使用自定义类加载器从爆炸模块加载类

Question

我一直在使用Java中的简单自定义类加载器,到目前为止,一切都按预期用于非模块相关类.但是,我似乎无法找到使用我的类加载器从模块加载类的任何方法,即使模块相关的find*()方法已经重载.我试图做的是从模块"HelloModularWorld"加载一个类并运行它的主要.但是,当我指定包所在的目录时,它会"正常"加载并报告为未命名的模块.我错过了什么？

类加载器只是从文件系统的其他地方加载类,没什么特别的.

类加载器实现:

package arch.classloaders;

import java.io.*;
import java.net.MalformedURLException;
import java.net.URL;

public class ModifiableClassLoader extends ClassLoader {
    private File searchPath;
    //...other ctors...
    public ModifiableClassLoader(File path, String name, ClassLoader parent) {
        super(name, parent); //Delegate to parent classloader as required.
        if (!path.isDirectory()) throw new IllegalArgumentException("Path must be a directory");
        searchPath = path;
    }

    public void setPath(File newPath) {...}

    public File getPath() {...}

    //Responsible for actual loading
    public Class<?> findClass(String binName) throws ClassNotFoundException {
        File classfile = new File(searchPath.getPath() + File.separator 
                + binName.replace('.', File.separatorChar) + ".class");
        byte[] buf;
        FileInputStream fis;
        try {
            fis = new FileInputStream(classfile);
            buf = fis.readAllBytes();
            fis.close();
        } catch (IOException e) {
            throw new ClassNotFoundException("Error in defining " + binName + " in " + searchPath.getPath(),e);
        }
        return defineClass(binName, buf, 0, buf.length);
    }

    //Modules are expected to be in a folder with the same name as the module.
    //e.g. module hellomodularworld is expected to be in a folder
    //<SEARCHPATH>/<MODNAME>/
    //NOTE: Module-overloaded methods return null rather than throw when class isn't found.
    public Class<?> findClass(String modName, String binName) {
        if (null == modName) {
            try {
                return findClass(binName);
            } catch (ClassNotFoundException e) {
                return null;
            }
        }
        File classfile = new File(searchPath.getPath() + File.separator 
                + modName + File.separator
                + binName.replace('.', File.separatorChar) + ".class");
        byte[] buf;
        FileInputStream fis;
        try {
            fis = new FileInputStream(classfile);
            buf = fis.readAllBytes();
            fis.close();
        } catch (IOException e) {
            return null;
        }
        return defineClass(binName, buf, 0, buf.length);
    }

    //Non-module
    public URL findResource(String resPath) {...}

    //Module version
    public URL findResource(String modName, String resPath) throws IOException {...}

    //Enumeration version; does nothing.
    public java.util.Enumeration<URL> findResources(String resPath) {...}
}

测试代码:

public class Test {
    public static void main(String[] args) {
        ModifiableClassLoader mcl = new ModifiableClassLoader(
                new File("C:\\Users\\archd\\Desktop\\"));
        try {
            Class<?> clazz = mcl.loadClass(
                    "hellomodularworld/com.archdukeliamus.hellomodularworld.HelloWorld"
            );
            java.lang.reflect.Method mth = clazz.getMethod("main", String[].class);
            mth.invoke(null,new Object[] {null});
            System.out.println(clazz.getModule().getName());
        } catch (...) {
                //omitted
        }
}

在线Class<?> clazz = mcl.loadClass("hellomodularworld/com.archdukeliamus.hellomodularworld.HelloWorld");我尝试过:

• "hellomodularworld/com.archdukeliamus.hellomodularworld.HelloWorld" - 不起作用.ClassNotFoundException异常.
• "hellomodularworld.com.archdukeliamus.hellomodularworld.HelloWorld" - NoClassDefFoundException.
  com/archdukeliamus/hellomodularworld/HelloWorld (wrong name: hellomodularworld/com/archdukeliamus/hellomodularworld/HelloWorld)
• "com.archdukeliamus.hellomodularworld.HelloWorld" - 按预期工作(类加载文件夹已正确更改)但使用未命名的模块.

编辑:module-info.java

module hellomodularworld {

}

测试类不在任何模块中.(我不完全确定为什么这很重要,我应该得到一个例外,因为"这个包没有导出",我没有得到.)

编辑2:修改模块包括exports com.archdukeliamus.hellomodularworld;.结果没有变化.

Answer 1

模块加载是与类加载不同的过程。要在运行时加载模块，您需要使用该类创建一个新的模块层，并从 a （在本例中为磁盘）ModuleFinder提供 a 。然后，您将需要创建一个可用于解析模块的文件。为了确保模块加载过程的完整性，您需要导出引导配置。然后，您需要创建配置，包括告诉在哪里找到模块以及要解析的一组模块。然后实例化您希望用来加载这些模块的类的类加载器，并将其传递给定义模块方法。最后你实例化你的类。PathFileSystemConfigurationModuleFinder

新测试：

package arch.classloaders;

import java.lang.module.*;
import java.lang.reflect.InvocationTargetException;
import java.net.URI;
import java.io.*;
import java.nio.*;
import java.nio.file.*;
import java.util.*;

public class Test2 {
    public static void main(String[] args) {
        //Get paths to module, and instantiate a ModuleFinder.
        Path pth = FileSystems.getDefault().getPath("C:\\Users\\archd\\Desktop");
        ModuleFinder mf = ModuleFinder.of(pth);
        //Create a new Configuration for a new module layer deriving from the boot configuration, and resolving
        //the "hellomodularworld" module.
        Configuration cfg = ModuleLayer.boot().configuration().resolve(mf,ModuleFinder.of(),Set.of("hellomodularworld"));
        //Create classloader
        ModifiableClassLoader mcl = new ModifiableClassLoader(
                new File("C:\\Users\\archd\\Desktop\\"));
        //make the module layer, using the configuration and classloader.
        ModuleLayer ml = ModuleLayer.boot().defineModulesWithOneLoader(cfg,mcl);
        //Show the configuration.
        System.out.println(ml.configuration()); //prints "hellomodularworld"
        try {
            //load and run class
            Class<?> clazz = ml.findLoader("hellomodularworld").loadClass(
                    "com.archdukeliamus.hellomodularworld.HelloWorld"
            );
            java.lang.reflect.Method mth = clazz.getMethod("main", String[].class);
            mth.invoke(null,new Object[] {null});
            //show the module this class is part of and list packages
            System.out.println(clazz.getModule()); //prints "module hellomodularworld"
            for (String pkgn : clazz.getModule().getPackages()) {
                System.out.println(pkgn); //prints "com.archdukeliamus.hellomodularworld"
            }
        } catch (ClassNotFoundException e) {
            ...omitted...
        }
    }
}

有趣的是，这仍然没有调用重载的基于模块的 findClass() 方法，尽管它似乎有效。