Question

我目前正在开展一个我和我的团队应该建立的学校项目一个MVC项目，我们有类Building和Room。关系是OnetoMany，Building-（OneToMany）-Room。当我们想要搜索建筑物名称并稍后显示该建筑物中的所有房间时，会出现问题。我们在没有jsp的情况下运行servlet时可以提取相关数据，但是当我们通过运行searchBuilding.jsp来启动项目时，我们只能输入建筑物名称，并且当需要查看连接的房间时，我们会收到消息 “java.lang.ClassCastException：java.util.ArrayList无法强制转换为org.ics.ejb.Room”。所有的代码可能有点乱，但我真的很感激，如果有人可以帮助我发现问题，因为我应该明天向我的教授展示这个。

这是我们的代码： BUILDING：

@Entity
    @Table(name = "Building")
    public class Building {
    private String bname;
private List<Room> rooms; // Building can have many Rooms

@Id
@Column(name = "Bname")
public String getBname() {
    return bname;
}

public void setBname(String bname) {
    this.bname = bname;
}

@OneToMany(mappedBy = "building", fetch = FetchType.EAGER)
public List<Room> getRooms() {
    return rooms;
}

public void setRooms(List<Room> rooms) {
    this.rooms = rooms;
}

}

房间：

@NamedQueries({
@NamedQuery(name="Room.findByBname",
 query="SELECT r FROM Room r WHERE r.bname LIKE :bname"),
})

@Entity
@Table(name = "Room")
public class Room implements Serializable {
/**
 * 
 */
private static final long serialVersionUID = 1L;
private RoomId id;
private String bname;
private Building building;

public String getBname() {
    return bname;
}

public void setBname(String bname) {
    this.bname = bname;
}

@Id
public RoomId getId() {
    return id;
}

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

@ManyToOne
@JoinColumn(name = "Bname", insertable = false, updatable = false)
public Building getBuilding() {
    return this.building;
}

public void setBuilding(Building building) {
    this.building = building;
}
}

ROOMID：

@Embeddable
public class RoomId implements Serializable {

private String bname;
private String rcode;

public RoomId() {
}

public RoomId(String bname, String rcode) {
    this.bname = bname;
    this.rcode = rcode;
}

@Column(name = "Bname", nullable = false)
public String getbname() {
    return bname;
}

public void setbname(String bname) {
    this.bname = bname;
}

@Column(name = "Rcode", nullable = false)
public String getrcode() {
    return rcode;
}

public void setrcode(String rcode) {
    this.rcode = rcode;
}

public boolean equals(Object other) {
    if ((this == other)) {
        return true;
    }

    if ((other == null)) {
        return false;
    }

    if (!(other instanceof RoomId)) {
        return false;
    }

    RoomId castOther = (RoomId) other;

    return ((this.getbname() == castOther.getbname()) || (this.getbname() != null
            && castOther.getbname() != null &&

    this.getbname().equals(castOther.getbname())))

            &&

((this.getrcode() == castOther.getrcode()) ||                                        (this.getrcode() != null               && castOther.getrcode() != null &&

            this.getrcode().equals(castOther.getrcode())));
}

public int hashCode() {
    return super.hashCode();
}

}

BUILDINGEAO：

@Stateless
public class BuildingEAOImpl implements BuildingEAOImplLocal {
@PersistenceContext(unitName = "LabEJBSql")
private EntityManager em;

public BuildingEAOImpl() {
    // TODO Auto-generated constructor stub
}

public Building findByBname(String bname) {
    return em.find(Building.class, bname);
}
}

FACADE：

@Stateless
public class Facade implements FacadeRemote, FacadeLocal {
@EJB
BuildingEAOImplLocal BuildingEAO;
@EJB
RoomEAOImplLocal RoomEAO;

public Facade() {
    // TODO Auto-generated constructor stub
}

public List<Room> findRoomsByBname(String bname) { 
     return RoomEAO.findByBname(bname); 
     }
 }

SERVLET：

@WebServlet("/TestClientServlet")
public class TestClientServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
@EJB
private FacadeLocal facade;

/**
 * @see HttpServlet#HttpServlet()
 */
public TestClientServlet() {
    super();
    // TODO Auto-generated constructor stub
}

protected void service(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException {
    PrintWriter out = response.getWriter();
    out.println("<!DOCTYPE html><html><head>");
    out.println("<title>Lab1</title>");
    out.println("<meta charset=\"ISO-8859-1\">");
    out.println("</head><body>");



    /*//THIS WORKS PERFECTLY FINE
List<Room> rooms = facade.findRoomsByBname("EC2");
    for (Room r : rooms) {
        out.println("<h4>Hittade: " + r.getId().getbname() + " "
                + r.getId().getrcode() + "</h4>");
        out.println("</body></html>");
    }
}*/

protected void doGet(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException {

    PrintWriter out = response.getWriter();
    out.println("TestClientServlet-doGet");
    out.close();

}

protected void doPost(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException {

    String url = null;
    // Get hidden field
    String operation = request.getParameter("operation");

    if (operation.equals("showbuilding")) {
        String bname = request.getParameter("txtBname");

        List<Room> r = facade.findRoomsByBname(bname);
        request.setAttribute("rooms", r);
        url = "/ShowBuilding.jsp";
    } else if (operation.equals("searchbuilding")) {
        System.out.println("TestClientServlet-searchbuilding");
        url = "/SearchBuilding.jsp";
    } else {
        url = "/SearchBuilding.jsp";
    }
    System.out.println(url);

    RequestDispatcher dispatcher = getServletContext()
            .getRequestDispatcher(url);
    dispatcher.forward(request, response);
}
*/
}

SEARCHBUILDING.JSP：

<html> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=ISO-
8859-1"> 
<title>Search Building</title> 
</head> 
<body> 
<form action="/BuildRoomClientProject/TestClientServlet" method="post"> 

<table cellspacing="0" cellpadding="0" border="0" align="left"> 
<tr> 
<td><h2>Search Building:</h2></td> 
</tr> 
<tr> 
<td> 

<input type= "text" name= "txtBname" size ="25" maxlength="25">
<input type="submit" name="submit" value="Search" /> 
</td> 
<td></td> 
</tr> 
</table> 

<input name="operation" value="showbuilding" type="hidden"> 

</form> 
</body> 
</html>

SHOWBUILDING.JSP：

<%@ page contentType="text/html;charset=windows-1252"%> 
<%@ page import = "org.ics.ejb.Building" %> 
<%@ page import = "org.ics.ejb.Room" %> 
<%@ page import = "org.ics.ejb.RoomId" %> 
<html> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> 
<title> 
Show Building 
</title> 
</head> 
<body> 
<%  Room r = (Room)request.getAttribute("rooms"); %>
<% Building b = (Building)request.getAttribute("building"); %>
<% for (int i=0; i<100; i++){
System.out.println(r.getBname() + " " + r.getId().getrcode());
}%> 
<h2> 
Building: 
</h2> 
<p>
<%= r.getId().getrcode()%>
<%= b.getBname()%> 
</p>
<form action="/BuildRoomClientProject/TestClientServlet" method="post"> 
<input type="submit" name="submit" value="Tillbaka"> 
<input name="operation" value="searchbuilding" type="hidden"> 
</form> 
</body> 
</html>

Answer 1

＆＃34; rooms＆＃34;属性被设置为servlet中的房间的ArrayList。但是当你试图在jsp中获得它时，你期待一个单独的房间。改变

<%  Room r = (Room)request.getAttribute("rooms"); %>

到

<%  List<Room> rooms = (List<Room>)request.getAttribute("rooms"); %>

然后遍历每个房间。

从JSP-Class检索数据（使用Servlet的MVC）

1 个答案: