What is difference between #{bean.function} and #{bean.function()}?

Question

i am new in JSF.I wonder one point at JSF/navigation rules.i have four pages, index,p1,p2,p3.When i am trying to navigate to a page with action="#{bean.gotoP1()}", it is giving error like that ;

"Unable to find matching navigation case with from-view-id '/index.xhtml' for action '#{bean.gotoP1()}' with outcome 'success'"

My question is simple; why can not I navigate with #{bean.gotoP1()} , and i have to remove parenthesis , #{bean.gotoP1} ?

My codes are below;

index.xhtml

<h:body>    
    <h:form>
        <h:commandButton action="#{mybean.gotoP1()}" value="P1"/>
        <h:commandButton action="#{mybean.gotoP2()}" value="P2"/>
        <h:commandButton action="#{mybean.gotoP3()}" value="P3"/>
    </h:form>
</h:body>

mybean.java

@ManagedBean
@RequestScoped
public class Mybean implements Serializable{

    private static final long serialVersionUID=1L;

    public Mybean() {
    }

    public String gotoP1(){
        return "success";
    }

    public String gotoP2(){
        return "success";
    }

    public String gotoP3(){
        return "positive";
    }
}

faces-config.xml

<navigation-rule>
    <from-view-id>/index.xhtml</from-view-id>

    <navigation-case>
        <from-action>#{mybean.gotoP1}</from-action>
        <from-outcome>success</from-outcome>
        <to-view-id>/p1.xhtml</to-view-id>
    </navigation-case>

    <navigation-case>
        <from-action>#{mybean.gotoP2}</from-action>
        <from-outcome>success</from-outcome>
        <to-view-id>/p2.xhtml</to-view-id>
    </navigation-case>

    <navigation-case>
        <from-action>#{mybean.gotoP3}</from-action>
        <from-outcome>positive</from-outcome>
        <to-view-id>/p3.xhtml</to-view-id>
    </navigation-case>
</navigation-rule>

Thanks....

BalusC BalusC · Accepted Answer · 2015-08-13T22:07:51

My question is simple; why can not I navigate with #{bean.gotoP1()} , and i have to remove parenthesis , #{bean.gotoP1} ?

Because the EL syntax doesn't match with the navigation case. You defined #{bean.gotoP1} instead of #{bean.gotoP1()} as from-action in navigation case. Simple as that.

Those argumentless parentheses are actually unnecessary. They started to spread over JSF pages since introduction of EL 2.2, because the average EL 2.2 aware IDE thinks to be smarter than it is and unnecessarily auto-completes the method expressions with parentheses and all, confusingly making the JSF starter to think that they are actually required. I've even seen code snippets coming along from starters who actually used #{bean.getProperty()} instead of #{bean.property} to output a property, which would then later fail with a javax.el.PropertyNotWritableException when used in an input component.

Just leave out those argumentless parentheses. It's not true that this syntax is required and "normal" in JSF. Moreover, navigation rules are very JSF 1.x-ish. Also, performing navigation using POST requests is very JSF 1.x-ish. Maybe you're just learning and playing around. That's OK, but to learn about the right ways and a bit of history, carefully read below links:

Last but not least, our JSF wiki page is a great place to start.

What is difference between #{bean.function} and #{bean.function()}?

1 Answers