Try with resource Context Classloaders
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various reasons I seem to end up writing a lot of code that fiddles
with the context class loader in order to get non-module code running in
the OSGi environment that JDeveloper runs in. This leads to a whole
bunch of code that looks like this:
public void doSomething() {
ClassLoader context = Thread.currentThread().getContextClassLoader();
try {
Thread.currentThread().setContextClassLoader(Example.class.getClassLoader());
// Class class that required the context class loader
Endpoint.publish(null, null);
}
finally {
Thread.currentThread().setContextClassLoader(context);
}
}
Now
it occurred to me that the try/with/resources feature in JDK 7 isn't
just for the nasty things in life, well resources, you can use it for
any operation that might previously used a try/finally for.
public void doSomething() {
try (CloseableContext c = contextClassLoader(Example.class)) {
// Class class that required the context class loader
Endpoint.publish(null, null);
}
}
It would have been nice to just call the method an not to allocate any
variables as in the following example but it isn't allowable in the spec.
public void doSomething() {
try (contextClassLoader(Example.class)) { // Compilation errors
// Class class that required the context class loader
Endpoint.publish(null, null);
}
}
Still
the implementation of this is rather trivial and does still tidy up the
original code. The only wrinkle is the need to have a public class/
interface subtype of AutoCloseable so that we can narrow the throws
clause on the close() operation. If you don't do this then the original
code has to deal with "throws Exception".
public static CloseableContext contextClassLoader(Class loader) {
return contextClassLoader(loader.getClassLoader());
}
public static CloseableContext contextClassLoader(ClassLoader loader) {
final Thread currentThread = Thread.currentThread();
final ClassLoader ocl = currentThread.getContextClassLoader();
currentThread.setContextClassLoader(loader);
return new CloseableContext(currentThread, ocl);
}
public static class CloseableContext implements AutoCloseable {
private Thread _currentThread;
private ClassLoader _ocl;
private CloseableContext(Thread currentThread, ClassLoader ocl) {
this._currentThread = currentThread;
this._ocl = ocl;
}
@Override
public void close() {
this._currentThread.setContextClassLoader(this._ocl);
}
}
Java Development Kit
Java (programming language)
Loader (equipment)
Interface (computing)
JDeveloper
Implementation
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