The FieldSet
When working with flat files in Spring Batch, regardless of whether it is for input or
output, one of the most important classes is the FieldSet. Many architectures and
libraries contain abstractions for helping you read in from a file, but they usually
return a String or an array of String objects. This really only gets you halfway
there. A FieldSet is Spring Batch’s abstraction for enabling the binding of fields from
a file resource. It allows developers to work with file input in much the same way as
they would work with database input. A FieldSet is conceptually similar to a JDBC
ResultSet. A FieldSet requires only one argument: a String array of tokens.
Optionally, you can also configure the names of the fields so that the fields may be
accessed either by index or name as patterned after ResultSet, as shown in the following
example:
String[] tokens = new String[]{"foo", "1", "true"};
FieldSet fs = new DefaultFieldSet(tokens);
String name = fs.readString(0);
int value = fs.readInt(1);
boolean booleanValue = fs.readBoolean(2);There are many more options on the FieldSet interface, such as Date, long,
BigDecimal, and so on. The biggest advantage of the FieldSet is that it provides
consistent parsing of flat file input. Rather than each batch job parsing differently in
potentially unexpected ways, it can be consistent, both when handling errors caused by a
format exception, or when doing simple data conversions.
