Available in Community Designer

Short Description
FlatFileReader Attributes
Best Practices
See also

Short Description

FlatFileReader reads data from flat files such as CSV (comma-separated values) file and delimited, fixed-length, or mixed text files.

The component can read a single file as well as a collection of files placed on a local disk or remotely. Remote files are accessible via HTTP, HTTPS, FTP, or SFTP protocols. Using this component, ZIP and TAR archives of flat files can be read. Also reading data from an input port, or dictionary is supported.

FlatFileReader has an alias - UniversalDataReader.

Component Data source Input ports Output ports Each to all outputs Different to different outputs Transformation Transf. req. Java CTL Auto-propagated metadata
FlatFileReaderflat file0-11-2



Port typeNumberRequiredDescriptionMetadata
for Input Port Reading include specific byte/ cbyte/ string field
for correct data recordsany
for incorrect data recordsspecific structure, see table below


FlatFileReader does not propagate metadata.

This component has Metadata Templates available.

The optional logging port for incorrect records has to define the following metadata structure - the record contains exactly five fields (named arbitrarily) of given types in the following order:

Table 55.5. Error Metadata for FlatFileReader

Field numberField nameData typeDescription
0recordNo longa position of the erroneous record in the dataset (record numbering starts at 1)
1fieldNo integera position of the erroneous field in the record (1 stands for the first field, i.e. that of index 0)
2originalData string | byte | cbytean erroneous record in raw form (including all field and record delimiters)
3errorMessage string | byte | cbytean error message - detailed information about this error
4fileURLstringa source file in which the error occurred

Metadata on output port 0 can use Autofilling Functions.

the source_timestamp and source_size functions work only when reading from a file directly (if the file is an archive or it is stored at a remote location, timestamp will be empty and size will be 0).

FlatFileReader Attributes

AttributeReqDescriptionPossible values
File URL
A path to a data source (flat file, input port, dictionary) to be read, see Supported File URL Formats for Readers.  

Character encoding of input records (character encoding does not apply to byte fields, if the record type is fixed).

The default encoding depends on DEFAULT_CHARSET_DECODER in defaultProperties.

UTF-8 | <other encodings>
Data policy  Specifies handling of misformatted or incorrect data, see Data Policy.strict (default) | controlled | lenient
Trim strings Specifies whether a leading and trailing whitespace should be removed from strings before setting them to data fields, see Trimming Data below.default | true | false
Quoted strings 

Fields containing a special character (comma, newline or double quote) have to be enclosed in quotes. Only a single/double quote is accepted as the quote character. If true, special characters are removed when read by the component (they are not treated as delimiters).

Example: To read input data "25"|"John", switch Quoted strings to true and set Quote character to ". This will produce two fields: 25|John.

By default, the value of this attribute is inherited from metadata on output port 0. See also Record Details.

false | true
Quote character Specifies which kind of quotes will be permitted in Quoted strings. By default, the value of this attribute is inherited from metadata on output port 0. See also Record Details. both | " | '
Skip leading blanks specifies whether to skip a leading whitespace (e.g. blanks) before setting input strings to data fields. If not explicitly set (i.e. having the default value), the value of the Trim strings attribute is used. See Trimming Data. default | true | false
Skip trailing blanks Specifies whether to skip a trailing whitespace (e.g. blanks) before setting input strings to data fields. If not explicitly set (i.e. having the default value), the value of the Trim strings attribute is used. See Trimming Data. default | true | false
Number of skipped records A number of records/rows to be skipped from the source file(s); see Selecting Input Records. 0 (default) - N
Max number of records A number of records to be read from the source file(s) in turn; all records are read by default; See Selecting Input Records. 1 - N
Number of skipped records per source A number of records/rows to be skipped from each source file. By default, the value of the Skip source rows record property in output port 0 metadata is used. In case the value in metadata differs from the value of this attribute, the Number of skipped records per source value is applied, having a higher priority. See Selecting Input Records. 0 (default)- N
Max number of records per source A number of records/rows to be read from each source file; all records from each file are read by default; See Selecting Input Records. 1 - N
Max error count A maximum number of tolerated error records in input file(s); applicable only if Controlled Data Policy is set.0 (default) - N
Treat multiple delimiters as one If a field is delimited by a multiplied delimiter character, it will be interpreted as a single delimiter when setting to true. false (default) | true
Incremental file [ 1] The name of a file storing the incremental key, including path. See Incremental Reading. 
Incremental key[ 1]The variable storing a position of the last read record. See Incremental Reading. 
Verbose By default, less comprehensive error notification is provided and the performance is slightly higher. However, if switched to true, more detailed information with less performance is provided.false (default) | true
Parser By default, the most appropriate parser is applied. Besides, the parser for processing data may be set explicitly. If an improper one is set, an exception is thrown and the graph fails. See Data Parsers auto (default) | <other>

[ 1] Either both or neither of these attributes must be specified


Parsed data records are sent to the first output port. The component has an optional output logging port for getting detailed information about incorrect records. Only if Data Policy is set to controlled and a proper Writer (Trash or FlatFileWriter) is connected to port 1, all incorrect records together with the information about the incorrect value, its location and the error message are sent out through this error port.

Trimming Data

  1. Input strings are implicitly (i.e. the Trim strings attribute kept at the default value) processed before converting to a value according to the field data type as follows:

    • Whitespace is removed from both the start and the end in case of boolean, date, decimal, integer, long, or number.

    • Input string is set to a field including a leading and trailing whitespace in case of byte, cbyte, or string.

  2. If the Trim strings attribute is set to true, all leading and trailing whitespace characters are removed. A field composed of only whitespaces is transformed to null (zero length string). The false value implies preserving all leading and trailing whitespace characters. Remember that input string representing a numerical data type or boolean can not be parsed including whitespace. Thus, use the false value carefully.

  3. Both the Skip leading blanks and Skip trailing blanks attributes have a higher priority than Trim strings. So, the input strings trimming will be determined by the true or false values of these attributes, regardless the Trim strings value.

Data Parsers

  1. org.jetel.data.parser.SimpleDataParser - is a very simple but fast parser with limited validation, error handling, and functionality. The following attributes are not supported:

    • Trim strings

    • Skip leading blanks

    • Skip trailing blanks

    • Incremental reading

    • Number of skipped records

    • Max number of records

    • Quoted strings

    • Treat multiple delimiters as one

    • Skip rows

    • Verbose

    On top of that, you cannot use metadata containing at least one field with one of these attributes:

    • the field is fixed-length

    • the field has no delimiter or, on the other hand, more of them

    • Shift is not null (see Details Pane)

    • Autofilling set to true

    • the field is byte-based

  2. org.jetel.data.parser.DataParser - an all-round parser working with any reader settings

  3. org.jetel.data.parser.CharByteDataParser - can be used whenever metadata contain byte-based fields mixed with char-based ones. A byte-based field is a field of one of these types: byte, cbyte or any other field whose format property starts with the "BINARY:" prefix. See Binary Formats.

  4. org.jetel.data.parser.FixLenByteDataParser - used for metadata with byte-based fields only. It parses sequences of records consisting of a fixed number of bytes.


Choosing org.jetel.data.parser.SimpleDataParser while using Quoted strings will cause the Quoted strings attribute to be ignored.

Tips & Tricks

  • Handling records with large data fields: FlatFileReader can process input strings of even hundreds or thousands of characters when you adjust the field and record buffer sizes. Just increase the following properties according to your needs: Record.MAX_RECORD_SIZE for record serialization, DataParser.FIELD_BUFFER_LENGTH for parsing, and DataFormatter.FIELD_BUFFER_LENGTH for formatting. Finally, don't forget to increase the DEFAULT_INTERNAL_IO_BUFFER_SIZE variable to be at least 2*MAX_RECORD_SIZE. Go to Chapter 19, Engine Configuration to understand how to change these property variables.


Processing files with headers

If the first rows of your input file do not represent real data but field labels instead, set the Number of skipped records attribute. If a collection of input files with headers is read, set the Number of skipped records per source

Handling typist's error when creating the input file manually

If you wish to ignore accidental errors in delimiters (such as two semicolons instead of a single one as defined in metadata when the input file is typed manually), set the Treat multiple delimiters as one attribute to true. All redundant delimiter characters will be replaced by the proper one.

Best Practices

We recommend users to explicitly specify encoding of the input file (with the Charset attribute). It ensures better portability of the graph across systems with different default encoding.

The recommended encoding is UTF-8.


FlatFileReader is available since CloverETL 4.2.0-M1. In 4.2.0-M1, the UniversalDataReader was renamed to FlatFileReader.

In 4.4.0-M2, the default encoding was changed from ISO-8859-1 to UTF-8.


With default charset (UTF-8),FlatFileReader cannot parse csv files with binary data. To parse csv files with binary data, change Charset attribute.

See also

Common Properties of Components
Specific Attribute Types
Common Properties of Readers
Readers Comparison