Fix incorrect usage of StringBuilder#append in TransactionAwareBufferedWriter

Issue #3745

Author: nfjcore

spring-batch-infrastructure/src/main/java/org/springframework/batch/support/transaction/TransactionAwareBufferedWriter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2020 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.
@@ -33,6 +33,7 @@
  *
  * @author Dave Syer
  * @author Michael Minella
+ * @author Niels Ferguson
  *
  */
 public class TransactionAwareBufferedWriter extends Writer {
@@ -244,6 +245,6 @@ public void write(String str, int off, int len) throws IOException {
 		}
 
 		StringBuilder buffer = getCurrentBuffer();
-		buffer.append(str, off, len);
+		buffer.append(str, off, off + len);
 	}
 }

spring-batch-infrastructure/src/test/java/org/springframework/batch/support/transaction/TransactionAwareBufferedWriterTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2012 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.
@@ -40,6 +40,7 @@
  * @author Dave Syer
  * @author Michael Minella
  * @author Will Schipp
+ * @author Niels Ferguson
  * 
  */
 public class TransactionAwareBufferedWriterTests {
@@ -337,6 +338,27 @@ public void testResourceKeyCollision() throws Exception {
 		}				
 	}
 
+	//BATCH-3745
+	@Test
+	public void testWriteInTransactionWithOffset() throws IOException{
+		ArgumentCaptor<ByteBuffer> bb = ArgumentCaptor.forClass(ByteBuffer.class);
+		when(fileChannel.write(bb.capture())).thenReturn(3);
+
+		new TransactionTemplate(transactionManager).execute((TransactionCallback<Void>) status -> {
+
+			try {
+				writer.write("hamburger", 4, 3);
+			} catch (IOException e) {
+				throw new IllegalStateException("Unexpected IOException", e);
+			}
+			return null;
+		});
+
+		String s = getStringFromByteBuffer(bb.getValue());
+
+		assertEquals("urg", s);
+	}
+
 	private String getStringFromByteBuffer(ByteBuffer bb) {
 		byte[] bytearr = new byte[bb.remaining()];
 		bb.get(bytearr);