title: java.lang.NoClassDefFoundError: org/apache/commons/lang/Validate
body: <p>Why does the following happen and how can I fix it?</p>
  
  <pre><code>Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/commons/lang/Validate
      at org.jsoup.DataUtil.load(DataUtil.java:47)
      at org.jsoup.Jsoup.parse(Jsoup.java:57)
      at linksfind.main(linksfind.java:12)
  Caused by: java.lang.ClassNotFoundException: org.apache.commons.lang.Validate
      at java.net.URLClassLoader$1.run(Unknown Source)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.net.URLClassLoader.findClass(Unknown Source)
      at java.lang.ClassLoader.loadClass(Unknown Source)
      at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
      at java.lang.ClassLoader.loadClass(Unknown Source)
      ... 3 more
  </code></pre>