Alternative to fatJar - modular solution?
Glavo
zjx001202 at gmail.com
Thu Oct 14 16:49:35 UTC 2021
>
> There's no requirements that a module must be stored in a JAR file. In
> fact, your program will not work if it was packaged into an image
> produced by jlink. That's why we have the ModuleReader::list() API.
I understand this, but it is not uncommon for code that has made such
assumptions. Maintaining this assumption can reduce some pain.
Take my program as an example. It is a plugin. I hope it can be used
in a modular way, but I'm sure no one will use it for jlink in this
century. The module API does solve the problem, but I will avoid using
it because I am careful to maintain compatibility with Java 8, whether
I call these APIs with reflection or multi jar, the build or test process
becomes more complex. If the old API still works, I don't want to use
the new API.
Could you explain what the actual scenario is? Is it for patching the
> contents of a module (similar to --patch-module)?
Ah, these are some strange use cases. They splice an exe file and a jar
file together so that the file can be executed directly and is a jar
file. It also needs to find its own location and read the contents of
exe from its own head. I think this is a strange and rare use case.
I vaguely remember several use cases that assume their own jar state,
but I can't recall it for a moment, so I casually use it as an example.
Ioi Lam <ioi.lam at oracle.com> 于2021年10月15日周五 上午12:07写道：
> On 10/14/21 8:29 AM, Glavo wrote:
> >
> > In fact, I don't understand why people started packing JAR files
> > inside
> > JAR files. Maybe there were some esoteric reasons (related to
> > Class-Path: attribute in manifest files???).
> >
> >
> > Sometimes it's necessary to keep jars intact and distribute them as
> > they are. In fact, a program I just developed today is not compatible
> > with your solution: It uses
> > cls.getProtectionDomain().getCodeSource().getLocation()
> > find its place, create a zip file system and traverse some of its
> folders.
> >
>
> Since we are discussing about a solution for storing modules in a single
> file, there's an API to list all the contents of a module --
> java.lang.module.ModuleReader::list().
>
> Here's an example:
>
> import java.lang.module.*;
>
> public class FindAllInModule {
> public static void main(String args[]) throws Exception {
> Module module = java.lang.Object.class.getModule();
> ModuleReference mref = module.getLayer().configuration()
> .findModule(module.getName())
> .orElseThrow(() -> new RuntimeException())
> .reference();
> try (ModuleReader reader = mref.open()) {
> reader.list().forEach(n -> System.out.println(n));
> }
> }
> }
>
>
> There's no requirements that a module must be stored in a JAR file. In
> fact, your program will not work if it was packaged into an image
> produced by jlink. That's why we have the ModuleReader::list() API.
>
> > We also have some strange use cases that require additional data to be
> > appended before the jar content. Dismantling the jar will destroy the
> > data.
>
> Could you explain what the actual scenario is? Is it for patching the
> contents of a module (similar to --patch-module)?
>
>
> Thanks
> - Ioi
>
>
>
> > Ioi Lam <ioi.lam at oracle.com <mailto:ioi.lam at oracle.com>>
> > 于2021年10月14日周四 上午8:57写道：
> >
> > Hi Glavo,
> >
> > I have simplified my prototype so now there's no need to implement
> > new
> > URL handlers.
> >
> > https://github.com/iklam/tools/tree/main/jigsaw/uberjar
> > <
> https://urldefense.com/v3/__https://github.com/iklam/tools/tree/main/jigsaw/uberjar__;!!ACWV5N9M2RV99hQ!e5b75N_Cpd4IjSBjjO1rN9cnWFTiv-dPnb8qKrG9xrFoL9LH9NDBuNVoO-O7nQ$
> >
> >
> > Please see the "Super-JAR Demo" section.
> >
> > The new demo uses standard features supported by the JDK's built-in
> > "jar:" URL handler. The only difference with my previous demo is
> > that we
> > store the "exploded" version of the modules. I.e., the JAR file looks
> > like this:
> >
> > modules/com.lib/com/lib/Lib.class
> > modules/com.lib/module-info.class
> > ...
> > modules/com.simple/com/simple/Simple.class
> > modules/com.simple/com/simple/Simple$Foo.class
> > modules/com.simple/module-info.class
> >
> > All the modules are loaded from the /modules directories in the
> > JAR file.
> >
> > The URI for a class looks like this:
> >
> >
> jar:file:///tmp/apps/super-launcher.jar!/modules/com.lib/com/lib/Lib.class
> >
> > For modularized apps, I think this is a much better approach than the
> > traditional Uber-JARs that store JAR files inside a JAR file,
> > which will
> > require more complex decompression.
> >
> > In fact, I don't understand why people started packing JAR files
> > inside
> > JAR files. Maybe there were some esoteric reasons (related to
> > Class-Path: attribute in manifest files???).
> >
> > But, whatever reason they had would not apply to a modular
> > application,
> > where every component is already in a Jigsaw module. Packing the
> > exploded image into a JAR file will be good enough.
> >
> > **********************
> >
> > Going forward, I would suggest --
> >
> > [1] Frameworks such as SpringBoot can consider the idea in this
> > demo for
> > a possible solution for packaging modules
> >
> > [2] For the JDK, we should investigate supporting a single-file
> > packaging format for modules. E.g. extend the --module-path
> > command-line
> > option to support modules that are stored in a single file (either
> > a JAR
> > file or an image file produced by jlink).
> >
> > java --module-path=super-jar.jar -m com.simple
> > or
> > java --module-path=super-jar.jar -m com.simple
> >
> > Or even this (with appropriate attributes in the JAR manifest):
> >
> > java -jar super-jar.jar
> >
> > I believe [2] is doable as the underpinning support is already in the
> > JDK. We need to decide what format to support, how to specify the
> > location of the modules directory inside a JAR file, etc.
> >
> > As always, since the Oracle Java team has limited resources,
> > participation from the Java community is very much appreciated and
> > encouraged :-)
> >
> > Thanks
> > - Ioi
> >
> >
> >
> > On 10/11/21 3:48 PM, Glavo wrote:
> > > I mistakenly believe that the implementation of the filesystem
> > corresponds
> > > exactly to the URL. The problem I really want to express is that
> JDK
> > > does not support URLs of nested jar file systems. It seems that
> this
> > > problem still exists in JDK 17. To make matters worse, we can
> > use toUri()
> > > to convert the path of the file in the nested jar into a URI,
> > but this
> > > URI is neither accepted by Paths.get
> > (java.lang.IllegalArgumentException：
> > > URI does not contain path info ex. jar:file:/c:/foo.zip!/BAR) nor
> > > converted into a URL (java.net
> > <
> https://urldefense.com/v3/__http://java.net__;!!ACWV5N9M2RV99hQ!e5b75N_Cpd4IjSBjjO1rN9cnWFTiv-dPnb8qKrG9xrFoL9LH9NDBuNXMJHaheg$
> >.MalformedURLException:
> > Nested JAR URLs
> > > are not supported). Is this a bug or an expected behavior?
> > >
> > > Alan Bateman <Alan.Bateman at oracle.com
> > <mailto:Alan.Bateman at oracle.com>> 于2021年10月12日周二 上午2:58写道：
> > >
> > >> On 11/10/2021 15:09, Glavo wrote:
> > >>> I think this is a great prototype. Based on it, I think such
> > requirements
> > >>> can also be realized by enhancing jar in these aspects:
> > >>>
> > >>> 1. Nested jar file system (The ujar file system seems
> > unnecessary.
> > >>> I never understand why jar file systems cannot be nested.)
> > >> This was fixed in JDK 12, are you seeing issues with release
> recent
> > >> releases? If so then would it be possible to submit a bug with
> > a test
> > >> case or bring the issue to core-libs-dev?
> > >>
> > >> -Alan
> > >>
> >
>
>
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