Java – get request parameters in @ viewscoped bean

I have a list from which the user can select "PQ" (link list) When clicking or otherwise entering the browser, the main page of each PQ shall be displayed Each PQ page is a table

Http: / / local host: 8080 / project name / main jsf ID = 2

This is the first PQ bean:

@Named
@ViewScoped
public class PqHome implements Serializable
{
    @PersistenceContext(unitName="...")
    private EntityManager em;

    private Integer id;
    private PQ instance;

    @postconstruct
    public void init()
    {
        System.out.println("ID is " + id); // ID from URL param

        instance = em.find(PQ.class,id);       
    }

    public Integer getId()
    {
        return id;
    }

    public void setId(Integer id)
    {
        this.id = id;
    }

    public PQ getInstance()
    {
        return instance;
    }
}

This is main xhtml：

<ui:composition xmlns="http://www.w3.org/1999/xhtml"
                ...>
  <ui:define name="Metadata">
    <f:Metadata>
      <f:viewParam name="id" value="#{pqHome.id}">
        <f:convertNumber integerOnly="#{true}" />
      </f:viewParam>
      <!--f:event type="preRenderView" listener="#{pqHome.init}" /-->
    </f:Metadata>
  </ui:define>
  <ui:define name="title">
    <h:outputText value="Main" />
  </ui:define>
  ...
</ui:composition>

Whenever I choose or otherwise refresh a page / url, I get a NullPointerException from the entitymanager:

org.jboss.weld.exceptions.WeldException: WELD-000049 Unable to invoke [method] @postconstruct public de.mycomp.myproj.beans.PqHome.init() on de.mycomp.myproj.beans.PqHome@4f0ea68f
    at org.jboss.weld.bean.AbstractClassBean.defaultpostconstruct(AbstractClassBean.java:595)
...
Caused by: java.lang.IllegalArgumentException: id to load is required for loading
at org.hibernate.event.spi.LoadEvent.<init>(LoadEvent.java:87)
at org.hibernate.event.spi.LoadEvent.<init>(LoadEvent.java:59)
at org.hibernate.internal.SessionImpl.get(SessionImpl.java:961)
at org.hibernate.internal.SessionImpl.get(SessionImpl.java:957)
at org.hibernate.ejb.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:787)
at org.hibernate.ejb.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:762)
at org.jboss.as.jpa.container.AbstractEntityManager.find(AbstractEntityManager.java:221)
at de.mycomp.myproj.beans.PqHome.init(PqHome.java:47)
... 56 more

[line 47 is em.find (...)]

This line

<f:event type="preRenderView" listener="#{pqHome.init}" />

It won't make things better I'm depressed now

How to pass URL get request parameters into @ viewscoped bean?

Note: I bet it's not a trivial matter I may have made a conceptual mistake, so any tips on how to improve are welcome I think I need to select @ viewscoped because there will be a more complex Ajax based GUI on this page. I really want to access it through the URL get parameter

thank you

Solution

Call @ postconstruct directly after bean construction and all dependency injection (for example, @ persistencecontext, @ EJB, @ managedproperty, @ inject, etc.)

< F: viewparam > set its value in the update model value stage, which is the long-term (post) construction of the bean Therefore, the < F: viewparam > value has not been set in @ postconstruct It was still empty then

You are close to < F: event type = "prerenderview" >, but you must delete the @ postconstruct comment

So:

<f:viewParam name="pq" value="#{pqHome.id}">
    <f:convertNumber integerOnly="#{true}" />
</f:viewParam>
<f:event type="preRenderView" listener="#{pqHome.init}" />

with

private Integer id;

public void init() {
    instance = em.find(PQ.class,id);       
}

It has nothing to do with the specific problem. I suggest using a converter instead See also communication in JSF 2.0 – converting and validating get request parameters

@The named @ viewscoped combination also does not work as expected JSF specific @ viewscoped is only used with JSF specific @ managedbean Your CDI specific @ named will appear as @ requestscoped. In this way Use @ managedbean instead of @ named or CDI specific @ conversationscoped instead of @ viewscoped