Restore Java 7 Compatibility (#9103)

Summary:
RocksDB should still compile on Java 7.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9103

Reviewed By: pdillinger

Differential Revision: D32067561

Pulled By: mrambacher

fbshipit-source-id: bbe9c18c8007ab3e113de4add56a84c9bde61c8e

java/src/main/java/org/rocksdb/AbstractMutableOptions.java

@@ -341,11 +341,8 @@ public abstract class AbstractMutableOptions {
           return setIntArray(key, value);
 
         case ENUM:
-          final Optional<CompressionType> compressionType =
-              CompressionType.getFromInternal(valueStr);
-          if (compressionType.isPresent()) {
-            return setEnum(key, compressionType.get());
-          }
+          final CompressionType compressionType = CompressionType.getFromInternal(valueStr);
+          return setEnum(key, compressionType);
       }
 
       throw new IllegalStateException(key + " has unknown value type: " + key.getValueType());

java/src/main/java/org/rocksdb/CompressionType.java

@@ -5,8 +5,6 @@
 
 package org.rocksdb;
 
-import java.util.Optional;
-
 /**
  * Enum CompressionType
  *
@@ -81,13 +79,15 @@ public enum CompressionType {
    *
    * @return CompressionType instance (optional)
    */
-  public static Optional<CompressionType> getFromInternal(final String internalName) {
+  static CompressionType getFromInternal(final String internalName) {
     for (final CompressionType compressionType : CompressionType.values()) {
       if (compressionType.internalName_.equals(internalName)) {
-        return Optional.of(compressionType);
+        return compressionType;
       }
     }
-    return Optional.empty();
+
+    throw new IllegalArgumentException(
+        "Illegal internalName '" + internalName + " ' provided for CompressionType.");
   }
 
   /**