Using ‘tasks’ in Eclipse

Update, 11/13/2009:  If you are looking for help with tasks using Mylyn (integrated into later versions of eclipse), you don’t want this post.  Instead, you’ll want to read and watch the resources here.  This post is all about simple text based code markers, not Mylyn’s implementation.

In Eclipse (version 3.2–one revision behind the current latest), I use a feature called ‘Tasks’. Using this feature, I can, anywhere in a file managed by Eclipse, put in a tag like ‘XXX’ and write a note to myself. It’s very handy because when I’m developing, I’ll often think of a problem or situation that I’d like my code to handle, but not have time to deal with it just then. I could add it to a bug tracker, or an excel spreadsheet, or write it down, but I find adding it to the source code works just as well. Then, I can use the ‘Tasks’ view in Eclipse to gather all of these notes at a later time, and deal with them one by one. I add it using this type of comment (for java–if I add the task in an XML file, I use XML comments):

//XXX need to revisit this class.

The way you include the tasks view in the java perspective is: go to the java perspective, then choose ‘Window’ from the menubar, then ‘Show View’ then ‘Tasks’. According to the help, Tasks are usually only shown in the ‘Resources’ perspective.

My one gripe with tasks is that it seems to be easy to create them, but darn hard to delete them. You can add new task tags via this path: ‘Window’ / ‘Preferences’ / ‘Web and XML’ / ‘Task Tags’, and use the ‘clean and redetect task tags’ button. This does appear to pick up new tasks (or tasks marked with tags that you’ve added), but doesn’t seem to remove tasks that are no longer marked in the source code (whether they are no longer marked because you removed them from the source code, or because you removed that task [TODO] tag from the list of task tag).

If you add a task via the mouse, you can remove it by right clicking on the checkbox. However, that doesn’t remove the task comment from the source file. Also, if you add a task via a comment, you cannot mark it done in the ‘Task’ view.

What I’d like is some synchronicity between the source file and the view. If I add a task in the source file, it should show up in the ‘Task’ view. If I then delete that line from the source file, I’d like the view to reflect that. If I mark it as completed in the view, then choose ‘Delete Completed tasks’ from the context menu, the line in the source file should be removed as well.

Am I missing something here? Am I using tasks incorrectly?

I looked through the Eclipse help, on google, and in the Eclipse newsgroups but did not find anything that helped. No mention of this issue in the release notes for version 3.3. Browsing around the buglist didn’t turn up anything that applied to what I want to do (via a quick scan).

I’ll probably file a bug sometime soon, but should really review all the entered bugs to see if someone else has my issue. In the meantime, I’ll just bleat a bit here.

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The ant jar task and duplicate files can cause bizarre behavior and missing/incorrect files when unzipping

I just ran into some bizarre behavior. I’m building a web application on Windows XPSP2, using Ant 1.6.1. The application worked fine. Then, I added one more copy instruction, to move a GWT component I’d just added to the appropriate place in the war file. Suddenly, the application ceased to work.

After a few hours of tracking down the issue, I found that it didn’t matter whether it was the new GWT component or an old one; it didn’t matter whether the copy went to the same directory or a new one–simply adding the new set of files caused the issue. Then I noticed that the unzipped version of the application differed. In particular, the configuration files differed. That explained why the application wasn’t working–it wasn’t configured correctly.

But, why were the configuration files different?

I examined the generated jar file. When I unjarred it, the configuration files were correct. I was using the jar command, whereas the ant script was using unzip. I made sure the jar file was copied correctly. I made sure the old directory was deleted, and that the ant unzip task would overwrite existing files. Still, no fix–I was seeing the incorrect configuration files.

Then, this part of the jar task documentation jumped out at me:

Please note that the zip format allows multiple files of the same fully-qualified name to exist within a single archive. This has been documented as causing various problems for unsuspecting users. If you wish to avoid this behavior you must set the duplicate attribute to a value other than its default, “add”.

The other possible values for the duplicate attribute to the jar task listed are “fail” and “preserve”. It doesn’t explain what the other options actually do; “fail” causes the jar task to fail when duplicate files are encountered. This seems to be sane default behavior, and I’m not sure why it’s not the case. “preserve” seems to preserve the first file added, and doesn’t add duplicates, but doesn’t tell you that duplicates exist.

Update, 2:09:   “preserve” does tell you that duplicates exist, in this form: WEB-INF/web.xml already added, skipping

I had, for a variety of reasons, a jar task that was adding two sets of the configuration files, with the same names and paths, to the war file. Something about adding a few extra files seemed to flip a switch, and change existing behavior. Whereas before, the unzip task picked the correct configuration file, now the unzip task picked the incorrect file. I don’t know more than that, because I didn’t dig down into the source.

The answer is to move the correct files to the top of the jar task, and change the “duplicate” attribute to be “preserve”.

I hope this post saves someone a few hours of banging their head.

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InvocationException using GWT RPC and custom objects

If you are using GWT 1.4 and sending custom objects over the wire, and see an exception like this in your log files:


2007-11-09 11:06:13 Exception while dispatching incoming RPC call
com.google.gwt.user.client.rpc.SerializationException: Type 'com.foo.common.data.User' was not assignable to 'com.google.gwt.user.client.rpc.IsSerializable'
and did not have a custom field serializer.  For security purposes, this type will not be serialized.
at com.google.gwt.user.server.rpc.impl.LegacySerializationPolicy.validateSerialize(LegacySerializationPolicy.java:136)
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:331)
at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamWriter.writeObject(AbstractSerializationStreamWriter.java:81)
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeValue(ServerSerializationStreamWriter.java:259)
at com.google.gwt.user.server.rpc.RPC.encodeResponse(RPC.java:574)
at com.google.gwt.user.server.rpc.RPC.encodeResponseForSuccess(RPC.java:442)
at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:530)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:265)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.doPost(RemoteServiceServlet.java:187)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:760)

You may be very interested in this release note from the 1.4.59 release:

RPC now generates a serialization policy file during compilation. The serialization policy file contains a whitelist of allowed types which may be serialized. Its name is a strong hash name followed by .gwt.rpc. This file must be deployed to your web server as a public resource, accessible from a RemoteServiceServlet via ServletContext.getResource(). If it is not deployed properly, RPC will run in 1.3.3 compatibility mode and refuse to serialize types implementing Serializable. Updated 3/6/2011 to correct link location.

This exception caused me a world of grief, first because I wasn’t seeing anything in standard out (it logged to a different file), then because I couldn’t find the source of LegacySerializationPolicy, then because I have the gwt source in one directory, but because of rewrites, it appears to be served from another directory. It manifests on the client side as an InvocationException with a fantasticly unhelpful error message.

The fix is simple: copy the serialization policy file to wherever the GWT files appear to be served from.



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