well there you go, that wont work,
http://tomcat.apache.org/tomcat-5.5-doc/class-loader-howto.html
take a look at the hierarchy of the tomcat class loaders, and a class
can only load up in the tree, not down.
so mvpservlet is unable to load your web-inf/classes directory
from your description, you got it backwards.
the singleton classes should be in common/lib or common/classes, or if
you want it clean, shared/lib or shared/classes
then the class loading the singleton, would be in WEB-INF/lib or
WEB-INF/classes,
not the other way around
Filip
Mike Peremsky wrote:
The class that is trying to load the singleton (SingletonLoader) is in a common
JAR located at /common/lib/mvpservlet.jar
The Singletons that I am trying to load can be from ANY app and are in the WEB-INF/classes folder of whichever application is trying to use the SingletonLoader.
Filip Hanik - Dev Lists <[EMAIL PROTECTED]> wrote:
that work around is probably not what you want. You've just disabled the
ability to reload your app correctly.
Try using another classloader, maybe the
Thread.currentThread().getContextClassLoader()
where are you storing the class that is trying to load the singleton? it
should be in your webapp as well.
Filip
Mike Peremsky wrote:
I have resolved this issue, but am wondering if the way I did it is the
"correct" way to resolve this issue.
I modified the catalina.properties file entry common.loader by adding the path
to the applications WEB-INF/classes directory, this seems to have resolved the
issue with finding the class.
common.loader=${catalina.home}/common/classes,,${catalina.home}/webapps/myExternalApp/WEB-INF/classes
I also had to fix a bug in the retrieval of the method (I read the API docs
incorrectly)
private static final Object OBJECT_ARG_LIST[] = new Object[0];
private static final Class CLASS_ARG_LIST[] = new Class[0];
Method method = singletonClassObj.getMethod(GET_INSTANCE_METHOD,
CLASS_ARG_LIST);
method.invoke(null, OBJECT_ARG_LIST);
Mike Peremsky wrote:
I tried the modification you suggested (with the correct method name on the
end) but still with the same results. I also printed out a debug message just
to see what class loader was being used (not that I know what to do with it :-P
)
log.debug("this class loader: " +
this.getClass().getClassLoader().getClass().getName());
Class singletongClassObj =
this.getClass().getClassLoader().loadClass(singletonClassName);
The class loader for the SingletonLoader is:
org.apache.catalina.loader.StandardClassLoader.
The classes that it is looking for are located in the
/apache-tomcat-5.5.23/webapps/myExternalApp/WEB-INF/classes directory.
Filip Hanik - Dev Lists wrote:
did you try
Class singletongClassObj = this.getClass().getClassLoader().loadName(singletonClassName);
Filip
Mike Peremsky wrote:
I think this may be a class loader issue, but am not sure as I have never really worked with them before. I am putting together a JAR file that contains a set of classes to be used throughout a suite of applications. I have a class called SingletonLoader that was working when it was within the main application, but when I broke out the reusable classes into a separate jar file and modified the contextInitialized() method to dynamically load the classes it is failing to fid the classes. The contextInitialized() method is properly reading the class names from the property file (e.g. SINGLETON_LOADER_CLASSES=com.externalApp.singleton.Countries,com.externalApp.singleton.SecurityQuestions) and looping through them, but I always get the following error message when the line
Class singletongClassObj = Class.forName(singletonClassName);
is executed:
Unable to load singleton: com.externalApp.singleton.Countries
java.lang.ClassNotFoundException: com.externalApp.singleton.Countries
ALL of the singleton classes to be loaded implement the Singleton interface (which has
nothing in it, it is just used to denote a class that MUST specify a "public static
anyReturnVal getInstance()" method.
public class SingletonLoader implements ServletContextListener, SystemConsts {
/**
* Logger for this class
*/
private static final Logger log = Logger.getLogger(SingletonLoader.class);
private static final String SINGLETON_LOADER_CLASSES
= "SINGLETON_LOADER_CLASSES";
private static final String DELIMITER = ",";
// This is the method defined
private static final String GET_INSTANCE_METHOD = "getInstance";
private static final Object ARG_LIST[] = new Object[0];
/**
* Constructs a new SingletonLoader object.
*/
public SingletonLoader() {
}
/**
* Notification that the web application is ready to process requests.
*
* Initializes all of the singletons so they are ready for immediate use
* after the containet server starts.
*
* @param sce This is the event object for notifications about changes to the
* servlet context of a web application.
*
*/
public void contextInitialized(ServletContextEvent sce) {
log.debug("contextInitialized: BEGIN");
String singletons = ExtProperties.getProperty(SYS_PROPS,
SINGLETON_LOADER_CLASSES);
if (!StringUtils.isNullOrZeroLen(singletons)) {
DelimitedString ds = new DelimitedString(singletons, DELIMITER);
int max = ds.size();
String singletonClassName = null;
for (int ndx=0; ndx < max; ndx++) {
try {
singletonClassName = ds.getEntry(ndx);
log.debug("Get singletonClassName: " + singletonClassName);
// Get the singleton class to load
Class singletongClassObj = Class.forName(singletonClassName);
log.debug("singletongClassObj: " + singletongClassObj);
Method method = singletongClassObj.getMethod(GET_INSTANCE_METHOD,
singletongClassObj);
method.invoke(null, ARG_LIST);
} catch (Exception e) {
log.error("Unable to load singleton: " + singletonClassName, e);
}
}
}
log.debug("contextInitialized: END");
}
/**
* Notification that the servlet context is about to be shut down.
*
* @param sce the ServletContextEvent
*/
public void contextDestroyed(ServletContextEvent sce) {
}
}
Example of the Countries singleton
public class Countries implements DbConsts, Singleton {
private static Logger log = Logger.getLogger(Countries.class);
/** Creates a new instance of Countries */
private Countries() {
refreshData();
}
/**
* Returns the single instance of this class.
*
* @return the instance of this class.
*/
public static Countries getInstance() {
if (instance == null) {
synchronized (Countries.class) {
if (instance == null) {
instance = new Countries();
}
}
}
return instance;
}
}
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