What is the accepted best practice for Java type conversions?

Question

What is the current best practice for all the type conversions necessary in a Java web application? For example, HttpServletRequest.getParameters(...) returns String[], but Hibernate does not allow String[] to be used in an IN clause for a numeric column. Therefore I need to convert String[] to Long[] via Long.valueOf(). What is the best way to handle this, short of rewriting in another language? Do people just create a class full of little static methods to do this?

Answer 1

If you use a JAX-RS implementation like Jersey, you'll get much improved parameter handling and could map it directly to a List.

If you don't want to go that far, you could also pull tricks like using Guava Collections2.transform and a Function<String, Long> on an Arrays.asList view of the array. Not the most compact way, but each piece is reusable so it wouldn't be so bad.

Answer 2

What is the best way to handle this, short of rewriting in another language?

Seriously? Just because all those hip new languages have a compact syntax for transforming lists/arrays, it doesn't mean using a loop will infect you with a terminal disease or anything.

Long[] result = new Long[param.length];
for(int i=0; i<param.length; i++){
    result[i] = Long.valueOf(param[i]);
}

There, that wasn't so bad, was it? And yeah, you can and should put it in a static helper method if you use it in several places.

Edit: Since Hibernate can also take collections, a somewhat cleaner version:

List<Long> result = new ArrayList<Long>();
for(String s : param){
    result.add(Long.valueOf(s));
}

Answer 3

Apache Commons NumberUtils is best. The conversion routines in the JDK like to just throw a NumberFormatException on unparseable strings. This lib allows you to specify a default value for failed parsing.