August 17, 2023

tHDFSList – Docs for ESB 5.x

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tHDFSList

tHDFSList_icon32_white.png

Warning

This component will be available in the Palette of
Talend Studio on the condition that you have subscribed to one of
the Talend
solutions with Big Data.

tHDFSList properties

Component family

Big Data/File

  

Function

tHDFSList iterates on files or
folders of a set directory.

Purpose

tHDFSList retrieves a list of
files or folders based on a filemask pattern and iterates on each
unity.

Basic settings

Property type

Either Built-in or Repository

Built-in: No property data stored
centrally.

Repository: Select the repository
file in which the properties are stored. The fields that follow are
completed automatically using the data retrieved.

Since version 5.6, both the Built-In mode and the Repository mode are
available in any of the Talend solutions.
 

Use an existing connection

Select this check box and in the Component List click the
HDFS connection component from which you want to reuse the connection details already
defined.

Note

When a Job contains the parent Job and the child Job, Component
list presents only the connection components in the same Job
level.

Version

Distribution

Select the cluster you are using from the drop-down list. The options in the list vary
depending on the component you are using. Among these options, the following ones requires
specific configuration:

  • If available in this Distribution drop-down list, the
    Microsoft HD Insight option allows you to use a
    Microsoft HD Insight cluster. For this purpose, you need to configure the
    connections to the WebHCat service, the HD Insight service and the Windows Azure
    Storage service of that cluster in the areas that are displayed. A demonstration
    video about how to configure this connection is available in the following link:
    https://www.youtube.com/watch?v=A3QTT6VsNoM

  • The Custom option allows you to connect to a
    cluster different from any of the distributions given in this list, that is to
    say, to connect to a cluster not officially supported by Talend.

In order to connect to a custom distribution, once selecting Custom, click the dotbutton.png button to display the dialog box in which you can
alternatively:

  1. Select Import from existing version to import an
    officially supported distribution as base and then add other required jar files
    which the base distribution does not provide.

  2. Select Import from zip to import a custom
    distribution zip that, for example, you can download from http://www.talendforge.org/exchange/index.php.

    Note

    In this dialog box, the active check box must be kept selected so as to import
    the jar files pertinent to the connection to be created between the custom
    distribution and this component.

    For an step-by-step example about how to connect to a custom distribution and
    share this connection, see Connecting to a custom Hadoop distribution.
 

Hadoop version

Select the version of the Hadoop distribution you are using. The available options vary
depending on the component you are using. Along with the evolution of Hadoop, please note
the following changes:

  • If you use Hortonworks Data Platform V2.2, the
    configuration files of your cluster might be using environment variables such as
    ${hdp.version}. If this is your situation, you
    need to set the mapreduce.application.framework.path property in the Hadoop properties table of this component with the path value
    explicitly pointing to the MapReduce framework archive of your cluster. For
    example:

  • If you use Hortonworks Data Platform V2.0.0, the
    type of the operating system for running the distribution and a Talend
    Job must be the same, such as Windows or Linux. Otherwise, you have to use Talend
    Jobserver to execute the Job in the same type of operating system in which the
    Hortonworks Data Platform V2.0.0 distribution you
    are using is run. For further information about Talend Jobserver, see
    Talend Installation
    and Upgrade Guide    .

Authentication

Use kerberos authentication

If you are accessing the Hadoop cluster running with Kerberos security, select this check
box, then, enter the Kerberos principal name for the NameNode in the field displayed. This
enables you to use your user name to authenticate against the credentials stored in
Kerberos.

This check box is available depending on the Hadoop distribution you are connecting
to.
  Use a keytab to authenticate

Select the Use a keytab to authenticate check box to log
into a Kerberos-enabled Hadoop system using a given keytab file. A keytab file contains
pairs of Kerberos principals and encrypted keys. You need to enter the principal to be used
in the Principal field and the access path to the keytab
file itself in the Keytab field.

Note that the user that executes a keytab-enabled Job is not necessarily the one a
principal designates but must have the right to read the keytab file being used. For
example, the user name you are using to execute a Job is user1 and the principal to be used is guest; in this situation, ensure that user1 has the right to read the keytab file to be used.

 

NameNode URI

Type in the URI of the Hadoop NameNode. The NameNode is the master node of a Hadoop system.
For example, we assume that you have chosen a machine called masternode as the NameNode of an Apache Hadoop distribution, then the
location is hdfs://masternode:portnumber.

 

User name

Enter the user authentication name of HDFS.
 

Group

Enter the membership including the authentication user under which the HDFS instances were
started. This field is available depending on the distribution you are using.

HDFS Directory

Browse to, or enter the directory in HDFS where the data you need to use is.

 

FileList Type

Select the type of input you want to iterate on from the
list:

Files if the input is a set of
files,

Directories if the input is a set
of directories,

Both if the input is a set of the
above two types.

 

Include subdirectories

Select this check box if the selected input source type includes
sub-directories.

 

Case Sensitive

Set the case mode from the list to either create or not create
case sensitive filter on filenames.

 

Use Glob Expressions as Filemask

This check box is selected by default. It filters the results
using a Global Expression (Glob
Expressions).

 

Files

Click the plus button to add as many filter lines as needed:

Filemask: in the added filter
lines, type in a filename or a filemask using special characters or
regular expressions.

 

Order by

The folders are listed first of all, then the files. You can
choose to prioritise the folder and file order either:

By default: alphabetical order, by
folder then file;

By file name: alphabetical order or
reverse alphabetical order;

By file size: smallest to largest
or largest to smallest;

By modified date: most recent to
least recent or least recent to most recent.

Note

If ordering by file name, in
the event of identical file names then modified date takes precedence. If ordering
by file size, in the event
of identical file sizes then file
name takes precedence. If ordering by modified date, in the event of
identical dates then file name
takes precedence.
  Order action

Select a sort order by clicking one of the following radio
buttons:

ASC: ascending order;

DESC: descending order;

Advanced settings

Use Exclude Filemask

Select this check box to enable Exclude
Filemask field to exclude filtering condition based
on file type:

Exclude Filemask: Fill in the
field with file types to be excluded from the Filemasks in the Basic
settings view.

Note

File types in this field should be quoted with double
quotation marks and seperated by comma.

 

Hadoop properties

Talend Studio uses a default configuration for its engine to perform
operations in a Hadoop distribution. If you need to use a custom configuration in a specific
situation, complete this table with the property or properties to be customized. Then at
runtime, the customized property or properties will override those default ones.

  • Note that if you are using the centrally stored metadata from the Repository, this table automatically inherits the
    properties defined in that metadata and becomes uneditable unless you change the
    Property type from Repository to Built-in.

For further information about the properties required by Hadoop and its related systems such
as HDFS and Hive, see the documentation of the Hadoop distribution you
are using or see Apache’s Hadoop documentation on http://hadoop.apache.org/docs and then select the version of the documentation you want. For demonstration purposes, the links to some properties are listed below:
 

tStatCatcher Statistics

Select this check box to gather the Job processing
metadata at a Job level as well as at each component level.

Dynamic settings

Click the [+] button to add a row in the table and fill the
Code field with a context variable to choose your HDFS
connection dynamically from multiple connections planned in your Job. This feature is useful
when you need to access files in different HDFS systems or different distributions,
especially when you are working in an environment where you cannot change your Job settings,
for example, when your Job has to be deployed and executed independent of Talend Studio.

The Dynamic settings table is available only when the
Use an existing connection check box is selected in the
Basic settings view. Once a dynamic parameter is
defined, the Component List box in the Basic settings view becomes unusable.

For more information on Dynamic settings and context
variables, see Talend Studio User Guide.

Global Variables

CURRENT_FILE: the current file name. This is a Flow
variable and it returns a string.

CURRENT_FILEDIRECTORY: the current file directory. This
is a Flow variable and it returns a string.

CURRENT_FILEEXTENSION: the extension of the current file.
This is a Flow variable and it returns a string.

CURRENT_FILEPATH: the current file path. This is a Flow
variable and it returns a string.

NB_FILE: the number of files iterated upon so far. This is
a Flow variable and it returns an integer.

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.

Connections

Outgoing links (from this component to another):

Row: Iterate

Trigger: On Subjob Ok; On Subjob
Error; Run if; On Component Ok; On Component Error.

Incoming links (from one component to this one):

Row: Iterate.

Trigger: Run if; On Subjob Ok; On
Subjob Error; On component Ok; On Component Error; Synchronize;
Parallelize.

For further information regarding connections, see Talend Studio
User Guide.

Usage

tHDFSList provides a list of
files or folders from a defined HDFS directory on which it iterates.

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
    hadoophadoop-VERSIONlib
    ative    . For example, the library for
    Windows is lib
    ativeMapRClient.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.

Log4j

The activity of this component can be logged using the log4j feature. For more information on this feature, see Talend Studio User
Guide.

For more information on the log4j logging levels, see the Apache documentation at http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/Level.html.

Limitation

JRE 1.6+ is required.

Scenario: Iterating on a HDFS directory

This scenario uses a two-component Job to iterate on a specified directory in HDFS so
as to select the files from there towards a local directory.

use_case-thdfslist2.png

Preparing the data to be used

  • Create the files to be iterated on in the HDFS you want to use. In this
    scenario, two files are created in the directory: /user/ychen/data/hdfs/out.

    use_case-thdfslist1.png

    You can design a Job in the Studio to create the two files. For further
    information, see tHDFSPut or tHDFSOutput.

Linking the components

  1. In the Integration perspective
    of Talend Studio, create an empty Job, named HDFSList for example, from the Job
    Designs     node in the Repository tree view.

    For further information about how to create a Job, see the Talend Studio User
    Guide    .

  2. Drop tHDFSList and tHDFSGet onto the workspace.

  3. Connect them using the Row > Iterate
    link.

Configuring the iteration

  1. Double-click tHDFSList to open its
    Component view.

    use_case-thdfslist3.png

  2. In the Version area, select the Hadoop
    distribution you are connecting to and its version.

  3. In the Connection area, enter the values
    of the parameters required to connect to the HDFS.

    In the real-world practice, you may use tHDFSConnection to create a connection and reuse it from the
    current component. For further information, see tHDFSConnection.

  4. In the HDFS Directory field, enter the
    path to the folder where the files to be iterated on are. In this example,
    as presented earlier, the directory is /user/ychen/data/hdfs/out/.

  5. In the FileList Type field, select
    File.

  6. In the Files table, click Button_Plus.png to add one row and enter * between the quotation marks to iterate on any files
    existing.

Selecting the files

  1. Double-click tHDFSGet to open its
    Component view.

    use_case-thdfslist4.png

  2. In the Version area, select the Hadoop
    distribution you are connecting to and its version.

  3. In the Connection area, enter the values
    of the parameters required to connect to the HDFS.

    In the real-world practice, you may have used tHDFSConnection to create a connection; then you can reuse
    it from the current component. For further information, see tHDFSConnection.

  4. In the HDFS directory field, enter the
    path to the folder holding the files to be retrieved.

    To do this with the auto-completion list, place the mouse pointer in this
    field, then, press Ctrl+Space to display
    the list and select the
    tHDFSList_1_CURRENT_FILEDIRECTORY     variable to reuse the
    directory you have defined in tHDFSList. In
    this variable, tHDFSList_1 is the label
    of the component. If you label it differently, select the variable
    accordingly.

    Once selecting this variable, the directory reads, for example, ((String)globalMap.get(“tHDFSList_1_CURRENT_FILEDIRECTORY”))
    in this field.

    For further information about how to label a component, see the Talend Studio User
    Guide    .

  5. In the Local directory field, enter the
    path, or browse to the folder you want to place the selected files in. This
    folder will be created if it does not exist. In this example, it is
    C:/hdfsFiles.

  6. In the Overwrite file field, select
    always.

  7. In the Files table, click Button_Plus.png to add one row and enter * between the quotation marks in the Filemask column in order to get any files existing.

Executing the Job

  • Press F6 to execute this Job.

Once done, you can check the files created in the local directory.

use_case-thdfslist5.png
Document get from Talend https://help.talend.com
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Docs 5.x
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