How to retrieve filtered value from a stream and use it - java-8

Question

I'm new to Java 8:
I have to convert this piece of java 6 code to java 8 version:
List<String> unvalidnumbers = new ArrayList<>();
StringBuilder content = new StringBuilder();
String str = "current_user"
for (Iterator<String> it = numbers.iterator(); it.hasNext();) {
String number = it.next();
try {
PersIdentifier persIdentifier = this.getPersIdentifierByNumber(number);
if (persIdentifier != null) {
content.append(number).append(";").append(str);
if (StringUtils.equals(persIdentifier.getType(), "R")) {
content.append(";X");
}
if (it.hasNext()) {
content.append("\r\n");
}
}
} catch (BusException e) {
LOGGER.warn("Pers not found", e);
unvalidnumbers.add(number);
}
}
So i wrote this:
numbers.stream().filter((String number) -> {
try {
return this.getPersIdentifierByNumber(number) != null;
} catch (BusinessException e1) {
LOGGER.warn("Pers not found", e1);
return false;
}
}).forEach(number -> contentConstruction.append(number).append(";").append(str));
I know it's missing this part:
if (StringUtils.equals(persIdentifier.getType(), "R")) {
content.append(";X");
}
if (it.hasNext()) {
content.append("\r\n");
}
But i didn't found way to retrieve the corresponding persIdentifier object.
Any idea please

Answer 1

You should use a more functional approach if you use Java 8.
Instead of a forEach, favor collect(). Here Collectors.joining() looks suitable.
Not tested but you should have an overall idea :
String result =
numbers.stream()
.map(number -> new SimpleEntry<String, PersIdentifier>(number, this.getPersIdentifierByNumber(number) )
.filter(entry -> entry.getValue() != null)
.map(entry ->{
final String base = entry.getKey() + ";" + str;
return "R".equals(entry.getValue().getType()) ? base + ";X" : base;
})
.collect(joining("\r\n")); // Or not OS dependent : System.lineSeparator()