登录时报错
servlet层
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String username = request.getParameter("username");
String password = request.getParameter("password");
System.out.println(username+password);
User user = userService.login(username, password);
System.out.println("user:"+user);
if (null != user){
request.getSession().setAttribute("user", user);
request.getRequestDispatcher("/JDBCMessageBoard/message/list.do").forward(request, response);
} else {
request.getRequestDispatcher("/login.do").forward(request, response);
}
}service层
public User login(String username,String password){
return userDao.login(username, password);
}dao层
public User login(String username,String password){
Connection conn = ConnectionUtil.getConnection();
String sql = "select * from user where username = ? and password = ?";
PreparedStatement stmt = null;
ResultSet rs = null;
User user = null;
try {
stmt = conn.prepareStatement(sql);
stmt.setString(1, username);
stmt.setString(2, password);
rs = stmt.executeQuery();
while(rs.next()){
user = new User();
user.setId(rs.getLong("id"));
user.setName(rs.getString("username"));
user.setPassword(rs.getString("password"));
user.setRealName(rs.getString("real_name"));
user.setBirthday(rs.getDate("birthday"));
user.setPhone(rs.getString("phone"));
user.setAddress(rs.getString("address"));
}
} catch (SQLException e) {
System.out.println("登录失败！");
e.printStackTrace();
} finally{
ConnectionUtil.release(rs, stmt, conn);
}
return user;
}运行登录页面报错
严重: Servlet.service() for servlet [LoginServlet] in context with path [/JDBCMessageBoard] threw exception
java.lang.NullPointerException
at com.imooc.jdbc.servlet.LoginServlet.service(LoginServlet.java:34)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:956)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:625)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
正在回答
如下图所示，测试了你的代码，是不会出现空指针，建议你清空一下tomcat
因为你的代码逻辑是没有问题的，我这头代入老师的源码中测试也是可以打印出user的，建议你重新Rebuild Project试试，祝学习愉快~
package com.imooc.jdbc.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.imooc.jdbc.bean.User;
import com.imooc.jdbc.service.UserService;
/**
* 用户登录的servlet
* @author Administrator
*
*/
public class LoginServlet extends HttpServlet {
private UserService userService;
public void init() throws ServletException {
// Put your code here
userService = new UserService();
}
@Override
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String username = request.getParameter("username");
String password = request.getParameter("password");
System.out.println(username+password);
User user = userService.login(username, password);
System.out.println(user);
if (null != user){
request.getSession().setAttribute("user", user);
request.getRequestDispatcher("/JDBCMessageBoard/message/list.do").forward(request, response);
} else {
request.getRequestDispatcher("/login.do").forward(request, response);
}
}
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
}
}
你好同学，应该在Servlet中的init初始化方法中创建userService，而不是在destroy()中创建哦，根据报错提示的描述，就是你的userService为null，因为你只声明了userService，并没有创建实例，所以会出现空指针异常，祝学习愉快~
servlet层
package com.imooc.jdbc.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.imooc.jdbc.bean.User;
import com.imooc.jdbc.service.UserService;
/**
* 用户登录的servlet
* @author Administrator
*
*/
public class LoginServlet extends HttpServlet {
private UserService userService;
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
userService = new UserService();
}
@Override
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String username = request.getParameter("username");
String password = request.getParameter("password");
System.out.println(username+password);
User user = userService.login(username, password);//报错的地方！！！！！
System.out.println("user:"+user);
if (null != user){
request.getSession().setAttribute("user", user);
request.getRequestDispatcher("/JDBCMessageBoard/message/list.do").forward(request, response);
} else {
request.getRequestDispatcher("/login.do").forward(request, response);
}
}
public void init() throws ServletException {
// Put your code here
}
}
你好同学，将你的代码粘贴到老师的源码中，并没有出现空指针异常，LoginServlet类中的第34行的代码是什么？建议你将LoginServlet完成的代码粘贴一下，方便我们具有针对性的为你解答，要将代码粘贴到回答中哦，否则会失去代码格式，祝学习愉快~
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