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Stripes framework and jQuery: AJAX forms and HTTP Session Validation

October 23rd, 2008

This example was greatly inspired by the Stripes and jQuery AJAX Forms article from Freddy Daoud, but with some nice improvements

Last week I was working on a new Stripes/AJAX example. It involves having a table listing entities, being the last row of the table a form for adding new ones.
The form gets submitted via AJAX, using jQuery, and the response is validated in order to check if the HTTP session is still valid.

If everything is OK, the list is refreshed and a success message appears. On the other hand, if validation errors occur, the list is refreshed and an error message appears.
Also, if the user’s session has expired on the server, an alert is shown to inform the user that his session is invalid, and the page is reloaded so the user can login once more.
» Read more: Stripes framework and jQuery: AJAX forms and HTTP Session Validation

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BIRT/Stripes framework example

June 23rd, 2008

A long time has passed since my previous BIRT examples Deploying BIRT Report Engine API with Jakarta Struts and Deploying BIRT Report Engine API with Stripes.
Although they have received a lot of attention and downloads, the examples were really basic and are now outdated.

Since I had to use BIRT in my last projects I decided to update my BIRT/Stripes example.
This example doesn’t depend on the Tribix project anymore since BIRT supports HTML/Paginated HTML, PDF, Excel, Word, PowerPoint, and PostScript outputs (images/charts are not embedded in Excel output).

BIRT WebReport Example

I’ve tried to follow some good practices that I think are important to use in a production application:

  • There is a significant cost associated with creating an engine instance, due primarily to the cost of loading extensions. Therefore, each application should create just one ReportEngine instance and use it to run multiple reports. In this example the engine is started in the context listener and the same instance is always used.
  • All texts in the report should be loaded from the resources so the application can be fully localizable and fully internationalized.
  • You should use a JDBC data set to preview your report with BIRT designer but you must swap the data set in runtime to use data from your business logic.
  • You should use predefined styles instead of custom styles as much as you can.
  • Not a good practice but often a requirement, hide the master page when generating a HTML report, and change the visibility of elements so they are visible only to specified outputs.

For this example BIRT Runtime Engine 2.2.2 2.3.1, and Stripes Framework 1.5 were used.
» Read more: BIRT/Stripes framework example

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Alfresco and Web Content Management – Part II

March 26th, 2008

I’ve had a lot of feedback with my article Exactly what is Alfresco?. A recurrent question I’ve received was where to find more info about WCM with Alfresco.

You can Download Alfresco Web Content Management 2.1 under Download Alfresco Community Network. There you can find Alfresco 2.1 Web Content Management Product Evaluation Guide which is a very complete guide about the WCM module.

Hope this helps.

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Stripes framework and EJB3

January 21st, 2008

Inspired by the Spring with Stripes integration I made a new one named EJB3 with Stripes.

This extension allows you to inject your EJB beans into your Action beans.

Please fell free to use it, and to visit the Stripes and EJB3 project at Google Code.

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Classloader leaks and PermGen space

October 2nd, 2007

After googling a bit for error “java.lang.OutOfMemoryError: PermGen space” I found many sites talking about that problem. Some tried passing command line arguments to the JVM or changing the size of the PermGen space, others end up recommending using a VM from BEA or IBM, all without success.

But after a closer look at their comments I ended up at Frank Kieviet blog.
Frank explains what really is a PermGen error

The problem in a nutshell

Application servers such as Glassfish allow you to write an application (.ear, .war, etc) and deploy this application with other applications on this application server. Should you feel the need to make a change to your application, you can simply make the change in your source code, compile the source, and redeploy the application without affecting the other still running applications in the application server: you don’t need to restart the application server. This mechanism works fine on Glassfish and other application servers (e.g. Java CAPS Integration Server).

The way that this works is that each application is loaded using its own Classloader. Simply put, a Classloader is a special class that loads .class files from jar files. When you undeploy the application, the Classloader is discarded and it and all the classes that it loaded, should be garbage collected sooner or later.

Somehow, something may hold on to the Classloader however, and prevent it from being garbage collected. And that’s what’s causing the java.lang.OutOfMemoryError: PermGen space exception.

PermGen space

What is PermGen space anyways? The memory in the Virtual Machine is divided into a number of regions. One of these regions is PermGen. It’s an area of memory that is used to (among other things) load class files. The size of this memory region is fixed, i.e. it does not change when the VM is running. You can specify the size of this region with a commandline switch: -XX:MaxPermSize. The default is 64 Mb on the Sun VMs.

If there’s a problem with garbage collecting classes and if you keep loading new classes, the VM will run out of space in that memory region, even if there’s plenty of memory available on the heap. Setting the -Xmx parameter will not help: this parameter only specifies the size of the total heap and does not affect the size of the PermGen region.

… and how to use new profiling tools in Java 6 to fix Classloader leaks.
Resuming, the steps are:

  1. start your application server
  2. deploy and run your application
  3. undeploy the application that is leaking (just the application not the server)
  4. trigger a memory dump jmap -dump:format=b,file=leak <PID>
  5. run jhat (with modification, Java SE SDK 6.0 update 1 has the updated code) jhat -J-Xmx512m leak
  6. go to jhat report http://localhost:7000/ (http://localhost:7000/oql/ if you need the OQL (Object Query Language))
  7. find a leaked class (any class of your application since you shouldn’t see any objects of the classes that you deployed)
  8. locate the Classloader
  9. find the “Reference chains from root set”
  10. inspect the chains, locate the accidental reference, and fix the code

Some try even to go further on finding Orphaned Classloaders others try to nicely present the leaking classes in a form of a HTML table histogram.

These tools can really help, use them!

Resources

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Code conventions and programming style

October 1st, 2007

Coding conventions are rules that computer programmers follow to ensure that their source code is easy to read and maintain.

Why is that important?

Sun Microsystems provides the following rationale for the Java Programming Language:

Code conventions are important to programmers for a number of reasons:

  • 80% of the lifetime cost of a piece of software goes to maintenance.
  • Hardly any software is maintained for its whole life by the original author.
  • Code conventions improve the readability of the software, allowing engineers to understand new code more quickly and thoroughly.
  • If you ship your source code as a product, you need to make sure it is as well packaged and clean as any other product you create.

Crossbow Software has gather a set of code conventions and programming style documents, take a look at their Coding Style Standards download page.

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JBoss Web and PHP Install Tutorial

July 15th, 2007

Approximately 2 years ago I’ve written a set of PHP Tutorials that served as a guideline for a Beginner’s PHP Training Course. These tutorials were made with the WAMP solution stack in mind.

Since I’ve been working with Java EE Technologies and Servers recently, I’ve decided do add another one explaining how to install JBoss Web 1.0.1 GA with PHP support (PHP Handler Servlet).

This was based on a tutorial by Philippe Fievet that is now offline for some reason.

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Maven 2 Cobertura Plugin

June 24th, 2007

The Maven 2 Cobertura Plugin web site lacks information to successfully generate Cobertura reports. Worse, some of the usage examples are incorrect and don’t work.

The most common problem when generating Cobertura reports is when the generated report shows 100% test coverage while in reality many of the classes don’t even have tests.

The following example shows how to configure the reports so that it would reflect real test coverage and then check if the specified packages achieved the wanted test coverage:

<build>
    <plugins>
        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>cobertura-maven-plugin</artifactId>
            <version>2.1</version>
            <configuration>
                <check>
                    <haltOnFailure>false</haltOnFailure>
                    <regexes>
                        <regex>
                            <pattern>com.samaxes.business.*</pattern>
                            <branchRate>90</branchRate>
                            <lineRate>90</lineRate>
                        </regex>
                        <regex>
                            <pattern>com.samaxes.persistence.*</pattern>
                            <branchRate>90</branchRate>
                            <lineRate>90</lineRate>
                        </regex>
                    </regexes>
                </check>
                <instrumentation>
                    <includes>
                        <include>com/samaxes/**/*.class</include>
                    </includes>
                </instrumentation>
            </configuration>
            <executions>
                <execution>
                    <id>clean</id>
                    <phase>pre-site</phase>
                    <goals>
                        <goal>clean</goal>
                    </goals>
                </execution>
                <execution>
                    <id>instrument</id>
                    <phase>site</phase>
                    <goals>
                        <goal>instrument</goal>
                        <goal>cobertura</goal>
                        <goal>check</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>
<reporting>
    <plugins>
        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>cobertura-maven-plugin</artifactId>
        </plugin>
    </plugins>
</reporting>

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JBoss – Stacking Login Modules

May 27th, 2007

Sometimes no single login module is enough to meet our needs. Imagine the case of using an external LDAP server to provide the user authentication and a database server to provide the user authorization. A user would be in one repository or the other, and login should succeed if the user is found in either repository.

JBoss allows you to specify multiple login modules for a single security domain. But simple module stacking doesn’t resolve the problem on its own. For that, you need to use password stacking.

Password stacking allows modules to skip the actual authentication and to provide supplemental roles. The modules require the password-stacking option to useFirstPass for this to work.

<application-policy name="myRealm">
  <authentication>
    <login-module code="org.jboss.security.auth.spi.LdapLoginModule" flag="optional">
      <module-option name="password-stacking">useFirstPass</module-option>
      <module-option name="java.naming.factory.initial">com.sun.jndi.ldap.LdapCtxFactory</module-option>
      <module-option name="java.naming.provider.url">ldap://LDAP_SERVER:LDAP_PORT/</module-option>
      <module-option name="java.naming.security.authentication">simple</module-option>
      <module-option name="principalDNPrefix">MY_DOMAIN\</module-option>
    </login-module>
    <login-module code="org.jboss.security.auth.spi.DatabaseServerLoginModule" flag="required">
      <module-option name="password-stacking">useFirstPass</module-option>
      <module-option name="dsJndiName">java:myDS</module-option>
      <module-option name="principalsQuery">SELECT passwd FROM user WHERE login = ?</module-option>
      <module-option name="rolesQuery">SELECT role, 'Roles' FROM user_roles r, user u WHERE u.userid = r.userid AND u.login = ?</module-option>
    </login-module>
  </authentication>
</application-policy>

The option principals query is optional; it’s a fallback in the case the authentication fails in the LDAP server. Notice that the LDAP configuration omits the roles query option set so the authorization is only provided by the database server module.

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Where does .NET beat Java?

May 9th, 2007

Werner Schuster posted at InfoQ an article entitled “Microsoft Surpasses Java’s Dynamic Language Support” trying to show where .NET is doing better than Java.

Some of the highlights are:

  • Microsoft CLR (Common Language Runtime), LINQ and the support for multiple languages
  • DLR (Dynamic Language Runtime)
  • .NET modularization and versioning

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