appsmithorg/appsmith · error · AppsmithPluginException

PE-JSN-4000

PE-JSN-4000

Error message

Plugin failed to parse JSON "{0}"

What it means

In execute(), the action body string is parsed as a JSON HashMap via objectMapper.readValue(body, HashMap.class). If parsing fails (IOException), the plugin throws PLUGIN_JSON_PARSE_ERROR (PE-JSN-4000) with the raw body and the parser's error detail. The body must be a valid JSON object representing the DynamoDB request parameters.

Source

Thrown at app/server/appsmith-plugins/dynamoPlugin/src/main/java/com/external/plugins/DynamoPlugin.java:219

                        final String action = actionConfiguration.getPath();
                        if (!StringUtils.hasLength(action)) {
                            throw new AppsmithPluginException(
                                    AppsmithPluginError.PLUGIN_EXECUTE_ARGUMENT_ERROR,
                                    DynamoErrorMessages.MISSING_ACTION_NAME_ERROR_MSG);
                        }
                        requestData.put("action", action);
                        requestParams.add(new RequestParamDTO(ACTION_CONFIGURATION_PATH, action, null, null, null));
                        requestParams.add(new RequestParamDTO(ACTION_CONFIGURATION_BODY, body, null, null, null));

                        Map<String, Object> parameters = null;
                        try {
                            if (StringUtils.hasLength(body)) {
                                parameters = objectMapper.readValue(body, HashMap.class);
                            }
                        } catch (IOException e) {
                            final String message = "Error parsing the JSON body: " + e.getMessage();
                            log.warn(message, e);
                            throw new AppsmithPluginException(
                                    AppsmithPluginError.PLUGIN_JSON_PARSE_ERROR, body, e.getMessage());
                        }
                        requestData.put("parameters", parameters);

                        final Class<?> requestClass;
                        try {
                            requestClass = Class.forName(
                                    "software.amazon.awssdk.services.dynamodb.model." + action + "Request");
                        } catch (ClassNotFoundException e) {
                            throw new AppsmithPluginException(
                                    DynamoPluginError.UNKNOWN_ACTION_NAME,
                                    String.format(DynamoErrorMessages.UNKNOWN_ACTION_NAME_ERROR_MSG, action),
                                    e.getMessage());
                        }

                        try {
                            final Method actionExecuteMethod = DynamoDbClient.class.getMethod(
                                    // Convert `ListTables` to `listTables`, which is the name of the method to execute

View on GitHub (pinned to 8cd9021c24)

Solutions

1. Validate the body with a JSON linter before saving the action.
2. Ensure mustache bindings inject valid JSON fragments — wrap string values in quotes or use JSONPath-style bindings.
3. Use double quotes for all keys and string values; remove trailing commas.
4. Confirm the body is a JSON object (starts with '{'), not an array or scalar.

Example fix

// before — unquoted keys, trailing comma
String body = "{ TableName: 'Music', }";

// after
String body = "{\"TableName\":\"Music\"}";

String body = actionConfiguration.getBody();
if (StringUtils.hasLength(body)) {
    try {
        objectMapper.readTree(body); // validate parseability
    } catch (IOException e) {
        throw new IllegalArgumentException(
            "Action body is not valid JSON: " + e.getMessage());
    }
}

plugin.execute(actionConfiguration, dsConfig)
    .onErrorResume(e -> e instanceof AppsmithPluginException ape
            && "PE-JSN-4000".equals(ape.getErrorDTO().getAppErrorCode()),
        e -> { log.warn("Bad JSON body", e); return Mono.just(errorResult(e)); });

When it happens

Trigger: The action body contains malformed JSON — trailing commas, unquoted keys, single-quoted strings, unmatched braces, or a non-JSON value injected by a mustache binding.

Common situations: Hand-typed JSON with syntax errors; a mustache binding that injects a raw string or unquoted value into the JSON; a body that is whitespace-only or contains a JSON array instead of an object; copy-paste introducing smart quotes.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• PE-ARG-5000
• PE-DYN-5001
• PE-DYN-5000
• PE-DSE-5003
• PE-JSN-4000

AI-assisted analysis of appsmithorg/appsmith@8cd9021c24 (2026-08-12). Data as JSON: /api/errors/e763994beba5125f. Report an issue: GitHub.