Fix JsonFileItemWriter to produce valid JSON when append allowed

[quaff]

Closes GH-5272

[banseok1216]

how about when

writer.setAppendAllowed(true);

writer.open(new ExecutionContext());
writer.close();

writer.open(new ExecutionContext());
writer.write(Chunk.of("ccc"));
writer.close();

resourceShouldContains("ccc");

[quaff]

how about when

writer.setAppendAllowed(true);

writer.open(new ExecutionContext());
writer.close();

writer.open(new ExecutionContext());
writer.write(Chunk.of("ccc"));
writer.close();

resourceShouldContains("ccc");

how about when

writer.setAppendAllowed(true);

writer.open(new ExecutionContext());
writer.close();

writer.open(new ExecutionContext());
writer.write(Chunk.of("ccc"));
writer.close();

resourceShouldContains("ccc");

Thanks for spotting, please review again.

[banseok1216]

Thank you. Minor case I found.

@Test
void appendAllowed() throws Exception {
	File file = Files.createTempFile("test", ".json").toFile();
	WritableResource resource = new FileSystemResource(file);

	Files.writeString(file.toPath(), "[\n \"foo\"]", StandardCharsets.UTF_8);

	JsonFileItemWriter<String> writer =
			new JsonFileItemWriter<>(resource, new JacksonJsonObjectMarshaller<>());
	writer.setAppendAllowed(true);

	String before = Files.readString(file.toPath(), StandardCharsets.UTF_8);
	System.out.println("before:\n" + before + "\n");
	System.out.println("json mapper act: " + Arrays.toString(new JsonMapper().readValue(before, String[].class)) + "\n");

	writer.open(new ExecutionContext());
	writer.close();

	String after = new String(resource.getContentAsByteArray(), StandardCharsets.UTF_8);
	System.out.println("after:\n" + after + "\n");
}

before:
[
 "foo"]

json mapper act: [foo]

after:
[
 "fo
]

[quaff]

JsonFileItemWriter will never generate [\n \"foo\"], you should write [\n \"foo\"\n]\n instead.

[banseok1216]

Okay then, I think the writer needs to validate that the existing file matches its expected format

[quaff]

Thank you. Minor case I found.

@Test
void appendAllowed() throws Exception {
	File file = Files.createTempFile("test", ".json").toFile();
	WritableResource resource = new FileSystemResource(file);

	Files.writeString(file.toPath(), "[\n \"foo\"]", StandardCharsets.UTF_8);

	JsonFileItemWriter<String> writer =
			new JsonFileItemWriter<>(resource, new JacksonJsonObjectMarshaller<>());
	writer.setAppendAllowed(true);

	String before = Files.readString(file.toPath(), StandardCharsets.UTF_8);
	System.out.println("before:\n" + before + "\n");
	System.out.println("json mapper act: " + Arrays.toString(new JsonMapper().readValue(before, String[].class)) + "\n");

	writer.open(new ExecutionContext());
	writer.close();

	String after = new String(resource.getContentAsByteArray(), StandardCharsets.UTF_8);
	System.out.println("after:\n" + after + "\n");
}

before:
[
 "foo"]

json mapper act: [foo]

after:
[
 "fo
]

@banseok1216 I updated PR to fix this also.