Java.lang.ClassCastException : [Ljava.lang.Object; 无法投射到 com.hms.pro

Question

我是 java 新手，我正在创建一个登录页面，通过 spring 与 hibernate 集成来与数据库交互。我正在使用两个类 Controler 和 Dao。 我在 Hms pojo 类中使用了休眠注释与数据库交互。

当涉及到 controller1 类中的登录方法时，我收到类转换异常。 有人可以让我知道我哪里出错了。

hms.java

package com.hms.project;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="register")
public class Hms {
    private int id;
    @Id
    @GeneratedValue
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    private String firstname;
    private String lastname;
    private String username;
    private String password;
    private String emailid;

    @Column(name="firstname")
    public String getFirstname() {
        return firstname;
    }
    public void setFirstname(String firstname) {
        this.firstname = firstname;
    }
    @Column(name="lastname")
    public String getLastname() {
        return lastname;
    }
    public void setLastname(String lastname) {
        this.lastname = lastname;
    }
    @Column(name="username")
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    @Column(name="password")
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    @Column(name="emailid")
    public String getEmailid() {
        return emailid;
    }
    public void setEmailid(String emailid) {
        this.emailid = emailid;
    }


}

控制器.java

@Controller
public class Controller1 {
    @Autowired
    private Dao dao;


    public Dao getDao() {
        return dao;
    }


    public void setDao(Dao dao) {
        this.dao = dao;
    }


    @RequestMapping("register")
    public void register(Hms hms){
        System.out.println("save data ");

        dao.save(hms);
        System.out.println(" after save data ");
    }
    @RequestMapping("login")
    public String login(String username,String password){ 
        System.out.println("searching for data base");

        List<Hms> l1=dao.listUser(username,password);

        /*String name=req.getParameter("username");
        String pwd=req.getParameter("pwd");*/
        for(Hms l : l1){
            System.out.println("after coming from database");

            System.out.println(l.getUsername());
            System.out.println(l.getPassword());

        /*for(Hms l:obj){

            String s=l.getUsername();
            String s1=l.getPassword();
            if((name==s)&&(pwd==s1)){
                System.out.println("login success");

            }
            else{
                System.out.println("login failed");
            }

        }*/

        //return hms;
    }
        return null;
    }
}

道.java

public class Dao {
    private HibernateTemplate hibernatetemplate;

    public HibernateTemplate getHibernatetemplate() {
        return hibernatetemplate;
    }

    public void setHibernatetemplate(HibernateTemplate hibernatetemplate) {
        this.hibernatetemplate = hibernatetemplate;
    }

    public void save(Hms hms){
                          System.out.println("going to database");
                         // hibernatetemplate.save(hms);

    }
     public List<Hms> listUser(String username,String password) {
         System.out.println("going to database");
         String hql="select username,password from Hms";
                    List<Hms> h=hibernatetemplate.find(hql);
                    System.out.println("Fetched data");
                    return h;
        // return hibernatetemplate.find("select username,password from Hms");

}
}

堆栈跟踪：

SEVERE: Servlet.service() for servlet [springs] in context with path [/HmsProject] threw exception [Request processing failed; nested exception is java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to com.hms.project.Hms] with root cause
    java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to com.hms.project.Hms
        at com.hms.project.Controller1.login(Controller1.java:42)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:497)
        at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176)
        at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:440)
        at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:428)
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925)
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
        at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:936)
        at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:827)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:812)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
        at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
        at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
        at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
        at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:745)

Answer 1

您的查询正在返回 Object 数组，您不能调用类的 getter 方法，直到将其强制转换为该类类型您可以试试这个

Query q = session.createQuery(sql); 
List<Object[]> li= (List<Object[]>)q.list();
for(Object[] ob: li)
{ 
user=ob[0].toString();
Pass=ob[1].toString();
}