老实说，我不知道是什么原因导致了这个错误，我所知道的是，当我试图在servlet中示例化一个DAO对象，并使用请求调度程序发送对象时，就会发生这种情况。

SRVE0777E: Exception thrown by application class 'com.projecteden.mainmenu.SelectSurvivorData.doGet:27'
java.lang.ClassCastException: class com.projecteden.livingobjects.entities.SurvivorPO cannot be cast to class com.projecteden.livingobjects.entities.SurvivorPO (com.projecteden.livingobjects.entities.SurvivorPO is in unnamed module of loader com.ibm.ws.classloading.internal.AppClassLoader @3a649edc; com.projecteden.livingobjects.entities.SurvivorPO is in unnamed module of loader com.ibm.ws.classloading.internal.AppClassLoader @3c834c19)
at com.projecteden.mainmenu.SelectSurvivorData.doGet(SelectSurvivorData.java:27)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:686)
at [internal classes]

package com.projecteden.mainmenu;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.projecteden.livingobjects.DAO.SurvivorDAO;

@WebServlet("/GetSurvivorData")
public class SelectSurvivorData extends HttpServlet 
{
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
    SurvivorDAO getList = new SurvivorDAO();
    response.setContentType("text/html;charset=UTF-8");
    request.setAttribute("test", getList.getAllSurvivors().get(0).getName());
    
    request.getRequestDispatcher("WebPages/MainMenu/SelectPlayer.jsp").forward(request, response);
}

}

package com.projecteden.livingobjects.DAO;

import java.util.List;

import com.projecteden.livingobjects.entities.SurvivorPO;



public class SurvivorDAO extends LivingObjectsEM
{

    
    public List<SurvivorPO> findWithId(String id) 
     {      
        return em.createQuery(
            "SELECT c FROM SurvivorPO c WHERE c.id LIKE :id")
            .setParameter("id", id)
            .setMaxResults(1)
            .getResultList();
     }
     
    
    public List<SurvivorPO> getAllSurvivors() 
     {      
        return em.createQuery(
            "SELECT c FROM SurvivorPO c")
            .setMaxResults(10)
            .getResultList();
     }
      
}

package com.projecteden.livingobjects.entities;

import javax.persistence.Column;
import javax.persistence.Embedded;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;

@Entity
@Table(name = "survivor_stats")
public class SurvivorPO
{
    @Id
    @Column(name ="id")
    @GeneratedValue(strategy=GenerationType.AUTO, generator="SurvivorIdGenerator")
    @SequenceGenerator(name="SurvivorIdGenerator", sequenceName="SurvivorSequencesId")
    private int id;
    
    @Column(name ="name")
    private String name;
    
    @Embedded
    private StatsPO stats;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public StatsPO getStats() {
        return stats;
    }

    public void setStats(StatsPO stats) {
        this.stats = stats;
    }

    @Override
    public String toString() {
        return "HeroPO [id=" + id + ", name=" + name + ", stats=" + stats + "]";
    }
    
    

}

至于我正在使用的其他东西：这是一个包含JPA2.2、JSP、 Bootstrap 5、MySQL、动态Web模块4.0、Java16、JS 1.0和EclpipseLink的Maeven项目
如果你需要进一步的解释，尽管问。