Develop Reference

ObjectInputStream#readObject raises ClassNotFoundException with External Jar classes

So I have a Spring Boot application that loads external jars from the paths below:
java -cp "main-0.0.1-SNAPSHOT.jar" -Dloader.path="%USERPROFILE%\Addons\" -Dloader.main=moe.ofs.backend.BackendApplication org.springframework.boot.loader.PropertiesLauncher
The main jar doesn't know external jars at compile time. External jars are loaded like "plugins" or "addons" by specifying
-Dloader.path=...
All of external jars depend on an interface from "main-0.0.1-SNAPSHOT.jar", and they are supposed to do object serializations more or less.
The interface is called Configurable, and it provides two default methods like these:
default <T extends Serializable> void writeFile(T object, String fileName) throws IOException {
Path configFilePath = configPath.resolve(fileName + ".data");
FileOutputStream fileOutputStream = new FileOutputStream(configFilePath.toFile());
ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
objectOutputStream.writeObject(object);
objectOutputStream.close();
}
default <T extends Serializable> T readFile(String fileName) throws IOException, ClassNotFoundException {
Path configFilePath = configPath.resolve(fileName + ".data");
FileInputStream fileInputStream = new FileInputStream(configFilePath.toFile());
ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
return (T) objectInputStream.readObject();
}
Classes in external jars implement this interface, and they call readFile() and writeFile().
writeFile() works perfectly fine and doesn't seem to cause any problem; readFile(), however, throws a ClassNotFoundException, and that's what I'm trying to figure out.
java.lang.ClassNotFoundException: moe.ofs.addon.navdata.domain.Navaid
at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at java.io.ObjectInputStream.resolveClass(ObjectInputStream.java:719)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1922)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1805)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2096)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1624)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:464)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:422)
at java.util.ArrayList.readObject(ArrayList.java:797)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1170)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2232)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2123)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1624)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:464)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:422)
at moe.ofs.backend.Configurable.lambda$readFile$0(Configurable.java:186)
at java.lang.Thread.run(Thread.java:748)
After some testing it seems to me that ClassNotFoundException is thrown by Class.forName() because the default ClassLoader has a hard time looking for moe.ofs.addon.navdata.domain.Navaid, which is the class I'm trying to deserialize.
Navaid implements Serializable, and it also has a static final long serialVersionUID.
I had hoped that I could solve this by setting a context class loader for current thread, so that ObjectInputStream will use Spring Boot class loader to resolve Navaid class:
Thread.currentThread().setContextClassLoader(getClass().getClassLoader());
This, when printed out, gives something like
Thread.currentThread().getContextClassLoader() = org.springframework.boot.loader.LaunchedURLClassLoader#7a0b4753
Except that ObjectInputStream#readObject still throws ClassNotFoundException.
If I explicitly make a call to load Navaid class from Spring Boot loader such as:
getClass().getClassLoader().loadClass("moe.ofs.addon.navdata.domain.Navaid");
It returns a Navaid instance without any issue.
And as expected, when directly calling
Class.forName("moe.ofs.addon.navdata.domain.Navaid")
a ClassNotFoundException is thrown, even if the thread context loader has been explicitly set to LaunchedURLClassLoader; ObjectInputStream#readObject always tries to resolve the class by making a call to system default classloader to load the class.
Then I tried to load an ObjectInputStream using LaunchedURLClassLoader, but the instance still used Class.forName() from system default class loader.
ClassLoader cl = getClass().getClassLoader();
Thread.currentThread().setContextClassLoader(cl);
System.out.println("Thread.currentThread().getContextClassLoader() = " + Thread.currentThread().getContextClassLoader());
Class<?> tClass = getClass().getClassLoader().loadClass("java.io.ObjectInputStream");
System.out.println("tClass = " + tClass);
Path configFilePath = configPath.resolve(fileName + ".data");
FileInputStream fileInputStream = new FileInputStream(configFilePath.toFile());
Constructor<?> constructor = tClass.getConstructor(InputStream.class);
ObjectInputStream objectInputStream = (ObjectInputStream) constructor.newInstance(fileInputStream);
objectInputStream.readObject(); // throws ClassNotFoundException
Any input is appreciated. Thanks in advance.

As far as i know, you should override the method resolveClass on ObjectInputStream
Something like that:
default <T extends Serializable> T readFile(String fileName, ClassLoader loader) throws IOException, ClassNotFoundException {
Path configFilePath = configPath.resolve(fileName + ".data");
FileInputStream fileInputStream = new FileInputStream(configFilePath.toFile());
ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream){
protected Class<?> resolveClass(ObjectStreamClass desc)
throws IOException, ClassNotFoundException {
try {
return Class.forName(desc.getName(), false, loader);
} catch(ClassNotFoundException cnfe) {
return super.resolveClass(desc);
}
}
};
return (T) objectInputStream.readObject();
}
Never tried it myself, but it is worth a shot.
There is also http://commons.apache.org/proper/commons-io/javadocs/api-2.4/org/apache/commons/io/input/ClassLoaderObjectInputStream.html if you aready have commons-io in your project.
https://github.com/apache/commons-io/blob/master/src/main/java/org/apache/commons/io/input/ClassLoaderObjectInputStream.java

Launch JavaFX project using reflection

I have a program, that downloads a Git repository, builds it and launches defined Main class. It works properly with ordinary projects, but when I want to launch a JavaFX project, I get strange errors like:
Exception in thread "main" java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at Main.main(Main.java:31)
Caused by: java.lang.RuntimeException: java.lang.ClassNotFoundException: app.UI_Main
at javafx.application.Application.launch(Application.java:260)
at app.UI_Main.main(UI_Main.java:31)
... 5 more
Caused by: java.lang.ClassNotFoundException: app.UI_Main
at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at javafx.application.Application.launch(Application.java:248)
... 6 more
My Main class is:
public class Main {
private static final String GIT_ADDRESS = "https://github.com/lerryv/CheckCheckerDesktop";
private static final String MAIN_PATH = "app/";
private static final String MAIN_CLASS = "app.UI_Main";
public static void main(String[] args) throws GitAPIException, IOException, ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
Git.cloneRepository().setURI(GIT_ADDRESS).setDirectory(Paths.get("./dir/").toFile()).call();
Collection<String> result = compile(Paths.get("./dir/src/").toFile());
String command = System.getProperty("java.home") + "/../bin/javac -d dirOut -cp \".:json-simple-1.1.jar\" " + result.join(" ");
Runtime.getRuntime().exec(command);
URLClassLoader urlClassLoader = URLClassLoader.newInstance(
new URL[]{
new File("dirOut/").toURI().toURL()
}
);
Class clazz = urlClassLoader.loadClass(MAIN_CLASS);
Method main = clazz.getDeclaredMethod("main", String[].class);
assert Modifier.isStatic(main.getModifiers());
main.invoke(null, (Object) args);
}
private static Collection<String> compile(File directory) {
assert directory.isDirectory();
Collection<String> result = new Collection<>();
boolean hasFiles = false;
for (File file: directory.listFiles()) {
if (file.isDirectory()) {
result.addAll(compile(file));
} else {
if (!hasFiles) {
String path = file.getAbsolutePath();
String extension = path.substring(path.lastIndexOf(".") + 1);
if (extension.equals("java")) hasFiles = true;
}
}
}
if (hasFiles) result.add(directory.getAbsolutePath() + "/*.java");
return result;
};
}
At first I thought it cannot find the class, but when I removed the method.invoke statement, errors disappeared. Why does it happen and are there any workarounds?

Runtime.getRuntime().exec(command)
This is starting another process, so after this line is executed compilation is not yet finished, you need to wait for this process to end, and probably you should also handle output/error stream of process to check if it succeed or not.
Process compileProc = Runtime.getRuntime().exec(command);
compileProc.waitFor();
Also I don't know what are you trying to do, but remember that not everyone might have compiler available and configured java.hame property, or configured it to different java version. (like older one and your code will not compile or newer one and you code will not run)

The program opens a new thread to start the project, but it executes the next line without monitoring its completion, so the thread can be removed if it is not necessary. If necessary, you need to write a monitoring thread to monitor and schedule all threads so that it can continue to execute after it has finished its work. Tasks of the main thread.

Class defined in another plugin cannot be found by the main plugin - Eclipse Product

I exported my plugin project as a Product and when I run the product (eclipse application), the main plugin (org.example.framework.core) cannot find a class defined in another plugin (org.example.abc) which implements an extension to an extension point provided by the main plugin. The class is one of the elements defined in the extension. However, when I run the project in Eclipse, everything runs fine!
Here is the log (atvste.ppt.ptfwDescription.abc.decoderInfo is a package in org.example.abc plugin):
0 [Worker-2] ERROR org.example.framework.core.ptfw.codec.decode.MsgDecoderInfo org.example.framework.core.ptfw.codec.decode.MsgDecoderInfo.createInstance(MsgDecoderInfo.java:114) : can not create class for :atvste.ppt.ptfwDescription.abc.decoderInfo.MsgDecoderInfoABC atvste.ppt.ptfwDescription.abc.decoderInfo.MsgDecoderInfoABC cannot be found by org.example.framework.core_1.0.0.201404111439
java.lang.ClassNotFoundException: atvste.ppt.ptfwDescription.abc.decoderInfo.MsgDecoderInfoABC cannot be found by org.example.framework.core_1.0.0.201404111439
at org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:501)
at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:421)
at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:412)
at org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader.loadClass(DefaultClassLoader.java:107)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at org.example.framework.core.ptfw.codec.decode.MsgDecoderInfo.createInstance(MsgDecoderInfo.java:104)
at org.example.framework.core.ptfw.codec.decode.DecoderInfo.<init>(DecoderInfo.java:56)
at org.example.framework.core.ptfw.codec.decode.DecoderInfo.createInstance(DecoderInfo.java:125)
at org.example.framework.core.ptfw.codec.ptfwObjectsFactory.decoderInfoItf_createInstance(ptfwObjectsFactory.java:200)
at org.example.framework.persistence.jaxb.ptfwDescriptionPersistenceJaxb.createptfwDescription(ptfwDescriptionPersistenceJaxb.java:326)
at org.example.framework.persistence.jaxb.ptfwDescriptionPersistenceJaxb.fillptfwDescription(ptfwDescriptionPersistenceJaxb.java:247)
at org.example.framework.persistence.jaxb.ptfwDescriptionPersistenceJaxb.createInstance(ptfwDescriptionPersistenceJaxb.java:232)
at org.example.framework.persistence.jaxb.ptfwDescriptionPersistenceJaxb.open(ptfwDescriptionPersistenceJaxb.java:146)
at org.example.framework.core.ptfw.codec.ptfwDescription.createInstance(ptfwDescription.java:152)
at org.example.framework.core.ptfw.codec.command.CmdLoadptfwDescription.loadptfwDescription(CmdLoadptfwDescription.java:50)
at org.example.framework.core.ptfw.codec.command.CmdLoadptfwDescription.execute(CmdLoadptfwDescription.java:40)
at org.example.framework.core.runtime.JobService$2.run(JobService.java:93)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)
EDIT: Function for creating instance of the class not found
public static IMessageDecoderInfo createInstance(XmlgMsgDecoderInfo pMsgDecoderInfoType,
IMessageDecoderInfo msgDecoder)
{
String className = pMsgDecoderInfoType.getClassName();
if(className!=null)
{
try
{
Class<?> formalArgs[] = new Class[1];
formalArgs[0] = XmlgMsgDecoderInfo.class;
Class<?> clazz;
if (msgDecoder != null)
{
clazz = msgDecoder.getClass();
}
else
{
clazz = Class.forName( className );
}
Constructor<?> constructor = clazz.getConstructor(formalArgs);
java.lang.Object actualArgs[] =
{ pMsgDecoderInfoType };
return (IMessageDecoderInfo)constructor.newInstance(actualArgs);
}catch(Exception e) {
String error = "can not create class for :" +className+ " " + e.getMessage();
if (LOGGER.isEnabledFor(Level.ERROR)) {
LOGGER.error(error, e);
}
throw new CreatePtfwElementRuntimeException(error, e);
}
}
return new MsgDecoderInfo(pMsgDecoderInfoType);
}`

Because of the complex class loader system used by Eclipse you cannot use Class.forName to load a class in another plugin.
If your code is processing an extension point definition you will have the IConfigurationElement for the configuration element that specifies the class name. You can use
IConfigurationElement configElement = ....;
Object classInstance = configElement.createExecutableExtension("class attribute name");
where 'class attribute name' is the name of the attribute in the extension point element that specifies the class to load. The class being created must have a no argument constructor.
Alternatively you can load a class using:
Bundle bundle = Platform.getBundle("plugin id");
Class<?> theClass = bundle.loadClass("class name");
... construct as usual ...
If you have the IConfigurationElement you can get the plugin id using
String pluginId = configElement.getContributor().getName();

Java make class available from JAR

I am making a program that operates as multiple JAR file dependencies. Basically, the thing loops through the .class files in a JAR file and gets a Class object for each of them. Each JAR has a Plugin.class file that I don't want to be available, but I want all the Classes to be accessible by other JAR dependencies as well as the main program. For example, in one JAR I have the class something.somethingelse.SomeClass, and from a second one (I made sure it is loaded second) I want to be able to import (at execution because it's in a separate JARfile) something.somethingelse.SomeClass and use it. I Have tried this after loading it into a Class object but it gives me ClassNotFound errors. I am using the newest java update and the newest version of eclipse IDE. I have three projects, "main", "aaa", and "aab". I have aaa and aab exported to JARs of which the contents are loaded into Class objects by main. aaa is loaded before aab, and I want aab to be able to access the classes from aaa through import aaa.Class. How can I (from main) make the classes of both jarfiles available to each other?
Here is my load plugin function:
public static void load(File file) throws Exception
{
JarFile jarFile = new JarFile(file);
Enumeration e = jarFile.entries();
URL[] urls = new URL[] { file.toURI().toURL() };
ClassLoader cl = new URLClassLoader(urls);
while (e.hasMoreElements()) {
JarEntry je = (JarEntry) e.nextElement();
if(je.isDirectory() || !je.getName().endsWith(".class") || je.getName() == "Plugin.class"){
continue;
}
// -6 because of .class
String className = je.getName().substring(0,je.getName().length()-6);
className = className.replace('/', '.');
Class c = cl.loadClass(className);
}
ClassLoader loader = new URLClassLoader(urls);
Class c = loader.loadClass("Plugin");
Object cobj = c.newInstance();
Method[] allMethods = c.getDeclaredMethods();
Method method = null;
boolean found = false;
for (Method m : allMethods) {
String mname = m.getName();
if (mname == "startPlugin"){
method = m;
found = true;
}
}
if(found)
{
method.invoke(cobj);
}
else
{
//skip class
}
}
And then my first JAR (aaa.jar) declares a class called hlfl.ui.UserInterface.
My second JAR's Plugin class is as follows:
import hlfl.ui.*;
public class Plugin {
//THIS DEPENDENCY EXPORTS TO: aab.jar
public void startPlugin()
{
System.out.println("Plugin Loading Interface Loaded [AAB]");
UserInterface c = new UserInterface();
}
}
But when I run it it gives me the following:
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun. reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at sf.htmlguy.hlaunch.PluginLoader.load(PluginLoader.java:58)
at sf.htmlguy.hlaunch.PluginLoader.loadAll(PluginLoader.java:22)
at sf.htmlguy.hlaunch.HLaunch.main(HLaunch.java:14)
Caused by: java.lang.NoClassDefFoundError: hlfl/ui/UserInterface
at Plugin.startPlugin(Plugin.java:7)
... 7 more
Caused by: java.lang.ClassNotFoundException: hlfl.ui.UserInterface
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 8 more
Just in case, the code is on SourceForge (the three projects are in subdirectories, "hlaunch for linux" is the main one.):
https://sourceforge.net/p/hlaunch/code

As far as I can tell your load method is creating a URLClassLoader containing just one JAR file. So you're going to end up with a classloader structure like this
main
/ \
/ \
UCL with aaa.jar UCL with aab.jar
thus classes in aaa and in aab can both see classes in main, but aaa and aab cannot see each other. If you want each plugin to be able to see the classes of those plugins that were loaded before it, then you need to arrange things so that each plugin you load uses the classloader of the previous plugin as its parent
main
|
UCL with aaa.jar
|
UCL with aab.jar
To do this you'd have to cache the loader you create when you load one plugin, and then pass that as a parameter when you create the next plugin's classloader.
private static ClassLoader lastPluginClassLoader = null;
public static void load(File file) throws Exception {
//...
ClassLoader loader = null;
if(lastPluginClassLoader == null) {
loader = new URLClassLoader(urls);
} else {
loader = new URLClassLoader(urls, lastPluginClassLoader);
}
lastPluginClassLoader = loader;
// ...
}
But all this (a) is not thread safe unless synchronized and (b) makes the behaviour critically dependent on the order in which the plugins are loaded. To do things properly you'd need some way to declare which plugins depend on which other plugins, and set up the classloader tree appropriately, etc. etc.
... and if you go too far down that road you've just re-invented OSGi.

ClassNotFoundException loading runtime compiled subclass

I am using JavaCompiler to compile CustomProcessor.java from within a web application at runtime
package com.notmycompany;
import com.mycompany.Processor;
import com.mycompany.Event;
public class CustomProcessor extends Processor {
#Override
public void process( Event evt) {
// Do you own stuff
System.out.println( "My Own Stuff");
}
}
Compilation goes well, I end up with a class file that I am trying to load using URLClassLoader
URL[] urls = new URL[]{ new URL("file://d:/temp/") };
URLClassLoader ucl = new URLClassLoader(urls);
Class clazz = ucl.loadClass("com.notmycompany.CustomProcessor");
The problem is I am hitting a ClassNotFoundException on Processor which I am using elsewhere in the application (as in I known it's there).
What do I need to do so com.mycompany.Processor is visible at runtime?
Caused by: java.lang.ClassNotFoundException: com.mycompany.Processor
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 30 more
Thanks.

It is a matter of using a URLClassLoader fed with a complete classpath
As per this question I used
URLClassLoader ucl2 = new URLClassLoader( new URL[] { new URL( "file://d:/temp/")}, urlClassLoader);
Class<?> clazz = ucl2.loadClass("com.notmycompany.CustomProcessor");