Using Jackson JsonFormat pattern for custom date string

Question

Summary

I am attempting to parse dates such as 25/Sep/17 hence the SimpleDateFormat annotation seems to be @JsonFormat(pattern = "dd/MMM/yy"). However, when I try to parse this, I get an InvalidFormatException where the essence is (full exception below after example):

Text '25/Sep/17' could not be parsed at index 3

What is wrong with my date format string? I can't see any issues. It looks like it doesn't like the Sep paired with MMM.

I am using Amazon Corretto Java version "11.0.5" 2019-10-15 LTS

Example to reproduce

package example;

import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;

import java.time.LocalDate;

public class HelloMapperApp {
  private static final ObjectMapper MAPPER = new ObjectMapper();

  public static void main(String[] args) {
    MAPPER.registerModule(new JavaTimeModule());
    try {
      Example example = MAPPER.readValue("{ \"name\": \"example\", \"date\": \"25/Sep/17\"", Example.class);
      System.out.println("Deserialised is: " + example);
    } catch (Exception e) {
      throw new RuntimeException("Could not parse JSON: " + e);
    }
  }

  static class Example {
    @JsonProperty
    String name;
    @JsonProperty
    @JsonFormat(pattern = "dd/MMM/yy")
    LocalDate date;

    @Override
    public String toString() {
      return String.format("name: %s%ndate: %s", name, date);
    }
  }
}

Full Exception

Exception in thread "main" java.lang.RuntimeException: Could not parse JSON: com.fasterxml.jackson.databind.exc.InvalidFormatException: 
Cannot deserialize value of type 
`java.time.LocalDate` from String "25/Sep/17": Failed to deserialize java.time.LocalDate: 
(java.time.format.DateTimeParseException) Text '25/Sep/17' could not be parsed at index 3
 at [Source: (String)"{ "name": "example", "date": "25/Sep/17""; line: 1, column: 30] (through reference chain: example.HelloMapperApp$Example["date"])
        at example.HelloMapperApp.main(HelloMapperApp.java:19)

I just tried that with the usual ```java.time``` stuff and this pattern works with the given input. — akuzminykh, Mar 20 '20 at 01:41
Since it works for you this gave me an idea. I tried the above example in Java 8 and it worked fine. However in Java 11 it fails with the above error. So it seems *Java 11* specific. At least the Corretto JDK 11 does not work with the above example. If you have time/inclination could you share which Java version you tried with? — Friedrich 'Fred' Clausen, Mar 20 '20 at 01:49
I've used Java 11.0.3 (Oracle). I'm having a look [here](https://stackoverflow.com/questions/12463049/date-format-mapping-to-json-jackson) right now. Maybe this is something. Try out ```@JsonFormat(locale = "en", shape = JsonFormat.Shape.STRING, pattern = "dd/MMM/yy")```. — akuzminykh, Mar 20 '20 at 01:51
Ah that works so, in this case anyway, having the `locale = "en"` is probably key. I could leave off the shape and just use `@JsonFormat(locale = "en", pattern = "dd/MMM/yy")` and it worked. A previous answer, since deleted, suggested using `LLL` since it is a local date. So using `dd/LLL/yy` is also working when specifying locale. Feel free to add an answer. — Friedrich 'Fred' Clausen, Mar 20 '20 at 01:55

akuzminykh · Accepted Answer · 2020-03-20T02:12:07.520

It could be the case that the given input has a wrong format for the locale used by the formatter. Here is a similar post where someone had a problem with Sep where the formatter expected Sep. for Locale.CANADA.

Here and here you can check out how to set the locale for the formatter. E.g.:

@JsonFormat(locale = "en", pattern = "dd/MMM/yy")

FYI: You don't need to use LLL for months as a text. Have a look on DateTimeFormatter.

Number/Text: If the count of pattern letters is 3 or greater, use the Text rules above. Otherwise use the Number rules above.

When you use MMM, i.e. three times M, the formatter will implicitly use the text format.

Using Jackson JsonFormat pattern for custom date string

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