JSF h：selectOneMenu故障：java.lang.IllegalArgumentException無法將類型類java.lang.String的“字符串”轉換為接口java.util.List

Question

我在使用h：selectOneMenu和后端bean中的列表時遇到了一些JSF問題：我的xhtml文件如下所示：

  <f:view>
    <h:form id="serverOptions">
      <h:selectOneMenu id="preset" value="#{overview.pdfPresets}" >
        <f:selectItems value="#{overview.pdfPresets}" />
      </h:selectOneMenu>
      <h:commandButton action="submit" value="Submit" />
    </h:form>
  </f:view>

相應的管理bean如下所示：

private List<String> pdfPresets;
private String pdfPreset;

/**
 * Returns a list of pdfPresets
 * @return a List<String> of pdf preset names
 */
public final List<String> getPdfPresets() {
    return pdfPresets;
}

/**
 * Sets the name of the selected pdfPreset
 * (trying to overload setPdfPresets here)
 * @param presetName
 * @see setPdfPreset
 */
public final void setPdfPresets(String presetName) {
    // write preset name somehwere else
    this.presetName = presetName;
}

/**
 * Sets the pdfPresets
 * @param list
 */
public final void setPdfPresets(List<String> list) {
    pdfPresets = list;
}

在我的瀏覽器中提交表單時出現問題，完整的錯誤堆棧如下所示：

EVERE: An exception occurred
javax.faces.component.UpdateModelException: java.lang.IllegalArgumentException: Cannot convert screen_druckbogen of type class java.lang.String to interface java.util.List
    at javax.faces.component.UIInput.updateModel(UIInput.java:398)
    at javax.faces.component.UIInput.processUpdates(UIInput.java:299)
    at javax.faces.component.UIForm.processUpdates(UIForm.java:187)
    at javax.faces.component.UIComponentBase.processUpdates(UIComponentBase.java:1258)
    at javax.faces.component.UIViewRoot._processUpdatesDefault(UIViewRoot.java:1317)
    at javax.faces.component.UIViewRoot.access$600(UIViewRoot.java:75)
    at javax.faces.component.UIViewRoot$UpdateModelPhaseProcessor.process(UIViewRoot.java:1419)
    at javax.faces.component.UIViewRoot._process(UIViewRoot.java:1278)
    at javax.faces.component.UIViewRoot.processUpdates(UIViewRoot.java:761)
    at org.apache.myfaces.lifecycle.UpdateModelValuesExecutor.execute(UpdateModelValuesExecutor.java:34)
    at org.apache.myfaces.lifecycle.LifecycleImpl.executePhase(LifecycleImpl.java:171)
    at org.apache.myfaces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:189)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:390)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:440)
    at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:230)
    at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:943)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:756)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:410)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)
Caused by: java.lang.IllegalArgumentException: Cannot convert screen_druckbogen of type class java.lang.String to interface java.util.List
    at com.sun.el.lang.ELSupport.coerceToType(ELSupport.java:397)
    at com.sun.el.parser.AstValue.setValue(AstValue.java:164)
    at com.sun.el.ValueExpressionImpl.setValue(ValueExpressionImpl.java:273)
    at org.apache.myfaces.view.facelets.el.TagValueExpression.setValue(TagValueExpression.java:117)
    at javax.faces.component.UIInput.updateModel(UIInput.java:380)
    ... 29 more

Answer 1

您的value屬性必須是String而不是List<String>因為它將保存選擇。 而且您的bean並不是真正的bean，因為它需要字段的唯一設置器才能由JSF處理。

因此，您應該更改bean代碼，使其具有帶有getter和setter的List<String>和帶有單獨的 getter和setter的選擇String ：

private List<String> pdfPresets;
private String selectedPdfPreset;

public List<String> getPdfPresets() {
  return pdfPresets;
}

public void setPdfPresets(List<String> pdfPresets) {
  this.pdfPresets = pdfPresets;
}

public String getSelectedPdfPreset() {
  return selectedPdfPreset;
}

public void setSelectedPdfPreset(String selectedPdfPreset) {
  this.selectedPdfPreset = selectedPdfPreset;
}

並在視圖中：

<h:selectOneMenu id="preset" value="#{overview.selectedPdfPreset}" >
        <f:selectItems value="#{overview.pdfPresets}" />
</h:selectOneMenu>

Answer 2

嘗試這個：

  <f:view>
    <h:form id="serverOptions">
      <h:selectOneMenu id="preset" value="#{overview.pdfPreset}" > <!-- typo here -->
        <f:selectItems value="#{overview.pdfPresets}" />
      </h:selectOneMenu>
      <h:commandButton action="submit" value="Submit" />
    </h:form>
  </f:view>

相應的管理bean如下所示：

private List<String> pdfPresets;
private String pdfPreset;

/**
 * Returns a list of pdfPresets
 * @return a List<String> of pdf preset names
 */
public final List<String> getPdfPresets() {
    return pdfPresets;
}

/**
 * Sets the name of the selected pdfPreset
 * (trying to overload setPdfPresets here)
 * @param presetName
 * @see setPdfPreset
 */
public final void setPdfPreset(String presetName) { //renamed method
    // write preset name somehwere else
    pdfPreset = presetName; //use the correct variable
}

/**
 * Sets the pdfPresets
 * @param list
 */
public final void setPdfPresets(List<String> list) {
    pdfPresets = list;
}