Hi all, This is a request for feedback on how to distinquish null from empty string for LocalDate and LocalDateTime deserialization, issue #114 <https://github.com/FasterXML/jackson-modules-java8/issues/114>
To summarize the issue and possible solutions: beytun (issue submitter) writes: > For LocalDate and LocalDateTime deserialization, empty string is mapped to >> null by LocalDateDeserializer >> <https://github.com/FasterXML/jackson-modules-java8/blob/master/datetime/src/main/java/com/fasterxml/jackson/datatype/jsr310/deser/LocalDateDeserializer.java> >> >> and LocalDateTimeDeserializer >> <https://github.com/FasterXML/jackson-modules-java8/blob/master/datetime/src/main/java/com/fasterxml/jackson/datatype/jsr310/deser/LocalTimeDeserializer.java> >> >> respectively. So something like {"date": null} can't be distinguished from >> {"date": ""}. From the view of a strict API, the latter is an error. >> >> It would be good to add some feature to treat empty string as invalid >> format, that LocalDateDeserializer and LocalDateTimeDeserializer could >> report this as an error instead of mapping to null. >> > Tatu writes: *Perhaps use of DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT > would work here, although my main concern is that since default value is > false, adding a check would make formerly accepted values invalid with > 2.10...* > > *Alternative way would be to add a new option/feature in JavaTimeModule, > where it could be locally enabled/disabled.* > Now, given beytun's point about 'strict', perhaps another solution is to use the lenient/strict setting here? That is already used in LocalDateDeserializer to throw an exception: if (parser.hasToken(JsonToken.VALUE_NUMBER_INT)) { if (!isLenient()) { return _failForNotLenient(parser, context, JsonToken.VALUE_STRING); } return LocalDate.ofEpochDay(parser.getLongValue()); } Test case to illustrate issue: private final TypeReference<Map<String, LocalDate>> MAP_TYPE_REF = new TypeReference<Map<String, LocalDate>>() { }; private final ObjectMapper LOCAL_DATE_MAPPER = newMapper(); private final ObjectReader LOCAL_DATE_READER = LOCAL_DATE_MAPPER.readerFor(MAP_TYPE_REF); @Test public void testDeserializationNullAndEmptyString() throws Exception { String dateValAsNullStr = null; String valueFromNullStr = LOCAL_DATE_MAPPER.writeValueAsString(asMap("date", dateValAsNullStr)); Map<String, LocalDate> actualMapFromNullStr = LOCAL_DATE_READER.readValue(valueFromNullStr); assertNull(actualMapFromNullStr.get("date")); String dateValAsEmptyStr = ""; String valueFromEmptyStr = LOCAL_DATE_MAPPER.writeValueAsString(asMap("date", dateValAsEmptyStr)); Map<String, LocalDate> actualMapFromEmptyStr = LOCAL_DATE_READER.readValue(valueFromEmptyStr); // this test fails! assertNotEquals(actualMapFromEmptyStr,actualMapFromNullStr); } Researching a bit, there doesn't seem to be anything in the spec that says *not *to do it as beytun suggests: https://stackoverflow.com/questions/9619852/what-is-the-convention-in-json-for-empty-vs-null?noredirect=1&lq=1 https://www.ibm.com/support/knowledgecenter/SSTLXK_7.5.1/com.ibm.wbpm.wid.integ.doc/topics/rjsonnullunsempprops.html Speaking of nulls, Tony Hoare calls this his "billion-dollar" mistake. Initially I disagreed but now I'm not so sure :) https://www.lucidchart.com/techblog/2015/08/31/the-worst-mistake-of-computer-science/ -- You received this message because you are subscribed to the Google Groups "jackson-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to jackson-dev+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/jackson-dev/f98b3a71-c408-4eb9-a029-743dcf1f73af%40googlegroups.com.
