StringUtils.java

/**
 * splits the string at every nth position
 * @param str
 * @param position
 * @return a list of Strings each string has a length <= position
 */
public static List<String> splitEveryPosition(String str, Integer position) {
	
	List<String> strings = new ArrayList<String>();
	
	Integer length = str.length(); 
	Integer actualPosition = Math.min(length, position);
	for(int i = 0; i < length;) {
		int toPos = i + actualPosition;
		if(toPos > length) {
			toPos = length;
		}
		strings.add( str.substring(i, toPos) );
		i += actualPosition;
	}
	
	return strings;
}

StringUtilsSplitTest.java

@Test
public void testSplitEveryPosition_LargerPosition() throws Exception {
	String str = "1234567890";
	Integer position = 12;
	List<String> split = StringUtils.splitEveryPosition(str, position);
	assertEquals(1, split.size());
	assertEquals(str, split.get(0));
}

@Test
public void testSplitEveryPosition() throws Exception {
	String str = "12345678901";
	Integer position = 2;
	List<String> split = StringUtils.splitEveryPosition(str, position);
	assertEquals(6, split.size());
	assertEquals("12", split.get(0));
	assertEquals("34", split.get(1));
	assertEquals("56", split.get(2));
	assertEquals("78", split.get(3));
	assertEquals("90", split.get(4));
	assertEquals("1", split.get(5));
}