NullPointerException when get a row from a list

[dago]

here is a class
package book;

import static javax.ejb.TransactionAttributeType.REQUIRES_NEW;
import static org.jboss.seam.ScopeType.SESSION;

import java.io.Serializable;
import java.util.List;

import javax.ejb.Remove;
import javax.ejb.Stateful;
import javax.ejb.TransactionAttribute;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import org.jboss.seam.ScopeType;
import org.jboss.seam.annotations.Logger;
import org.jboss.seam.annotations.Destroy;
import org.jboss.seam.annotations.Factory;
import org.jboss.seam.annotations.In;
import org.jboss.seam.annotations.Name;
import org.jboss.seam.annotations.Observer;
import org.jboss.seam.annotations.Out;
import org.jboss.seam.annotations.Scope;
import org.jboss.seam.annotations.datamodel.DataModel;
import org.jboss.seam.annotations.datamodel.DataModelSelection;
import org.jboss.seam.core.FacesMessages;
import org.jboss.seam.log.Log;

@Stateful
@Scope(ScopeType.SESSION)
@LoggedIn
@Name("cnMessageActionTest")
public class CnMessageActionTest implements CnMessageTestInterface
{
@PersistenceContext
private EntityManager em;

@DataModel
private List cnMessages;

//@Out(required=false)
//@PersistenceContext
private CnMessage cnMessage;

@Factory
//@Observer("CnMessage hello")
public void getCnMessages()
{
cnMessages = em.createQuery("from CnMessage").getResultList();
//cnMessage = cnMessages.get(0);
}
public void getCnMessage(String enMsg){
cnMessage = cnMessages.get(1);

//return "#{cnMessages.cnMsg}";
}


@Destroy @Remove
public void destroy()
{}
}

when i call the method "getCnMessage" from another class


public class UITicker extends UIOutput {
private CnMessageActionTest cmat;


public void encodeBegin(FacesContext ctx) throws IOException {

ResponseWriter writer = ctx.getResponseWriter();
writer.startElement("div", this);

String enMsg = (String)getAttributes().get("enMsg");

cmat = new CnMessageActionTest();
cmat.getCnMessage(enMsg);


if (enMsg!=null)
writer.writeAttribute("enMsg", enMsg, null);


String style = (String)getAttributes().get("style");
if (style!=null)
writer.writeAttribute("style", style, null);

String styleClass = (String)getAttributes().get("styleClass");
if (styleClass!=null)
writer.writeAttribute("class", styleClass, null);
}

public void encodeEnd(FacesContext context) throws IOException {
ResponseWriter writer = context.getResponseWriter();
writer.endElement("div");
}
}

it thow exception:

java.lang.NullPointerException
at book.CnMessageActionTest.getCnMessage(CnMessageActionTest.java:60)
at ticker.UITicker.encodeBegin(UITicker.java:55)
at com.sun.facelets.tag.jsf.ComponentSupport.encodeRecursive(ComponentSupport.java:232)
at com.sun.facelets.tag.jsf.ComponentSupport.encodeRecursive(ComponentSupport.java:239)
at com.sun.facelets.FaceletViewHandler.renderView(FaceletViewHandler.java:554)
at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:352)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at book.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:42)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.jboss.seam.servlet.SeamRedirectFilter.doFilter(SeamRedirectFilter.java:30)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:175)
at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:74)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:664)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.MasterSlaveWorkerThread.run(MasterSlaveWorkerThread.java:112)
at java.lang.Thread.run(Thread.java:619)

[smokingapipe]

If the cnMessages component has not been accessed from a page, then Seam will not have initialized it (ie, called the factory). Just because your other class is trying to access it, Seam doesn't know anything about that and won't magically call the factory method. That class will have to call the factory method manually, or do it some other way.

[dago]

thank u SmokingAPipe!

you say:
"That class will have to call the factory method manually, or do it some other way"

how can i do it?

[smokingapipe]

You need to have a @Begin method that initializes the cnMessages member. You're calling getCnMessage() before cnMessages has been set to anything. Tell me where is cnMessages being set? If you can answer that question you'll see what's going on.

[dago]

hello SmokingAPipe.

you said:

Tell me where is cnMessages being set?

see the red code bellow:

public class UITicker extends UIOutput {
private CnMessageActionTest cmat;

public void encodeBegin(FacesContext ctx) throws IOException {

ResponseWriter writer = ctx.getResponseWriter();
writer.startElement("div", this);

String enMsg = (String)getAttributes().get("enMsg");

cmat = new CnMessageActionTest();
cmat.getCnMessage(enMsg);
if (enMsg!=null)
writer.writeAttribute("enMsg", enMsg, null);

String style = (String)getAttributes().get("style");
if (style!=null)
writer.writeAttribute("style", style, null);

String styleClass = (String)getAttributes().get("styleClass");
if (styleClass!=null)
writer.writeAttribute("class", styleClass, null);
}

public void encodeEnd(FacesContext context) throws IOException {
ResponseWriter writer = context.getResponseWriter();
writer.endElement("div");
}
}

thanks! (I am a newer to seam)

[dago]

this is the javabean:

@Entity
@Name("cnMessage")
public class CnMessage implements Serializable
{
 private int idt;
 private String cnMsg;
 private String enMsg;


 public CnMessage() {}

 public CnMessage(
 int idt,
 String cnMsg,
 String enMsg)
 {
 this.idt = idt;
 this.cnMsg = cnMsg;
 this.enMsg = enMsg;
 }

 @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
 public int getIdt()
 {
 return idt;
 }

 public void setIdt(int idt)
 {
 this.idt=idt;
 }

 public String getCnMsg()
 {
 return cnMsg;
 }

 public void setCnMsg(String cnMsg)
 {
 this.cnMsg=cnMsg;
 }

 public String getEnMsg()
 {
 return enMsg;
 }

 public void setEnMsg(String enMsg)
 {
 this.enMsg=enMsg;
 }




}