Improve TransactionAwareBufferedWriter

TransactionAwareBufferedWriter offers a number of optimization
potentials. First it creates an unnecessary local, temporary char[]
in write(char[], int, int). Second it does not overwrite any of the
#write(String) methods leading to unnecessary intermediate copies.

 * avoid local, temporary char[] in #write(char[], int, int)
 * overwrite #write(String) methods to avoid copies

Together these two changes should help to reduce allocation rate.

Issue: #1166

Author: marschall

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2012 the original author or authors.
+ * Copyright 2006-2020 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.
@@ -210,9 +210,7 @@ public void flush() throws IOException {
 	public void write(char[] cbuf, int off, int len) throws IOException {
 
 		if (!transactionActive()) {
-			char [] subArray = new char[len];
-			System.arraycopy(cbuf, off, subArray, 0, len);
-			byte[] bytes = new String(subArray).getBytes(encoding);
+			byte[] bytes = new String(cbuf, off, len).getBytes(encoding);
 			int length = bytes.length;
 			ByteBuffer bb = ByteBuffer.wrap(bytes);
 			int bytesWritten = channel.write(bb);
@@ -225,4 +223,27 @@ public void write(char[] cbuf, int off, int len) throws IOException {
 		StringBuilder buffer = getCurrentBuffer();
 		buffer.append(cbuf, off, len);
 	}
+
+	/*
+	 * (non-Javadoc)
+	 *
+	 * @see java.io.Writer#write(String, int, int)
+	 */
+	@Override
+	public void write(String str, int off, int len) throws IOException {
+
+		if (!transactionActive()) {
+			byte[] bytes = str.substring(off, off + len).getBytes(encoding);
+			int length = bytes.length;
+			ByteBuffer bb = ByteBuffer.wrap(bytes);
+			int bytesWritten = channel.write(bb);
+			if(bytesWritten != length) {
+				throw new IOException("Unable to write all data.  Bytes to write: " + len + ".  Bytes written: " + bytesWritten);
+			}
+			return;
+		}
+
+		StringBuilder buffer = getCurrentBuffer();
+		buffer.append(str, off, len);
+	}
 }