title: Java convert string to md5 and vise versa
body: <p>I have java three strings. let say example. </p>
  
  <pre><code>String test = "Hi, ";
  String test1 = "this is ";
  String test2 = "Java programming!";
  </code></pre>
  
  <p>I wanna combine those 3 string and change it to md5 format. How could I do? I use MessageDigest class for one string but i have no idea how to append 3 string before change to md5. And I wanna to change back md5 to string. Do i need external library. </p>