DockerDateFormat.java

/*-
 * -\-\-
 * docker-client
 * --
 * Copyright (C) 2016 Spotify AB
 * --
 * 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.spotify.docker.client;

import com.fasterxml.jackson.databind.util.StdDateFormat;

import java.text.ParseException;
import java.util.Date;

/**
 * Docker returns timestamps with nanosecond precision
 * (e.g. <tt>2014-10-17T21:22:56.949763914Z</tt>),
 * but {@link Date} only supports milliseconds. Creating a Date from the nanosecond timestamp
 * results in the date being set to several days after what date should be. This class converts the
 * timestamp from nanoseconds to milliseconds by removing the last six digits of the timestamp, so
 * we can generate a Date with the correct value (albeit with less precision).
 *
 * <p>Note: a more complete solution would be to introduce a custom date type which can store the
 * nanosecond value in an additional field, so users can access the complete value. Or just use Java
 * 8 which has date objects with nanosecond support.
 */
public class DockerDateFormat extends StdDateFormat {

  private static final long serialVersionUID = 249048552876483658L;

  // either a literal Z or an offset like -04:00 or +1200 with an optional colon separator
  private static final String TIMEZONE_PATTERN = "(Z|[+-]\\d{2}:?\\d{2})";

  @Override
  public Date parse(String source) throws ParseException {
    // If the date has nanosecond precision (e.g. 2014-10-17T21:22:56.949763914Z), remove the last
    // digits so we can create a Date object, which only support milliseconds.
    // Docker doesn't always return nine digits for the fractional seconds part,
    // so we need to be more flexible when trimming to milliseconds.
    // Also allow for flexible timezone formats, either 'Z' for zulu/UTC or hour offsets.
    // StdDateFormat has logic for handling these other timezones, but only if the time portion of
    // the string matches hh:mm:ss or hh:mm:ss.SSS
    if (source.matches(".+\\.\\d{4,9}" + TIMEZONE_PATTERN + "$")) {
      source = source.replaceAll("(\\.\\d{3})\\d{1,6}" + TIMEZONE_PATTERN + "$", "$1$2");
    }

    return super.parse(source);
  }

  @Override
  @SuppressWarnings("CloneDoesntCallSuperClone")
  public DockerDateFormat clone() {
    // Normally clone should call super.clone(), but that works only if StdDateFormat calls
    // super.clone(), which it does not. We must create a new instance and disable the warning.
    return new DockerDateFormat();
  }
}