h：selectManyCheckBox获取NullPointerException

Question

This is a Seam application.

HTML

<h:selectManyCheckbox value="#{officeCriteria.carrier}">
    <f:selectItem itemValue="ATT" itemLabel="ATT" />
    <f:selectItem itemValue="VZB" itemLabel="VZB" />
</h:selectManyCheckbox>

backing bean OfficeCriteria:

private List<String> carrier;

public List<String> getCarrier() {
    return carrier;
}

public void setCarrier(List<String> carrier) {
    this.carrier = carrier;
}

When I load the page I get a null pointer exception on carrier. What am I doing wrong?

    2:10,963 ERROR [viewhandler] Error Rendering View[/ONDSearchPage.xhtml]
javax.faces.FacesException: javax.el.ELException: /ONDSearchPage.xhtml @264,81 value="#{officeCriteria.carrier}": Error reading 'carrier' on type dne.nmt.ond.model.OfficeCriteria_$$_javassist_seam_6
    at javax.faces.component.UIOutput.getValue(UIOutput.java:187)
    at com.sun.faces.renderkit.html_basic.MenuRenderer.getCurrentSelectedValues(MenuRenderer.java:593)
    at com.sun.faces.renderkit.html_basic.SelectManyCheckboxListRenderer.encodeEnd(SelectManyCheckboxListRenderer.java:117)
    ....
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:601)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
    at java.lang.Thread.run(Unknown Source)
Caused by: javax.el.ELException: /ONDSearchPage.xhtml @264,81 value="#{officeCriteria.carrier}": Error reading 'carrier' on type dne.nmt.ond.model.OfficeCriteria_$$_javassist_seam_6
    at com.sun.facelets.el.TagValueExpression.getValue(TagValueExpression.java:76)
    at javax.faces.component.UIOutput.getValue(UIOutput.java:184)
    ... 95 more
Caused by: java.lang.NullPointerException
    at dne.nmt.ond.model.OfficeCriteria.getCarrier(OfficeCriteria.java:108)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    .....
    at org.jboss.el.parser.AstPropertySuffix.getValue(AstPropertySuffix.java:53)
    at org.jboss.el.parser.AstValue.getValue(AstValue.java:67)
    at org.jboss.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:186)
    at com.sun.facelets.el.TagValueExpression.getValue(TagValueExpression.java:71)
    ... 96 mor

Answer 1

What is in OfficeCriteria.java line 108? Something you are referencing there is null, and I guess you aren't expecting it to be.

Answer 2

What I suggest is that you set an empty list (and not null ) for the property carrier :

private List<String> carrier = new ArrayList<String>();

public List<String> getCarrier() {
        return carrier;
}

public void setCarrier(List<String> carrier) {
        this.carrier = carrier;
}

Answer 3

The answer is that my original code works as it is.

The difficulty (and what I left out) was a debugging statement that referenced an element in the list. Thanks to the person who suggested I actually look at line 108. :-)

And BTW to the person who suggested initializing this with a new List, I had tried that already and got some error (I can't remember what).

Thanks for the help.