[SPARK-13823][SPARK-13397][SPARK-13395][CORE] More warnings, StandardCharset follow up

## What changes were proposed in this pull request?

Follow up to https://github.com/apache/spark/pull/11657

- Also update `String.getBytes("UTF-8")` to use `StandardCharsets.UTF_8`
- And fix one last new Coverity warning that turned up (use of unguarded `wait()` replaced by simpler/more robust `java.util.concurrent` classes in tests)
- And while we're here cleaning up Coverity warnings, just fix about 15 more build warnings

## How was this patch tested?

Jenkins tests

Author: Sean Owen <sowen@cloudera.com>

Closes #11725 from srowen/SPARK-13823.2.

3 files changed, 6 insertions, 14 deletions

diff --git a/common/unsafe/pom.xml b/common/unsafe/pom.xml
index 5250014739..93b9580f26 100644
--- a/common/unsafe/pom.xml
+++ b/common/unsafe/pom.xml
@@ -98,7 +98,7 @@
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-compiler-plugin</artifactId>
           <configuration>
-            <compilerArgs>
+            <compilerArgs combine.children="append">
               <!-- This option is needed to suppress warnings from sun.misc.Unsafe usage -->
               <arg>-XDignore.symbol.file</arg>
             </compilerArgs>
diff --git a/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java b/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
index e16166ade4..54a5456924 100644
--- a/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
+++ b/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
@@ -106,15 +106,7 @@ public final class UTF8String implements Comparable<UTF8String>, Externalizable,
    * Creates an UTF8String from String.
    */
   public static UTF8String fromString(String str) {
-    if (str == null) return null;
-    try {
-      return fromBytes(str.getBytes("utf-8"));
-    } catch (UnsupportedEncodingException e) {
-      // Turn the exception into unchecked so we can find out about it at runtime, but
-      // don't need to add lots of boilerplate code everywhere.
-      throwException(e);
-      return null;
-    }
+    return str == null ? null : fromBytes(str.getBytes(StandardCharsets.UTF_8));
   }
 
   /**
diff --git a/common/unsafe/src/test/java/org/apache/spark/unsafe/types/UTF8StringSuite.java b/common/unsafe/src/test/java/org/apache/spark/unsafe/types/UTF8StringSuite.java
index bef5d712cf..d4160ad029 100644
--- a/common/unsafe/src/test/java/org/apache/spark/unsafe/types/UTF8StringSuite.java
+++ b/common/unsafe/src/test/java/org/apache/spark/unsafe/types/UTF8StringSuite.java
@@ -17,7 +17,7 @@
 
 package org.apache.spark.unsafe.types;
 
-import java.io.UnsupportedEncodingException;
+import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.HashMap;
 
@@ -30,9 +30,9 @@ import static org.apache.spark.unsafe.types.UTF8String.*;
 
 public class UTF8StringSuite {
 
-  private static void checkBasic(String str, int len) throws UnsupportedEncodingException {
+  private static void checkBasic(String str, int len) {
     UTF8String s1 = fromString(str);
-    UTF8String s2 = fromBytes(str.getBytes("utf8"));
+    UTF8String s2 = fromBytes(str.getBytes(StandardCharsets.UTF_8));
     assertEquals(s1.numChars(), len);
     assertEquals(s2.numChars(), len);
 
@@ -51,7 +51,7 @@ public class UTF8StringSuite {
   }
 
   @Test
-  public void basicTest() throws UnsupportedEncodingException {
+  public void basicTest() {
     checkBasic("", 0);
     checkBasic("hello", 5);
     checkBasic("大 千 世 界", 7);