loading a modified class directly from a ClassFile

[johncoleman]

I got this to work, just that the classes subclasses now throw java.lang.AbstractMethodError exceptions!

// get the class file as a resource
InputStream is = getClass().getResourceAsStream(resourceName);
DataInputStream dis = new DataInputStream(is);
// create a class file object from the class file
ClassFile cf = new ClassFile(dis);
// modify the class
cf.addInterface(interfaceName);
// create an output stream for the new class
ByteArrayOutputStream baos = new ByteArrayOutputStream();
DataOutputStream dos = new DataOutputStream(baos);
// write the new class into a byte array using the data output stream
cf.write(dos);
// close resources
dos.close();
baos.close();
dis.close();
// get the modified class and pass to this classes class loader
is = new ByteArrayInputStream(baos.toByteArray());
// make a class anonymously
CtClass ptc = pool.makeClass(is);
is.close();
// force the class loader to load the modified class
ptc.toClass(getClass().getClassLoader());

At least the class loader gets your new version of the class.

[chiba]

I think it would be better to use ClassPool, CtClass, etc.
Your problem is that you added an interface but did not
change your class to be an abstract class (your class does
not implement all methods from the interface.)

[johncoleman]

"chiba" wrote:
I think it would be better to use ClassPool, CtClass, etc.
Your problem is that you added an interface but did not
change your class to be an abstract class (your class does
not implement all methods from the interface.)

You are correct. I tried using ClassPool before but kept getting duplicate class exceptions. I have tried again and have everything working perfectly. This is my code to implement an interface and create getters and setters to inherit from a superclass if required....

CtClass ptc = pool.get(className);
CtClass pti = pool.get(interfaceName);
CtMethod[] ptims = pti.getDeclaredMethods();
if (!pti.isInterface()) {
log.fatal("The class " + interfaceName
+ " is not an interface.");
return;
}
for (int m = 0; m < ptims.length; m++) {
// see if class defines the method when method is get or set
if (ptims[m].getMethodInfo().isMethod()
&& (ptims[m].getName().startsWith("get") || ptims[m]
.getName().startsWith("set"))) {
try {
// see if method already declared in class
CtMethod ptcm = ptc.getDeclaredMethod(ptims[m]
.getName(), ptims[m].getParameterTypes());
} catch (NotFoundException ex1) {
// the method is not declared and needs to be added
// if not in superclass then a problem!
boolean inSuper;
try {
CtMethod ptcm = ptc.getMethod(ptims[m].getName(),
ptims[m].getSignature());
inSuper = true;
} catch (NotFoundException ex2) {
inSuper = false;
}
// quit if method unavailable from superclass
if (!inSuper) {
log.fatal("Method " + ptims[m].getName()
+ " not available in " + className
+ " class.");
return;
}
// class does not define method so add it
if (ptims[m].getName().startsWith("get")) {
String body = "public "
+ ptims[m].getReturnType().getName() + " "
+ ptims[m].getName() + "() { return super."
+ ptims[m].getName() + "(); }";
log.debug("add " + body + " to class " + className);
CtMethod nm = CtNewMethod.make(body, ptc);
ptc.addMethod(nm);

}
if (ptims[m].getName().startsWith("set")) {
String type = ptims[m].getParameterTypes()[0]
.getName();
String body = "public void " + ptims[m].getName()
+ "(" + type + " x" + ") { super."
+ ptims[m].getName() + "(x); }";
log.debug("add " + body + " to class " + className);
CtMethod nm = CtNewMethod.make(body, ptc);
ptc.addMethod(nm);
}
}
}
}
ptc.addInterface(pti);
// force the class loader to load the modified class
ptc.toClass(getClass().getClassLoader());