JSONWriter

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Short Description
Ports
Metadata
JSONWriter Attributes
Details
Best Practices
See also

Short Description

JSONWriter writes data in the JSON format.

Component Data output Input ports Output ports Each to all outputs Different to different outputs Transformation Transf. req. Java Auto-propagated metadata
JSONWriterJSON file1-n0-1
yes
no
no
no
no
no

Icon

Ports

Port typeNumberRequiredDescriptionMetadata
Input0-NAt least oneInput records to be joined and mapped into the JSON structure. Any (each port can have different metadata)
Output0
no
Optional. For port writing. Only one field (byte or cbyte or string) is used. The field name is used in File URL to govern how the output records are processed - see Writing to Output Port

Metadata

JSONWriter does not propagate metadata.

JSONWriter has no metadata template.

JSONWriter Attributes

AttributeReqDescriptionPossible values
Basic
File URLyes The target file for the output JSON. See Supported File URL Formats for Writers. 
Charset 

The encoding of an output file generated by JSONWriter.

The default encoding depends on DEFAULT_SOURCE_CODE_CHARSET in defaultProperties.

UTF-8 | <other encodings>
Mapping [1] Defines how input data is mapped onto an output JSON. See Details.  
Mapping URL[1] External text file containing the mapping definition.  
Advanced
Create directories By default, non-existing directories are not created. If set to true, they are created. false (default) | true
Omit new lines wherever possible  By default, each element is written to a separate line. If set to true, new lines are omitted when writing data to the output JSON structure. Thus, all JSON elements are on one line only. false (default) | true
Cache size A size of of the database used when caching data from ports to elements (the data is first processed then written). The larger your data is, the larger cache is needed to maintain fast processing. auto (default) | e.g. 300MB, 1GB etc.
Cache in Memory Cache data records in memory instead of JDBM's disk cache (default). Note that while it is possible to set maximal size of the cache for the disk cache, this setting is ignored in case in-memory-cache si used. As a result, an OutOfMemoryError may occur when caching too many data records. false (default) | true
Sorted input Tells JSONWriter whether the input data is sorted. Setting the attribute to true declares you want to use the sort order defined in Sort keys, see below. false (default) | true
Sort keys Tells JSONWriter how the input data is sorted, thus enabling streaming. The sort order of fields can be given for each port in a separate tab. Working with Sort keys has been described in Sort Key.
Records per file Maximum number of records that are written to a single file. See Partitioning Output into Different Output Files 1-N
Max number of records Maximum number of records written to all output files. See Selecting Output Records. 0-N
Partition key A key whose values control the distribution of records among multiple output files. See Partitioning Output into Different Output Files for more information.
Partition lookup table The ID of a lookup table. The table serves for selecting records which should be written to the output file(s). See Partitioning Output into Different Output Files for more information.
Partition file tag By default, output files are numbered. If this attribute is set to Key file tag, output files are named according to the values of Partition key or Partition output fields. See Partitioning Output into Different Output Files for more information. Number file tag (default) | Key file tag
Partition output fields Fields of Partition lookup table whose values serve for naming output file(s). See Partitioning Output into Different Output Files for more information.
Partition unassigned file name The name of a file that the unassigned records should be written into (if there are any). If it is not given, the data records whose key values are not contained in Partition lookup table are discarded. See Partitioning Output into Different Output Files for more information.  
Create empty files If set to false, prevents the component from creating empty output file when there are no input records.true (default) | false

[1]  One of these has to be specified. If both are specified, Mapping URL has a higher priority.

Details

JSONWriter receives data from all connected input ports and converts records to JSON objects based on the mapping you define. Finally, the component writes the resulting tree structure of elements to the output: a JSON file, port or dictionary. JSONWriter can write lists.

Every JSON object can contain other nested JSON objects. Thus, the JSON format resembles XML and similar tree formats.

As a consequence, you map the input records to the output file in a manner which is very close to what you already know from XMLWriter. Mapping editors in both components have similar logic. The very basics of mapping are:

  • Connect input edges to JSONWriter and edit the component's Mapping attribute. This will open the visual mapping editor:

    Mapping editor in JSONWriter after first open. Metadata on the input edge(s) are displayed on the left hand side. The right hand pane is where you design the desired JSON tree. Mapping is then performed by dragging metadata from left to right (and performing additional tasks described below).

    Figure 56.14. Mapping editor in JSONWriter after first open. Metadata on the input edge(s) are displayed on the left hand side. The right hand pane is where you design the desired JSON tree. Mapping is then performed by dragging metadata from left to right (and performing additional tasks described below).


  • In the right hand pane, design your JSON tree consisting of

    • Elements

      [Important]Important

      Unlike XMLWriter, you do not map metadata to any 'attributes'.

    • Arrays - arrays are ordered sets of values in JSON enclosed between the [ and ] brackets. To learn how to map them in JSONWriter, see Example 56.6, “Writing arrays”.

    • Wildcard elements - another option to mapping elements explicitly. You use the Include and Exclude patterns to generate element names from respective metadata.

  • Connect input records to output (wildcard) elements to create Binding.

    Example 56.5. Creating Binding


    Example mapping in JSONWriter - employees are joined with projects they work on. Fields in bold (their content) will be printed to the output file - see below.

    Figure 56.15.  Example mapping in JSONWriter - employees are joined with projects they work on. Fields in bold (their content) will be printed to the output file - see below.


    Excerpt from the output file related to the figure above (example of one employee written as JSON):

    		  		
    
        "employee" : {
        "firstName" : "Jane",
        "lastName" : "Simson",
        "projects" : {
          "project" : {
            "name" : "JSP",
            "manager" : "John Smith",
            "start" : "06062006",
            "end" : "in progress",
            "customers" : {
              "customer" : {
                "name" : "Sunny"
              },
              "customer" : {
                "name" : "Weblea"
              }
            }
          },
          "project" : {
            "name" : "OLAP",
            "manager" : "Raymond Brown",
            "start" : "11052004",
            "end" : "31012006",
            "customers" : {
              "customer" : {
                "name" : "Sunny"
              }
            }
          }
        }
      },
    		  		
    			

    Example 56.6. Writing arrays

    Let us have the following mapping of the input file which contains information about actors. For explanatory reasons, we will part actors' personal data from their countries of origin. The summary of all countries will then be written into an array


    Mapping arrays in JSONWriter - notice the array contains a dummy element 'State' which you bind the input field to.

    Figure 56.16.  Mapping arrays in JSONWriter - notice the array contains a dummy element 'State' which you bind the input field to.


    The output JSON:

    		  		
    			{
    			  "Actor" : {
    			    "Name" : "John Malkovich",
    			    "Sex" : true,
    			    "Age" : 50
    			  },
    			  "Actor" : {
    			    "Name" : "Liz Hurley",
    			    "Sex" : false,
    			    "Age" : 42
    			  },
    			  "Actor" : {
    			    "Name" : "Antonio Banderas",
    			    "Sex" : true,
    			    "Age" : 33
    			  },
    			  "Summary" : {
    			    "Countries" : [ "USA", "ENG", "ESP" ]
    			  }
    			}
    			
    			

  • At any time, you can switch to the Source tab and write/check the mapping yourself in code.

  • If the basic instructions found here were not satisfying, please consult XMLWriter's Details where the whole mapping process is described profusely.

Best Practices

We recommend users to explicitly specify Charset.

See also

JSONReader
JSONExtract
Common Properties of Components
Specific Attribute Types
Common Properties of Writers
Writers Comparison