Java Reference
In-Depth Information
File-Based ItemWriters
Large amounts of data are moved via files in enterprise batch processing. There is a reason for this: files
are simple and reliable. Backups are easy. So is recovery if you need to start over. This section looks at
how to generate flat files in a variety of formats including formatted records (fixed width or other) and
delimited files as well as how Spring Batch handles the issue of file creation.
FlatFileItemWriter
org.springframework.batch.item.file.FlatFileItemWriter
is the ItemWriter implementation provided
to generate text file output. Similar to
FlatFileItemReader
in many respects, this class addresses the
issues with file-based output in Java with a clean, consistent interface for you to use. Figure 9-2 shows
how the
FlatFileItemWriter
is constructed.
FlatFileItemWriter
Resource
LineAggregator
Figure 9-2.
FlatFileItemWriter
pieces
FlatFileItemWriter
, as shown in Figure 9-2 consists of a resource to write to and a
LineAggregator
implementation. The
org.springframework.batch.item.file.transform.LineAggregator
interface
replaces the
LineMapper
of the FlatFileItemReader discussed in Chapter 7. Here, instead of parsing a
String
into an object as the
LineMapper
is responsible for doing, the
LineAggregator
is responsible for the
generating of an output
String
based on an object.
In many of the previous examples, you used
PassThroughLineAggregator
to generate the output files.
This particular implementation of the
LineAggregator
interface just calls the item's
toString()
method
to generate the output. But there are other implementations that you look at in the coming sections.
FlatFileItemWriter
has a number of interesting configuration options, which are reviewed in Table
9-1.
