json-path/JsonPath · error · MappingException

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

Error message

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

What it means

JsonSmartMappingProvider's LongReader.convert() cannot convert the source object to a java.lang.Long. It supports Long, Integer, Short, Byte, Double, BigDecimal, Float and String sources; any other runtime type (containers, booleans, dates, arbitrary beans) is rejected with MappingException. The provider deliberately maps only well-known scalar types.

Source

Thrown at json-path/src/main/java/com/jayway/jsonpath/spi/mapper/JsonSmartMappingProvider.java:153

        }
        public Long convert(Object src) {
            if(src == null){
                return null;
            }
            if(Long.class.isAssignableFrom(src.getClass())){
                return (Long) src;
            } else if (Integer.class.isAssignableFrom(src.getClass())) {
                return ((Integer) src).longValue();
            } else if (Double.class.isAssignableFrom(src.getClass())) {
                return ((Double) src).longValue();
            } else if (BigDecimal.class.isAssignableFrom(src.getClass())) {
                return ((BigDecimal) src).longValue();
            } else if (Float.class.isAssignableFrom(src.getClass())) {
                return ((Float) src).longValue();
            } else if (String.class.isAssignableFrom(src.getClass())) {
                return Long.valueOf(src.toString());
            }
            throw new MappingException("can not map a " + src.getClass() + " to " + Long.class.getName());
        }
    }

    private static class DoubleReader extends JsonReaderI<Double> {
        public DoubleReader() {
            super(null);
        }
        public Double convert(Object src) {
            if(src == null){
                return null;
            }
            if(Double.class.isAssignableFrom(src.getClass())){
                return (Double) src;
            } else if (Integer.class.isAssignableFrom(src.getClass())) {
                return ((Integer) src).doubleValue();
            } else if (Long.class.isAssignableFrom(src.getClass())) {
                return ((Long) src).doubleValue();
            } else if (BigDecimal.class.isAssignableFrom(src.getClass())) {

View on GitHub (pinned to 62a4c9f0f6)

Solutions

  1. Confirm the source resolves to a number or numeric String before requesting Long.class.
  2. Narrow the JsonPath so it selects a scalar leaf value rather than a container node.
  3. Pre-convert: read as Object, check instanceof Number / parse the String yourself.
  4. Use JacksonMappingProvider or GsonMappingProvider if you need richer type coercion.
  5. Register a custom MappingProvider implementation for your types.

Example fix

// before
Long id = cfg.mappingProvider().map(node, Long.class, cfg); // node is a JSONObject
// after
Object v = JsonPath.read(json, "$.id");
Long id = Long.valueOf(v.toString());
Defensive patterns

Strategy: type-guard

Validate before calling

Object v = JsonPath.read(json, "$.field");
if (!(v instanceof Number || v instanceof String))
    throw new IllegalArgumentException("Cannot map " + (v == null ? "null" : v.getClass()) + " to Long");

Type guard

static Long toLong(Object v) {
    if (v instanceof Number) return ((Number) v).longValue();
    if (v instanceof String) return Long.valueOf((String) v);
    return null;
}

Try / catch

try {
    Long n = cfg.mappingProvider().map(value, Long.class, cfg);
} catch (MappingException e) {
    Long n = toLong(value);
    if (n == null) throw new IllegalArgumentException("Non-numeric value", e);
}

Prevention

When it happens

Trigger: Calling map(obj, Long.class, configuration) on the JsonSmart mapping provider where obj's runtime class is not a numeric type or String — e.g. obj is a JSONObject, JSONArray, Boolean or Date.

Common situations: Mapping a JSON node that is actually an object/array to Long; mapping boolean fields to numeric IDs; migrating code from a provider (Jackson/Gson) that coerced more types; timestamp fields that arrived as strings with non-numeric content.

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/4a6d2a93b18035a9. Report an issue: GitHub.