Fix line tokenizer validation in FlatFileItemReaderBuilder

Resolves #766

Author: fmbenhassine

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2020 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.
@@ -454,7 +454,7 @@ public FlatFileItemReader<T> build() {
 
 			DefaultLineMapper<T> lineMapper = new DefaultLineMapper<>();
 
-			if(this.lineTokenizer != null && this.fieldSetMapper != null) {
+			if(this.lineTokenizer != null) {
 				lineMapper.setLineTokenizer(this.lineTokenizer);
 			}
 			else if(this.fixedLengthBuilder != null) {

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2018 the original author or authors.
+ * Copyright 2016-2020 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.
@@ -519,6 +519,24 @@ public void testCustomEncoding() {
 		assertEquals(encoding, ReflectionTestUtils.getField(reader, "encoding"));
 	}
 
+	@Test
+	public void testErrorMessageWhenNoFieldSetMapperIsProvided() {
+		try {
+			new FlatFileItemReaderBuilder<Foo>()
+					.name("fooReader")
+					.resource(getResource("1;2;3"))
+					.lineTokenizer(line -> new DefaultFieldSet(line.split(";")))
+					.build();
+		} catch (IllegalStateException exception) {
+			String exceptionMessage = exception.getMessage();
+			if (exceptionMessage.equals("No LineTokenizer implementation was provided.")) {
+				fail("Error message should not be 'No LineTokenizer implementation was provided.'" +
+						" when a LineTokenizer is provided");
+			}
+			assertEquals("No FieldSetMapper implementation was provided.", exceptionMessage);
+		}
+	}
+
 	private Resource getResource(String contents) {
 		return new ByteArrayResource(contents.getBytes());
 	}