use Regexp::Common;

$_ = q{
    public void readExternal() {
        this { is } not {
            { real } java
        } code but an {
            {
                { example }
            }
        }
    }
};

my ($function) =
    /( public \s+ void \s+ readExternal [^{]+ $RE{balanced}{-parens=>'{}'} )/x;