We Keep Coding

Compiling a program inside of another program [to a jar file?] [duplicate]

I have the class name stored in a property file. I know that the classes store will implement IDynamicLoad. How do I instantiate the class dynamically?
Right now I have
Properties foo = new Properties();
foo.load(new FileInputStream(new File("ClassName.properties")));
String class_name = foo.getProperty("class","DefaultClass");
//IDynamicLoad newClass = Class.forName(class_name).newInstance();
Does the newInstance only load compiled .class files? How do I load a Java Class that is not compiled?

How do I load a Java Class that is not compiled?
You need to compile it first. This can be done programmatically with the javax.tools API. This only requires the JDK being installed at the local machine on top of JRE.
Here's a basic kickoff example (leaving obvious exception handling aside):
// Prepare source somehow.
String source = "package test; public class Test { static { System.out.println(\"hello\"); } public Test() { System.out.println(\"world\"); } }";
// Save source in .java file.
File root = new File("/java"); // On Windows running on C:\, this is C:\java.
File sourceFile = new File(root, "test/Test.java");
sourceFile.getParentFile().mkdirs();
Files.write(sourceFile.toPath(), source.getBytes(StandardCharsets.UTF_8));
// Compile source file.
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
compiler.run(null, null, null, sourceFile.getPath());
// Load and instantiate compiled class.
URLClassLoader classLoader = URLClassLoader.newInstance(new URL[] { root.toURI().toURL() });
Class<?> cls = Class.forName("test.Test", true, classLoader); // Should print "hello".
Object instance = cls.newInstance(); // Should print "world".
System.out.println(instance); // Should print "test.Test#hashcode".
Which yields like
hello
world
test.Test#ab853b
Further use would be more easy if those classes implements a certain interface which is already in the classpath.
SomeInterface instance = (SomeInterface) cls.newInstance();
Otherwise you need to involve the Reflection API to access and invoke the (unknown) methods/fields.
That said and unrelated to the actual problem:
properties.load(new FileInputStream(new File("ClassName.properties")));
Letting java.io.File rely on current working directory is recipe for portability trouble. Don't do that. Put that file in classpath and use ClassLoader#getResourceAsStream() with a classpath-relative path.
properties.load(Thread.currentThread().getContextClassLoader().getResourceAsStream("ClassName.properties"));

In the same vein as BalusC's answer, but a bit more automatic wrapper is here in this piece of code from my kilim distribution.
https://github.com/kilim/kilim/blob/master/src/kilim/tools/Javac.java
It takes a list of strings containing Java source, extracts the package and public class/interface names and creates the corresponding directory/file hierarchy in a tmp directory. It then runs the java compiler on it, and returns a list of name,classfile pairs (the ClassInfo structure).
Help yourself to the code. It is MIT licensed.

Your commented code is correct if you know that the class has a public no-arg constructor. You just have to cast the result, as the compiler can't know that the class will in fact implement IDynamicLoad. So:
IDynamicLoad newClass = (IDynamicLoad) Class.forName(class_name).newInstance();
Of course the class has to be compiled and on the classpath for that to work.
If you are looking to dynamically compile a class from source code, that is a whole other kettle of fish.

WILDFLY - Loading jar dynamically java.lang.ClassNotFoundException

I have an EAR deployed in wildfly and I'm loading a jar from source with this code:
File file = new File("C:\\XXXX\\XXXX\\ProcessTest.jar");
String lcStr = "com.package.test.TestProcess";
URLClassLoader cl = URLClassLoader.newInstance(new URL[]{file.toURL()});
Class<?> loadedClass;
try {
loadedClass = cl.loadClass(lcStr);
IProcess data = (IProcess)loadedClass.newInstance();
data.start();
} catch (Exception e) {
e.printStackTrace();
}
The TestProcess class implements IProcess that is loaded in another jar with the EAR.
When I run the server code and the class is being casted I receive:
java.lang.NoClassDefFoundError: com/package/test/process/IProcess
If I added the interface in the JAR that I'm loading the problem is a CastException because com/package/test/process/IProcess loaded by wildfly is different of the loaded with the JAR.
I need receive the IProcess (casting the object), because a solution is call directly the method with Mehtod.invoke but it's not solution for my problem.
Thanks in advanced.

With this tip works perfectly:
URLClassLoader.newInstance(new URL[]{file.toURL()}, IProcess.class.getClassLoader())
Thanks to Steve C!

Load jar dynamically at runtime?

My current java project is using methods and variables from another project (same package). Right now the other project's jar has to be in the classpath to work correctly. My problem here is that the name of the jar can and will change because of increasing versions, and because you cannot use wildcards in the manifest classpath, it's impossible to add it to the classpath. So currently the only option of starting my application is using the -cp argument from the command line, manually adding the other jar my project depends on.
To improve this, I wanted to load the jar dynamically and read about using the ClassLoader. I read a lot of examples for it, however I still don't understand how to use it in my case.
What I want is it to load a jar file, lets say, myDependency-2.4.1-SNAPSHOT.jar, but it should be able to just search for a jar file starting with myDependency- because as I already said the version number can change at anytime. Then I should just be able to use it's methods and variables in my Code just like I do now (like ClassInMyDependency.exampleMethod()).
Can anyone help me with this, as I've been searching the web for a few hours now and still don't get how to use the ClassLoader to do what I just explained.
Many thanks in advance

(Applies to Java version 8 and earlier).
Indeed this is occasionally necessary. This is how I do this in production. It uses reflection to circumvent the encapsulation of addURL in the system class loader.
/*
* Adds the supplied Java Archive library to java.class.path. This is benign
* if the library is already loaded.
*/
public static synchronized void loadLibrary(java.io.File jar) throws MyException
{
try {
/*We are using reflection here to circumvent encapsulation; addURL is not public*/
java.net.URLClassLoader loader = (java.net.URLClassLoader)ClassLoader.getSystemClassLoader();
java.net.URL url = jar.toURI().toURL();
/*Disallow if already loaded*/
for (java.net.URL it : java.util.Arrays.asList(loader.getURLs())){
if (it.equals(url)){
return;
}
}
java.lang.reflect.Method method = java.net.URLClassLoader.class.getDeclaredMethod("addURL", new Class[]{java.net.URL.class});
method.setAccessible(true); /*promote the method to public access*/
method.invoke(loader, new Object[]{url});
} catch (final java.lang.NoSuchMethodException |
java.lang.IllegalAccessException |
java.net.MalformedURLException |
java.lang.reflect.InvocationTargetException e){
throw new MyException(e);
}
}

I needed to load a jar file at runtime for both java 8 and java 9+. Here is the method to do it (using Spring Boot 1.5.2 if it may relate).
public static synchronized void loadLibrary(java.io.File jar) {
try {
java.net.URL url = jar.toURI().toURL();
java.lang.reflect.Method method = java.net.URLClassLoader.class.getDeclaredMethod("addURL", new Class[]{java.net.URL.class});
method.setAccessible(true); /*promote the method to public access*/
method.invoke(Thread.currentThread().getContextClassLoader(), new Object[]{url});
} catch (Exception ex) {
throw new RuntimeException("Cannot load library from jar file '" + jar.getAbsolutePath() + "'. Reason: " + ex.getMessage());
}
}

load class from another class within same jar in java web start fails

I've a javafx application which is run by web start. In my fx application, I try to load the classes using ClassLoader as in below code. The parameter passed is a package name like "com.example.project.abcd"
public final static List<Class<?>> find(final String scannedPackage)
{
final ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
final String scannedPath = scannedPackage.replace(DOT, SLASH);
final Enumeration<URL> resources;
try {
resources = classLoader.getResources(scannedPath);
} catch (IOException e) {
throw new IllegalArgumentException(String.format(BAD_PACKAGE_ERROR, scannedPath, scannedPackage), e);
}
final List<Class<?>> classes = new LinkedList<Class<?>>();
while (resources.hasMoreElements()) {
final File file = new File(resources.nextElement().getFile());
classes.addAll(find(file, scannedPackage));
}
return classes;
}
Now I'm not able to get all the classes present inside "com.example.project.abcd" package when I run it thru java web start but through IDE it is working fine.
I'm using JDK 7, JavaFX 2.
As per http://docs.oracle.com/javase/7/docs/technotes/guides/javaws/developersguide/faq.html#s211 Thread.currentThread().getContextClassLoader() should work fine but it is not!.
Tried searching on net/googling but in vain. Checked http://lopica.sourceforge.net/faq.html#customcl as well and tried using URLClassLoader as suggested. But that didn't work as well (Though did not know what should be passed to the parameter 'urls')
Any help is much apreciated.

I think this works in IDE because your BIN/classes directory is used to get all the files.
In Webstart-Mode, all your classes are inside JARs.

List all interfaces in a package in a jar file

Hello stackoverflow'ers!
I am trying to list all classes from an interface in a specific package.
I came across multiple solutions and tried the following:
Using Reflections:
AllCommands = new ArrayList<ICommand>();
Reflections reflections = new Reflections(this.getClass().getPackage().getName());
commandClasses = reflections.getSubTypesOf(ICommand.class);
for (Class<? extends ICommand> c :commandClasses){
AllCommands.add((ICommand)c.newInstance());
}
Using extcos:
AllCommands = new ArrayList<ICommand>();
ComponentScanner scanner = new ComponentScanner();
scanner.getClasses(new ComponentQuery() {
#Override
protected void query() {
select().
from(this.getClass().getPackage().getName()).
andStore(thoseImplementing(ICommand.class).into(commandClasses)).
returning(none());
}
});
for (Class<? extends ICommand> c :commandClasses){
AllCommands.add((ICommand)c.newInstance());
}
Both solutions are successfully listing all my classes when debugging in NetBeans (7.3), but when i compile the jar and execute it, the commandClasses collections seems to stay empty. I am not used to java but i guess it has to do something with the classpath, and the debugging-time taking the classes from the \target\classes folder and not from the jar.
Can someone help me out with a solution that would allow me to list classes in the .jar?
Is it possible that this.getClass().getPackage().getName() just has to change to something that points into the jar?

I figured it out myself.. Using this.getClass().getPackage().getName() as Packagename does only point at the files in the classes folder, to reference classes in the jar i needed to replace the '.' to '/'. Thank you anyway.