json-path/JsonPath · error · MappingException

can not map a " + src.getClass() + " to " + Date.class.getNa

Error message

can not map a " + src.getClass() + " to " + Date.class.getName()

What it means

JsonSmartMappingProvider's DateReader.convert() cannot convert the source object to java.util.Date. It only accepts Date instances and Strings, and Strings are parsed with DateFormat.getInstance() (a SHORT locale format); every other runtime type throws MappingException. Note that a String in a non-default format throws MappingException wrapping the ParseException instead.

Source

Thrown at json-path/src/main/java/com/jayway/jsonpath/spi/mapper/JsonSmartMappingProvider.java:246

        public DateReader() {
            super(null);
        }
        public Date convert(Object src) {
            if(src == null){
                return null;
            }
            if(Date.class.isAssignableFrom(src.getClass())){
                return (Date) src;
            } else if(Long.class.isAssignableFrom(src.getClass())){
                return new Date((Long) src);
            } else if(String.class.isAssignableFrom(src.getClass())){
                try {
                    return DateFormat.getInstance().parse(src.toString());
                } catch (ParseException e) {
                    throw new MappingException(e);
                }
            }
            throw new MappingException("can not map a " + src.getClass() + " to " + Date.class.getName());
        }
    }
    private static class BooleanReader extends JsonReaderI<Boolean> {
        public BooleanReader() {
            super(null);
        }
        public Boolean convert(Object src) {
            if(src == null){
                return null;
            }
            if (Boolean.class.isAssignableFrom(src.getClass())) {
                return (Boolean) src;
            }
            throw new MappingException("can not map a " + src.getClass() + " to " + Boolean.class.getName());
        }
    }
}

View on GitHub (pinned to 62a4c9f0f6)

Solutions

  1. Convert timestamps yourself before mapping: new java.util.Date(longValue) for epoch millis.
  2. Pre-format String values to the locale SHORT pattern DateFormat.getInstance() expects, or parse with a dedicated formatter (Instant.parse / SimpleDateFormat).
  3. Check the JsonPath resolves to a Date-compatible scalar, not a container node.
  4. Use JacksonMappingProvider with a configured date deserializer for robust date handling.
  5. Register a custom MappingProvider with your own DateReader.

Example fix

// before
Date d = cfg.mappingProvider().map(1715000000000L, Date.class, cfg); // MappingException
// after
Long ts = JsonPath.read(json, "$.createdAt");
Date d = new java.util.Date(ts);
Defensive patterns

Strategy: type-guard

Validate before calling

Object v = JsonPath.read(json, "$.field");
if (!(v instanceof java.util.Date || v instanceof String))
    throw new IllegalArgumentException("Cannot map " + (v == null ? "null" : v.getClass()) + " to Date; pre-convert timestamps yourself");

Type guard

static java.util.Date toDate(Object v) {
    if (v instanceof java.util.Date) return (java.util.Date) v;
    if (v instanceof Number) return new java.util.Date(((Number) v).longValue());
    if (v instanceof String) {
        try { return java.time.Instant.parse((String) v); }
        catch (Exception ignored) { }
    }
    return null;
}

Try / catch

try {
    Date d = cfg.mappingProvider().map(value, Date.class, cfg);
} catch (MappingException e) {
    Date d = toDate(value);
    if (d == null) throw new IllegalArgumentException("Unparseable date value", e);
}

Prevention

When it happens

Trigger: map(obj, Date.class, configuration) on JsonSmartMappingProvider where obj is a Long timestamp, a JSONObject, JSONArray, or any non-Date/non-String type.

Common situations: Trying to map epoch-millis Long values to Date (unsupported); ISO-8601 strings like "2024-01-15T10:00:00Z" that DateFormat.getInstance() cannot parse; provider swap from Jackson which binds timestamps differently.

Understand the failure class

Background: "is not a compatible type" / "cannot merge" errors: when a value's type doesn't match what the library requires — this error's family across 65 libraries.

Related errors

AI-assisted analysis of json-path/JsonPath@62a4c9f0f6 (2026-09-11). Data as JSON: /api/errors/b33325cf05a5c681. Report an issue: GitHub.