title: How to convert String to BigInteger representation and back in Java?
body: <p>Let's suppose I have a <code>String</code>, let's call it <code>foo</code>. This <code>String</code> can contain any value, like letters, numbers, special characters, <code>UTF-8</code> special characters, such as á and so on. For instance, this might be a real value:</p>
  
  <pre><code>"Érdekes szöveget írtam a tegnap, 84 ember olvasta."
  </code></pre>
  
  <p>I would like to have the following two methods:</p>
  
  <pre><code>public BigInteger toBigInteger(String foo)
  {
      //Returns a BigInteger value that can be associated with foo
  }
  
  public String fromBigInteger(BigInteger bar)
  {
      //Returns a String value that can be associated with bar
  }
  </code></pre>
  
  <p>Then:</p>
  
  <pre><code>String foo = "Érdekes szöveget írtam a tegnap, 84 ember olvasta.";
  System.out.println(fromBigInteger(toBigInteger(foo)));
  //Output should be: "Érdekes szöveget írtam a tegnap, 84 ember olvasta."
  </code></pre>
  
  <p>How can I achieve this?
  Thanks</p>