[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.

1 files changed, 1 insertions, 9 deletions

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));
   }
 
   /**