【发布时间】：2016-10-22 20:58:43
【问题描述】：
我正在尝试在 jsp 页面中使用 AJAX 脚本显示 Cassandra 数据库中的所有用户用户名。单击查看全部按钮时，这将显示用户用户名列表。但是服务器在 Session session = cluster.connect(""); 上抛出 Null 指针异常；
java.lang.NullPointerException
User.searchAll(User.java:87)
Search.doGet(Search.java:82)
javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
型号 公共类用户{
Cluster cluster;
public User() {
}
public java.util.LinkedList<ProfileBean> searchAll(){
Session session = cluster.connect("instagrim");
LinkedList<ProfileBean> profileBeanList = new LinkedList();
String cqlQuery = "select * from userprofiles";
PreparedStatement ps = session.prepare(cqlQuery);
ResultSet rs;
BoundStatement bs = new BoundStatement(ps);
rs = session.execute(bs.bind());
if(rs.isExhausted()){
System.out.println("Profile not found");
}
else
{
for (Row row : rs){
ProfileBean profile = new ProfileBean();
profile.setLogin(row.getString("login"));
profileBeanList.add(profile);
}
}
session.close();
return profileBeanList;
}
Servlet
public class Search extends HttpServlet {
Cluster cluster = null;
public void init(ServletConfig config)
{
cluster = CassandraHosts.getCluster();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
User us = new User();
String output ="";
LinkedList<ProfileBean> profileBeanList = new LinkedList();
profileBeanList = us.searchAll();
for (int i=0;i<profileBeanList.size();i++)
{
output="<p>"+profileBeanList.get(i).getLogin() +"</p>";
}
response.getWriter().write(output);
RequestDispatcher rd = request.getRequestDispatcher("search.jsp");
rd.forward(request,response);
}
【问题讨论】：
-
看来，连接失败。检查您的密钥空间名称“instagram”是否正确。如果正确，请确保您的集群已在您的应用程序中初始化并且可以访问。