SpringBatch ItemProcessor: process a List<?> not one Item - json

Question

I have to modify a process made with SpringBatch, the procedure it's easy.
Actually, the program reads records from a database and exports the results to XML files (one by each table)
Now, I want to write JSON files instead XML files, I didn't find how to make it possible, but reading and reading I have something close to that I want.
I wrote an ItemProcessor class like this
#Component("jSONObjectProcessor")
public class JSONObjectProcessor implements ItemProcessor<Object, String> {
private Gson gson = new Gson();
private List<Object> array = new ArrayList<Object>();
#Override
public String process(Object item) throws Exception {
array.add(item);
return gson.toJson(array);
}
}
Obviously, if I have 6 items; this going to return 6 List, like it does right now
1st item
[
{
"number":0,
"string":"abc",
"desc":"abcdefg"
}
]
2nd item
[
{
"number":0,
"string":"abc",
"desc":"abcdefg"
},
{
"number":1000,
"string":"xyz",
"desc":"uvwxyz"
}
]
//more lists by the total of items
To write the files I'm using org.springframework.batch.item.file.FlatFileItemWriter class.
I want to find the way to return all the items in a List and give it JSON form and write this json in the file. I'm in the correct way or there are another, more elegant form. It's possible?
Thanks!
Update
I have made the changes (thanks #Sanj), but I miss the comma (,) delimiter between each object.
My ItemWriter it's defined like this
<bean id="itemWriterRegConstantes" scope="step"
class="org.springframework.batch.item.file.FlatFileItemWriter">
<property name="resource" value="#{jobParameters['fileOutput']}" />
<property name="shouldDeleteIfExists" value="true" />
<property name="lineAggregator">
<bean class="org.springframework.batch.item.file.transform.DelimitedLineAggregator">
<property name="delimiter" value="," />
</bean>
</property>
<property name="footerCallback" ref="headerFooterCallback" />
<property name="headerCallback" ref="headerFooterCallback" />
</bean>
The output file now looks like this
[
{"number":0,"string":"abcd","desc":"efgh"} //no comma
{"number":1000,"string":"xyz","valor":"xyzw"}
]
How add it?
Additionaly, how can I print all the content in a single line? (to minify the content) It's possible?
My Solution
I had to create my own class (really I made change to the FlatFileItemWriter SpringBatch class, it's here
Output: a file with an one line JSON array content.
Thanks!

Answer 1

Return single json for every item from ItemProcessor
#Component("jSONObjectProcessor")
public class JSONObjectProcessor implements ItemProcessor<Object, String> {
private Gson gson = new Gson();
#Override
public String process(Object item) throws Exception {
return gson.toJson(item);
}
}
Create header and footer call backs. Basically they will be used to start and close the array respectively.
public class JSONHeaderFooterCallBack implements FlatFileHeaderCallback, FlatFileFooterCallback{
#Override
public void writeHeader(Writer writer) throws IOException {
writer.write("[" + System.getProperty("line.separator"));
}
#Override
public void writeFooter(Writer writer) throws IOException {
writer.write("]");
}
}
Associate the callbacks with FlatFileItemWriter
FlatFileItemWriter<String> writer = new FlatFileItemWriter<String>();
//Setting header and footer.
JSONHeaderFooterCallBack headerFooterCallback = new JSONHeaderFooterCallBack();
writer.setHeaderCallback(headerFooterCallback);
writer.setFooterCallback(headerFooterCallback);
writer.setResource(new FileSystemResource(System.getProperty("user.dir") + "/output.json"));
Now you can use "writer" to write all records as a json array to a file.
---update--
Use CustomLineAggregator to append comma at the end of every record:
public class CustomLineAggregator<String> implements LineAggregator<String> {
#Override
public String aggregate(String item) {
return item+",";
}
}