無法使用[1]參數找到方法[屬性]

Question

我爲我的JSF應用程序實現了HttpSessionListener。

我有一個List<HttpSession>所有活動會話的對象到我的應用程序。在每個SessionCreated Event上，我將實際的HttpSession添加到List。在登錄時，我將一些屬性添加到活動會話中，並替換List中修改的會話。到目前爲止，這很好，它工作。但是現在我創建了一個PrimeFaces數據表來顯示哪個Session是一個未使用的Session。這意味着哪個會話沒有登錄屬性。 Login屬性是一個簡單的String對象。

這裏是DataTable的實現：

<p:dataTable var="sessions" value="#{applicationListener.sessions}" paginator="false" id="dt_sessions"> 
    <f:facet name="header"> 
     Sessions 
    </f:facet> 

    <p:column headerText="ID" style="font-size: 12px; text-align: center" > 
     #{sessions.id} 
    </p:column> 
    <p:column headerText="Name" style="font-size: 12px; text-align: center" > 
     #{sessions.attribute(login)} 
    </p:column> 
</p:dataTable> 

的Tomcat拋出一個HTTP 500堆棧跟蹤：

Feb 6, 2013 2:00:50 PM org.apache.catalina.core.StandardWrapperValve invoke 
SEVERE: Servlet.service() for servlet [Faces Servlet] in context with path [] threw  exception [/rmlcon.xhtml: Unable to find method [attribute] with [1] parameters] with root cause 
javax.el.ELException: /rmlcon.xhtml: Unable to find method [attribute] with [1] parameters 
at com.sun.faces.facelets.compiler.TextInstruction.write(TextInstruction.java:88) 
at com.sun.faces.facelets.compiler.UIInstructions.encodeBegin(UIInstructions.java:82) 
at com.sun.faces.facelets.compiler.UILeaf.encodeAll(UILeaf.java:183) 
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782) 
at org.primefaces.component.datatable.DataTableRenderer.encodeRegularCell(DataTableRenderer.java:741) 
at org.primefaces.component.datatable.DataTableRenderer.encodeRow(DataTableRenderer.java:693) 
at org.primefaces.component.datatable.DataTableRenderer.encodeTbody(DataTableRenderer.java:601) 
at org.primefaces.component.datatable.DataTableRenderer.encodeRegularTable(DataTableRenderer.java:220) 
at org.primefaces.component.datatable.DataTableRenderer.encodeMarkup(DataTableRenderer.java:192) 
at org.primefaces.component.datatable.DataTableRenderer.encodeEnd(DataTableRenderer.java:74) 
at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:875) 
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1786) 
at javax.faces.render.Renderer.encodeChildren(Renderer.java:168) 
at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:845) 
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1779) 
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782) 
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782) 
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:424) 
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:124) 
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:121) 
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) 
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139) 
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:594) 
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305) 
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) 
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222) 
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123) 
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) 
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168) 
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99) 
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929) 
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) 
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407) 
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1002) 
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585) 
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312) 
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) 
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) 
at java.lang.Thread.run(Thread.java:662) 

我真的不明白爲什麼它被拋出。請有人能解釋我的錯誤嗎？

謝謝。

Answer 1

正確的方法名稱是getAttribute()，而不是attribute()。

#{sessions.getAttribute(login)} 

記住，你調用一個方法，而不是訪問屬性，所以get前綴仍然是必須的。

---

無關的具體問題，我解決var="sessions"是var="session"，因爲它只涉及一個會話實例，而不是多個。否則，你的代碼讀取非常混亂（即它不是自我記錄）。

#{session.getAttribute(login)} 

Answer 2

我找到了一個解決辦法

<p:inputText id="valore" value="#{myBean.getValObj(0).val}" /> 

的bean是

public class MyBean{ 
    public ValObj getValObj(int idx){ 
    return new ValObj(this, idx); 
    } 

    public class ValObj{ 
     MyBean bean; 
     int idx = -1; 
     public ValObj(MyBean bean, int idx){ 
      this.bean = bean; 
      this.idx = idx; 
     } 

     public double getVal(){ 
      return valori[idx]; 
     } 
     public void setVal(double val){ 
      valori[idx] = val; 
     } 
    } 
}