CDI-JSF: Injecting HTTP parameters via a producer method

Remeber from the Inject a Java logger via a CDI producer method post that the InjectionPoint can be used to access metadata of the class where the artifact is injected. Based on this statement, we can write a producer method capable to inject HTTP parameters.

Typically, as a JSF developer you write a form like below:

<h:form>

 Name: <h:inputText value="#{playerBean.name}"/>

 Surname: <h:inputText value="#{playerBean.surname}"/>

 <h:commandButton value="Register" action="#{playerBean.registerAction()}"/>

</h:form>

The two fields, name and surname are declared in a bean private and with some getters and setters:

@Named

@RequestScoped

public class PlayerBean {

 private static final Logger LOG = Logger.getLogger(PlayerBean.class.getName());

 private String name;

 private String surname;

 public String getName() {

  return name;

 }

 public void setName(String name) {

  this.name = name;

 }

 public String getSurname() {

  return surname;

 }

 public void setSurname(String surname) {

  this.surname = surname;

 }

 public void registerAction() {

  LOG.info("Register: " + name + " " + surname);

 }

}

Well, nothing fancy here, and even a JSF novice can understand what this code do just by looking over it in a second. But, now let's replace the <h:inputText/> with simple HTML <input/> as below:

<h:form>

 Name: <input type="text" name="name" id="name"/>

 Surname: <input type="text" name="surname" id="surname"/>

 <h:commandButton value="Register" action="#{playerBean.registerAction()}"/>

</h:form>

This time our getters and setters become useless, but we can still obtain these two HTTP parameters like this:

FacesContext facesContext = FacesContext.getCurrentInstance();

ExternalContext externalContext = facesContext.getExternalContext();

ServletRequest request = (ServletRequest) externalContext.getRequest();

request.getParameter("name");

request.getParameter("surname");

Now, let's generalize this  case in CDI style. Instead of writing request.getParameter("name"); we want to inject the HTTP parameter. For this, we start by defining a qualifier and instruct the container to ignore the value:

@Qualifier

@Retention(RUNTIME)

@Target({METHOD, FIELD, PARAMETER, TYPE})

public @interface HttpParam {

 @Nonbinding public String value();

}

Furthermore, we write the producer method as below - instead of explicitly nominated the HTTP parameter name, we use the InjectionPoint metadata features:

public class HttpParams {

 @Produces

 @HttpParam("")

 String getParamValue(InjectionPoint ip) {

  // obtain the current request

  FacesContext facesContext = FacesContext.getCurrentInstance();

  ExternalContext externalContext = facesContext.getExternalContext();

  ServletRequest request = (ServletRequest) externalContext.getRequest();

  // obtain the desired parameter

  Annotated annotated = ip.getAnnotated();

  HttpParam httpParam = annotated.getAnnotation(HttpParam.class);

  return request.getParameter(httpParam.value());

 }

}

Finally, we adjust the PlayerBean to inject the desired HTTP parameters:

@Named

@RequestScoped

public class PlayerBean {

 private static final Logger LOG = Logger.getLogger(PlayerBean.class.getName());

 @HttpParam("name") @Inject String name;

 @HttpParam("surname") @Inject String surname;

 public void registerAction() {

  LOG.log(Level.INFO, "Register: {0} {1}", new Object[]{name, surname});

 }

}

Done! Following this example you can inject any other HTTP parameter. The complete example is available here.

Now, you can use this with <f:param/> or in place of <f:event type="preRenderView/> or <f:viewAction/>. In addition, you may be interested in converting and validating the HTTP parameters. Check out a great implementation from OmniFaces which is materialized in the CDI annotation @Param that allows us to inject, convert and validate a HTTP request parameter in a CDI managed bean.