FasterXML/jackson-databind · error · IllegalArgumentException

maxProblems must be positive

Error message

maxProblems must be positive

What it means

Thrown by ObjectReader.problemCollectingReader(int maxProblems) when the maxProblems argument is zero or negative. This method creates a problem-collecting reader that buffers deserialization errors instead of failing immediately; a non-positive limit would mean zero problems can be collected, which defeats the purpose and is rejected.

Solutions

1. Pass a positive integer: use problemCollectingReader() with no argument for the default limit, or ensure your value is >= 1.
2. Validate the value before calling: if (maxProblems < 1) maxProblems = CollectingProblemHandler.DEFAULT_MAX_PROBLEMS;
3. Use reader.problemCollectingReader() (no-arg) if you just want the default problem collection behavior.

Example fix

// before
int limit = getConfigInt("max.problems", 0); // defaults to 0
ObjectReader r = reader.problemCollectingReader(limit); // throws
// after
int limit = Math.max(1, getConfigInt("max.problems", CollectingProblemHandler.DEFAULT_MAX_PROBLEMS));
ObjectReader r = reader.problemCollectingReader(limit);

// Validate before calling
if (maxProblems <= 0) {
    throw new IllegalArgumentException("maxProblems must be > 0, got: " + maxProblems);
}
reader.problemCollectingReader(maxProblems);

When it happens

Trigger: Calling reader.problemCollectingReader(0) or reader.problemCollectingReader(-1) or passing a computed value that evaluates to <= 0 (e.g., an uninitialized int field defaulting to 0, or a size derived from an empty collection).

Common situations: Passing a configurable limit from a properties file or environment variable that defaults to 0 when unset. Deriving maxProblems from a list size that is zero in edge cases. Copy-paste from other builder methods that allow 0.

Related errors

• deserialization problems (showing first 5):%n
• argument " " is null
• argument " " is null
• Cannot pass null property name
• Cannot set maxDeserializerCacheSize to a negative value

AI-assisted analysis of FasterXML/jackson-databind@87876ca5c0 (2026-08-11). Data as JSON: /api/errors/49b989352d3c1725. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/tools/jackson/databind/ObjectReader.java:743

     * @since 3.1
     */
    public ObjectReader problemCollectingReader() {
        return problemCollectingReader(CollectingProblemHandler.DEFAULT_MAX_PROBLEMS);
    }

    /**
     * Variant of {@link #problemCollectingReader()} that allows overriding maximum
     * number of problems to collect.
     *
     * @param maxProblems Maximum number of problems to collect (must be {@code >} 0)
     * @return A new ObjectReader configured for problem collection
     * @throws IllegalArgumentException if maxProblems is {@code <= 0}
     *
     * @since 3.1
     */
    public ObjectReader problemCollectingReader(int maxProblems) {
        if (maxProblems <= 0) {
            throw new IllegalArgumentException("maxProblems must be positive");
        }
        return problemCollectingReader(new CollectingProblemHandler(maxProblems));
    }

    /**
     * Variant of {@link #problemCollectingReader()} that allows passing custom
     * {@link CollectingProblemHandler} (usually sub-class).
     *
     * @param problemHandler Custom handler instance to use
     *
     * @return A new ObjectReader configured for problem collection
     *
     * @since 3.1
     */
    public ObjectReader problemCollectingReader(CollectingProblemHandler problemHandler)
    {
        DeserializationConfig newConfig = _config.withHandler(problemHandler);
        return _new(this, newConfig, _valueType, _rootDeserializer, _valueToUpdate,

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