42¢ glxn.net

Implementing @RequestParam in CDI/WELD using Qualifier and InjectionPoint as @HttpParam

Implementing RequestParam as HttpParam is quite easy. This is the example discussed in the Weld Reference Documentation. What we do is set up a Qualifier like this:

public @interface HttpParam {
    public String value() default "";

Then all we need to do is create a Producer Method: and utilize the InjectionPoint metadata to set the proper value based on either the name of the attribute or the value of the annotation. This example will ensure that both:

 @Inject @HttpParam("trackId")
 String currentTrackId;


 @Inject @HttpParam
 String trackId;

Makes the request parameter “trackId” available to the field. Example url: http://www.glxn.net/listen?trackId=16180339 will set currentTrackId in the first example above to 16180339, and in the second set trackId to the same value.

public class HttpParamProducer {

    FacesContext facesContext;

    String getHttpParameter(InjectionPoint ip) {
        String name = ip.getAnnotated().getAnnotation(HttpParam.class).value();
        if ("".equals(name)) name = ip.getMember().getName();
        return facesContext.getExternalContext()

Now we can access the request parameter in our Bean simply by annotating the field with Inject and HttpParam. In the example below I am injecting the SessionScoped bean SpotifyWeb, and calling its wrap method to enrich my request parameter "trackId" using a Producer method to create a Named parameter “trackReqParam” available to another bean, or in my case the view. So in my view page i print out #{trackReqParam} and it shows the initial request parameter trackId with some modification done in the wrap method. Just a simple example of it’s application. The key here is that you can’t inject a request parameter to a session scoped bean and expect it to not live in the dependent scope of its parent. That means if you do inject it to a session scoped bean, it is injected and set once, then lives in that scope until the scope is terminated. This enforces good design in my opinion. If you are using a session scoped bean and want values from it, it’s variables and methods are readily available to a request scoped bean, so just inject it and do your work there. This ensures a slim application.

public class TrackProducer {

    @Inject @HttpParam
    String trackId;

    SpotifyWeb spotifyWeb;

    String getTrack() {
        return spotifyWeb.wrap(trackId);

You may also want to look at Injection point metadata API for Web Beans by Gavin King

comments powered by Disqus

Moar stuffs

12 Sep 2017 Building an executable WS client using maven and metro
07 Jun 2015 Deploy an Ember app to gh-pages using npm run-script
06 Jun 2015 JSON Contract testing using unit tests to assert full stack integration across REST services
03 May 2015 simple http serve a directory from terminal
07 Jan 2014 civu, a CLI for cloning git repositories from jenkins views
06 Jan 2014 PyramidSort, a Sublime Text plugin for for reformatting text
05 Jan 2014 Git commit-message hook for JIRA issue tags
31 May 2013 hacking kitchen tiles with coffeescript
30 May 2013 Nuke, ps grep kill something
24 May 2013 mvnr: recursive mvn command runner
23 May 2013 Query By Example for JPA
22 May 2013 gitr: recursive git command runner
21 May 2013 Keeping gh-pages branch in sync with master
19 May 2013 Migrated from wordpress to jekyll and github pages
14 Aug 2012 Using Sublime Text 2 as git commit message editor
10 Mar 2012 QRGen, a small wrapper on top of ZXING for generating QRCodes in java
04 Jan 2012 My Bash PS1 with git branch info
17 Aug 2010 Making a swing project using IntelliJ IDEA GUI builder with maven, Including executable jar
01 May 2010 Using Arquillian to test against a remote jboss container from within IDEA
06 Apr 2010 WELD/CDI lightningtalk from Know IT 2010 annual conference
03 Apr 2010 Solving Sudoku using java swing and junit
01 Mar 2010 Simple CDI/WELD login example
01 Mar 2010 Implementing @RequestParam in CDI/WELD using Qualifier and InjectionPoint as @HttpParam
01 Nov 2009 Seam Maven Refimpl