FlatFileItemWriter now uses charset to determine default encoding

resolves spring-projects#1154

It now matches the encoding scheme of FlatFileItemReader

Author: cppwfs

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/file/FlatFileItemWriter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2018 the original author or authors.
+ * Copyright 2006-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@
 
 package org.springframework.batch.item.file;
 
+import java.nio.charset.Charset;
 import java.util.List;
 
 import org.springframework.batch.item.file.transform.LineAggregator;
@@ -39,11 +40,15 @@
  * @author Dave Syer
  * @author Michael Minella
  * @author Mahmoud Ben Hassine
+ * @author Glenn Renfro
  */
 public class FlatFileItemWriter<T> extends AbstractFileItemWriter<T> {
 
 	protected LineAggregator<T> lineAggregator;
 
+	// default encoding for writing to flat files - set to charset of this Java virtual machine.
+	public static final String DEFAULT_CHARSET = Charset.defaultCharset().name();
+
 	public FlatFileItemWriter() {
 		this.setExecutionContextName(ClassUtils.getShortName(FlatFileItemWriter.class));
 	}

spring-batch-infrastructure/src/test/java/org/springframework/batch/item/file/builder/FlatFileItemWriterBuilderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStreamReader;
+import java.nio.charset.Charset;
 import java.util.Arrays;
 
 import org.junit.Test;
@@ -38,6 +39,7 @@
  * @author Michael Minella
  * @author Mahmoud Ben Hassine
  * @author Drummond Dawson
+ * @author Glenn Renfro
  */
 public class FlatFileItemWriterBuilderTests {
 
@@ -275,13 +277,13 @@ public void testFlags() throws Exception {
 				.transactional(false)
 				.lineAggregator(new PassThroughLineAggregator<>())
 				.build();
-
 		assertFalse((Boolean) ReflectionTestUtils.getField(writer, "saveState"));
 		assertTrue((Boolean) ReflectionTestUtils.getField(writer, "append"));
 		assertFalse((Boolean) ReflectionTestUtils.getField(writer, "transactional"));
 		assertTrue((Boolean) ReflectionTestUtils.getField(writer, "shouldDeleteIfEmpty"));
 		assertFalse((Boolean) ReflectionTestUtils.getField(writer, "shouldDeleteIfExists"));
 		assertTrue((Boolean) ReflectionTestUtils.getField(writer, "forceSync"));
+		assertEquals( Charset.defaultCharset().name(), ReflectionTestUtils.getField(writer, "encoding"));
 	}
 
 	private String readLine(String encoding, Resource outputFile ) throws IOException {