Fix JsonFileItemWriter for multiple write's

Resolves BATCH-2749

spring-batch-infrastructure-tests/src/test/java/org/springframework/batch/item/json/JsonFileItemWriterFunctionalTests.java

@@ -59,6 +59,8 @@ public abstract class JsonFileItemWriterFunctionalTests {
 	private ExecutionContext executionContext;
 	private Trade trade1 = new Trade("123", 5, new BigDecimal("10.5"), "foo");
 	private Trade trade2 = new Trade("456", 10, new BigDecimal("20.5"), "bar");
+	private Trade trade3 = new Trade("789", 15, new BigDecimal("30.5"), "foobar");
+	private Trade trade4 = new Trade("987", 20, new BigDecimal("40.5"), "barfoo");
 
 	protected abstract JsonObjectMarshaller<Trade> getJsonObjectMarshaller();
 	protected abstract JsonObjectMarshaller<Trade> getJsonObjectMarshallerWithPrettyPrint();
@@ -93,6 +95,20 @@ public abstract class JsonFileItemWriterFunctionalTests {
 				this.resource.getFile());
 	}
 
+	@Test
+	public void testJsonWritingWithMultipleWrite() throws Exception {
+		// when
+		this.writer.open(this.executionContext);
+		this.writer.write(this.items);
+		this.writer.write(Arrays.asList(trade3, trade4));
+		this.writer.close();
+
+		// then
+		assertFileEquals(
+				new File(EXPECTED_FILE_DIRECTORY + "expected-trades-with-multiple-writes.json"),
+				this.resource.getFile());
+	}
+
 	@Test
 	public void testJsonWritingWithPrettyPrinting() throws Exception {
 		// given

spring-batch-infrastructure-tests/src/test/resources/org/springframework/batch/item/json/expected-trades-with-multiple-writes.json

@@ -0,0 +1,6 @@
+[
+ {"isin":"123","quantity":5,"price":10.5,"customer":"foo"},
+ {"isin":"456","quantity":10,"price":20.5,"customer":"bar"},
+ {"isin":"789","quantity":15,"price":30.5,"customer":"foobar"},
+ {"isin":"987","quantity":20,"price":40.5,"customer":"barfoo"}
+]

spring-batch-infrastructure-tests/src/test/resources/org/springframework/batch/item/json/trades.json

@@ -10,5 +10,17 @@
     "quantity": 2,
     "price": 1.4,
     "customer": "bar"
+  },
+  {
+    "isin": "789",
+    "quantity": 3,
+    "price": 1.6,
+    "customer": "foobar"
+  },
+  {
+    "isin": "100",
+    "quantity": 4,
+    "price": 1.8,
+    "customer": "barfoo"
   }
 ]