RFR: 8368333: [lworld] Add preview mode to ImageReader and JRT file-system [v6]

[Roger Riggs]

On Wed, 8 Oct 2025 23:26:55 GMT, David Beaumont <duke at openjdk.org> wrote:

>> Java changes for supporting preview mode when preview mode resources (with new location flags) are available.
>> 
>> At the moment, this code will operate on non-preview jimage files (1.0) and act as if no preview resources are available by virtue of the default value for missing attributes and package flags being zero (which matches jimage 1.0).
>> 
>> This should be reviewed on top of https://github.com/openjdk/valhalla/pull/1618
>
> David Beaumont has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Changing existing package flags during writing to match altered flag values.

src/java.base/share/classes/jdk/internal/jimage/ModuleReference.java line 133:

> 131: 
> 132:     /** Returns whether this reference exists only in preview mode. */
> 133:     public boolean isPreviewOnly() {

Pick either PreviewOnly or hasNormal and use consistently. (Even if one is the opposite of the other).

src/java.base/share/classes/jdk/internal/jrtfs/SystemImage.java line 83:

> 81:         if (mode.isPreviewModeEnabled())
> 82:             throw new UnsupportedOperationException(
> 83:                     "Preview mode not yet supported for exploded images");

I'd remove "yet", it implies some planned work.

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1619#discussion_r2417236879
PR Review Comment: https://git.openjdk.org/valhalla/pull/1619#discussion_r2417256303