[SPARK-19550][BUILD][CORE][WIP] Remove Java 7 support

- Move external/java8-tests tests into core, streaming, sql and remove
- Remove MaxPermGen and related options
- Fix some reflection / TODOs around Java 8+ methods
- Update doc references to 1.7/1.8 differences
- Remove Java 7/8 related build profiles
- Update some plugins for better Java 8 compatibility
- Fix a few Java-related warnings

For the future:

- Update Java 8 examples to fully use Java 8
- Update Java tests to use lambdas for simplicity
- Update Java internal implementations to use lambdas

## How was this patch tested?

Existing tests

Author: Sean Owen <sowen@cloudera.com>

Closes #16871 from srowen/SPARK-19493.

1 files changed, 4 insertions, 6 deletions

diff --git a/docs/streaming-custom-receivers.md b/docs/streaming-custom-receivers.md
index 117996db9d..d4ddcb16bd 100644
--- a/docs/streaming-custom-receivers.md
+++ b/docs/streaming-custom-receivers.md
@@ -113,15 +113,13 @@ public class JavaCustomReceiver extends Receiver<String> {
     port = port_;
   }
 
+  @Override
   public void onStart() {
     // Start the thread that receives data over a connection
-    new Thread()  {
-      @Override public void run() {
-        receive();
-      }
-    }.start();
+    new Thread(this::receive).start();
   }
 
+  @Override
   public void onStop() {
     // There is nothing much to do as the thread calling receive()
     // is designed to stop by itself if isStopped() returns false
@@ -189,7 +187,7 @@ The full source code is in the example [CustomReceiver.scala]({{site.SPARK_GITHU
 {% highlight java %}
 // Assuming ssc is the JavaStreamingContext
 JavaDStream<String> customReceiverStream = ssc.receiverStream(new JavaCustomReceiver(host, port));
-JavaDStream<String> words = lines.flatMap(new FlatMapFunction<String, String>() { ... });
+JavaDStream<String> words = lines.flatMap(s -> ...);
 ...
 {% endhighlight %}