[英]java.lang.ClassCastException: cannot be cast to java.util.List
[英]java.lang.ClassCastException: java.util.Collections$UnmodifiableMap cannot be cast to Param
我正在嘗試將轉換器寫入到我不想選擇對象的selectonemenu中。 我的對象(“ Param”)類如下所示:
public class Param {
private Integer id;
private String name;
public Param(Integer id, String name){
this.id = id;
this.name = name;
}
public Integer getId(){
return this.id;
}
public String getName(){
return this.name;
}
@Override
public boolean equals(Object object) {
return (object instanceof Param) && (id != null)
? id.equals(((Param) object).getId())
: (object == this);
}
@Override
public int hashCode() {
return (id != null)
? (this.getClass().hashCode() + id.hashCode())
: super.hashCode();
}
}
豆角,扁豆:
@ManagedBean
@SessionScoped
public class MainBean {
private List<Param> params;
private Param selectedParam;
public List<Param> getParams(){
return this.params;
}
public Param getSelectedParam(){
return this.selectedParam;
}
public void setSelectedParam(Param param){
this.selectedParam = param;
}
public MainBean(){
//filling params - works good
}
}
轉換器(我知道那里應該是null檢查和東西):
@FacesConverter(value = "paramConverter", forClass = Param.class)
public class ParamConverter implements Converter {
private List<Param> getParams(){
ExternalContext tmpEC;
Map sMap;
tmpEC = FacesContext.getCurrentInstance().getExternalContext();
sMap = tmpEC.getSessionMap();
MainBean mainBean = (MainBean) sMap.get("mainBean");
return mainBean.getParams();
}
@Override
public Object getAsObject(FacesContext context, UIComponent component, String value)
{
Integer id = Integer.valueOf(value);
List<Param> params = this.getParams();
Param param = null;
for(int i=0; i < params.size(); i++){
if(id == params.get(i).getId()){
param = params.get(i);
break;
}
}
return param;
}
@Override
public String getAsString(FacesContext context, UIComponent component, Object value)
{
Param param = (Param)value;
return String.valueOf(param.getId());
}
}
SelectOneMenu:
<h:selectOneMenu value="#{mainBean.selectedParam}">
<f:converter converterId="paramConverter" />
<f:selectItems value="#{mainBean.params}"
var="param"
itemValue="#{param}"
itemLabel="#{param.name}"
/>
</h:selectOneMenu>
Tomcat輸出:
HTTP Status 500 - java.util.Collections$UnmodifiableMap cannot be cast to Param
--------------------------------------------------------------------------------
type Exception report
message java.util.Collections$UnmodifiableMap cannot be cast to Param
description The server encountered an internal error that prevented it from fulfilling this request.
exception
javax.servlet.ServletException: java.util.Collections$UnmodifiableMap cannot be cast to Param
javax.faces.webapp.FacesServlet.service(FacesServlet.java:659)
root cause
java.lang.ClassCastException: java.util.Collections$UnmodifiableMap cannot be cast to Param
ParamConverter.getAsString(ParamConverter.java:40)
com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.getFormattedValue(HtmlBasicRenderer.java:521)
com.sun.faces.renderkit.html_basic.MenuRenderer.renderOption(MenuRenderer.java:534)
com.sun.faces.renderkit.html_basic.MenuRenderer.renderOptions(MenuRenderer.java:794)
com.sun.faces.renderkit.html_basic.MenuRenderer.renderSelect(MenuRenderer.java:847)
com.sun.faces.renderkit.html_basic.MenuRenderer.encodeEnd(MenuRenderer.java:297)
javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:919)
javax.faces.component.UIComponent.encodeAll(UIComponent.java:1903)
javax.faces.render.Renderer.encodeChildren(Renderer.java:176)
javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:889)
com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeRecursive(HtmlBasicRenderer.java:304)
com.sun.faces.renderkit.html_basic.GroupRenderer.encodeChildren(GroupRenderer.java:115)
javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:889)
javax.faces.component.UIComponent.encodeAll(UIComponent.java:1896)
javax.faces.render.Renderer.encodeChildren(Renderer.java:176)
javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:889)
javax.faces.component.UIComponent.encodeAll(UIComponent.java:1896)
javax.faces.component.UIComponent.encodeAll(UIComponent.java:1899)
javax.faces.component.UIComponent.encodeAll(UIComponent.java:1899)
com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:451)
com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131)
com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
javax.faces.webapp.FacesServlet.service(FacesServlet.java:647)
我猜想getAsString方法獲取UnmodifiableMap對象作為值,但它應該是Param對象,對嗎?
請幫我
PS。 如果我犯了一些錯誤,對不起我的英語;
問題在var
屬性中。
<f:selectItems value="#{mainBean.params}"
var="param"
itemValue="#{param}"
itemLabel="#{param.name}"
/>
#{param}
是一個保留的EL變量,引用了ServletRequest#getParameterMap()
,其類型為Map<String, String[]>
,實際上是一個不可修改的映射。
您不應為自己的變量使用保留的EL變量名。 將其重命名為其他名稱,例如_param
左右。
<f:selectItems value="#{mainBean.params}"
var="_param"
itemValue="#{_param}"
itemLabel="#{_param.name}"
/>
您的轉換器雖然比較笨拙,但並不完全健壯,但完全可以。
在這里檢查該工作代碼並嘗試自己查找錯誤。 它將使您記憶猶新:)
<h:selectOneMenu rendered="#{categoryConverterBean.rendered}" class="subcategory" id="subcategory" converter="#{subcategoryConverterBean}" value="#{auctionBean.subCategory}">
<f:selectItems
value="#{categoryListBean.subcategory}"
var="subcategory"
itemLabel="#{subcategory.subName}"
itemValue="#{subcategory}"
/>
</h:selectOneMenu>
auctionBean(沒什么特別的):
public Subcategory getSubCategory() {
return subCategory;
}
public void setSubCategory(Subcategory subCategory) {
this.subCategory = subCategory;
}
subcategoryConverter:
@ManagedBean(name = "subcategoryConverterBean")
@FacesConverter(value = "subcategoryConverter")
public class SubcategoryConverter implements Converter {
@PersistenceContext()
private transient EntityManager em;
@Override
public Object getAsObject(FacesContext arg0, UIComponent arg1, String value) {
// TODO Auto-generated method stub
System.out.println("wybrales: " + value);
Query query = em.createQuery("SELECT c FROM Subcategory c WHERE c.subId=?1");
query.setParameter("1", Integer.parseInt(value));
return query.getSingleResult();
}
@Override
public String getAsString(FacesContext arg0, UIComponent arg1, Object value) {
// TODO Auto-generated method stub
return ((String) String.valueOf(((Subcategory) value).getSubId()));
}
}
最后是categoryListBean:
@ManagedBean
public class CategoryListBean {
private List<CategoryBean> category;
private List<SubcategoryBean> subcategory;
@EJB
CategoryEAO service;
public List<CategoryBean> getCategory() {
category = service.getCategories();
return category;
}
public void setCategory(List<CategoryBean> category) {
this.category = category;
}
public List<SubcategoryBean> getSubcategory() {
subcategory = service.getSubcategories();
return subcategory;
}
public void setSubcategory(List<SubcategoryBean> subcategory) {
this.subcategory = subcategory;
}
}
我將重點放在您的getAsObject方法上,因為它看起來像您認為的那樣沒有獲得Param對象
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