exception org.apache.jasper.JasperException: An exception occurred processing JSP page /deleteSong.jsp at line 3936: </tr>
37: <%
38: List songList =(List)(request.getAttribute("songList"));
39: out.println(songList.size());
40: for(int i=0;i<songList.size();i++)
41: {
42: SongDTO song=new SongDTO();
这是怎么回事?我明明数据库中有数据,而且用DAO都获取了
DAO:
public static List findAllSongs()
{
List songList=new ArrayList();
Connection con = null;
Statement stat=null;
ResultSet rs=null;
try {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
con = DriverManager.getConnection("jdbc:odbc:music","sa","");
stat=con.createStatement();
String queryString="select * from song";
rs=stat.executeQuery(queryString);
while(rs.next())
{
SongDTO song=new SongDTO();
song.setSgID(rs.getString("sgID"));
song.setSgName(rs.getString("sgName"));
song.setSingerID(rs.getString("singerID"));
song.setStID(rs.getString("stID"));
song.setSlID(rs.getString("slID"));
songList.add(song);
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return songList;
}
以下代码是:
<tr>
<form action="servlet/HandleDeleteSong" method="post">
<td><%=song.getSgID()%></td>
<td><%=song.getSgName() %></td>
<td><%=song.getSingerID()%></td>
<td><%=song.getStID() %></td>
<td><%=song.getSlID()%></td>
<td><a href="(deleteSongById)?sgID=<%=song.getSgID() %>">删除</a></td>
</form>
</tr>
<%
} %>
37: <%
38: List songList =(List)(request.getAttribute("songList"));
39: out.println(songList.size());
40: for(int i=0;i<songList.size();i++)
41: {
42: SongDTO song=new SongDTO();
这是怎么回事?我明明数据库中有数据,而且用DAO都获取了
DAO:
public static List findAllSongs()
{
List songList=new ArrayList();
Connection con = null;
Statement stat=null;
ResultSet rs=null;
try {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
con = DriverManager.getConnection("jdbc:odbc:music","sa","");
stat=con.createStatement();
String queryString="select * from song";
rs=stat.executeQuery(queryString);
while(rs.next())
{
SongDTO song=new SongDTO();
song.setSgID(rs.getString("sgID"));
song.setSgName(rs.getString("sgName"));
song.setSingerID(rs.getString("singerID"));
song.setStID(rs.getString("stID"));
song.setSlID(rs.getString("slID"));
songList.add(song);
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return songList;
}
以下代码是:
<tr>
<form action="servlet/HandleDeleteSong" method="post">
<td><%=song.getSgID()%></td>
<td><%=song.getSgName() %></td>
<td><%=song.getSingerID()%></td>
<td><%=song.getStID() %></td>
<td><%=song.getSlID()%></td>
<td><a href="(deleteSongById)?sgID=<%=song.getSgID() %>">删除</a></td>
</form>
</tr>
<%
} %>
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throws ServletException, IOException {
response.setContentType("text/html;charset=gb2312");
List songList=new ArrayList();
SongDAO song=new SongDAO();
songList=SongDAO.findAllSongs();
session.setAttribute("songList",songList);
RequestDispatcher rd=request.getRequestDispatcher("deleteSong.jsp");
rd.forward(request,response);
}
没有一个叫sonList的属性,所以返回null
没有一个叫songList的属性,所以返回null
前台怎么是request.getAttribute呢?
前台改成
List songList =(List)request.getSession().getAttribute("songList");
songList=SongDAO.findAllSongs();session.setAttribute("songList",songList);哦不是设置了吗?怎么说没有呢????
提示LIST为原始类型,要List<E>引用参数化,什么意思?
并说这是个断点
songList =(List<SongDTO>)(request.getAttribute("songList"));
我改了啊
可是还是有问题的
类型安全:未经检查的从 Object 到 List 的强制类型转换
看看返回的songList 是不是null