I have a task to check a set of conditions for unknown set of classes from classpath. I want to scan it for classes, load each of them and perform my checks. Now I have a set of urls to class files and I try to use URLClassLoader. But to load a class I need to specify a fully qualified class name, but I don't have them (I have only file path). I don't think that building class name from class file path is relieble, is it a better way to do it?
Thanks!
I'd just parse the beginning of the class file, looking for "package" keyword and first occurrence of "class" keyword. Then, when you combine those two (packageName + "." + className), it should result in a proper class name.
I started a project once to automatically test classes found on the class path for run time exceptions, by calling constructors and methods reflectively with dodgy arguments like null, 0, 1, -1, "" etc.
That project has a class called Finder wich does roughly what you need:
static List<Class<?>> findClassesForPackage(String packagename, Report report) throws ClassNotFoundException {
// 'classes' will hold a list of directories matching the package name.
// There may be more than one if a package is split over multiple
// jars/paths
List<Class<?>> classes = new ArrayList<Class<?>>();
List<File> directories = new ArrayList<File>();
try {
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
if (classLoader == null) {
throw new ClassNotFoundException("Can't get class loader.");
}
// Ask for all resources for the path
String path = packagename.replace('.', '/');
Enumeration<URL> resources = classLoader.getResources(path);
while (resources.hasMoreElements()) {
URL res = resources.nextElement();
if (res.getProtocol().equalsIgnoreCase("jar")) {
JarURLConnection conn = (JarURLConnection) res.openConnection();
JarFile jar = conn.getJarFile();
for (JarEntry entry : Collections.list(jar.entries())) {
if (entry.getName().startsWith(path) && entry.getName().endsWith(".class")
&& !entry.getName().contains("$")) {
String className = entry.getName().replace("/", ".").substring(0,
entry.getName().length() - 6);
LOG.debug("Adding JAR className " + className);
try {
Class<?> clazz = Class.forName(className);
classes.add(clazz);
report.addClass(className);
} catch (Throwable throwable) {
ParamSet params = new ParamSet();
params.addParamValue(new ParamValue(className, "fully qualified classname"));
report.addError(className, new Error("Class.forName()", params, throwable));
}
}
}
} else
directories.add(new File(URLDecoder.decode(res.getPath(), "UTF-8")));
}
} catch (NullPointerException e) {
throw new ClassNotFoundException(String.format("%s does not appear to be a valid package", packagename), e);
} catch (UnsupportedEncodingException e) {
throw new ClassNotFoundException(String.format("%s does not appear to be a valid package", packagename), e);
} catch (IOException e) {
throw new ClassNotFoundException(String.format("Could not get all resources for %s", packagename), e);
}
List<String> subPackages = new ArrayList<String>();
// For every directory identified capture all the .class files
for (File directory : directories) {
if (directory.exists()) {
// Get the list of the files contained in the package
File[] files = directory.listFiles();
for (File file : files) {
// add .class files to results
String fileName = file.getName();
if (file.isFile() && fileName.endsWith(".class")) {
// removes the .class extension
String className = packagename + '.' + fileName.substring(0, fileName.length() - 6);
LOG.debug("Adding FILE className " + className);
try {
Class<?> clazz = Class.forName(className);
classes.add(clazz);
report.addClass(className);
} catch (Throwable throwable) {
ParamSet params = new ParamSet();
params.addParamValue(new ParamValue(className, "fully qualified classname"));
report.addError(className, new Error("Class.forName()", params, throwable));
}
}
// keep track of subdirectories
if (file.isDirectory()) {
subPackages.add(packagename + "." + fileName);
}
}
} else {
throw new ClassNotFoundException(String.format("%s (%s) does not appear to be a valid package",
packagename, directory.getPath()));
}
}
// check all potential subpackages
for (String subPackage : subPackages) {
classes.addAll(findClassesForPackage(subPackage, report));
}
return classes;
}
You probably have to strip some code that does reporting etc.
