Category Archives: java

How to solve CoreMessageLogger NoClassDefFoundError in Weblogic

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When deploying an application in Weblogic you can come across a HibernateĀ CoreMessageLogger NoClassDefFoundError on Weblogic:

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Caused By: java.lang.NoClassDefFoundError: org/hibernate/internal/CoreMessageLogger
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.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at weblogic.utils.classloaders.GenericClassLoader.defineClass(GenericClassLoader.java:342)
at weblogic.utils.classloaders.GenericClassLoader.findLocalClass(GenericClassLoader.java:301)
at weblogic.utils.classloaders.GenericClassLoader.findClass(GenericClassLoader.java:269)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at weblogic.utils.classloaders.GenericClassLoader.loadClass(GenericClassLoader.java:178)
at org.hibernate.ejb.Ejb3Configuration.(Ejb3Configuration.java:142)
at org.hibernate.ejb.HibernatePersistence.createContainerEntityManagerFactory(HibernatePersistence.java:72)
at weblogic.persistence.BasePersistenceUnitInfo.initializeEntityManagerFactory(BasePersistenceUnitInfo.java:446)
at weblogic.persistence.BasePersistenceUnitInfo.initializeEntityManagerFactory(BasePersistenceUnitInfo.java:439)
at weblogic.persistence.BasePersistenceUnitInfo.init(BasePersistenceUnitInfo.java:117)
at weblogic.persistence.BaseJPAIntegrationProvider.createPersistenceUnitInfo(BaseJPAIntegrationProvider.java:53)
at weblogic.persistence.AbstractPersistenceUnitRegistry.storeDescriptors(AbstractPersistenceUnitRegistry.java:404)
at weblogic.persistence.EarPersistenceUnitRegistry.initialize(EarPersistenceUnitRegistry.java:72)
at weblogic.persistence.PersistenceDeployment$PersistenceDeploymentExtension.prepare(PersistenceDeployment.java:81)
at weblogic.application.internal.flow.AppDeploymentExtensionFlow.prepare(AppDeploymentExtensionFlow.java:23)
at weblogic.application.internal.BaseDeployment$1.next(BaseDeployment.java:706)
at weblogic.application.utils.StateMachineDriver.nextState(StateMachineDriver.java:35)
at weblogic.application.internal.BaseDeployment.prepare(BaseDeployment.java:237)
at weblogic.application.internal.EarDeployment.prepare(EarDeployment.java:61)
at weblogic.application.internal.DeploymentStateChecker.prepare(DeploymentStateChecker.java:158)
at weblogic.deploy.internal.targetserver.AppContainerInvoker.prepare(AppContainerInvoker.java:60)
at weblogic.deploy.internal.targetserver.operations.ActivateOperation.createAndPrepareContainer(ActivateOperation.java:207)
at weblogic.deploy.internal.targetserver.operations.ActivateOperation.doPrepare(ActivateOperation.java:96)
at weblogic.deploy.internal.targetserver.operations.AbstractOperation.prepare(AbstractOperation.java:229)
at weblogic.deploy.internal.targetserver.DeploymentManager.handleDeploymentPrepare(DeploymentManager.java:747)
at weblogic.deploy.internal.targetserver.DeploymentManager.prepareDeploymentList(DeploymentManager.java:1216)
at weblogic.deploy.internal.targetserver.DeploymentManager.handlePrepare(DeploymentManager.java:250)
at weblogic.deploy.internal.targetserver.DeploymentServiceDispatcher.prepare(DeploymentServiceDispatcher.java:159)
at weblogic.deploy.service.internal.targetserver.DeploymentReceiverCallbackDeliverer.doPrepareCallback(DeploymentReceiverCallbackDeliverer.java:171)
at weblogic.deploy.service.internal.targetserver.DeploymentReceiverCallbackDeliverer.access$000(DeploymentReceiverCallbackDeliverer.java:13)
at weblogic.deploy.service.internal.targetserver.DeploymentReceiverCallbackDeliverer$1.run(DeploymentReceiverCallbackDeliverer.java:46)
at weblogic.work.SelfTuningWorkManagerImpl$WorkAdapterImpl.run(SelfTuningWorkManagerImpl.java:545)
at weblogic.work.ExecuteThread.execute(ExecuteThread.java:256)
at weblogic.work.ExecuteThread.run(ExecuteThread.java:221)

SolvingĀ CoreMessageLogger NoClassDefFoundError

This problem can occur when you have a Hibernate 3.x and a Hibernate 4.x dependency in your classpath, and the Hibernate 3 dependency was first on your classpath.

Look in your Maven Dependency hierarchy to see where the Hibernate 3 / 4 dependencies come from and solve it by eg. excluding transitive dependencies in your POM.

Devoxx 08: HTML 5 WebSockets and Server Sent Events

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A few weeks back on Devoxx 08, Jonas Jacobi and John R. Fallows did a talk about 2 future web technologiesĀ  that’ll change the way we architect our webapplications.
(in the same manner then AJAX did a few years back).

The technologies are called WebSockets and Server Sent events and are part of the HTML5 specification. (which is now in Editor’s draft and thus not finished)

WebSockets and Server Sent events can enable us to create a full-duplex web application. Eg. a sample application could be a poker game with thousands of viewers connected and that those viewers need to be notified in realtime. Another example could be a continuously updated stock ticker.

Prior to the introduction of WebSockets, bi-directional browser communication was an elusive beast, commonly known as Comet or ReverseAjax and typically achieved with an astonishing assortment of browser hacks. But, with the emerging standards outlined in the HTML 5 specification, developers can now take advantage of a full-duplex communications channel that operates over a single socket.

Real time web

With real time web, we mean that web clients can receive server updates (server initiated communication) and end users receive those updates concurrently.

Long polling with AJAX (XML Http Request) gives us near real time updates, but they are requested from the client and cause increased network traffic. Also these short AJAX requests generally have a small payload and relatively high amount of http headers. (wasted bandwith)

Comet technologies support HTTP Streaming, this setups a persistent http connection which only has to be setup/teardown only once. (especially nice for performance for https traffic)

HTML 5 Overview

HTML 5 not only contains WebSockets and Server Sent events.Ā  It also contains standard features like:

  • communication (sockets, cross-site)
  • graphics (2D)
  • drag n drop
  • storage (transient, (offline)Ā Ā Ā  persistent)
  • compatibility

Here we focus on two: Server-sent events and WebSockets

Server-sent events

Server-sent events standardizes how we stream data from the server to the client (in fact standardizing comet/reverse ajax).

It introduces a new DOM Element: eventsource. The eventsource element provides a simple interface for allowing servers to dispatch DOM events into documents that expect it.

Here is how to create it:

var es = document.createElement(“eventsource”);
es.addEventSource(“http://www.javablog.be”);

(where the event source is an URL).

WebSockets

WebSockets provide a full duplex TCP connection to communicate between the browser and the server. It traverses firewalls and routers and allows authorized cross domain communication.

An example is provided below:

var myWebSocket = new WebSocket(“ws://www.websocket.org”);

The WebSocket(url) constructor takes one argument, url, which specifies the URL to which to connect. When a WebSocket object is created, the User Agent must parse this argument and verify that the URL parses without failure and has a <scheme> component whose value is either “ws” or “wss”. Only then the user agent must asynchronously establish a Web Socket connection to url.

myWebSocket.postMessage(“Hello”);

=> text based data transmission using the connection.

myWebSocket.onopen = function(evt) { }

=> The openĀ  event is fired when the Web Socket connection is established.

myWebSocket.onmessage = function(evt) { }

=> The message event is fired when when data is received for a connection.

myWebSocket.onclose = function(evt) { }

=> The close event is fired when the connection is closed

myWebSocket.disconnect();

=> close the conncetion

Browser support

Opera already has Server sent events, for Mozilla/Firefox there is patch available (bug 338583)
WebSockets is not yet available natively in browsers.

But fortunately for current browsers Kaazing.com provides an emulation Javascript library. (IE5.5+, Firefox 1.5, Chrome 0.2+, Safari 3.1+, Opera9+)
The Javascript only emulates the parts which are not yet implemented in a certain browser.
It can be any of the following layers: ByteSocket, Websockets, Server sent events, Cross site XML HTTP Request, XML Http Request IFrame postMessage

Devoxx 08: Major Servlet 3.0 features

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Martin Marinschek divided his talk in two main topics: Servlet 3.0 and JSF 2.0.

The first part of the talk showed us the new features planned for Servlet 3.0.

What follows is based on the Public Review draft.
So be sure to check if the following still applies to the final Servlet 3.0 version.

Modularization of the web.xml settings

Right now the web.xml is one big configuration file. In Servlet 3.0 it’s possible to modularize it into multiple files.
These files are called “web-fragment.xml” files and they are merged together on application initialization.
Because these fragments can conflict with each other, the specification has specified rules for conflict resolution. (we could take a deeper look at this in a future blog post).

Martin also said that fragment ordering is not defined; this eg. could mean that a filter you want to be executed first may have to be repeated in multiple fragments.

Annotation support in your servlets

A few annotations were added that you can use in your servlets:

@WebServlet

This annotation is used to define a Servlet component in a web application. The urlPatterns or the value attribute on the annotation MUST be present. (value is for 1 URL mapping, urlPatterns for multiple URL mappings)
Classes annotated with @WebServlet class MUST extend javax.servlet.http.HttpServlet class except when applied on a JAX-RS / JAX-WS endpoint.

Example:

@WebServlet(name=”MyServlet”, urlPatterns={“/foo”, “/bar”})
public class SampleUsingAnnotationAttributes extends HttpServlet{
public void doGet(HttpServletRequest req, HttpServletResponse res) {
}
}

Other optional attributes for the @WebServlet annotation are: supportAsync and asyncTimeout

@ServletFilter

This annotation is used to define a Filter in a web application. Classes annotated with @ServletFilter MUST implement javax.servlet.Filter

@InitParam

This annotation is used to specify Init Parameters for a servlet or a filter

@WebServletContextListener

The WebServletContextListener annotation is used to annotate a context listener to get events for various operations on the particular web application context.
Classes annotated with @WebServletContextListener MUST implement javax.servlet.ServletContextListener

Asynchronous requests

Sometimes a filter and/or servlet is unable to complete the processing of a request without waiting for a resource or event before generating a response. For example, a servlet may need to wait for an available JDBC connection, for a response from a remote web service, for a JMS message, or for an application event, before
proceeding to generate a response. Waiting within the servlet is an inefficient operation as it is a blocking operation that consumes a thread and other limited resources. Frequently a slow resource such as a database may have many threads blocked waiting for access and can cause thread starvation and poor quality of serviceĀ  for an entire web container.

Servlet 3.0 introduces the ability for asynchronous processing of requests so that the thread may return to the container and perform other tasks.

When asyncSupported is set to true in the filter/servlets annotation the application can start asynchronous
processing in a separate thread by calling the HttpServletRequest.startAsync method passing it a
reference to the request and response objects.

After I’ve played with the asynchronous requests I’ll post some code samples to Java Blog to explain how exactly it works.

Fix your Flex HTTP Error / Stream Error with IE6 / IE7 on HTTPS

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When using the Flex HttpService object to access an http resource from within your application, take care to test it under Internet Explorer too. Due to a bug in IE you could receive a Http Error or Stream Error in your Flex application when it’s running in https (secure) mode.

Normally when your backend responds to the HTTP request, it’ll use a Cache-control: no-cache, so the browser doesn’t cache the response in its browser cache. (as the response is normally dynamic and could change anytime).

As Flex is running in the Adobe Flash ActiveX player this however instructs IE to already delete the response, before the ActiveX plugin manages to get the results.

You’ll need to change your backend to set the following HTTP Response header:

Cache-Control: no-store

This means: “do not store this response for any longer than necessary to display it” (more info at Atlassian)

Also check out Jim Robson’s blog and Mark Speck’s blog for more research regarding this issue.

Devoxx 08: Xtreme Programming

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This university session given by Yves Hanoulle and Jef Cumps was covering two main topics: an introduction to Xtreme Programming and an overview of the very popular SCRUM agile methodology. In this post we delve deeper into Xtreme Programming. A detailed Scrum post will come soon.

Xtreme Programming

Three loops were described where an XP team loops through endlessly: the organisational loop, the team loop and the code loop. Below we give a short introduction of the 3 loops.

Organisational loop

The outer loop is the release loop, which interacts with the outer world, and which will let a predefined amount of requirements come in and working quality software pop out of the team regularly.

The organisational loop consists of 2 main values: close collaboration with the customer and small releases.

An XP project generally has an onsite customer who’s able to take business decisions. The technical decisions are taken by the developers.

Small releases are iterations of 2-to-4 weeks of coding work which consist of a number of finished user stories. Stories describe the requirements (high level – as the cards are not big enough to tell it all. But they enable communication with the business.) Besides that the stories are also ordered by the team in function of complexity, while the onsite customer will assign a business value. Together they’ll form the priority of taks to execute.

The fast releases allow for fast feedback cycles, allowing the customer to change direction faster if needed.

Team loop

The middle loop is the team loop, which handles day to day team activities.

The idea is that the developers work in a sustainable pace and as a team.

A daily standup meeting is organized. Because it’s standing the meeting doesn’t last too long (should be max 15 minutes). Here the team talks about 3 things:

  • what you’ve done the previous day
  • what do you commit to do today (it is a small line between what you’ll do and what you’ll commit to finish today, but it is a very important one)
  • tell others: “I need help with …”

It’s very important todo it every day, for it to work well.

Code loop

The inner loop is the coding loop, where two programmers, sitting side by side, produce a unit of tested code.

Pair programming, programming with two together, in the long term costs less then not doing it. Switching keyboards every 10-15minutes work best. (should not be longer then 30 minutes). One of the positive effects of pair programming is that you get instant code review and generally the code will look a lot different (read better) then if the two would have implemented the task alone.

Unit tests, are a safety net as you’ll know what is working / what’s not working. It’ll also make refactorings easier, less dangerous because of the safety net. They assure the quality of your code.

Test driven design, means writing your unit tests first. It’l make you think about the problem and how you’re going to implement the solution. As a result the design of your code will be better.
Continuous integration, is also very important for an XP project. Fast and automatic integration means that you’re project doesn’t stay stuck at 90% finished and just some integration work to finish (which you have no idea how long it’ll take). Automating everything can be a huge investment, but generally pays off in the longer term.

Collective code ownership, means anybody can change anyone’s code as long as the rules are followed. Those rules are defined by the team itself and could eg. be “tests not failing”, “no findbugs errors”, … Sometimes collective code ownership is hard but this generally indicates an underlying problem of Trust.
Acceptance tests, are defined by the proxy customer. It defines when are we done? => When all acceptance tests pass. The customer should write it just-in-time. (eg. for the next iteration when the developers are currently working on the current iteration).

That ends our little overview of Xtreme Programming. Retrospectives and Velocity we’ll leave for our coming Scrum article!

You can find the slides from this Xtreme Programming talk at Yves Hanoulle’s blog

Devoxx 2008: my session picks for University day 1

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I’ll be again present on Europe’s largest Java conference Javapolis Devoxx.

Here is a list of what sessions I’ll be following.

If you want to meet me let me know via my Twitter.

Scrum in Practice

The agile Scrum process will be explained: its roles, its artefacts and the challenges in implementing it in an organization.

Servlet 3.0 & JSF 2.0

I’m especially interested in the new features in JSF2.0 and the modularization support for web applications in Servlets 3.0

JFreeChart

Having used JFreeChart v0.9.x a few years ago, I’m looking forward to seeing the enhancements/new features in the current version.

Agile Testing of Java Rich Clients

Traditionally a difficult area to automate tests for, I’m wondering how Fit, FEST and TestNG will fare.

Bringing Designers and Developers Together with JavaFX and Project Nile

As a Flex developer, I’m wondering how JavaFX and Flex compare to each other.

Weblets 1.1 now officially released

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Weblets 1.1 has been released at weblets.dev.java.net

Weblets is a Java servlet based framework that provides an easy way of loading resources (Javascript, CSS, images, …) directly out of JAR files. For an overview of what Weblets can do for you, check our Weblets overview.

Below we’ll highlight some of the new features in Weblets v1.1:

  • Weblets 1.1 provides a stable api to build your own Weblets upon
  • Asynchronous In-server reporting of url usage is possible. (eg. for traffic analysis). In-server means that the logging is done in the same JVM server process. Asynchronous because reports that are triggered and executed can run for a longer period of time.
  • General reporting API for in server reporting instances
  • Configurable cache timeouts for better browser cache control

Weblets 1.0 only had the possibility to host resources within your classpath. It was only possible to host Weblets related resources within a jar or within your WEB-INF/classes directory!

Weblets 1.1 now enhances this with a very common usecase. expanded application hosted resources . This means you can put any resource hosted within your local web application under Weblet control. For instance if your application is hosted under /myapplication and your resource under /myapplication/images/myimage.png it until now was not possible to put this resource under Weblets control.

  • Server Mime Type overrides: some servers don’t set default mime types. (eg Weblogic 8.1). If you’re not able to edit them in the web.xml, the Weblets configuration provides another possibility.
  • Resource Whitelists: a mechanism to allow the serving of resources only for certain filetypes given in a resource whitelist (eg. only allow serving of png files)
  • Weblets 1.1 corrects Maven2.0 transitive dependencies (Maven should now pickup all needed dependencies of Weblets)

See http://weblets.dev.java.net/doc_11/longdoc/whatsnew.html for a more detailed description of the new features!

How to install Flex3 builder in RAD7

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The IBM Rational Application Developer 7 (RAD 7) IDE, based on Eclipse 3.3 doesn’t work out-of-the-box with Flex Builder 3. This is due to the IBM Java SDK using a different Xerces version then the one Flex Builder needs.

You’ll likely receive the following error:

java.lang.IllegalAccessError:
org.apache.xerces.util.XMLAttributesImpl$Attribute

Here is an easy guide to get you up and running quickly:

  1. Install RAD7
  2. Install Flex Builder 3
  3. At the end of the install, the installer will complain about not being able to automatically setup an Extension Location. Be sure to execute the given instructions manually
  4. Quit RAD7 if running
  5. Edit the eclipse.ini file in c:\Program Files\IBM\SDP70 (directory where you installed RAD7)
  6. Add the following line on a new line at the end of the file:
-Xbootclasspath/a:c:\progra~1\adobe\flexbu~1\sdks\3.0.0\lib\xercesImpl.jar

Restart RAD7 and open the Flex Development perspective to start developing the next-gen Flex app :-)

JSF 1.1 performance fixes

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JSF 1.1_02 is the latest officially released reference implementation of JSF1.1 by Sun. It’s still widely used by companies who have not yet migrated to Java5 (as it is not always easy to migrate all applications to a new target platform).

While looking through the FishEye source code view, I came accross some interesting unreleased performance fixes:

https://javaserverfaces.dev.java.net/issues/show_bug.cgi?id=125

I have been investigating the size of views as they are stuffed in the session for scalability reasons, and have found a couple of issues with the RI code:

1. The biggest problem I found was in StateManagerImpl.The function removeTransientChildrenAndFacets causes the lazy init of the child list, facet map, and client id of every component in the tree! Very, very sloppy.

Fixing this literally halved the size of the view in memory.

https://javaserverfaces.dev.java.net/issues/show_bug.cgi?id=223

StateManager for stateSaving Server has a synchronization lock on (this), blocking all threads. I thought this was fixed a while back.

https://javaserverfaces.dev.java.net/issues/show_bug.cgi?id=222

Currently the checkIdUniqueness forces creation of child and facet arrays onevery component, the suggestion is to switch over togetFacetsAndChildren() which is now optimized within UIComponentBase to avoid unecessary eden creation in memory.

Has anybody already used these JSF 1.1_03 rolling fixes and noticed memory reduction? If so please let us know in the comments!