java.lang.String API suggestion : make String return read-only CharBuffer (original) (raw)

Martin Buchholz martinrb at google.com
Wed Apr 10 18:04:29 PDT 2013

It's a reasonable suggestion, although the natural signature is

public CharBuffer asReadOnlyBuffer()

but where do you stop? What about

public List asReadOnlyList()

On Thu, Apr 4, 2013 at 7:40 PM, Eugene Chung(정의근) <euigeun_chung at tmax.co.kr>wrote:

Hello, Java SE 8 EG.

I'm a member of TmaxSoft, which is making the JEUS web application server. And the implementor of a Servlet container. I am writing to you that I'd like to suggest a new method to java.lang.String like below: /** * Returns a read-only char buffer that shares this string's content. * @return a read-only char buffer */ public java.nio.CharBuffer getAsCharBuffer() { return CharBuffer.wrap(value).asReadOnlyBuffer(); } Since Java EE Servlet 3.1, a Servlet container provides non-blocking I/O to web applications. So, javax.servlet.ServletOutputStream#print(String s) supports non-blocking write. Before writing 's' to a socket stream, we must convert it to a byte array. We can use s.getBytes(charset), if 's' is small enough. But if 's' is big enough, we cannot use getBytes() because it can cause memory exhaustion or more seriously OutOfMemoryError. To avoid the problem, we need a fixed-size char array and byte array for intermediate conversion. Here's the pseudo code to explain why String should return read-only CharBuffer. Let's call the name of char array 'cbuff' and the name of result byte array 'bbuff'. for (toStringEnd) { s.getChars(b, e, cbuff, cbuff.length); // 1 charsetEncoder.encode(CharBuffer.wrap(cbuff), ByteBuffer.wrap(bbuff), false); // 2 // write 'bbuff' to socket } >From above code, '1' and '2' are necessary operations but definitely memory copy overhead. Copy overhead of '2' is unavoidable but we can remove overhead of '1' if String offers backing CharBuffer as I've suggested. CharBuffer charBuffer = s.getAsCharBuffer(); for (charBuffer.hasRemaining()) { // NO OVERHEAD Of 1 charsetEncoder.encode(charBuffer, ByteBuffer.wrap(bbuff), false); // 2 // write 'bbuff' to socket } It doesn't harm immutability of String because CharBuffer returned from it is read-only. (CharBuffer.asReadOnlyBuffer()) And I think this new method can help many applications to reduce memory copy overhead of String. Best regards, Eugene Chung (Korean : 정의근)

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