JSF h:selectOneMenu 问题：java.lang.IllegalArgumentException 无法将类 java.lang.String 类型的“字符串”转换为接口 java.util.List
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JSF h:selectOneMenu trouble: java.lang.IllegalArgumentException Cannot convert "string" of type class java.lang.String to interface java.util.List
提问by Rob
I have some JSF-trouble using h:selectOneMenu with a list from my backend bean: My xhtml file looks like this:
我在使用 h:selectOneMenu 和后端 bean 中的列表时遇到了一些 JSF 问题：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>
where the corresponding managing bean looks like this:
相应的管理 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;
}
The problem occurs on submitting the form in my browser, the full error stack looks like this:
在我的浏览器中提交表单时出现问题，完整的错误堆栈如下所示：
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.access0(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
采纳答案by barsju
Try this:
尝试这个：
<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>
where the corresponding managing bean looks like this:
相应的管理 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;
}
回答by Matt Handy
Your value attribute needs to be a Stringinstead of a List<String>because it will hold the selection. And your bean is not really a bean since it needs unique setters for the fields in order to be processed by JSF.
您的 value 属性需要是 aString而不是 aList<String>因为它将保存选择。而且您的 bean 并不是真正的 bean，因为它需要为字段设置唯一的 setter 才能由 JSF 处理。
So you should change your bean code in a way that it has a List<String>with getters and setters and a Stringfor the selection with separategetters and setters:
因此，您应该更改 bean 代码，使其具有List<String>带有 getter 和 setter的方式，以及String带有单独的getter 和 setter的用于选择的代码：
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;
}
And in the view:
在视图中：
<h:selectOneMenu id="preset" value="#{overview.selectedPdfPreset}" >
<f:selectItems value="#{overview.pdfPresets}" />
</h:selectOneMenu>
