AsTeRICS

# JsonReader

# Component Type: Processor (Subcategory: Easy Reading)

Receives a JSON string and JSON field name as input and parses it into a JSON object to send one or more field values (several ones, only if the ``is true and other jsonFieldName input values follow).

# Input Port Description

  • jsonInputString [string]: The JSON-formatted string to be converted into a JSON object.
  • jsonFieldName [string]: The key/name of the JSON object’s field, of which the value shall be sent to the output port (most recent name from this port is used, “” causes an error at readNextField event).
  • ** [oolean, default: true]**: Optional. If connected, it overwrites the keepParsedObject property.

# Output Port Description

  • jsonFieldValue [string]: The value of the JSON field, identified by jsonFieldName, converted to a string (also "" is valid; an explicit null is converted to "null"). In case of failure, it will be "" and the error port provides details.
  • latestReadFieldName [string]: The name of the field whenever an attempt of reading a field value (from the parsed JSON object) has been completed. This output can only be "" if the field name was ""|null|unset, in which case the error output port provides details.
  • error [string]: Receives a value (different from "") whenever an attempt of input parsing or reading the next field fails. No matter whether it is because of a missing JSON object (as needed for reading a field but not previously parsed) or missing or invalid input port values. It receives "" (= no error) at the next successful parse or read. Thus it can be used for showing error messages.

# Event Listener Description

For details on which errors are handled and error messages are provided for, see description of the error output port and of the event triggers that cause an error port output.

  • parseInput: Parses the most recently received value from the input port jsonInputString into a JSON object - from which later the desired JSON field (identified by the jsonFieldName input) value is read and sent to the jsonFieldValue output port.
  • readNextField: Triggers the next attempt of reading the value of the currently desired JSON field (identified by jsonFieldName) from an already parsed JSON object.
    This event must be used after parseInput (which must be repeated if keepParsedObject is set to false). parseInput, in combination with a well-matched keepParsedObject property/port, has to assure that there is already a JSON object from which values can be read when firing readNextField.
  • rejectParsedObject: Unsets the parsed JSON object for the case that keepParsedObject is true (via property or overwritten by input port value) or if it is false but no successful reading of any JSON field has happened (see property description).

# Event Trigger Description

  • inputParsed: Triggers to indicate that the plugin is done with parsing the JSON input (string) into a JSON object.
  • fieldValueAvailable: Triggers when the value of the desired JSON field (specified by the input jsonFieldName and now identified by the output latestReadFieldName) is available at the jsonFieldValue output port.

    Note

    Event Triggers that cause an error port output

  • fieldValueNotFound: Triggers when trying to read a field but when there is no field with the name given at the input port within the parsed JSON object (string).
  • fieldValueInvalidFormat: Triggers when trying to read a field but when there has been an error returning the value of the desired JSON field. The value has a wrong/an invalid format but is found (i.e. the key is existent). This is the case whenever a found value cannot be parsed to a string (which is the output format at the output port jsonFieldValue).
  • invalidInputFormat: Triggers when trying to parse the JSON input string but when it cannot be parsed into a JSON object (to later read values from).
  • missingJsonInput: When trying to parse the JSON input string but when there has been no value at the input port jsonInputString.
  • missingFieldName: Triggers when trying to read from an already parsed JSON object but when there has been no value at the input port jsonFieldName.

# Properties

  • keepParsedObject [boolean, default: true]: Specifies, whether to keep the parsed JSON object (the one resulting from the latest parsing of jsonInputString) until the next value appears at the jsonInputString port – to read further fields in the meanwhile.

Usage Note: If a field reading attempt fails, a JSON object that has potentially been stored will not be unset, independently from the value of this property. This is to assure that each JSON input delivers at least one field value or otherwise is replaced by the next JSON input. In order to force the parsed JSON object’s rejection, rejectParsedObject must be triggered.

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