为什么（（整数）weightModel.getObject（））.intValue（）；抛出异常

我正在通过“使用Wicket享受Web开发”这本书学习Wicket。它是为Wicket 1.4.7编写的
在一个示例中：

int-weight=（（整数）weightModel.getObject（））.intValue（）；

使用了
。 当我单击Submit按钮时，它会在第一行抛出意外的RuntimeException：

WicketMessage:org.apache.wicket.markup.html.form.IFormSubmitListener接口的方法onFormSubmitted针对组件[MarkupContainer[component id=form]]引发了异常

根本原因：

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

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)

可能weightModel.getObject（）无法转换为字符串

完整的异常消息位于底部

但将代码更改为：

int-weight=Integer.parseInt（（字符串）weightModel.getObject（））；

它很好用。它应该工作得很好。引发异常的原因是什么

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:

---

工作的函数返回哪个整数？ 哪个异常抛出

如果为零，则getObject（）可能根本不返回整数

可能无法将weightModel.getObject（）转换为字符串

否。返回的对象是一个字符串，而不是整数，因为您希望它与整数强制转换一起使用

---

一种解决方案是解析返回的字符串Integer.parseInt（str）（但我认为wicket可以为您做到这一点…

如果您使用的是wicket 1.4及更高版本，您应该使用泛型并使用它们告诉wicket您期望的类型。维克特会帮你做转换的

我建议进行以下更改（对于重量，另一个字段留作练习；）：

在页面中添加一个字段，该字段将保存用户的输入：

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，将添加权重文本字段的代码替换为：

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

form.add（新文本字段（“权重”）
，新PropertyModel（此“重量”）；

Wicket将用户输入转换成整数，并将其存储到字段权重中。PropertyModel使用页面本身访问字段

希望有帮助

提示：如果用户输入了无法转换的内容，Wicket将在文本字段中添加一个错误。您应该在页面中添加一个反馈面板来查看此信息

---

在以下过程中享受

：int-weight=（（整数）weightModel.getObject（））.intValue（）；并且getObject肯定会返回一个整数您使用的Wicket版本是什么？因为1.4您可以也应该使用泛型。另外，您可以显示用于添加表单字段的代码吗？啊，我看到了代码，抱歉。我是从手机上发布的，无法滚动。您确定需要setter+getter吗？不完全是。但我记得遇到了异常我重新编写了代码，它工作得很好。我真的不知道为什么它不工作。Wicket不会只使用尖括号进行转换，因为它不能。Java的泛型使用擦除，并且这种泛型类型信息在运行时保留。您必须提供一个正确类型的模型“后端”（例如，一个属性，如您的示例中所示）要使转换正常工作，请显式地向组件提供一个转换器，或者，如果特定组件支持转换，请告诉组件要转换的类型（TextField支持在构造函数中传递它）。我重新编写了代码，它工作得很好。我真的不知道为什么它不工作

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