I have to retrieve the value of all fields in a class loaded from a jar.
So I need an instance to do that :
field.get(gameClassInstance);
for each field.
Here the code that load the class and try to create an instance :
private Loader() throws IOException, ClassNotFoundException, InstantiationException, IllegalAccessException {
File jarFile = new File(System.getProperty("user.dir")+File.separator+"games"+File.separator+gameName+".jar");
// Create the URLClassLoader
URL url = jarFile.toURI().toURL();
URL[] urls = new URL[]{url};
URLClassLoader cl = new URLClassLoader(urls);
// Search the class
JarFile jar = new JarFile(jarFile.toString());
Enumeration<JarEntry> e = jar.entries();
while (e.hasMoreElements()) {
JarEntry je = (JarEntry) e.nextElement();
if(je.isDirectory() || !je.getName().endsWith(".class")){
continue;
}
if (je.getName().contains(gameName)){
String className = je.getName().substring(0,je.getName().length()-6); // Remove ".class"
className = className.replace('/', '.');
gameClass = cl.loadClass(className);
gameClassInstance = gameClass.newInstance(); // Create an instance of the class
}
}
jar.close();
cl.close();
}
Here the loaded class :
public class Solitaire {
public Board board = new Board("Board1", "");
public Layout layout = new Layout();
public Player player = new Player();
public Solitaire() {
}
}
There is a StackOverflowError at the line where I create an instance.
I found the solution to my problem, I just make the fields static and retrieve them with field.get(null)
Related
I create Bukkit-Plugins and I want to load a class dynamicly. I wrote this code:
private static Class<?> getClassFromFile(File folder, File file) {
if (!folder.exists())
return null;
try {
URL url = folder.toURL();
URL[] urls = new URL[] { url };
ClassLoader loader = new URLClassLoader(urls);
Class<?> cls = loader.loadClass(getNameWithoutExtension(file));
return cls;
} catch (Exception e) {
return null;
}
}
But I must use the main class loader, for example ClassLoader cl;
How can I load the file "file" from the folder "folder" with this existing class loader?
Thank you for your help
I found a very simple solution :D!
For all the other peoples out there:
Change
ClassLoader loader = new URLClassloader(urls);
to
URLClassLoader loader = new URLClassLoader(urls, cl);
Works fine for me!
I have used this code to get a list of class names from a package:
private List<String> getClasses()
{
List<String> classes = new ArrayList<String>();
String packageName = "algorithm/impl";
URL directoryUrl = Thread.currentThread().getContextClassLoader().
getResource(packageName);
File directory = new File(directoryUrl.getFile());
if(directory.exists())
{
String [] files = directory.list();
for(String filename : files)
{
classes.add(filename.substring(0, filename.lastIndexOf(".")));
}
}
return classes;
}
but this does not work when the app is packaged as an executable jar file. Why?
You can make use of this class JarFile.
JarFile file = new JarFile("YourFileName.jar");
for (Enumeration<JarEntry> enum = file.entries(); enum.hasMoreElements();) {
JarEntry entry = enum.next();
System.out.println(entry.getName());
}
Or if you want to search for particular class inside your jar you can use ZipFile class.
JarFile jar = new JarFile(YourJarFile);
ZipEntry e = jar.getEntry(CLASS_FILE_TO_FIND);
if (e == null) {
e = jar.getJarEntry(CLASS_FILE_TO_FIND);
if (e != null) {
foundIn.add(f.getPath());
}
} else {
foundIn.add(f.getPath());
}
I need to read class names(just the simple name) from a jar file(OSGified). I've placed the jar file in the lib folder and it's added to class path. Here is the code I've written:
public void loadClassName() throws IOException {
JarFile jf = new JarFile("/lib/xxxx-1.0.0.jar");
List<String> list = new ArrayList<String>();
for (JarEntry entry : Collections.list(jf.entries())) {
if (entry.getName().endsWith(".class")) {
String className = entry.getName().replace("/", ".").replace(".class", "");
list.add(className);
}
}
}
Somehow, I"m getting Filenotfound exception while constructing the jarfile object. Can somebody let me know how we should give the jar path to the JarFile constructor ?
try this:
JarFile jf = new JarFile("lib/xxxx-1.0.0.jar");
Thanks to the user #Perception. His answer has worked flawlessly.
This is the working code:
final InputStream jarStream = Thread.currentThread().getContextClassLoader().getResourceAsStream("lib/xxxxx-1.0.0.jar");
JarInputStream jfs = new JarInputStream(jarStream);
List<String> list = new ArrayList<String>();
JarEntry je = null;
while (true) {
je = jfs.getNextJarEntry();
if (je == null) {
break;
}
if (je.getName().endsWith(".class")) {
String className = je.getName().replace("/", ".").replace(".class", "");
list.add(className);
}
}
This question already has answers here:
Can you find all classes in a package using reflection?
(30 answers)
Closed 9 years ago.
So I have a package that has classes that extend JPanel and I want to add them as tabs dynamically. At the beginning I used a factory and I registered all the classes in it and it worked, but now I want load all the classes in the package without knowing their names. I've tried several things including Reflections library (which I found very confusing) and I couldn't get them to work. I appreciate any help.
Here's one of my trials:
public static void registerTab() {
String pkg = TabA.class.getPackage().getName();
String relPath = pkg.replace('.', '/');
URL resource = ClassLoader.getSystemClassLoader().getResource(relPath);
if (resource == null) {
throw new RuntimeException("Unexpected problem: No resource for "
+ relPath);
}
File f = new File(resource.getPath());
String[] files = f.list();
for (int i = 0; i < files.length; i++) {
String fileName = files[i];
String className = null;
String fileNm = null;
if (fileName.endsWith(".class")) {
fileNm = fileName.substring(0, fileName.length() - 6);
className = pkg + '.' + fileNm;
}
if (className != null) {
if (!tabClasses.containsKey(className))
tabClasses.put(fileNm, className);
}
}
}
Here is a custom solution I developed to find all the classes of a package:
public class ClassFinder {
private static final char PKG_SEPARATOR = '.';
private static final char DIR_SEPARATOR = '/';
private static final String CLASS_FILE_SUFFIX = ".class";
private static final String BAD_PACKAGE_ERROR = "Unable to get resources from path '%s'. Are you sure the package '%s' exists?";
public static List<Class<?>> find(String scannedPackage) {
String scannedPath = scannedPackage.replace(PKG_SEPARATOR, DIR_SEPARATOR);
URL scannedUrl = Thread.currentThread().getContextClassLoader().getResource(scannedPath);
if (scannedUrl == null) {
throw new IllegalArgumentException(String.format(BAD_PACKAGE_ERROR, scannedPath, scannedPackage));
}
File scannedDir = new File(scannedUrl.getFile());
List<Class<?>> classes = new ArrayList<Class<?>>();
for (File file : scannedDir.listFiles()) {
classes.addAll(find(file, scannedPackage));
}
return classes;
}
private static List<Class<?>> find(File file, String scannedPackage) {
List<Class<?>> classes = new ArrayList<Class<?>>();
String resource = scannedPackage + PKG_SEPARATOR + file.getName();
if (file.isDirectory()) {
for (File child : file.listFiles()) {
classes.addAll(find(child, resource));
}
} else if (resource.endsWith(CLASS_FILE_SUFFIX)) {
int endIndex = resource.length() - CLASS_FILE_SUFFIX.length();
String className = resource.substring(0, endIndex);
try {
classes.add(Class.forName(className));
} catch (ClassNotFoundException ignore) {
}
}
return classes;
}
}
Then, just use:
List<Class<?>> classes = ClassFinder.find("com.package");
This is the common approach with working with loading class dynamically:
try {
File file = new File(JAR_FILE);
String classToLoad = "com.mycompany.MyClass";
URL jarUrl = new URL("jar", "","file:" + file.getAbsolutePath()+"!/");
URLClassLoader loader = new URLClassLoader(new URL[] {jarUrl}, Thread.currentThread().getContextClassLoader());
Class c = loader.loadClass(classToLoad);
} catch (Exception e) {
e.printStackTrace();
}
However, I need an approach where:
We don't need to create a File (as the jar I am trying to process is a byte array[] when fetched)
Or we won't need to create a temporary file from byte[] array (as AppEngine, the platform I work with does not allow to create temporary files)
You will have to create your own class loader.
Something like this, basic idea in pseudo code:
class MyClassLoader extends ClassLoader {
public Class findClass(String name) {
byte[] b = loadClassData(name);
return defineClass(name, b, 0, b.length);
}
private byte[] loadClassData(String name) {
JarInputStream jis = new JarInputStream(new ByteArrayInputStream(bytearrayJarData));
JarEntry entry = jis.getNextJarEntry();
while (entry != null) {
//compare entry to requested class
// if match, return Byte data
// else entry = jis.getNextJarEntry();
}
return null; // nothing found
}
}
Write your own ClassLoader and override findClass(). There you can use defineClass() to load your byte[].