Salient Soft

I received this error whilst performing a commit via Eclipse:-

The server reported an error while performing the "cvs add" command. cvs server: xxx added independently by second party

The error related to some test database scripts in the project. I searched for solutions to this, and found some comments about tagging the files as merged, but this was not really any help.

In the end, I examined the files using TortoiseCVS, and noted that the offending files were not flagged as being under source control – they did not have any icon decoration on them.

In the end the following steps solved the problem:-

1. I made sure I had copies of them elsewhere, and then deleted them from the (TortoiseCVS managed) directory under the eclipse project.
2. I then did an Update with TortoiseCVS – this reloaded the latest versions from CVS, and this time they were correctly icon-decorated as managed.
3. I then copied the new versions in to replace these. When I did this, the new versions were correctly decorated in red as updated versions but known to CVS/Tortoise.
4. I then did a commit with Eclipse, and this now proceeded without error.
5. Finally to be safe, I did a file compare to check that the correct latest versions were in place.

This solved the problem. It appeared that somehow I had lost the required CVS metadata such that the files did not appear to be CVS managed. Tortoise was very helpful here – if you see files with no icon decoration, this is immediately suspicious.

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Update 7/12/22

Previously I have implemented a composite iterator for iterating a tree of tags from a search on a PropertyTree implementation. Note that in this case, the abstract base class for the composites was a TagTree, and the concrete subclasses were a TagList and a Tag. As a Tag did not need a list, the list of children was in the concrete TagList and not the TagTree. Therefore, the TagTree did not need to have generic references to self referential subtypes in the way the example below does – in fact it did not need to be generic at all. Therefore it did not suffer this problem. For further clarity see the example below from Angelika Langer here. In her code, the list is in the abstract superclass which is why it suffers the problem below and potentially needs the infamous getThis trick per below.

Original Post

Some generic classes are recursively self-referential, such as in the following abstract class statement for a tree node :-

public abstract class Node <N extends Node<N>>  {
…
}

In this situation it is sometimes necessary for example to pass a reference to this from the superclass to a specific subclass which expects an argument of type N :-

public void methodA(N node) {
//do something with the passed node
}

public void methodB(N node) {
node.methodA(this); // error – incompatible types
}

In the above fragment, the error is because this in the superclass has a type of Node<N> which does not match N.

Another related use case is where a fluent API returns a ‘this’ reference from each of the fluent methods. If for example a fluent method in an abstract base class needs to return a ‘this’, as above the reference needs to be for the concrete subclass so the same problem occurs.

The topic is discussed in detail in Java Generics and Collections, section 9.4 on the Strategy pattern. The section from the book may be viewed online at Flylib here.

Angelika Langer also discusses it in more detail her Generics FAQ here

In the above case, the problem can be solved with the so-called getThis trick. An abstract getThis method is defined in the superclass, and implemented in each subclass:-

Superclass

protected abstract N getThis();

Subclass

protected Subtype getThis() {return this}; // where Subtype is the concrete subtype of N

Now the superclass can obtain a type correct reference to this and pass it without error:-

public void methodB(N node) {
node.methodA(getThis()); // this time it works
}

As Angelika Langer points out in her examples, there can be other ways around this kind of problem depending on the situation, but sometimes you do need the getThis trick.

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When a service layer EJB method is called locally from within the same class, any CDI interceptors on the method are not invoked. This is standard CDI behaviour, as interceptors are only designed to be called when a method is called from an external client.

I hit this issue when my OptimisticLockInterceptor (which converts OptimisticLockException to ChangeCollisionException) was not being called, and OptimisticLockExceptions where being propagated all the way up to the view layer -  Mantis issue 120 details this.

The solution to this is to ensure that any required interceptors are annotated on methods at the point of call from an external client. If they then call another EJB method locally, any interceptors on the second method will not be called, but this is not a problem if the first method is correctly annotated. If the second method is also used externally, then its interceptors will be correctly invoked.

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Weld 1.0 was failing with “WELD-001408 Injection point has unsatisfied dependencies” when nested parameterised types were present.

The referenced bean was correctly present and annotated.

I found that I could work around the problem by simplifying/removing some of the generics. This allowed the beans to inject, but also gave warnings about the use of raw types. For example:-

//Original code
    private @Inject TableCtrl<TreeNodePath<TaxonomyNode>, RowMetadata> selectionTable;

//was replaced with the following
    private @Inject TableCtrl<TreeNodePath, RowMetadata> selectionTable;

Attempts to use a CDI extension to find out more about what was happening did not reveal any more insight. This post discusses Weld performance and debugging and refers to a Stack Overflow post on the subject.

My solution to the problem (which I have also logged on Mantis) is  as follows :-

1. Injecting the bean into a raw type does not suffer from the problem.
2. I therefore inject into a temporary raw type, and cast that to the correct type.
3. Wrapping this in a method annotated with @Inject neatly solves the problem, as the method can take the raw types as arguments, and cast to the correctly parameterised fields in the method.
4. As all this is done in a method, warnings can be suppressed for the method. This is a tidy solution, as the method only has this specific purpose, and no other warnings in the class are incorrectly suppressed.
5. This is far better than the original workaround which involved hacking the generics back to non nested parameterised types throughout – this meant hacking a number of classes. The current solution entirely isolates the issue and allows the desired generics to be correctly used everywhere.

An example of the correct generic declarations and the method used follows :-

public abstract class TreeBrowser<N extends TreeNode<T>, T extends Tree<N>, P extends TreeNodePath<N>>
                            implements Serializable, BreadcrumbCtrlEvent<N> {
…
    private CrumbComparator<N> crumbComparator;
    private BreadcrumbCtrl<N> breadcrumb;   
    private TableCtrl<N, RowMetadata> treeNodeTable;
    private TableCtrl<P, RowMetadataStatusMap> trayTable;
…
    @Inject
    @SuppressWarnings({"rawtypes", "unchecked"})
    void injectWeldUnsatisfiedGenericBeans(CrumbComparator crumbComparator, BreadcrumbCtrl breadcrumb,
                           TableCtrl treeNodeTable, TableCtrl trayTable) {
        this.crumbComparator = crumbComparator;
        this.breadcrumb = breadcrumb;
        this.treeNodeTable = treeNodeTable;
        this.trayTable = trayTable;
    }

This solved the problem.

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This was done in order to resolve ongoing reliability issues with the OCZ Vertex and SATA port errors from the P6T as detailed here.

This post also follows on from my earlier post here concerning hot swap issues, where I went into some detail of the P6T flashing process. Reference should be made to that post for more details of P6T flashing.

The following steps were performed:-

1. I identified the current firmware version of my OCZ Vertex. To do this start device manager, find the disk under Disk drives, and open its properties. Then select the Harware Ids property and the version number of the firmware will be shown. There were hints in the forums of a more detailed revision number, but I could not find it. My initial version was 1.5.
2. I also tried to run the OCZ Toolbox which allows identification and upgrade of the firmware, and also auto downloads the correct new version. I nice idea if it had worked! In my case it failed to find the OCZ Vertex either before or after the upgrade process.
3. I did note that a number of posts suggested switching the SATA mode to AHCI in both the bios and windows. This OCZ post details the process, which (for the windows part) simply involves changing the value of HKLM\System\CurrentControlSet\Services\msahci\Start in the registry from 3 (=IDE mode) to 0 (= AHCI mode). However, when I tried this at this stage, the system froze at boot time. Fortunately, I was able to switch the setting back in the BIOS, boot into safe mode, and set the registry setting back to 3, to restore the system to a working state.
4. The latest version for my Vertex was 1.7, but it is not possible to upgrade directly from 1.5 to 1.7. It is necessary to upgrade to 1.6 first. Finding all the historical versions of the firmware is not easy on the OCZ site – the main download area only has the most recent version. Older version may be found from a forum post here which has all the historical downloads.
5. For my Vertex, here is  the 1.6 upgrade and here is the 1.7 upgrade.
6. Note that as per the 1.6 upgrade, I had the ‘filename error’ which meant that I had an older version which needed a destructive upgrade to 1.6 due to a change in the NAND/wear levelling algorithm. This would mean loss of all data on the drive and a restore afterwards, and the use of a different kit for upgrading. The upgrade also could not be done with the drive in use as the system disk. The links in the previous paragraph give all the instructions and the alternative versions of the upgrade.
7. I then made 2 full backups with Acronis, plus another daily file backup, to be sure I would be able to restore the drive.
8. As per the instructions, I jumpered the drive to set it into standalone/upgrade mode, and booted from the previous version of Windows 7 which I still had available on a standard Hard drive. I kept this available just in case, and on this occasion I was very glad I did.
9. The destructive upgrade is available as 16_win_vertex.zip. Unfortunately the zip contains 2 versions of the update, 641102VTX.exe and 661102VTXR.exe. There are no release notes to say which version to use or what they are (!) I wondered if they related to the internal firmware/drive version from which you were upgrading, but I didn’t know that either as I have said earlier. Another forum post hinted that as may be expected, the 661102VTXR.exe was a later version and the ’R’ indicated revised. I decided to try this one.
10. Having jumpered and rebooted, the drive correctly identified itself as YATAPDONG BAREFOOT, and I proceeded with the upgrade, which went successfully.
11. I then immediately upgraded from 1.6 to 1.7 using 17_updaters_1.zip.  This time, a standard non-destructive upgrade could be done (not that it mattered in my case), which mean burning an ISO on a CD, and booting that to do the upgrade. The zip contained ISOs for a number of OCZ products plus some release notes this time, so I burnt the ISO for the Vertex. I booted it and did the upgrade, which went with no problems. One point is that I cannot recall whether I removed the jumper on the drive before or after this final upgrade. I am fairly sure that it was after, in which case the upgrade does not mind whether the jumper is present, but if there are any issues it should be tried without the jumper present as would be normal for a non destructive upgrade.
12. Following this, I booted the system. Initially it could not see the Vertex, so I rebooted into the bios, found it was then visible, and did a bios save and another reboot. This time the drive was visible but not formatted.
13. I then booted Acronis from its rescue CD and restored the backup, plus the Master Boot Record. This proceeded normally.
14. After rebooting, the system came up and ran fine, however it did present the boot manager from the other disk, and the system had to be selected from there. To prevent the need for this, I copied the boot files back to the new SSD using bcdboot as per this post here. It was also necessary to reset the boot order in the bios so that the SSD was chosen first, otherwise the boot manager is still presented even after you have run bcdboot.

Now I had a working system with the updated SSD, I decided to reflash the P6T as well. Previously I had had hot swap and SATA issues with later bios versions, as detail here. However, since then I had disabled the onboard JMicron controller which was giving problems, and replaced it with a Startech controller, as detailed in the update to this post here. Therefore, the original issues which were preventing the use of a later bios were no longer present, so I opted to flash to the latest version which at the time of upgrade was version 1408 :-

1. I used the in-bios EZ-Flash, and the process and precautions are detailed in the original section of this post here.
2. I re-applied the required motherboard settings as per the process, and rebooted successfully.
3. I then retried switching into AHCI mode, as detail above when I tried it prior to the upgrade. This time it worked correctly with no problems. In the bios, I just set the onboard SATA to AHCI. The JMicron controller was disabled, and the Startech controller was not touched as this was an add-in card just used for SATA backups. It is possible that now either the onboard ICH10 SATA or JMicron SATA might work and hot swap reliably in eSATA mode with AHCI enabled, but as I was happy enough with the Startech I decided to leave this issue well alone for now.
4. As a final test, I re-ran the Windows Experience tests to see if AHCI had improved performance, and indeed the primary hard disk figure had increased from 7.1 to 7.3, which is good considering the fact that my original OCZ Vertex is now an old  technology which has been set to End-Of-Life by OCZ. The system certainly felt snappier, but this is highly subjective as I had not run before and after benchmarks – the goal of the whole excercise was reliability rather than speed.

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Update 30/1/2012

After further testing, I have found more issues trying to use a parameterised concrete class in a JPA constructor expression. EclipseLink was throwing MethodNotFoundException complaining that it could not find the constructor method for the class, due to the use of the parameterised type in one of the constructor arguments. The precise circumstances where this does and does not work are not clear.

My solution has been to not use a parameterised class at all in a JPA constructor expression. To avoid most of the code duplication, what I did was to subclass the parameterised class for each concrete type I was using, i.e. I created a concrete subclass which only contained a constructor calling the superclass constructor. This then allowed me to use a typed query in JPA, as the returned class was now non-parameterised and so I could create a class literal for it.

Original Post

Whilst in some situations this may be an issue, it is also a statement of fact!

This is due to type erasure at run time, and cannot be done.

It means, for example, that in some cases it is not possible to completely eliminate unchecked warnings.

One example of mine was the use of a parameterised type in a constructor expression class in JPA. I had a requirement to do fetches which involved returning an entity plus another column that could not be handled as a relationship/JPA entity property. The property in question was the count of children for a tree node entity. As I was using path enumeration to describe the tree, I could not use JPA relationships to handle it, and so had to return the child count separately. I had more than one type of tree, all handled polymorphically, and so wanted to re-use the constructor class by making it parameterised.

This all worked fine but the class could not have its class literal passed when created a TypedQuery to fetch the results back. The solution was to use some casting isolated in a specific method, and to suppress the generic warnings via @SuppressWarnings("unchecked").

The following posts detail this issue:-

http://stackoverflow.com/questions/2390662/java-how-do-i-get-a-class-literal-from-a-generic-type

http://www.angelikalanger.com/GenericsFAQ/FAQSections/ParameterizedTypes.html#Why is there no class literal for the concrete instantiation of a parameterized type?

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It is a design feature of servlet sessions that if you open the same application in multiple windows in the same browser type, the session data is shared across them all. This post on Stack Overflow discusses the issue.

Therefore, if for example you need multiple sessions present in order to test Optimistic Lock collisions, you need a way around this. There are 2 solutions :-

1. Use a different browser type in each window. For example, if you use Firefox and Chrome as a pair, or Firefox and Opera for example, you will in fact get separate sessions as there is no sharing of cookies and other related data across different browser types.
2. Log in from another computer, for example by using an RDP session to another computer on the same desktop and running the application from there. In this case, both browser types can be the same.

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I use the click event to validate a navigation, returning true to allow it and false to cancel it.
On some occasions, the toolbar buttons (which are based internally on h:link with pre-emptive Get style navigation based on an outcome) do not navigate event when the click event correctly returns true.

Some toolbar buttons always did this, others always worked. No explanation could be found for the failure to navigate, even after extensive testing and online searching for answers.

The solution to this was to return cancel in the click event, but to have the click event explicitly do the navigation itself via Javascript. The following code fragment illustrates the problem:-

<h:link id="link" disabled="#{disabled}" outcome="#{outcome}" href="#{href}" title="#{title}" tabindex="#{tabIndex}"
      onclick="if (#{empty onNavigate ? ‘true’ : el:format1(onNavigate, el:concat3(‘\”, component.clientId, ‘\”))})
      window.location.href=this.href; return false;">

The if test checks if the navigation is require, then if so, window.location.href is set to the target href in the component. False is always returned so that standard navigation is disabled.

This solved the problem consistently. (This has also been logged as Mantis issue 104).

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This is a tricky issue to control correctly. The following points have been found during testing (Mojarra 2.0.4 FCS / Primefaces 2.2.1 / Glassfish 3.0.1)

1. One key issue is that to start a new conversation on a page, the navigation to that page must not propagate any previously active conversation. This will then start a new transient (i.e. not long-running/not started) conversation on the new page, and conversation.begin() can be used to make it long-running (i.e. start it).
2. When doing a standard JSF Ajax postback, the current conversation is always propagated, and it does not appear to be possible to prevent this/start a new conversation from a postback. JSF always adds the current CID as a querystring parameter
3. To prevent propagation and to allow a new page to start a new conversation, GET navigation needs to be performed. This fits in well with my main toolbar options – I use pre-emptive GET navigation for the main pages with full page refreshes.
4. Primefaces p:button allows the new JSF 2 outcome style GET navigation but cannot be stopped from propagating a conversation – it always adds a CID parameter. If you add one with an empty or null value, you still get a “cid=” attribute which CDI then spits out as an invalid conversation on the new page.
5. h:link can be stopped from propagating by using an explicit f:param for the cid, providing the param has no value or an explicit null value (an empty string will not work).
6. Trying to refer to another inactive conversation, e.g. by storing conversation scoped bean references in a session level map and looking them up, seriously screws up CDI with an extremely long/possibly recursive stack trace. (See Mantis issue xxx for the stack dump). This is likely to be due to the proxying mechanism used for conversations.
7. Therefore, it is not possible to invent say a ‘onPageLeave’ event for a previous page and call it after a new page has started and had its conversation activated.
8. If therefore I need to refresh all pages for the application, for example if an OptimisticLockException occurred, I use a central workspace session bean to manage all the pages. I set a refresh pending flag in a map for each page, and then when the page is next visited, the workspace bean calls a refresh event of my own for the page, and then clears the pending flag. When processing the current page after an OptimisticLockException, I can refresh directly if the user requests it from a lock dialog.
9. My workspace bean holds the CID for each page against the page name in a map, and uses this when rendering the Toolbar, adding the appropriate cid= parameter for each toolbar option. In fact I use an outer map keyed on page group name (where the page group corresponds to a top level toolbar option), with an inner map containing all the cids and refresh pending flags for the individual pages in that group. This allows for example a report toolbar option to be a menu of currently active reports, and allows new reports to be created dynamically as new conversations and added to the list under the report menu on the toolbar.
10. Conversations are started and ended via calls to the workspace bean, which can then add/remove entries from the maps to keep track of what pages/cids are currently active.
11. Regarding navigation and cid propagation, another option is to call JSF directly to obtain the navigation case for an outcome. ConfigurableNavigationHandler allows you to pass an outcome and get the actual navigation case, from which you can then get the URL. This should allow full control of the cid= propagation parameter on the querystring, and allow control for components which do not support JSF 2.0 style GET pre-emptive navigation directly from an outcome. The url can be passed to any component which accepts a url, and should then still perform the correct navigation and conversation control. See CoreJSF 3 page 333 for a code example on this. This method could prove useful for example with a Primefaces MenuItem, which does either JSF postback style navigation, or URL navigation, but does not directly do pre-emptive GET navigation by giving it an outcome.

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Initially this looked very strange. When navigating to a new form, the rendered= methods for the old form were being called again, and were failing due to scoping issues – a new request scope bean was being created causing a null pointer exception in the method as required state had been lost.

This post and also this post on StackOverflow explain the problem. Apparently JSF rechecks the rendered conditions after the submit as part of an attack safeguard. This is what caused recreation of a new bean and the failure.

This behaviour was certainly unexpected, and I have not seen it documented ‘up front’ previously – so it is certainly one to be aware of! This is not the first time I have had issues with the render= attribute.

In my case, resolving issues in creation of conversations solved the problem – once I had conversations propagating properly, everything worked correctly and the state was present for the extra calls to the rendered= methods.

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