use standardcharset.utf-8 instead of literal (#3285)

* use standardcharset.utf-8 instead of literal

* remove unused import

Author: mjaow

dubbo-cluster/src/main/java/org/apache/dubbo/rpc/cluster/loadbalance/ConsistentHashLoadBalance.java

@@ -22,7 +22,7 @@
 import org.apache.dubbo.rpc.Invoker;
 import org.apache.dubbo.rpc.support.RpcUtils;
 
-import java.io.UnsupportedEncodingException;
+import java.nio.charset.StandardCharsets;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.util.List;
@@ -33,7 +33,6 @@
 
 /**
  * ConsistentHashLoadBalance
- *
  */
 public class ConsistentHashLoadBalance extends AbstractLoadBalance {
     public static final String NAME = "consistenthash";
@@ -126,12 +125,7 @@ private byte[] md5(String value) {
                 throw new IllegalStateException(e.getMessage(), e);
             }
             md5.reset();
-            byte[] bytes;
-            try {
-                bytes = value.getBytes("UTF-8");
-            } catch (UnsupportedEncodingException e) {
-                throw new IllegalStateException(e.getMessage(), e);
-            }
+            byte[] bytes = value.getBytes(StandardCharsets.UTF_8);
             md5.update(bytes);
             return md5.digest();
         }