MethodExpression.invoke() 上未找到方法异常

Question

我需要以编程方式调用/调用我的一个支持 bean 中的方法。我看过几个例子，据我所知，这个“应该”有效。

我的代码：

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);

“data.getValueExpression("value").getExpressionString() 返回字符串：

#{reports.customer}

有关我正在调用的 bean 的信息（不知道这些是否相关）：
类的托管 bean 名称是“report”
类在会话范围内
类实现可序列化
我调用的方法的访问修饰符是
方法签名中没有参数

我尝试调用的方法：

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

堆栈跟踪摘录

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)

非常感谢对此的任何帮助！

Answer 1

您试图将值表达式视为方法表达式。这是行不通的。值表达式指向 getter 方法（因此可以省略 get），而方法表达式指向操作方法，可能需要一个额外的参数。由于您已经有了 ValueExpression，因此只需直接从中获取值即可，而不是尝试将其视为 MethodExpression。

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

您不应更改视图中的 EL 字符串。只需保留它value="#{reports.customer}"。否则在普通视图下将无法工作。