Java 8 - Hashmap cannot find and return a ZonedDateTime value

Question

I'm working on a example project where we need to store some values in a Hashmap and fetch them via REST services.

POSTing the data as

{"timestamp":"2015-09-01T16:40:00.000Z", "temperature":"27.2"}

Save method:

@PostMapping
public ResponseEntity<?> createCalc(@Valid @RequestBody Calc calc) {
   store.add(measurement);
}
...

Store class

private HashMap<ZonedDateTime, Calc> calcHashMap;
...
public void add(Calc calc) {
  calcHashMap.put(calc.getTimestamp(), calc);
}

After saving we wanted to get data from Hashmap, none of the below can find it.

http://localhost:8000/measurements/2015-09-01T16:40:00.000Z
or 
http://localhost:8000/measurements/2015-09-01T16:40Z

Method we are using is

  @GetMapping("/{timestamp}")
  public ResponseEntity<Calc> getCalc(@PathVariable ZonedDateTime timestamp) {

  Calc calc = process.fetch(timestamp);

Process.java class

 public Calc fetch(ZonedDateTime timestamp) {
    return calcMap.get(timestamp);
 }

Adding that to a Hashmap and Timestamp as the key. We are seeing these differences:

1. When printing the value in console using System.out.println 2015-09-01T16:40Z
2. Return from REST GET method in POSTMAN shows this 2015-09-01T16:40:00Z
3. While the actual value is 2015-09-01T16:40:00.000Z

I need to find the stores timestamp and return the object, but is not being found because of the differences above. How to solve this?

Answer 1

After some research i was able to solve this as below

for (ZonedDateTime zdt : measurementHashMap.keySet()) {
  if (timestamp.toInstant().compareTo(measurementHashMap.get(zdt).getTimestamp().toInstant()) == 0) {
     return measurementHashMap.get(zdt);
  }
}

Option 2: There is another option to convert ZonedDateTime to OffSetDate and then compare. Ref: https://rextester.com/SIIIW97667

Answer 2

In your Calc class, you can use @JsonFormat from Jackson library and give the required pattern you want. In this case, "yyyy-MM-dd'T'HH:mm:ss.SSSX". Also, I suggest you to use OffsetDateTime directly instead of conversion.