tFileOutputJSON in Talend Map/Reduce Jobs - 6.1

Talend Components Reference Guide

EnrichVersion
6.1
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Talend Big Data
Talend Big Data Platform
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Talend Data Integration
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Talend Open Studio for Big Data
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Talend Studio
task
Data Governance
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Design and Development

Warning

The information in this section is only for users that have subscribed to one of the Talend solutions with Big Data and is not applicable to Talend Open Studio for Big Data users.

In a Talend Map/Reduce Job, tFileOutputJSON, as well as the whole Map/Reduce Job using it, generates native Map/Reduce code. This section presents the specific properties of tFileOutputJSON when it is used in that situation. For further information about a Talend Map/Reduce Job, see the Talend Big Data Getting Started Guide.

Component family

MapReduce / Output

 

Basic settings

Schema and Edit Schema

A schema is a row description. It defines the number of fields (columns) to be processed and passed on to the next component. The schema is either Built-In or stored remotely in the Repository.

Click Edit schema to make changes to the schema. If the current schema is of the Repository type, three options are available:

  • View schema: choose this option to view the schema only.

  • Change to built-in property: choose this option to change the schema to Built-in for local changes.

  • Update repository connection: choose this option to change the schema stored in the repository and decide whether to propagate the changes to all the Jobs upon completion. If you just want to propagate the changes to the current Job, you can select No upon completion and choose this schema metadata again in the [Repository Content] window.

  

Built-In: You create and store the schema locally for this component only. Related topic: see Talend Studio User Guide.

  

Repository: You have already created the schema and stored it in the Repository. You can reuse it in various projects and Job designs. Related topic: see Talend Studio User Guide.

 

Folder

Enter the folder on HDFS where you want to store the JSON output file(s).

The folder will be created automatically if it does not exist.

Note that you need to ensure you have properly configured the connection to the Hadoop distribution to be used in the Hadoop configuration tab in the Run view.

 

Output type

Select the structure for the JSON output file(s).

  • All in one block: the received data will be written into one data block.

  • One row per record: the received data will be written into separate data blocks row by row.

 

Name of data block

Type in the name of the data block for the JSON output file(s).

Warning

This field will be available only if you select All in one block from the Output type list.

 

Action

Select the action that you want to perform on the data:

  • Overwrite: the data on HDFS will be overwritten if it already exists.

  • Create: the data will be created.

Global Variables

ERROR_MESSAGE: the error message generated by the component when an error occurs. This is an After variable and it returns a string. This variable functions only if the Die on error check box is cleared, if the component has this check box.

A Flow variable functions during the execution of a component while an After variable functions after the execution of the component.

To fill up a field or expression with a variable, press Ctrl + Space to access the variable list and choose the variable to use from it.

For further information about variables, see Talend Studio User Guide.

Usage

Use this component to rewrite received data in a JSON structured output file.

In a Talend Map/Reduce Job, it is used as an end component and requires a transformation component as input link. The other components used along with it must be Map/Reduce components, too. They generate native Map/Reduce code that can be executed directly in Hadoop.

Once a Map/Reduce Job is opened in the workspace, tFileOutputJSON as well as the MapReduce family appears in the Palette of the Studio.

Note that in this documentation, unless otherwise explicitly stated, a scenario presents only Standard Jobs, that is to say traditional Talend data integration Jobs, and non Map/Reduce Jobs.

Hadoop Connection

You need to use the Hadoop Configuration tab in the Run view to define the connection to a given Hadoop distribution for the whole Job.

This connection is effective on a per-Job basis.

Prerequisites

The Hadoop distribution must be properly installed, so as to guarantee the interaction with Talend Studio. The following list presents MapR related information for example.

  • Ensure that you have installed the MapR client in the machine where the Studio is, and added the MapR client library to the PATH variable of that machine. According to MapR's documentation, the library or libraries of a MapR client corresponding to each OS version can be found under MAPR_INSTALL\ hadoop\hadoop-VERSION\lib\native. For example, the library for Windows is \lib\native\MapRClient.dll in the MapR client jar file. For further information, see the following link from MapR: http://www.mapr.com/blog/basic-notes-on-configuring-eclipse-as-a-hadoop-development-environment-for-mapr.

    Without adding the specified library or libraries, you may encounter the following error: no MapRClient in java.library.path.

  • Set the -Djava.library.path argument, for example, in the Job Run VM arguments area of the Run/Debug view in the [Preferences] dialog box. This argument provides to the Studio the path to the native library of that MapR client. This allows the subscription-based users to make full use of the Data viewer to view locally in the Studio the data stored in MapR. For further information about how to set this argument, see the section describing how to view data of Talend Big Data Getting Started Guide.

For further information about how to install a Hadoop distribution, see the manuals corresponding to the Hadoop distribution you are using.