code: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   *
   */
  
  package org.apache.skywalking.oap.server.library.util;
  
  public final class StringUtil {
      public static boolean isEmpty(String str) {
          return str == null || str.length() == 0;
      }
  
      public static boolean isNotEmpty(String str) {
          return !isEmpty(str);
      }
  
      public static boolean isBlank(String str) {
          return str == null || isEmpty(str.trim());
      }
  
      public static boolean isNotBlank(String str) {
          return !isBlank(str);
      }
  
      public static String join(final char delimiter, final String... strings) {
          if (strings.length == 0) {
              return null;
          }
          if (strings.length == 1) {
              return strings[0];
          }
          int length = strings.length - 1;
          for (final String s : strings) {
              if (s == null) {
                  continue;
              }
              length += s.length();
          }
          final StringBuilder sb = new StringBuilder(length);
          if (strings[0] != null) {
              sb.append(strings[0]);
          }
          for (int i = 1; i < strings.length; ++i) {
              if (!isEmpty(strings[i])) {
                  sb.append(delimiter).append(strings[i]);
              } else {
                  sb.append(delimiter);
              }
          }
          return sb.toString();
      }
  
      public static boolean substringMatch(CharSequence str, int index, CharSequence substring) {
          if (index + substring.length() > str.length()) {
              return false;
          }
          for (int i = 0; i < substring.length(); i++) {
              if (str.charAt(index + i) != substring.charAt(i)) {
                  return false;
              }
          }
          return true;
      }
  
      public static String cut(String str, int threshold) {
          if (isEmpty(str) || str.length() <= threshold) {
              return str;
          }
          return str.substring(0, threshold);
      }
  
      public static String trim(final String str, final char ch) {
          if (isEmpty(str)) {
              return null;
          }
  
          final char[] chars = str.toCharArray();
  
          int i = 0, j = chars.length - 1;
          // noinspection StatementWithEmptyBody
          for (; i < chars.length && chars[i] == ch; i++) {
          }
          // noinspection StatementWithEmptyBody
          for (; j > 0 && chars[j] == ch; j--) {
          }
  
          return new String(chars, i, j - i + 1);
      }
  }
  