java.lang.ClassCastException：java.lang.String 无法转换为 [Ljava.lang.Object

Question

我正在运行以下查询。它显示一条错误消息。如何解决这个错误？

        List<Route>routeList=null;
        List<?> companyList = session.createSQLQuery ("select name " +
                                                  "from company "+
                                                  "where company_id= " + companyId).list();                 
        if(companyList.size() <= 0){
            //throw(new AppException(1018,ErrorMessages.getString("INVALID_USER_ID"))); 
        }


        routeList = new ArrayList<Route>(companyList.size());
    Route vgDetails=null;

        for (int i = 0; i < companyList.size(); i++) {

            vgDetails = new Route(); 
            Object[] row = (Object[])companyList.get(i);                                 
            vgDetails.setRouteName ((String)row[0]);                     
            routeList.add(vgDetails);       
        }                   
    session.getTransaction().commit();
        return routeList;
    }

错误是：

java.lang.ClassCastException: java.lang.String cannot be cast to [Ljava.lang.Object;
    at com.claystone.server.user.UserListServiceImpl.getParticipantsDestination(UserListServiceImpl.java:902)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:527)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:166)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.doPost(RemoteServiceServlet.java:86)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:729)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.handler.RequestLogHandler.handle(RequestLogHandler.java:49)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:324)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:843)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:647)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:205)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488)

Answer 1

你可以写：

vgDetails = new Route();                                 
vgDetails.setRouteName ((String)companyList.get(i));

companyList 已经是一个字符串列表，因为您只选择了一列。

此外，正如 Thilo 的回答还建议的那样，您可以将结果直接转换为 List<string> 而不是使用 List<?>。

Answer 2

Hibernate 是返回一个 String 数组（又名 String 类型的 List）

 List<?> companyList = session.createSQLQuery ("select name " +
                                                  "from company "+
                                                  "where company_id= " + companyId).list();   

因为您的查询返回 Company 表中的名称字符串。

你必须做的返回一个列表

 List<String> companyList = (List<String>)session.createSQLQuery ("select name " +
                                                  "from company "+
                                                  "where company_id= " + companyId).list();

从这里改变你的错误：

 vgDetails = new Route(); 
            Object[] row = (Object[])companyList.get(i);                                 
            vgDetails.setRouteName ((String)row[0]);                     
            routeList.add(vgDetails);

到这里：

vgDetails = new Route();                                
vgDetails.setRouteName (companyList.get(i));                     
routeList.add(vgDetails);

companyList.get(i) 返回一个字符串。

Answer 3

您的 companyList 包含字符串，而不是 Object[]。

你应该写

List<String> companyList = (List<String>) session.createSQLQuery (
      "select name from company where company_id=?", companyId).list();


for (String routeName: companyList) {
        vgDetails = new Route();                            
        vgDetails.setRouteName (routeName);                     
        routeList.add(vgDetails);       
    }