JSONExtract

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Short Description

JSONExtract reads data from JSON files using SAX technology. It can also read data from compressed files, input port, and dictionary.

Component	Data source	Input ports	Output ports	Each to all outputs	Different to different outputs	Transformation	Transf. req.	Java	CTL	Auto-propagated metadata
JSONExtract	JSON file	0-1	1-n

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Ports

Port type	Number	Required	Description	Metadata
Input	0		For port reading. See Reading from Input Port.	One field (`byte`, `cbyte`, `string`).
Output	0		For correct data records	Any
Output	1-n	^[2]	For correct data records	Any
^[2] Other output ports are required if mapping requires that.

Metadata

JSONExtract does not propagate metadata.

JSONExtract has no metadata template.

Metadata on optional input port must contain string or byte or cbyte field.

Metadata on each output port does not need to be the same.

Each metadata can use Autofilling Functions.

JSONExtract Attributes

Attribute	Req	Description	Possible values
Basic
File URL	yes	Attribute specifying what data source(s) will be read (JSON file, input port, dictionary). See Supported File URL Formats for Readers.
Charset		Encoding of records which are read.	any encoding, default system one by default
Mapping	^[1]	Mapping of the input JSON structure to output ports. See XMLExtract Mapping Definition for more information.
Mapping URL	^[1]	Name of an external file, including its path which defines mapping of the input JSON structure to output ports. See XMLExtract Mapping Definition for more information.
Equivalent XML Schema		URL of the file that should be used for creating the Mapping definition. See JSONExtract Mapping Editor and XSD Schema for more information.
Use nested nodes		By default, nested elements are also mapped to output ports automatically. If set to `false`, an explicit `<Mapping>` tag must be created for each such nested element.	true (default) \| false
Trim strings		By default, white spaces from the beginning and the end of the elements values are removed. If set to `false`, they are not removed.	true (default) \| false
Advanced
Number of skipped mappings		Number of mappings to be skipped continuously throughout all source files. See Selecting Input Records.	0-N
Max number of rows to output		Maximum number of records to be read continuously throughout all source files. See Selecting Input Records.	0-N
^[1]One of these must be specified. If both are specified, Mapping URL has higher priority.

Details

JSONExtract reads data from JSON files using SAX technology. This component is faster than JSONReader which can read JSON files too. JSONExtract does not use DOM, so it uses less memory than JSONReader.

JSONExtract reads lists.

	Note
	Component JSONExtract is very similar to component XMLExtract. The JSONExtract internally transforms JSON to XML and uses XMLExtract to parsing the data. Therefore you can generate xsd file for corresponding xml file.

Mapping in JSONExtract is almost same as in XMLExtract. The main one difference is, that JSON does not have attributes. See XMLExtract's Details for details.

JSONExtract Mapping Editor and XSD Schema

JSONExtract Mapping Editor serves to setup of mapping from JSON tree structure to one ore more output ports without necessity of being aware how to create mapping of field using xml editor.

To be able to use the editor, the editor needs to have created equivalent xsd schema. The equivalent xsd schema is created automatically. Only the directory for the schema needs to be specified.

Any other operations to set up mapping are described in above mentioned XMLExtract.

Mapping Input Fields to the Output Fields

In JSONExtract, you can map input fields to the output in the same way as you map JSON fields. The input field mapping works in all three processing modes.

Examples

Reading lists

JSON file contains information about employees and orders. Each item contains employee id and list of order ids.

{
  "jsonextract_order" : {
    "employee" : "Henri",
    "orders" : [ "order01", "order08", "order15" ]
  },
  "jsonextract_order" : {
    "employee" : "Jane",
    "orders" : [ "order02", "order05", "order09" ]
  }
}

Read data for further processing.

Solution

Use File URL attribute to point to the source file and use Mapping attribute to define mapping.

Figure 48.10. JSONExtract - mapping the list

Best Practices

We recommend users to explicitly specify Charset.

Compatibility

3.5.0-M2

JSONExtract is available since CloverETL 3.5.0-M2.

4.1.0-M1

Since CloverETL 4.1.0-M1 you can map input fields to the output fields in this component.

4.1.0

Since CloverETL 4.1.0 you can read lists.