google/gson · error · JsonIOException

Accessor " + accessorDescription + " threw exception

Error message

Accessor " + accessorDescription + " threw exception

What it means

Thrown during serialization of a record when its accessor method (the implicitly or explicitly declared component accessor) throws an exception. Gson catches InvocationTargetException and rethrows a JsonIOException wrapping the original cause (e.getCause()). The failure originates in user code on the record, not in Gson internals.

Source

Thrown at gson/src/main/java/com/google/gson/internal/bind/ReflectiveTypeAdapterFactory.java:240

      void write(JsonWriter writer, Object source) throws IOException, IllegalAccessException {
        if (blockInaccessible) {
          if (accessor == null) {
            checkAccessible(source, field);
          } else {
            // Note: This check might actually be redundant because access check for canonical
            // constructor should have failed already
            checkAccessible(source, accessor);
          }
        }

        Object fieldValue;
        if (accessor != null) {
          try {
            fieldValue = accessor.invoke(source);
          } catch (InvocationTargetException e) {
            String accessorDescription =
                ReflectionHelper.getAccessibleObjectDescription(accessor, false);
            throw new JsonIOException(
                "Accessor " + accessorDescription + " threw exception", e.getCause());
          }
        } else {
          fieldValue = field.get(source);
        }

        @SuppressWarnings("ReferenceEquality")
        boolean isSameObject = fieldValue == source;
        if (isSameObject) {
          // avoid direct recursion
          return;
        }
        writer.name(serializedName);
        writeTypeAdapter.write(writer, fieldValue);
      }

      @Override
      void readIntoArray(JsonReader reader, int index, Object[] target)

View on GitHub (pinned to 8b8628c656)

Solutions

Inspect the wrapped cause (e.getCause()) in the JsonIOException to find the real failure in the accessor.
Fix the bug or defensive logic inside the record accessor method.
Register a JsonSerializer for the record type so Gson does not invoke the accessor.
Ensure the record instance is in a consistent, fully-initialized state before calling gson.toJson.

Example fix

// before
public record Money(long cents) {
  public Money { if (cents < 0) throw new IllegalArgumentException(); }
  public long cents() { return Math.toIntExact(cents); } // throws on overflow
}
gson.toJson(new Money(Long.MAX_VALUE));

// after: remove lossy accessor, keep domain check
public long cents() { return cents; }

Defensive patterns

Strategy: try-catch

Validate before calling

null

Type guard

// Guard before serializing a record: invoke its accessors once
static <T> void checkRecordAccessors(T value) throws Throwable {
  for (Method m : value.getClass().getMethods()) {
    if (m.getParameterCount()==0 && m.getDeclaringClass()==value.getClass()) {
      try { m.invoke(value); }
      catch (InvocationTargetException e) { throw e.getCause(); }
    }
  }
}

Try / catch

try {
  gson.toJson(record);
} catch (JsonIOException e) {
  Throwable cause = e.getCause();
  // handle the real failure thrown by the accessor
  log.error("record accessor failed", cause);
}

Prevention

Keep record accessors pure: no validation that can fail on already-valid state.
Unit-test record serialization with the full range of values you expect to round-trip.
Avoid delegating from accessors to services or external state.
Register a JsonSerializer for records whose accessors are non-trivial.

When it happens

Trigger: A record's accessor method throws because it contains custom logic, is annotated with validation that fails, lazily computes a value that errors, or its state is inconsistent at serialization time. Triggered in BoundField.write (ReflectiveTypeAdapterFactory.java:236) when accessor.invoke(source) raises InvocationTargetException.

Common situations: Records with accessor overrides that delegate to services not initialized at serialization time; records wrapping nullable fields whose accessor does unguarded .get(); records produced by deserialization with null components then re-serialized through a validating accessor; concurrent mutation of a record's components mid-serialize.

Related errors

AI-assisted analysis of google/gson@8b8628c656 (2026-08-04). Data as JSON: /data/errors/ff04c98e1df6ae71.json. Report an issue: GitHub.