I want to know about java problem

As Far as I understood, You are trying to show a message that the Database is unavailable,
To do that, You can use Excepion Handling Techniques offered by the Java Language,

The General Format of handling an exception is

try
{
  // erraneous code
}
catch(Exception e)
{
  // Exception Handling code
}

The catch statement can be different exception types and can be given different exception handling codes for different exceptions.

a quick but incomplete solution could be,

try
{
  // Your DB connection code
}
catch(Exception e)
{
  System.out.println("ERROR : Could not connect to database.");
}

If you also need the stack trace for debugging purposes you can also use e.printStackTrace();