Support empty delimiter in DelimitedBuilder of FlatFileItemWriterBuilder

Previously, if supplying an empty delimiter, to the delimited().delimiter() of DelimitedBuilder from the parent FlatFileItemWriterBuilder, it would be ignored and instead use the default delimiter ",".

Resolves BATCH-2844

Author: drumonii

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

@@ -33,7 +33,6 @@
 import org.springframework.batch.item.file.transform.LineAggregator;
 import org.springframework.core.io.Resource;
 import org.springframework.util.Assert;
-import org.springframework.util.StringUtils;
 
 /**
  * A builder implementation for the {@link FlatFileItemWriter}
@@ -464,9 +463,7 @@ public DelimitedLineAggregator<T> build() {
 					"A list of field names or a field extractor is required");
 
 			DelimitedLineAggregator<T> delimitedLineAggregator = new DelimitedLineAggregator<>();
-			if (StringUtils.hasLength(this.delimiter)) {
-				delimitedLineAggregator.setDelimiter(this.delimiter);
-			}
+			delimitedLineAggregator.setDelimiter(this.delimiter);
 
 			if (this.fieldExtractor == null) {
 				BeanWrapperFieldExtractor<T> beanWrapperFieldExtractor = new BeanWrapperFieldExtractor<>();

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2018 the original author or authors.
+ * Copyright 2016-2019 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.
@@ -119,6 +119,34 @@ public void testDelimitedOutputWithDefaultDelimiter() throws Exception {
 		assertEquals("HEADER$1,2,3$4,5,6$FOOTER", readLine("UTF-16LE", output));
 	}
 
+	@Test
+	public void testDelimitedOutputWithEmptyDelimiter() throws Exception {
+
+		Resource output = new FileSystemResource(File.createTempFile("foo", "txt"));
+
+		FlatFileItemWriter<Foo> writer = new FlatFileItemWriterBuilder<Foo>()
+				.name("foo")
+				.resource(output)
+				.lineSeparator("$")
+				.delimited()
+				.delimiter("")
+				.names("first", "second", "third")
+				.encoding("UTF-16LE")
+				.headerCallback(writer1 -> writer1.append("HEADER"))
+				.footerCallback(writer12 -> writer12.append("FOOTER"))
+				.build();
+
+		ExecutionContext executionContext = new ExecutionContext();
+
+		writer.open(executionContext);
+
+		writer.write(Arrays.asList(new Foo(1, 2, "3"), new Foo(4, 5, "6")));
+
+		writer.close();
+
+		assertEquals("HEADER$123$456$FOOTER", readLine("UTF-16LE", output));
+	}
+
 	@Test
 	public void testDelimitedOutputWithDefaultFieldExtractor() throws Exception {