bhanditz / clazz-loaderz

Experiments with Java class loaders

License

Apache 2.0

Load classes from resources

This project contains of 4 modules.

resource-clazz-loader this module contains main code that is used to load classes

packed here goes simplified code intended to be used from user's code all classes are renamed to fit version there is factory-name.txt file containing actual name

packed-impl generated code, intermediate package used to make IDEA compile renamed classes you should avoid any changed in sources under the module

packed-test this is a black-box tests module. There is only dependency to create artifact

Installation

• Take the .jar from packed artifact output and copy it's contents into the main .jar of your application/library

• Copy and rename factory-name.txt file and put in into your app's main .jar

• Add URLs of your .jar files to load in the file. One pre line

• Add those .jar files to the main .jar resources

• Use the following code in your app to make listed .jar files be loaded in a classloader

      private ClassLoader classLoaderFromResources(@NotNull ClassLoader parent) {
        try {
          final Scanner scanner = new Scanner(parent.getResourceAsStream("renamed-libraries-list"), "utf-8");
          return (ClassLoader)parent.loadClass(scanner.nextLine()).getMethod("scan", ClassLoader.class, Scanner.class).invoke(null, parent, scanner);
        } catch (Exception e) {
          throw new RuntimeException("Failed to load classloader. " + e.getMessage(), e);
        }
      }
  

Misc

You may use the following Ant pre/post-action in IDEA artifact to generate classpath for your lib:

        <pathconvert pathsep="&#xA;" property="classpath">
          <fileset dir="${artifact.output.path}" includes="**/*.jar"/>
          <chainedmapper>
            <flattenmapper />
            <globmapper from="*" to="PREFIX/*"/>
          </chainedmapper>
        </pathconvert>
        <echo append="true" file="${artifact.output.path}/classpath">&#xA;${classpath}&#xA;</echo>

See hint for more details

Limitations

• There is a custom (non URLClassLoader) implementation of classloader
• This classloader prefers local classes to classes from parent classloader
• Some libraries may fail to resolve patterns on resources (i.e. SpringFramework)
• Only .jar are supported in classpath