        <!--BOR_ASSIGN, BSR, BSR_ASSIGN, BXOR, BXOR_ASSIGN, COLON, DIV, DIV_ASSIGN,-->
+        <!--EQUAL, GE, GT, LAND, LE, LITERAL_CATCH, LITERAL_DO, LITERAL_ELSE,-->
+        <!--LITERAL_FINALLY, LITERAL_FOR, LITERAL_IF, LITERAL_RETURN,-->
+        <!--LITERAL_SYNCHRONIZED, LITERAL_TRY, LITERAL_WHILE, LOR, LT, MINUS,-->
+        <!--MINUS_ASSIGN, MOD, MOD_ASSIGN, NOT_EQUAL, PLUS, PLUS_ASSIGN, QUESTION,-->
+        <!--SL, SL_ASSIGN, SR_ASSIGN, STAR, STAR_ASSIGN"/>-->
+      <!--<property name="severity" value="error"/>-->
+    <!--</module>-->
+
+    <!--<module name="WhitespaceAfter">-->
+      <!--&lt;!&ndash; Checks that commas, semicolons and typecasts are followed by-->
+           <!--whitespace.-->
+      <!--&ndash;&gt;-->
+      <!--<property name="tokens" value="COMMA, SEMI, TYPECAST"/>-->
+    <!--</module>-->
+
+    <module name="NoWhitespaceAfter">
+      <!-- Checks that there is no whitespace after various unary operators.
+           Linebreaks are allowed.
+      -->
+      <property name="tokens" value="BNOT, DEC, DOT, INC, LNOT, UNARY_MINUS,
+        UNARY_PLUS"/>
+      <property name="allowLineBreaks" value="true"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="NoWhitespaceBefore">
+      <!-- Checks that there is no whitespace before various unary operators.
+           Linebreaks are allowed.
+      -->
+      <property name="tokens" value="SEMI, DOT, POST_DEC, POST_INC"/>
+      <property name="allowLineBreaks" value="true"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <!--<module name="OperatorWrap">-->
+      <!--&lt;!&ndash; Checks that operators like + and ? appear at newlines rather than-->
+           <!--at the end of the previous line.-->
+      <!--&ndash;&gt;-->
+      <!--<property name="option" value="NL"/>-->
+      <!--<property name="tokens" value="BAND, BOR, BSR, BXOR, DIV, EQUAL,-->
+        <!--GE, GT, LAND, LE, LITERAL_INSTANCEOF, LOR, LT, MINUS, MOD,-->
+        <!--NOT_EQUAL, PLUS, QUESTION, SL, SR, STAR "/>-->
+    <!--</module>-->
+
+    <module name="OperatorWrap">
+      <!-- Checks that assignment operators are at the end of the line. -->
+      <property name="option" value="eol"/>
+      <property name="tokens" value="ASSIGN"/>
+    </module>
+
+    <module name="ParenPad">
+      <!-- Checks that there is no whitespace before close parens or after
+           open parens.
+      -->
+      <property name="severity" value="error"/>
+    </module>
+
+    <!-- Required to support SuppressWarningsComment -->
+    <module name="FileContentsHolder"/>
+
+  </module>
+</module>
+
-- 
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