StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
text
Body
copied!<p>****UPDATE 1 (2012)****</p> <p>OK, I've finally gotten around to cleaning up the code snippet below. I stuck it into it's own github project and even added tests.</p> <p><a href="https://github.com/ddopson/java-class-enumerator" rel="noreferrer">https://github.com/ddopson/java-class-enumerator</a></p> <p>****UPDATE 2 (2016)****</p> <p>For an even more robust and feature-rich classpath scanner, see <a href="https://github.com/lukehutch/fast-classpath-scanner/wiki" rel="noreferrer">https://github.com/lukehutch/fast-classpath-scanner/wiki</a>. I'd recommend first reading my code snippet to gain a high level understanding, then using lukehutch's tool for production purposes.</p> <p>****Original Post (2010)****</p> <p>Strictly speaking, it isn't possible to list the classes in a <em>package</em>. This is because a package is really nothing more than a namespace (eg com.epicapplications.foo.bar), and any jar-file in the classpath could potentially add classes into a package. Even worse, the classloader will load classes on demand, and part of the classpath might be on the other side of a network connection.</p> <p>It is possible to solve a more restrictive problem. eg, all classes in a JAR file, or all classes that a JAR file defines within a particular package. This is the more common scenario anyways.</p> <p>Unfortunately, there isn't any framework code to make this task easy. You have to scan the filesystem in a manner similar to how the ClassLoader would look for class definitions.</p> <p>There are a lot of samples on the web for class files in plain-old-directories. Most of us these days work with JAR files.</p> <p>To get things working with JAR files, try this...</p> <pre><code>private static ArrayList<Class<?>> getClassesForPackage(Package pkg) { String pkgname = pkg.getName(); ArrayList<Class<?>> classes = new ArrayList<Class<?>>(); // Get a File object for the package File directory = null; String fullPath; String relPath = pkgname.replace('.', '/'); System.out.println("ClassDiscovery: Package: " + pkgname + " becomes Path:" + relPath); URL resource = ClassLoader.getSystemClassLoader().getResource(relPath); System.out.println("ClassDiscovery: Resource = " + resource); if (resource == null) { throw new RuntimeException("No resource for " + relPath); } fullPath = resource.getFile(); System.out.println("ClassDiscovery: FullPath = " + resource); try { directory = new File(resource.toURI()); } catch (URISyntaxException e) { throw new RuntimeException(pkgname + " (" + resource + ") does not appear to be a valid URL / URI. Strange, since we got it from the system...", e); } catch (IllegalArgumentException e) { directory = null; } System.out.println("ClassDiscovery: Directory = " + directory); if (directory != null && directory.exists()) { // Get the list of the files contained in the package String[] files = directory.list(); for (int i = 0; i < files.length; i++) { // we are only interested in .class files if (files[i].endsWith(".class")) { // removes the .class extension String className = pkgname + '.' + files[i].substring(0, files[i].length() - 6); System.out.println("ClassDiscovery: className = " + className); try { classes.add(Class.forName(className)); } catch (ClassNotFoundException e) { throw new RuntimeException("ClassNotFoundException loading " + className); } } } } else { try { String jarPath = fullPath.replaceFirst("[.]jar[!].*", ".jar").replaceFirst("file:", ""); JarFile jarFile = new JarFile(jarPath); Enumeration<JarEntry> entries = jarFile.entries(); while(entries.hasMoreElements()) { JarEntry entry = entries.nextElement(); String entryName = entry.getName(); if(entryName.startsWith(relPath) && entryName.length() > (relPath.length() + "/".length())) { System.out.println("ClassDiscovery: JarEntry: " + entryName); String className = entryName.replace('/', '.').replace('\\', '.').replace(".class", ""); System.out.println("ClassDiscovery: className = " + className); try { classes.add(Class.forName(className)); } catch (ClassNotFoundException e) { throw new RuntimeException("ClassNotFoundException loading " + className); } } } } catch (IOException e) { throw new RuntimeException(pkgname + " (" + directory + ") does not appear to be a valid package", e); } } return classes; } </code></pre>

Querying!

Guidance

An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload