如何为运行时编译设置上下文类加载器的类路径？

Question

我想在weblogic 10.3服务器中在运行时编译和加载新类.类加载似乎有点简单:

class ClassFileManager 
extends ForwardingJavaFileManager<StandardJavaFileManager> {

  Map<String, JavaClassObject> classes = new HashMap<String, JavaClassObject>();

  public ClassFileManager(StandardJavaFileManager standardManager) {
    super(standardManager);
  }

  @Override
  public ClassLoader getClassLoader(Location location) {
    return new SecureClassLoader(currentThread().getContextClassLoader()) {
      @Override
      protected Class<?> findClass(String name) throws ClassNotFoundException {
        byte[] b = classes.get(name).getBytes();
        return super.defineClass(name, b, 0, b.length);
      }
    };
  }

  @Override
  public JavaFileObject getJavaFileForOutput(
      Location location, String className, Kind kind, FileObject sibling)
      throws IOException {
    JavaClassObject result = new JavaClassObject(className, kind);
    classes.put(className, result);
    return result;
  }
}

执行类加载的最简单方法似乎是初始化a SecureClassLoader并让它使用它contextClassLoader作为父级.

但是当-classpath为JDK的运行时编译器设置选项时,我似乎无法以字符串形式找到"上下文类路径".以下是一个"足够好"的黑客攻击:

JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
ClassFileManager fileManager = 
    new ClassFileManager(compiler.getStandardFileManager(null, null, null));
List<String> options = new ArrayList<String>();
options.add("-classpath");
options.add(System.getProperty("java.class.path") + ";" +
    getClass().getProtectionDomain()
              .getCodeSource().getLocation()
              .toURI().toString()
              .replace("file:/", "").replace("/", "\\"));

但它不会生成上下文类加载器的完整类路径.我怎么能可靠地做到这一点？我可以吗？

Answer 1

WebLogic 10.3.6 的实现相当复杂ClassLoader。幸运的是，用于 Web 应用程序的类加载器公开了一个getClassPath方法。

ClassLoader cl = Thread.currentThread().getContextClassLoader();
String classPath = ((weblogic.utils.classloaders.GenericClassLoader)cl).getClassPath();

// Once we have a classpath it's standard procedure
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
StandardJavaFileManager sfm = compiler.getStandardFileManager(null, null, null);
List<String> optionList = new ArrayList<String>();
optionList.addAll(Arrays.asList("-classpath", classPath));
compiler.getTask(null, sfm, null, optionList, null, sources).call();