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Pentaho Documentation

JSON Input

This step reads data from JSON structures, files, or incoming fields using a JSONPath expression to extract data and output rows. JSONPath expressions can use either dot notation or square bracket notation.

General

Enter the following information in the transformation step name field:

  • Step name: Specifies the unique name of the JSON Input transformation step on the canvas. You can customize the name or leave it as the default.

You can use Preview rows to display the rows generated by this step. The JSON Input step determines what rows to input based on the information you provide in the option tabs. This preview function helps you to decide if the information provided accurately models the rows you are trying to retrieve.

Options

The JSON Input step features several tabs with fields. Each tab is described below.

File Tab

PDI_JSON_Input.png

Use the File tab to enter the following connection information for your source:

Option  Description
Source is from a previous step

Select to retrieve the source from a previously defined field. When selected, the following fields are available: 

  • Select field
  • Use field as file names
  • Read source as URL
  • Do not pass field downstream

When this option is cleared, the following fields are available:

  • File or directory
  • Regular Expression
  • Exclude Regular Expression
  • Selected files.
Select field Specify the field name to use as a source from a previous step. 
Use field as file names Select to indicate the source is a filename.
Read source as URL Select to indicate if the source should be accessed as a URL.
Do not pass field downstream Select to remove the source field from the output stream. This action improves performance and memory utilization with large JSON fields.
File or directory Specify the source location if the source is not defined in a field. Click Browse to navigate to your source file or directory. Click Add to include the source in the Selected files table.
Regular expression Specify a regular expression to match filenames within a specified directory.
Exclude regular expression Specify a regular expression to exclude filenames within a specified directory.

Selected Files Table

The Selected files table shows files or directories to use as source locations for input. This table is populated by clicking Add after you specify a File or directory. The JSON Input step tries to connect to the specified file or directory when you click Add to include it into the table.

The table contains the following columns:

Column Description
File/Directory The source location indicated by clicking Add after specifying it in File or directory 
Wildcard (RegExp) Wildcards as specified in Regular expression
Exclude wildcard Excluded wildcards as specified in Exclude regular expression
Required Required source location for input
Include subfolders Whether subfolders are included within the source location

Click Delete to remove a source from the table. Click Edit to remove a source from the table and return it back to the File or directory option.

Use Show filename(s) to display the file names of the sources successfully connected to the JSON Input step.

Content Tab

PDI_JSON_Input_Content.png

The Content tab contains the following options for configuring which data to retrieve:

Option Description
Ignore empty file Select to skip empty files. When cleared, empty files will cause the process to fail and stop.
Do not raise an error if no files Select to continue when no files are available to process.
Ignore missing path Select to continue processing files when an error occurs that (1) no fields match the JSON path or (2) that all the values are null. When cleared, no further rows are processed when an error occurs.
Default path leaf to null Select to return a null value for missing paths.
Limit Specify a limit on the number of records generated from the step. Results are not limited when set to zero.
Include filename in output Select to add a string field with the filename in the result.
Rownum in output Select to add an integer field with the row number in the result.
Add filenames to result Select to add processed files to the result file list.

Fields Tab

PDI_JSON_Input_Fields.png

The Fields tab displays field definitions to extract values from the JSON structure. The table in this tab contain the following columns:

Column Description
Name Name of field that maps to the corresponding field in the JSON input stream 
Path Complete path of the field name in the JSON input stream. All records can be retrieved by adding the asterisk (*) in the path. For example, $.mydata.*
Type Data type of the input field
Format An optional mask for converting the format of the original field. See Common Formats for information on common valid date and numeric formats you can use in this step.
Length Length of the field
Precision Number of floating point digits for number-type fields
Currency Currency symbol ($ or € for example)
Decimal A decimal point can be a "." (5,000.00 for example) or "," (5.000,00 for example)
Group A grouping can be a "," (10,000.00 for example) or "." (5.000,00 for example)
Trim type The trim method to apply to a string
Repeat The corresponding value from the last row repeated if a row is empty

Click Get Fields to have the step populate the table with fields derived from the source file. All fields identified by this step will be added to the table.

Select Fields

Click Get Fields in the Fields tab to open the Select Fields window. Select the checkbox next to each field in your source file that you want include in your output. All the fields selected in this step are added to the table. You can search for a field name by entering the field name in the Search box.

PDI_JSON_Input_GetFields_dlg.png

Additional Output Fields Tab

PDI_JSON_Input_AdditionalOutputFields.png

The Additional output fields tab contains the following options to specify additional information about the file to process:

Option Description
Short filename field Specify the field that contains the filename without path information but with an extension.
Extension field Specify the field that contains the extension of the filename.
Path field Specify the field that contains the path in operating system format.
Size field Specify the field that contains the size of the data.
Is hidden field Specify the field indicating if the file is hidden or not (Boolean).
Last modification field Specify the field indicating the date of the last time the file was modified.
Uri field Specify the field that contains the URI.
Root uri field Specify the field that contains only the root part of the URI.

Examples

The design-tools/data-integration/samples/transformations directory contains the following example KTRs that show how to use this step:

  • JsonInput - read a dynamic file.ktr
  • JsonInput - read a file.ktr
  • JsonInput - read incoming stream.ktr

A sample JSON file that displays the Select Field dialog box is data-integration/samples/transformations/files/JSON - read nested fields.js.

Metadata Injection Support

All fields of this step support metadata injection. You can use this step with ETL Metadata Injection to pass metadata to your transformation at runtime.