## What changes were proposed in this pull request?

After SPARK-6990, `dev/lint-java` keeps Java code healthy and helps PR review by saving much time.
This issue aims remove unused imports from Java/Scala code and add `UnusedImports` checkstyle rule to help developers.

## How was this patch tested?
```
./dev/lint-java
./build/sbt compile
```

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #11438 from dongjoon-hyun/SPARK-13583.

## What changes were proposed in this pull request?

Make some cross-cutting code improvements according to static analysis. These are individually up for discussion since they exist in separate commits that can be reverted. The changes are broadly:

- Inner class should be static
- Mismatched hashCode/equals
- Overflow in compareTo
- Unchecked warnings
- Misuse of assert, vs junit.assert
- get(a) + getOrElse(b) -> getOrElse(a,b)
- Array/String .size -> .length (occasionally, -> .isEmpty / .nonEmpty) to avoid implicit conversions
- Dead code
- tailrec
- exists(_ == ) -> contains find + nonEmpty -> exists filter + size -> count
- reduce(_+_) -> sum map + flatten -> map

The most controversial may be .size -> .length simply because of its size. It is intended to avoid implicits that might be expensive in some places.

## How was the this patch tested?

Existing Jenkins unit tests.

Author: Sean Owen <sowen@cloudera.com>

Closes #11292 from srowen/SPARK-13423.

Introduces a "ask" style ```store``` in ```ActorReceiver``` as a way to allow actor receiver blocked by back pressure or maxRate.

Author: Lin Zhao <lin@exabeam.com>

Closes #11176 from lin-zhao/SPARK-13069.

trait SynchronizedMap in package mutable is deprecated: Synchronization via traits is deprecated as it is inherently unreliable. Change to java.util.concurrent.ConcurrentHashMap instead.

Author: Huaxin Gao <huaxing@us.ibm.com>

Closes #11250 from huaxingao/spark__13186.

Building with Scala 2.11 results in the warning trait SynchronizedBuffer in package mutable is deprecated: Synchronization via traits is deprecated as it is inherently unreliable. Consider java.util.concurrent.ConcurrentLinkedQueue as an alternative - we already use ConcurrentLinkedQueue elsewhere so lets replace it.

Some notes about how behaviour is different for reviewers:
The Seq from a SynchronizedBuffer that was implicitly converted would continue to receive updates - however when we do the same conversion explicitly on the ConcurrentLinkedQueue this isn't the case. Hence changing some of the (internal & test) APIs to pass an Iterable. toSeq is safe to use if there are no more updates.

Author: Holden Karau <holden@us.ibm.com>
Author: tedyu <yuzhihong@gmail.com>

Closes #11067 from holdenk/SPARK-13165-replace-deprecated-synchronizedBuffer-in-streaming.

Author: cody koeninger <cody@koeninger.org>

Closes #9007 from koeninger/SPARK-10963.

This patch changes Spark's build to make Scala 2.11 the default Scala version. To be clear, this does not mean that Spark will stop supporting Scala 2.10: users will still be able to compile Spark for Scala 2.10 by following the instructions on the "Building Spark" page; however, it does mean that Scala 2.11 will be the default Scala version used by our CI builds (including pull request builds).

The Scala 2.11 compiler is faster than 2.10, so I think we'll be able to look forward to a slight speedup in our CI builds (it looks like it's about 2X faster for the Maven compile-only builds, for instance).

After this patch is merged, I'll update Jenkins to add new compile-only jobs to ensure that Scala 2.10 compilation doesn't break.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #10608 from JoshRosen/SPARK-6363.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #10868 from zsxwing/hotfix-akka-pom.

Include the following changes:

1. Add "streaming-akka" project and org.apache.spark.streaming.akka.AkkaUtils for creating an actorStream
2. Remove "StreamingContext.actorStream" and "JavaStreamingContext.actorStream"
3. Update the ActorWordCount example and add the JavaActorWordCount example
4. Make "streaming-zeromq" depend on "streaming-akka" and update the codes accordingly

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #10744 from zsxwing/streaming-akka-2.

Fix the style violation (space before , and :).
This PR is a followup for #10643.

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #10685 from sarutak/SPARK-12692-followup-streaming.

Author: Jacek Laskowski <jacek@japila.pl>

Closes #10698 from jaceklaskowski/streaming-kafka-typo-fixes.

This patch removes all non-Maven-central repositories from Spark's build, thereby avoiding any risk of future build-breaks due to us accidentally depending on an artifact which is not present in an immutable public Maven repository.

I tested this by running

```
build/mvn \
        -Phive \
        -Phive-thriftserver \
        -Pkinesis-asl \
        -Pspark-ganglia-lgpl \
        -Pyarn \
        dependency:go-offline
```

inside of a fresh Ubuntu Docker container with no Ivy or Maven caches (I did a similar test for SBT).

Author: Josh Rosen <joshrosen@databricks.com>

Closes #10659 from JoshRosen/SPARK-4628.

Fix most build warnings: mostly deprecated API usages. I'll annotate some of the changes below. CC rxin who is leading the charge to remove the deprecated APIs.

Author: Sean Owen <sowen@cloudera.com>

Closes #10570 from srowen/SPARK-12618.

This PR includes the following changes:

1. Rename `ActorReceiver` to `ActorReceiverSupervisor`
2. Remove `ActorHelper`
3. Add a new `ActorReceiver` for Scala and `JavaActorReceiver` for Java
4. Add `JavaActorWordCount` example

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #10457 from zsxwing/java-actor-stream.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #10582 from vanzin/SPARK-3873-tests.

Also included a few miscelaneous other modules that had very few violations.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #10532 from vanzin/SPARK-3873-streaming.

Author: Reynold Xin <rxin@databricks.com>

Closes #10387 from rxin/version-bump.

…means Value

Author: cody koeninger <cody@koeninger.org>

Closes #10132 from koeninger/SPARK-12103.

`ByteBuffer` doesn't guarantee all contents in `ByteBuffer.array` are valid. E.g, a ByteBuffer returned by `ByteBuffer.slice`. We should not use the whole content of `ByteBuffer` unless we know that's correct.

This patch fixed all places that use `ByteBuffer.array` incorrectly.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #10083 from zsxwing/bytebuffer-array.

We should upgrade to SBT 0.13.9, since this is a requirement in order to use SBT's new Maven-style resolution features (which will be done in a separate patch, because it's blocked by some binary compatibility issues in the POM reader plugin).

I also upgraded Scalastyle to version 0.8.0, which was necessary in order to fix a Scala 2.10.5 compatibility issue (see https://github.com/scalastyle/scalastyle/issues/156). The newer Scalastyle is slightly stricter about whitespace surrounding tokens, so I fixed the new style violations.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #10112 from JoshRosen/upgrade-to-sbt-0.13.9.

this is to fix some typo in external/kafka/src/main/scala/org/apache/spark/streaming/kafka/OffsetRange.scala

Author: microwishing <wei.zhu@kaiyuandao.com>

Closes #10121 from microwishing/master.

this is a trivial fix, discussed [here](http://stackoverflow.com/questions/28500401/maven-assembly-plugin-warning-the-assembly-descriptor-contains-a-filesystem-roo/).

Author: Prashant Sharma <scrapcodes@gmail.com>

Closes #10014 from ScrapCodes/assembly-warning.

Fixed the merge conflicts in #7410

Closes #7410

Author: Shixiong Zhu <shixiong@databricks.com>
Author: jerryshao <saisai.shao@intel.com>
Author: jerryshao <sshao@hortonworks.com>

Closes #9742 from zsxwing/pr7410.

Sometimes, EmbeddedZookeeper may need more than 6 seconds to setup up in a slow Jenkins worker. So just increase the timeout, it won't increase the test time if the test passes.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #9778 from zsxwing/SPARK-11790.

This PR just checks the test results and returns 1 if the test fails, so that `run-tests.py` can mark it fail.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #9669 from zsxwing/streaming-python-tests.

[SPARK-11361][STREAMING] Show scopes of RDD operations inside DStream.foreachRDD and DStream.transform in DAG viz

Currently, when a DStream sets the scope for RDD generated by it, that scope is not allowed to be overridden by the RDD operations. So in case of `DStream.foreachRDD`, all the RDDs generated inside the foreachRDD get the same scope - `foreachRDD  <time>`, as set by the `ForeachDStream`. So it is hard to debug generated RDDs in the RDD DAG viz in the Spark UI.

This patch allows the RDD operations inside `DStream.transform` and `DStream.foreachRDD` to append their own scopes to the earlier DStream scope.

I have also slightly tweaked how callsites are set such that the short callsite reflects the RDD operation name and line number. This tweak is necessary as callsites are not managed through scopes (which support nesting and overriding) and I didnt want to add another local property to control nesting and overriding of callsites.

## Before:
![image](https://cloud.githubusercontent.com/assets/663212/10808548/fa71c0c4-7da9-11e5-9af0-5737793a146f.png)

## After:
![image](https://cloud.githubusercontent.com/assets/663212/10808659/37bc45b6-7dab-11e5-8041-c20be6a9bc26.png)

The code that was used to generate this is:
```
    val lines = ssc.socketTextStream(args(0), args(1).toInt, StorageLevel.MEMORY_AND_DISK_SER)
    val words = lines.flatMap(_.split(" "))
    val wordCounts = words.map(x => (x, 1)).reduceByKey(_ + _)
    wordCounts.foreachRDD { rdd =>
      val temp = rdd.map { _ -> 1 }.reduceByKey( _ + _)
      val temp2 = temp.map { _ -> 1}.reduceByKey(_ + _)
      val count = temp2.count
      println(count)
    }
```

Note
- The inner scopes of the RDD operations map/reduceByKey inside foreachRDD is visible
- The short callsites of stages refers to the line number of the RDD ops rather than the same line number of foreachRDD in all three cases.

Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #9315 from tdas/SPARK-11361.

update twitter4j to 4.0.4 version
https://issues.apache.org/jira/browse/SPARK-11245

Author: dima <pronix.service@gmail.com>

Closes #9221 from pronix/twitter4j_update.

…reads.

Wait for a minute for the receiver threads to shutdown before interrupting them.

Author: Hari Shreedharan <hshreedharan@apache.org>

Closes #9041 from harishreedharan/flume-graceful-shutdown.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #8775 from vanzin/SPARK-10300.

This reverts commit 8abef21d.

This change does two things:

- tag a few tests and adds the mechanism in the build to be able to disable those tags,
  both in maven and sbt, for both junit and scalatest suites.
- add some logic to run-tests.py to disable some tags depending on what files have
  changed; that's used to disable expensive tests when a module hasn't explicitly
  been changed, to speed up testing for changes that don't directly affect those
  modules.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #8437 from vanzin/test-tags.

Author: Reynold Xin <rxin@databricks.com>

Closes #8350 from rxin/1.6.

Fix a few Java API test style issues: unused generic types, exceptions, wrong assert argument order

Author: Sean Owen <sowen@cloudera.com>

Closes #8706 from srowen/SPARK-10547.

The bulk of the changes are on `transient` annotation on class parameter. Often the compiler doesn't generate a field for this parameters, so the the transient annotation would be unnecessary.
But if the class parameter are used in methods, then fields are created. So it is safer to keep the annotations.

The remainder are some potential bugs, and deprecated syntax.

Author: Luc Bourlier <luc.bourlier@typesafe.com>

Closes #8433 from skyluc/issue/sbt-2.11.

Replace `JavaConversions` implicits with `JavaConverters`

Most occurrences I've seen so far are necessary conversions; a few have been avoidable. None are in critical code as far as I see, yet.

Author: Sean Owen <sowen@cloudera.com>

Closes #8033 from srowen/SPARK-9613.

…ult maxRatePerPartition setting of 0

Author: cody koeninger <cody@koeninger.org>

Closes #8413 from koeninger/backpressure-testing-master.

[SPARK-9791] [PACKAGE] Change private class to private class to prevent unnecessary classes from showing up in the docs

In addition, some random cleanup of import ordering

Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #8387 from tdas/SPARK-9791 and squashes the following commits:

67f3ee9 [Tathagata Das] Change private class to private[package] class to prevent them from showing up in the docs

This PR removed the `outputFile` configuration from pom.xml and updated `tests.py` to search jars for both sbt build and maven build.

I ran ` mvn -Pkinesis-asl -DskipTests clean install` locally, and verified the jars in my local repository were correct. I also checked Python tests for maven build, and it passed all tests.

Author: zsxwing <zsxwing@gmail.com>

Closes #8373 from zsxwing/SPARK-10168 and squashes the following commits:

e0b5818 [zsxwing] Fix the sbt build
c697627 [zsxwing] Add the jar pathes to the exception message
be1d8a5 [zsxwing] Fix the issue that maven publishes wrong artifact jars

Removed contents already included in Spark assembly jar from spark-streaming-XXX-assembly jars.

Author: zsxwing <zsxwing@gmail.com>

Closes #8069 from zsxwing/SPARK-9574.

…fails

Author: cody koeninger <cody@koeninger.org>

Closes #8133 from koeninger/SPARK-9780 and squashes the following commits:

406259d [cody koeninger] [SPARK-9780][Streaming][Kafka] prevent NPE if KafkaRDD instantiation fails