[noojung]

Overview

JsonFileItemWriter produces invalid JSON in append mode in two cases.

Empty chunk: if only empty chunks are written to a file that already contains items (for example, when the processor filters out every item), a trailing comma is left before the closing ]:

[
 "aaa",
 "bbb",

]

Restart: if a step is restarted after at least one chunk was committed, two separators are written before the first item after the restart:

[
 "aaa",
,
 "bbb"
]

The empty-chunk case occurs because doWrite() writes a separator for existing items without checking whether the chunk is empty. On restart, both hasExistingItems and the restored linesWritten cause a separator to be written.

This PR skips empty chunks and writes a single separator when either condition applies. Regression tests cover both cases.

Related PR

• Fix JsonFileItemWriter to produce valid JSON when append allowed #5273

[quaff]

Good catch!