Add streaming json item writer

Resolves BATCH-2692

spring-batch-docs/asciidoc/readersAndWriters.adoc

@@ -1748,9 +1748,9 @@ staxItemWriter.write(trade);
 ----
 
 [[jsonReadingWriting]]
-=== JSON Item Readers
+=== JSON Item Readers And Writers
 
-Spring Batch provides support for reading JSON resources in the following format:
+Spring Batch provides support for reading and Writing JSON resources in the following format:
 
 [source, json]
 ----
@@ -1805,6 +1805,35 @@ public JsonItemReader<Trade> jsonItemReader() {
 }
 ----
 
+==== `JsonFileItemWriter`
+
+The `JsonFileItemWriter` delegates the marshalling of items to the
+`org.springframework.batch.item.json.JsonObjectMarshaller` interface. The contract
+of this interface is to take an object and marshall it to a JSON `String`.
+Two implementations are currently provided:
+
+* link:$$https://github.com/FasterXML/jackson$$[Jackson] through the `org.springframework.batch.item.json.JacksonJsonObjectMarshaller`
+* link:$$https://github.com/google/gson$$[Gson] through the `org.springframework.batch.item.json.GsonJsonObjectMarshaller`
+
+To be able to write JSON records, the following is needed:
+
+* `Resource`: A Spring `Resource` that represents the JSON file to write
+* `JsonObjectMarshaller`: A JSON object marshaller to marshall objects to JSON format
+
+The following example shows how to define a `JsonFileItemWriter`:
+
+[source, java]
+----
+@Bean
+public JsonFileItemWriter<Trade> jsonFileItemWriter() {
+   return new JsonFileItemWriterBuilder<Trade>()
+                 .jsonObjectMarshaller(new JacksonJsonObjectMarshaller<>())
+                 .resource(new ClassPathResource("trades.json"))
+                 .name("tradeJsonFileItemWriter")
+                 .build();
+}
+----
+
 [[multiFileInput]]
 === Multi-File Input
 

spring-batch-docs/asciidoc/whatsnew.adoc

@@ -10,7 +10,7 @@ The Spring Batch 4.1 release adds the following features:
 
 * A new `@SpringBatchTest` annotation to simplify testing batch components
 * A new `@EnableBatchIntegration` annotation to simplify remote chunking configuration
-* A new `JsonItemReader` to support the JSON format
+* A new `JsonItemReader` and `JsonFileItemWriter` to support the JSON format
 
 [[whatsNewTesting]]
 === `@SpringBatchTest` Annotation
@@ -155,6 +155,8 @@ APIs to read JSON objects in chunks. Spring Batch supports two libraries:
 * link:$$https://github.com/google/gson$$[Gson]
 
 To add other libraries, you can implement the `JsonObjectReader` interface.
+
+Writing JSON data is also supported through the `JsonFileItemWriter`.
 For more details about JSON support, see the
 <<readersAndWriters.adoc#jsonReadingWriting,ItemReaders and ItemWriters>> chapter.