Re: Why maven-compiler-plugin seems to not take advantage of already compiled .class files?

[Robert Scholte <rf...@apache.org>]

Hi,

that's indeed quite a huge difference, but does this mean that the 55  
seconds is only for compilation?
The background about incremental builds is described/discussed in  
MCOMPILER-205[1] and Stack Overflow[2].

TLDR; If you change a method signature, you must also compile all classes  
that call this method (and throw a compilation error if you forgot to  
change this class).
Basically there are 2 options: analyze every class and decide if it must  
be recompiled OR simply recompile everything. The maven-compiler-plugin  
does the latter by default because the java compiler should be quite  
efficient.
Hence I'm kind of surprised by your numbers.

We're always interested in improvements, of course.

thanks,
Robert

[1] https://issues.apache.org/jira/projects/MCOMPILER/issues/MCOMPILER-205
[2]  
https://stackoverflow.com/questions/16963012/maven-compiler-recompile-all-files-instead-modified/49700942#49700942

On Fri, 30 Nov 2018 16:34:24 +0100, Francesco Caliumi - Diennea  
<fr...@diennea.com> wrote:

> Hi everyone,
> I'm wondering why, modifying just a single file, a "without clean" build  
> takes a time very close to a "clean" build.
>
> Some numbers about my build times:
> 1) mvn clean install: 01:13 min
> 2) mvn install (without file changes): 10.541 s
> 3) mvn install (with a single source file changed, among 2680 others  
> left unchanged): 01:06 min
>
> In case 3 I'm expecting a time closer to case 2, not to case 1. Both  
> case 1 and 3 reports "Compiling 2680 source files".
>
> Are there some options to make maven-compiler-plugin skip compiling  
> sources where the xxx.class file has a more recent update time than the  
> relative xxx.java file?
>
> Many thanks in advance,
> Francesco
>
>
> --
>
> Francesco Caliumi
> Developer @ Diennea - MagNews
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