为什么（（（integer）flowmodel.getObject（））。intvalue（）;抛出异常

StackOverflow https://stackoverflow.com/questions/4550419

  •  13-10-2019
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题

我正在通过“享受网络开发与检票口”的书来学习检票口。
在一个示例中：

int weight = ((Integer) weightModel.getObject()).intValue();

用来。当我单击“提交”按钮时，它会引发意外的Runtime Exception第一行：

WITCHETMESSAGE：接口org.apache.wicket.markup.html.form.form.sibort.sibortsubmitlistlistlistener的方法onformSubtem，旨在以组件[markupcontainer [component id = form id = form]]抛出一个例外

根本原因：

java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer*

大概 stroukeModel.getObject（） 无法转换 到字符串.

完整的异常消息在底部。

但是将代码更改为：

int weight=Integer.parseInt( (String) weightModel.getObject());

它可以正常工作。它应该很好。是什么 原因 为了抛出例外吗？


完整代码：

getrequest.java

package myapp.postage;
import java.util.HashMap;
import java.util.Map;

import org.apache.wicket.markup.html.WebPage;
import org.apache.wicket.markup.html.form.Form;
import org.apache.wicket.markup.html.form.TextField;
import org.apache.wicket.model.Model;

@SuppressWarnings("unchecked")
public class GetRequest extends WebPage {
 private Model weightModel=new Model();
 private Model patronCodeModel=new Model();
 private Map patronCodeToDiscount; 

 public GetRequest(){
  patronCodeToDiscount=new HashMap();
  patronCodeToDiscount.put("p1", new Integer(90));
  patronCodeToDiscount.put("p2", new Integer(95));

  Form form=new Form("form"){
   @Override
   protected void onSubmit(){
    int weight = ((Integer) weightModel.getObject()).intValue();
    Integer discount=(Integer)patronCodeToDiscount.get(patronCodeModel.getObject());
    int postagePerKg=10;
    int postage=weight*postagePerKg;
    if(discount!=null){
     postage=postage*discount.intValue()/100;
    }
    ShowPostage showPostage=new ShowPostage(postage);
    setResponsePage(showPostage);
   }
  };
  TextField weight=new TextField("weight",weightModel);
  form.add(weight);
  TextField patronCode=new TextField("patronCode",patronCodeModel);
  form.add(patronCode);
  add(form);
 }
}

html文件getRequest.html：

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
        <form wicket:id="form">
     <table>
      <tr>
       <td>Weight</td>
       <td><input type="text" wicket:id="weight"/></td>
      </tr>
      <tr>
       <td>Patron code:</td>
       <td><input type="text" wicket:id="patronCode"/></td>
      </tr>
      <tr>
       <td></td>
       <td><input type="submit"/></td>
      </tr>
     </table>
         </form>
    </html>

异常消息：WITCHETMESSAGE：接口org.apache.wicket.markup.html.form.form.sibort.sibortsubmitlistlistlistener的方法onformSubtem，旨在以组件[markupcontainer [component id = form id = form]]抛出一个例外

根本原因：

java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer
     at myapp.postage.GetRequest$1.onSubmit(GetRequest.java:26)
     at org.apache.wicket.markup.html.form.Form.delegateSubmit(Form.java:1538)
     at org.apache.wicket.markup.html.form.Form.process(Form.java:934)
     at org.apache.wicket.markup.html.form.Form.onFormSubmitted(Form.java:896)
     at java.lang.reflect.Method.invoke(Method.java:597)
     at org.apache.wicket.RequestListenerInterface.invoke(RequestListenerInterface.java:182)
     at org.apache.wicket.request.target.component.listener.ListenerInterfaceRequestTarget.processEvents(ListenerInterfaceRequestTarget.java:73)
     at org.apache.wicket.request.AbstractRequestCycleProcessor.processEvents(AbstractRequestCycleProcessor.java:92)
     at org.apache.wicket.RequestCycle.processEventsAndRespond(RequestCycle.java:1250)
     at org.apache.wicket.RequestCycle.step(RequestCycle.java:1329)
     at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1428)
     at org.apache.wicket.RequestCycle.request(RequestCycle.java:545)
     at org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:479)
     at org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:312)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
     at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
     at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
     at com.springsource.insight.collection.tcserver.request.HttpRequestOperationCollectionValve.invoke(HttpRequestOperationCollectionValve.java:60)
     at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
     at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
     at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
     at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
     at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:849)
     at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
     at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:379)
     at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
     at java.lang.Thread.run(Thread.java:619)

Complete stack:
org.apache.wicket.WicketRuntimeException: Method onFormSubmitted of interface org.apache.wicket.markup.html.form.IFormSubmitListener targeted at component [MarkupContainer [Component id = form]] threw an exception
     at org.apache.wicket.RequestListenerInterface.invoke(RequestListenerInterface.java:193)
     at org.apache.wicket.request.target.component.listener.ListenerInterfaceRequestTarget.processEvents(ListenerInterfaceRequestTarget.java:73)
     at org.apache.wicket.request.AbstractRequestCycleProcessor.processEvents(AbstractRequestCycleProcessor.java:92)
     at org.apache.wicket.RequestCycle.processEventsAndRespond(RequestCycle.java:1250)
     at org.apache.wicket.RequestCycle.step(RequestCycle.java:1329)
     at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1428)
     at org.apache.wicket.RequestCycle.request(RequestCycle.java:545)
     at org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:479)

java.lang.reflect.InvocationTargetException
     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
     at java.lang.reflect.Method.invoke(Method.java:597)
     at org.apache.wicket.RequestListenerInterface.invoke(RequestListenerInterface.java:182)
     at org.apache.wicket.request.target.component.listener.ListenerInterfaceRequestTarget.processEvents(ListenerInterfaceRequestTarget.java:73)
     at org.apache.wicket.request.AbstractRequestCycleProcessor.processEvents(AbstractRequestCycleProcessor.java:92)
     at org.apache.wicket.RequestCycle.processEventsAndRespond(RequestCycle.java:1250)
     at org.apache.wicket.RequestCycle.step(RequestCycle.java:1329)
     at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1428)
     at org.apache.wicket.RequestCycle.request(RequestCycle.java:545)
     at org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:479)
有帮助吗？

解决方案

如果您使用的是1.4及以上的检票口，则应使用仿制药并使用它们来告诉检票口您期望什么类型。然后，检票口会为您进行转换。

我建议采取以下更改（对于重量，另一个领域作为练习;）：）：

将字段添加到您的页面，以保存用户的输入： 

private Integer weight;

为此字段添加Getter和Setter：

public Integer getWeight() {return weight;}
public void SetWeight(Integer weight) {this.weight = weight;}

然后，替换代码以添加文本字段的权重：

form.add(new TextField<Integer>("weight"
     , new PropertyModel<Integer>(this, "weight"));

这样，检票员将将用户输入转换为整数并将其存储到现场重量中。 PropertyModel使用页面本身访问字段。

希望有帮助。

提示：如果用户输入无法转换的东西，检票员将为Textfield添加错误。您应该在页面中添加一个反馈panel，以查看此内容。

享受

其他提示

有效的功能返回哪个整数？还有哪个例外？

如果其为零，则可能根本不会返回整数。

可能无法将flowemodel.getObject（）转换为字符串。

不。返回的对象是字符串而不是整数，因为您需要使用整数铸件。

一种解决方案是解析返回的字符串integer.parseint（str）（但我认为检票口可以为您做到这一点...）

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