title: Spring configuration: long value out of a String property
body: <p>I am configuring a scheduler task in spring in this way:</p>
  
  <pre><code>&lt;bean id="someSchedulerTask" class="org.springframework.scheduling.concurrent.ScheduledExecutorTask"&gt;
          &lt;!-- start after 60 seconds --&gt;
          &lt;property name="delay" value="6000"/&gt;
          &lt;!-- depends on the enviroment --&gt;
          &lt;property name="period" value="${period}"/&gt;
          &lt;property name="runnable" ref="myScheduler"/&gt;
      &lt;/bean&gt;
  </code></pre>
  
  <p>The property <code>period</code> is set up in some configuration file, and it seems that the default type is String:</p>
  
  <pre><code>Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'someSchedulerTask' defined in class path resource [context.xml]: Initialization of b
  ean failed; nested exception is org.springframework.beans.TypeMismatchException: Failed to convert property value of type 'java.lang.String' to required type 'long' for property 'period'; nested exception is ja
  va.lang.NumberFormatException: For input string: "period"
  </code></pre>
  
  <p>How could I change in this step from Stirng to Long??</p>
  
  <p>Thanks in advance</p>
  
  <p><strong>EDIT</strong>
  There is no problem with the place holder configuration, I am using more values from this config file in another beans.
  Declaration:</p>
  
  <pre><code>period=30000
  </code></pre>