src/java/com/google/ipc/invalidation/util/Formatter.java

/*
 * Copyright 2011 Google Inc.
 *
 * Licensed 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 com.google.ipc.invalidation.util;

/**
 * A set of utilities needed to format strings by the external class implementations.
 *
 */
public class Formatter {

  /**
   * (Borrowed from the Preconditions code).
   * Substitutes each {@code %s} in {@code template} with an argument. These
   * are matched by position - the first {@code %s} gets {@code args[0]}, etc.
   * If there are more arguments than placeholders, the unmatched arguments will
   * be appended to the end of the formatted message in square braces.
   *
   * @param template a non-null string containing 0 or more {@code %s}
   *     placeholders.
   * @param args the arguments to be substituted into the message
   *     template. Arguments are converted to strings using
   *     {@link String#valueOf(Object)}. Arguments can be null.
   */
  public static String format(String template, Object... args) {
    template = String.valueOf(template); // null -> "null"

    // start substituting the arguments into the '%s' placeholders
    StringBuilder builder = new StringBuilder(
      template.length() + 16 * args.length);
    int templateStart = 0;
    int i = 0;
    while (i < args.length) {
      int placeholderStart = template.indexOf("%s", templateStart);
      if (placeholderStart == -1) {
        break;
      }
      builder.append(template.substring(templateStart, placeholderStart));
      builder.append(args[i++]);
      templateStart = placeholderStart + 2;
    }
    builder.append(template.substring(templateStart));

    // if we run out of placeholders, append the extra args in square braces
    if (i < args.length) {
      builder.append(" [");
      builder.append(args[i++]);
      while (i < args.length) {
        builder.append(", ");
        builder.append(args[i++]);
      }
      builder.append(']');
    }
    return builder.toString();
  }

  private Formatter() {  // To prevent instantiation.
  }
}