RFR: 8255729: com.sun.tools.javac.processing.JavacFiler.FilerOutputStream is inefficient

[Guoxiong Li]

On Mon, 21 Dec 2020 09:29:46 GMT, Joel Borggrén-Franck <jfranck at openjdk.org> wrote:

>> Hi all,
>> 
>> `FilerOutputStream` extends `FilterOutputStream` without overwriting the method `write(byte b[], int off, int len)` which would suffer from the performance problem.
>> This patch fixes it and adds some `@Override` to polish the code. But I can't find a good way to write a corresponding test case. Maybe it doesn't need a test case. And all existing tests in `test/langtools/tools/javac` passed locally.
>> 
>> Thank you for taking the time to review.
>> 
>> Best Regards.
>
> src/jdk.compiler/share/classes/com/sun/tools/javac/processing/JavacFiler.java line 282:
> 
>> 280:             if ((off | len | (b.length - (len + off)) | (off + len)) < 0)
>> 281:                 throw new IndexOutOfBoundsException();
>> 282:             out.write(b, off, len);
> 
> If I understand this `out` is the underlying `OutputStream` and calling `write(byte[], int, int)` performs the same one-byte-at-a-time write as without the override.

In my opinion, the `out` depends on the `FileObject.openOutputStream` which differ depending on the implementation of `FileObject` and  can be set by users in the implementation of `FileObject`.

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PR: https://git.openjdk.java.net/jdk/pull/1854