从我的迭代器next方法中获取ClassCastException

Question

我正在将Spring 3.1.0、Hibernate 4、JDK 7用于Tomcat 7，并在itr.next（）方法上获得ClassCastException。aaData对象不包含数据。

List<CustomerList> aaData = customerlistDaoimpl.getCustomerList();
/*
 * putting data in a JSON form that DataTables recognizes
 */
String data = "{"sEcho": 3, "iTotalRecords": " + count + ","iTotalDisplayRecords": " + count + ","aaData": [ ";
Iterator<CustomerList> itr = aaData.iterator();
while(itr.hasNext()){
    CustomerList cl = (CustomerList) itr.next();
    data += "["" + cl.getName() + "","" + cl.getAddress() + "","" + cl.getZipcode() + "","" + 
    cl.getPhone() + "","" + cl.getCity() + "","" + cl.getCountry() + "","" + cl.getNote() + "" ] ";
    count++;
}
data += "]}";

我的刀

@SuppressWarnings("unchecked")
@Override
public List<CustomerList> getCustomerList() {
    List<CustomerList> cuList = null;
    Session session = null;
    try{
        session = sessionfactory.openSession();
        session.beginTransaction();         
        cuList = session.createSQLQuery("select * from customer_list").list();      
        session.getTransaction().commit();
    }catch (RuntimeException e){
        System.out.println(e.getMessage());
    }
    finally
    {
        if(session != null){
            session.close();                
        }
    }
    return cuList;
}

追踪

SEVERE:上下文中Servlet[sptestjs]的Servlet.service（），路径为[/SPTestJs]引发异常[请求处理失败；嵌套异常为java.lang.ClassCastException：[Ljava.lang.Object；不能强制转换为具有根本原因的com.sptestjs.eimplementation.CustomerList]java.lang.ClassCastException：[Ljava.lang.Object；无法强制转换为com.sptestjs.implementation.CustomerListcom.sptestjs.eimplementation.controller.HomeController.getCustomerList（HomeController.java:85）位于的sun.reflect.NativeMethodAccessorImpl.invoke0（本机方法）位于的sun.reflect.NativeMethodAccessorImpl.invoke（未知源）sun.reflect.DelegatingMethodAccessorImpl.invoke（未知源）

我确实找到了的电话

SQLQuery cuSQLQuery = session.createSQLQuery("select * from customer_list");

返回一个SQLQuery实例，其列表的类型为ArrayList of Object元素，其中

Query cuQuery = session.createQuery("from customer_list");

返回CCD_ 1。

Answer 1

从我的迭代器下一个方法中获取ClassCastException

这意味着您的aaData实际上不是List<CustomerList>。您在某个地方进行了类型擦除，但您错误地更改了它的类型。如果你仔细查看ClassCastException，它会告诉你组件的真正类型

java.lang.ClassCastException：[Ljava.lang.Object；不能强制转换为com.sptestjs.implementation.CustomerList

这表明该类型实际上应该是

List<Object[]> cuList = session.createSQLQuery("select * from customer_list").list(); 

Answer 2

使用泛型。aaData可能包含不正确的数据

class CustomerlistDaoimpl{
public  List<CustomerList> getCustomerList(){
.....
}
}
    List<CustomerList> aaData = customerlistDaoimpl.getCustomerList();
    String data = "{"sEcho": 3, "iTotalRecords": " + count + ","iTotalDisplayRecords": " + count + ","aaData": [ ";
    Iterator<CustomerList> itr = aaData.iterator();
    while(itr.hasNext()){
        CustomerList cl = (CustomerList) itr.next();
        data += "["" + cl.getName() + "","" + cl.getAddress() + "","" + cl.getZipcode() + "","" + 
        cl.getPhone() + "","" + cl.getCity() + "","" + cl.getCountry() + "","" + cl.getNote() + "" ] ";
        count++;
    }
    data += "]}";

Answer 3

检查您导入的CustomerList类的完全限定类名是否与填充列表时使用的类名相同。我很好奇，既然您使用的是泛型，那么next()应该返回与Iterator构建目的相同的类型，为什么您无论如何都需要进行强制转换。换句话说，当调用itr.next()时，Iterator将始终返回T的实例。

Answer 4

已解决：

多个错误，异常是误导性的，我用一个不再存在的sessionFactory id限定了我的Dao-impl，同时自动连接了曾经修复过的sessionFactory到下一个错误。修复了所有这些问题，项目开始运行。