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FLDA - Fixed Length Data Accessor

Maven Status

FLDA supports reading data as well as writing data of records with a fix size.

Fix size means:

  • each record has n Attributes. An Attribute has an index.
  • or: each record has a fix length. An Attribute has an index and a length.

This project is only the core. For some usages of this project see:

Examples of different record types

Fixed-length - FixedLengthString

Fixed-length data consists of attributes that each have a specific position and length. Hence, every n-th attribute begins at the same character-index. In this example, every name of an item begins at character-index 10 and every amount of items begins at character-index 16:

Fruit    Cherry30
Fruit    Apple  5

Fix amount of Attributes - List<String>

Character-separated data consists of attributes that are separated by a character. In this example, the attributes are semicolon-separated and each record consists of three Attributes. The record type is List<String>.



To use FLDA, include the following artifact:


Java 9 Module

The Automatic Module Name of this library is:


Short Description of the Accessor Concept

Within the Accessor Concept there are different parts:

  1. the fixed size data record
  2. the definition of an attribute
  3. an accessor

1. Fixed Size Data Record

This is just the part of data to read from or to write to.

2. Definition of an attribute

This is the information how an attribute is addressed. There are different questions to answer:

  • of which type is the attribute?
  • on which index is the attribute located?
  • how long (e.g. in characters or bytes) is the attribute?

For some record types not all questions are relevant. For an index based record type, there is no need to know the size of one attribute.

Example of a FixedLengthString attribute with index and length:

FixedLengthStringAttribute<String> FIRST_NAME = new FixedLengthStringAttribute<>(String.class, 0, 10);

3. The Accessor

A ReadAccessor reads from a record and a WriteAccessor writes to the record. Therefore an attribute definition is needed. An AccessorConfig is needed too.

Read Example:

AccessorConfig<FixedLengthString, FixedLengthStringAttribute<?>> config = ...

ReadAccessor<FixedLengthString, FixedLengthStringAttribute<?>> readAccessor = new ReadAccessor<>(config, datarecord)
String firstname =

Example for write a record:

AccessorConfig<FixedLengthString, FixedLengthStringAttribute<?>> config = ...

WriteAccessor<FixedLengthString, FixedLengthStringAttribute<?>> writeAccessor = new WriteAccessor<>(config, record);
writeAccessor.write(PersonDescriptor.FIRST_NAME, person.getFirstname());

Record Factory

A record factory is used by AccessorConfig.createNewRecord. To use this method it is required to register a record factory:

AccessorConfig<FixedLengthString, FixedLengthStringAttribute<?>> config = new AccessorConfigBuilder<FixedLengthString, FixedLengthStringAttribute<?>>()
        // ...
        .withRecordFactory(new FixedLengthStringFactory(23, ' '))

The advantage of using a record factory is, that the code to create a new record is in one place.

There are different predefined record factories:

  • FixedLengthString => FixedLengthStringFactory
  • StringList => StringListFactory

Automatic Validation

It is possible to validate the records automatically. Just register the desired validators:

SizeValidator validator = new SizeValidator(5);

AccessorConfig<List<String>, StringListAttribute<?>> config =
        new AccessorConfigBuilder<List<String>, StringListAttribute<?>>()
                // ...

There are different predefined validators:

  • FixedLengthString => LengthValidator
  • StringList => SizeValidator

Change History

Migration to version 2.0

  • Move StringFitter from com.github.tinosteinort.flda.interfaces.fixedlengthstring.writer to com.github.tinosteinort.flda.interfaces.fixedlengthstring
  • StringFitter is renamed to StringUtils
  • Extract StringFitter.Alignment into own Class: com.github.tinosteinort.flda.interfaces.fixedlengthstring.Alignment
  • Remove Alignment Class from FixedLengthString Writer Classes into com.github.tinosteinort.flda.interfaces.fixedlengthstring.FixedLengthStringAttribute
  • Remove filler char from FixedLengthString Writer Classes into com.github.tinosteinort.flda.interfaces.fixedlengthstring.FixedLengthStringAttribute
  • Method FixedLengthString#getString() replaced by FixedLengthString#toString()
    • Output of old FixedLengthString#toString() Method is not supported anymore
  • Class StringReader is replaced by Method StringUtils#readAndTrim()
  • FixedLenghtString implements CharSequence
  • API Update: move filler char and alignment into FixedLengthStringAttribute
  • split project flda in flda-core, flda-fixedlengthstring and flda-stringlist
  • introduce own RecordFactory<T> interface. Supplier<T> was used before
  • change AccessorConfig from interface to abstract class. Needed to clean up the API


Fix Length Data Accessor - Core API




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