Allows bootstrapping a modularized environment from a classpath one.

BootstrapLauncher (BSL for short) uses the following information:

• The (legacy) classpath information. This is retrieved from the following, in descending order of priority:

  • The legacyClassPath.file system property, containing a path list (paths separated by ; on Windows and : on UNIX, as defined by File.pathSeparatorChar)
  • The legacyClassPath system property, containing a path list
  • The java.class.path system property.

  If none of the above is present, then an exception is thrown.

• The ignore list, specified by the ignoreList system property, as a comma-separated list of values. For any path within the classpath (as retrieved above) whose filename begins with any value in the ignore list, the path is ignored by BSL and not included in the bootstrap module layer created by BSL.

  By default, the ignore list is set to ignore filenames that start with asm or securejarhandler (the dependencies of BSL).

• The optional module merge information, specified by the mergeModules system property. This is used to combine multiple JAR files into a single logical module in the eyes of the module system. This property is a list of groups of comma-separated paths, where each group is separated by semicolons and denotes one module.

  For example: a.jar,b.jar;b.jar,c.jar means a.jar and b.jar are combined into one module, and b.jar and c.jar are combined into another module.

• The bootstrap service, which is a Consumer<String[]> service provided by a module in the bootstrap module layer. At least one such bootstrap service must exist, otherwise an exception is thrown. ModLauncher provides one such service: BootstrapLaunchConsumer.

Each JAR (unless included in the above module merge information) maps to one module in the bootstrap module layer. Because all modules share the same classloader, no module may share a package with another module. Therefore, packages are tracked and the first JAR which contains the module effectively 'owns' that package, and later JARs will not be searched for the same package.

BSL creates a new module layer which has the following properties:

• The name of the module layer is MC-BOOTSTRAP.
• Its parent layer and configuration is the boot configuration (from ModuleLayer#boot()).
• It contains all the modules as provided in the classpath information (excluded from which the JARs who match the ignore list) and mapped according to the optional module merge information.

For easier debugging, additional debugging information is printed to System.out if the bsl.debug system property is defined (regardless of its actual value).