use strict;

my $ex = 0;

while (<DATA>) 
{ 
    if ( /^java/ && /Exception$/ )
    {
        print "\n" if $ex;
        $ex++;
    }
    print;
    
}
__DATA__
java.io.IOException
        at com.mycompany.MyClass.myMethod(com.mycompany.MyClass.java:32)
        at com.mycompany.MyClass.main(com.mycompany.MyClass.java:18)
java.lang.IllegalStateException
       at com.mycompany.MyClass.myMethod(com.mycompany.MyClass.java:25)
       at com.mycompany.MyClass.main(com.mycompany.MyClass.java:18)