Eclipse和数据库链接问题

Question

HTTP Status 500 - An exception occurred processing JSP page /loginTest.jsp at line 41

type Exception report

message An exception occurred processing JSP page /loginTest.jsp at line 41

description The server encountered an internal error that prevented it from fulfilling this request.

exception
org.apache.jasper.JasperException: An exception occurred processing JSP page /loginTest.jsp at line 41

38: }
39: DBUtils db = new DBUtils();
40: String sql = "select * from user";
41: List> list = db.queryByList(sql, new String []{});
42: int j = 0;
43: for(int i = 0;i<list.size();i++){
44: boolean b = (password.equals(list.get(i).get("user_password"))&&username.equals(list.get(i).get("user_name")));

Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:580)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:477)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

root cause
java.lang.NullPointerException
com.shxt.DBUtils.DBUtils.queryByList(DBUtils.java:117)
org.apache.jsp.loginTest_jsp._jspService(loginTest_jsp.java:125)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:439)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

note The full stack trace of the root cause is available in the Apache Tomcat/7.0.77 logs.

Answer 1

在HTTP协议中，HTTP Status 500 是服务器内部错误。错误的直接现象是，JSP有错。
loginTest.jsp at line 41
提示你在loginTest.jsp 这个页面的41行出现了异常！
造成的原因是空指针异常（root cause java.lang.NullPointerException）
你可以打印一下db，看看db是不是空对象，在41行之前加上
System.out.println(db);
在看看你41行那个new String []{} 是不是空的，
个人觉得是后面那个String为null，
希望能帮助到你。