private static class StringPairConverter implements ValueConverter<Pair<String, String>> {
@Override
public Pair<String, String> convert(String input) {
int eqPos = input.indexOf('=');
if (eqPos == -1) {
throw new ValueConversionException("Parameter should be in the form key=value, which the " +
"following is not: '" + input + "'.");
}
String key = input.substring(0, eqPos).trim();
String value = input.substring(eqPos + 1).trim();
return Pair.newPair(key, value);