code: public static String getAPIBuildTimestamp(final Class<?> clazz) {
          if (buildDateMap.containsKey(clazz)) {
              return buildDateMap.get(clazz);
          }
  
          Attributes atts = null;
          String buildTimestamp = null;
          try {
              atts = getAttributesForClass(clazz);
          } catch (IOException ex) {
              LOG.debug("Unable to open Manifest stream for class: " + clazz.getName(), ex);
          }
  
          if (atts != null) {
              buildTimestamp = atts.getValue("Implementation-Build");
          }
  
          if (buildTimestamp == null) buildTimestamp = "unknown";
  
          buildDateMap.put(clazz, buildTimestamp);
  
          return buildTimestamp;
      }
docs: Get the Build Date for a specific class. The archive the class belongs to must have been built with maven and the
  "Implementation-Build" must exist in the MANIFEST.MF. This can be set by adding the following to the pom:
  <p/>
  <pre>
  {@code
  <build>
  <plugins>
  <plugin>
  <artifactId>maven-jar-plugin</artifactId>
  <configuration>
  <archive>
  <manifestEntries>
  <Implementation-Build>}${maven.build.timestamp}{@code</Implementation-Build>
  </manifestEntries>
  </archive>
  </configuration>
  </plugin>
  </plugins>
  </build>}
  </pre>
  <p/>
  Thanks to the Zanata Team for this method, it has just been edited for this libraries needs.
  
  @param clazz The class to find the Version Information for.
  @return The build timestamp or "unknown" if the timestamp couldn't be found.