com.publicobject.misc.Exceptions Maven / Gradle / Ivy
/* Glazed Lists (c) 2003-2006 */
/* http://publicobject.com/glazedlists/ publicobject.com,*/
/* O'Dell Engineering Ltd.*/
package com.publicobject.misc;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
/**
* This class contains a repository of strategies for dealing with Exceptions
* which occur anywhere in the application. Clients may register Exception
* handlers to deal with these exception in any way they see fit. If no
* registered Exception handler recognizes an exception that has been raised
* it is printed to {@link System#err} but otherwise ignored.
*
* @author James Lemieux
*/
public final class Exceptions {
/**
* The interface Exception handlers must implement. It has two methods to
* containing the logic for each of its concerns: recognizing Exceptions
* it can handle and handling those Exceptions appropriately.
*/
public interface Handler {
/**
* Return true if this Handler can handle the given
* Exception; false otherwise.
*/
public boolean recognize(Exception e);
/**
* React to the given Exception in any way seen fit. This may include
* notifying the user, writing to a log, or any other valid logic.
*/
public void handle(Exception e);
}
/** The one instance of the Exceptions class that is allowed. */
private static final Exceptions singleton = new Exceptions();
/**
* Returns a handle to the single instance of the Exceptions class which is
* allowed to exist.
*/
public static Exceptions getInstance() {
return singleton;
}
/**
* A list of handlers which handle Exceptions of a global nature.
*/
private final List handlers = new ArrayList();
/**
* Add h to the collection of {@link Handler}s consulted when
* an Exception is raised from within the application.
*/
public void addHandler(Handler h) {
handlers.add(h);
}
/**
* Remove h from the collection of {@link Handler}s consulted when
* an Exception is raised from within the application.
*/
public void removeHandler(Handler h) {
handlers.remove(h);
}
/**
* Attempt to locate a {@link Handler} which
* {@link Handler#recognize recognizes} the given Exception and give it a
* chance to {@link Handler#handle handle} it. If no appropriate
* {@link Handler} can be found, the Exception is printed to
* {@link System#err}.
*/
public void handle(Exception e) {
for (Iterator i = handlers.iterator(); i.hasNext();) {
Handler handler = i.next();
if (handler.recognize(e)) {
handler.handle(e);
return;
}
}
System.err.println("Exception was not recognized by any Exception Handler: " + e);
e.printStackTrace(System.err);
}
}