1:53 p.m.
Roland Käser [http://community.jboss.org/people/roli82001] created the discussion
"Problems with the tomcat classloader"
To view the discussion, visit: http://community.jboss.org/message/639418#639418
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Hello
While developing a very small and lightweight j2ee linke server, I try to extend a
abstract class at runtime using:
ClassPool pool = ClassPool.getDefault();
pool.insertClassPath(new ClassClassPath(this.getClass()));
CtClass cc =
pool.makeClass("HelloWorldClientBean");
cc.setSuperclass(pool.get("ch.isn.dante.comserver.test.HelloWorldSessionBean"));
Class beanClass = cc.toClass();
cc.defrost();
Constructor constructor = beanClass.getConstructor(argsClass);
Object[] params = new Object[]{new ComServerSession(),null};
HelloWorldSessionBean sessionBean =
(HelloWorldSessionBean)constructor.newInstance(params);
System.out.println("Hello World Output: " + sessionBean.getHelloWorld());
This works fine on the client side (regular java vm).
On the server side I get first a very strange exception which was stangely related to the
tomcats classloader.
javassist.CannotCompileException: by java.lang.LinkageError: loader (instance of
org/apache/catalina/loader/WebappClassLoader): attempted duplicate class definition for
name: "ch/isn/dante/comserver/test/HelloWorldSessionBeanExecutable"
javassist.CannotCompileException: by java.lang.LinkageError: loader (instance of
org/apache/catalina/loader/WebappClassLoader): attempted duplicate class definition for
name: "ch/isn/dante/comserver/test/HelloWorldSessionBeanExecutable"
at javassist.ClassPool.toClass(ClassPool.java:1089)
at javassist.ClassPool.toClass(ClassPool.java:1032)
at javassist.ClassPool.toClass(ClassPool.java:990)
at javassist.CtClass.toClass(CtClass.java:1125)
...
Caused by: java.lang.LinkageError: loader (instance of
org/apache/catalina/loader/WebappClassLoader): attempted duplicate class definition for
name: "ch/isn/dante/comserver/test/HelloWorldSessionBeanExecutable"
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
at java.lang.ClassLoader.defineClass(ClassLoader.java:465)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at javassist.ClassPool.toClass2(ClassPool.java:1102)
at javassist.ClassPool.toClass(ClassPool.java:1083)
To prevent this I wrote a very ugly hack to use the system class loader and add the
classpath in which this superclass:
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| URL url = new File(serverServlet.getInstallDir() +
"WEB-INF/classes/").toURL(); |
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| URLClassLoader sysloader = (URLClassLoader) ClassLoader.getSystemClassLoader(); |
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| Class sysclass = URLClassLoader.class; |
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| Method method = sysclass.getDeclaredMethod("addURL", parameters); |
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| method.setAccessible(true); |
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| method.invoke(sysloader, new Object[]{url}); |
and created the class using this modified classloader:
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| Class beanClass = cc.toClass(sysloader); |
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| cc.defrost(); |
Now I get a NoSuchMethodException:
java.lang.NoSuchMethodException:
HelloWorldServerBean.<init>(ch.isn.dante.comserver.server.ComServerSession,
ch.isn.dante.comserver.server.ServerApplication)
at java.lang.Class.getConstructor0(Class.java:2706)
at java.lang.Class.getConstructor(Class.java:1657)
at
ch.isn.dante.comserver.server.ComServerSession.loadClass(ComServerSession.java:239)
at ch.isn.dante.comserver.server.ComServer.doGet(ComServer.java:286)
at ch.isn.dante.comserver.server.ComServer.doPost(ComServer.java:417)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
I can't see from which this error comes. When I inspect the newly created class I get
one constructor:
public
HelloWorldClientBean(ch.isn.dante.comserver.server.ComServerSession,ch.isn.dante.comserver.server.ServerApplication)
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