Method not found exception on MethodExpression.invoke()

Question

I have a need to programmatically call/invoke a method in one of my backing beans. I've looked at several examples, and from what I can see, this "should" work.

My code:

UIData data = (UIData)component;
fc = FacesContext.getCurrentInstance();
elc = fc.getELContext();

elFactory = fc.getApplication().getExpressionFactory();
mexp =
    elFactory.createMethodExpression(elc, data.getValueExpression("value").getExpressionString(), Result.class, new Class[]{});
Object methodResult = mexp.invoke(elc, null);

The "data.getValueExpresssion("value").getExpressionString() returns the string:

#{reports.customer}

Info about the bean I'm calling (don't know if these are relevant):
Class's managed bean name is "report"
Class is in Session-scope
Class implements Serializable
The access modifier of the method I'm calling is
There are no parameters in the method signature

Method I'm trying to invoke:

public Result getCustomer() {
    Result result = null;
    try {
        ...perform database call
    } catch (Exception e) {
        log.error(e);
    }
    return result;
}

Stack-Trace Excerpt

SEVERE: javax.el.MethodNotFoundException: Method not found: [email protected]()
javax.faces.el.EvaluationException: javax.el.MethodNotFoundException: Method not found: [email protected]()
    at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:98)
    at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:98)
    at javax.faces.component.UICommand.broadcast(UICommand.java:311)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:781)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1246)
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:77)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:97)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:114)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:308)
...
Caused by: javax.el.MethodNotFoundException: Method not found: [email protected]()
    at com.sun.el.util.ReflectionUtil.getMethod(ReflectionUtil.java:155)
    at com.sun.el.parser.AstValue.invoke(AstValue.java:231)
    at com.sun.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:297)
    at com.npp.business.TableToExcelManager.initExcelWorker(TableToExcelManager.java:247)
    at com.npp.beans.reports.SharebackReportsBean.exportToExcel(SharebackReportsBean.java:439)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.sun.el.parser.AstValue.invoke(AstValue.java:234)
    at com.sun.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:297)
    at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:102)
    at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:84)
    ... 26 more
Mar 23, 2011 11:29:34 AM com.sun.faces.lifecycle.InvokeApplicationPhase execute
WARNING: #{reports.exportToExcel}: javax.el.MethodNotFoundException: Method not found: [email protected]()
javax.faces.FacesException: #{reports.exportToExcel}: javax.el.MethodNotFoundException: Method not found: [email protected]()
    at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:114)
    at javax.faces.component.UICommand.broadcast(UICommand.java:311)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:781)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1246)
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:77)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:97)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:114)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:308)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

Any help on this is greatly appreciated!

Answer 1

You're attempting to treat a value expression as a method expression. This isn't going to work. Value expressions points to getter methods (and thus get can be omitted) while method expressions points to action methods, possibly taking an extra argument. Since you already have the ValueExpression, just get value from it directly instead of attempting to treat it like a MethodExpression.

Result result = (Result) data.getValueExpression("value").getValue(elc);

You should not change the EL string in the view. Just keep it value="#{reports.customer}". Otherwise it won't work in the normal view.