AVRO-4066: Use JDK isBlank Method (#3182)

lang/java/avro/src/main/java/org/apache/avro/specific/SpecificData.java

@@ -324,7 +324,7 @@ public static String mangleMethod(String word, boolean isError) {
    * Utility for template use. Adds a dollar sign to reserved words.
    */
   public static String mangle(String word, Set<String> reservedWords, boolean isMethod) {
-    if (isBlank(word)) {
+    if (word == null || word.isBlank()) {
       return word;
     }
     if (word.contains(".")) {
@@ -354,21 +354,6 @@ protected static String unmangle(String word) {
     return word;
   }
 
-  private static boolean isBlank(CharSequence cs) {
-    int strLen = cs == null ? 0 : cs.length();
-    if (strLen == 0) {
-      return true;
-    } else {
-      for (int i = 0; i < strLen; ++i) {
-        if (!Character.isWhitespace(cs.charAt(i))) {
-          return false;
-        }
-      }
-
-      return true;
-    }
-  }
-
   /** Return the class that implements a schema, or null if none exists. */
   public Class getClass(Schema schema) {
     switch (schema.getType()) {
@@ -452,7 +437,7 @@ private Class getWrapper(Schema schema) {
   public static String getClassName(Schema schema) {
     String namespace = schema.getNamespace();
     String name = schema.getName();
-    if (namespace == null || "".equals(namespace))
+    if (namespace == null || namespace.isEmpty())
       return name;
     String dot = namespace.endsWith("$") ? "" : "."; // back-compatibly handle $
     return mangle(namespace) + dot + mangleTypeIdentifier(name);