有效沟通问答-【官方】百战程序员_IT在线教育培训机构

package com.xx.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(value = "/ann.do")
public class AnnotationServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        PrintWriter out = resp.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC '-//W3C//DTD HTML 4.0 Transitional//EN'>");
        out.println("<HTML>");
        out.println("<HEAD><TITLE> ITBZ </TITLE></HEAD>");
        out.println("<BODY>");
        out.println("Annotation Servlet");
        out.println("</BODY>");
        out.println("</HTML>");
        out.flush();
        out.close();
    }
}

结果：

JAVA 全系列/第五阶段：JavaWeb开发/Servlet技术详解（旧） 1217楼

老师，这里把设置响应类型这行注释了，服务servlet的时候还是能响应json格式内容，那加这一句的作用是什么啊

JAVA 全系列/第五阶段：JavaWeb开发/Ajax技术详解（旧） 1218楼

老师，这个session对象不是被缓存在ServletContext中的吗？那现在为什么可以用session对象去得到ServletContext对象呢？

JAVA 全系列/第五阶段：JavaWeb开发/Web实战案例 1219楼

老师，我想问一下这个绿框里的代码是表示销毁已存在的Value: HttpSession对象是吧？那这个红框的代码删除的是什么数据呢？

JAVA 全系列/第五阶段：JavaWeb开发/Web实战案例 1220楼

老师，我的退出登录怎么显示500，再点一次退出登录才会重新跳到登录界面

JAVA 全系列/第五阶段：JavaWeb开发/Web实战案例 1221楼

老师，我输入正确的用户和密码，这里也一直报错

java.sql.SQLException: No suitable driver found for jdbc:mysql://localhost:3306/bjsxt?useUnicode=true&characterEncoding=utf8 
	at java.sql.DriverManager.getConnection(DriverManager.java:689)
	at java.sql.DriverManager.getConnection(DriverManager.java:247)
	at com.bjsxt.commons.JdbcUtils.getConnection(JdbcUtils.java:30)
	at com.bjsxt.dao.impl.UserLoginDaoImpl.selectUsersByUserNameAndUserPwd(UserLoginDaoImpl.java:17)
	at com.bjsxt.service.impl.UserLoginServiceImpl.userLogin(UserLoginServiceImpl.java:13)
	at com.bjsxt.web.servlet.UserLoginServlet.doPost(UserLoginServlet.java:29)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1590)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:745)
java.lang.NullPointerException
	at com.bjsxt.dao.impl.UserLoginDaoImpl.selectUsersByUserNameAndUserPwd(UserLoginDaoImpl.java:18)
	at com.bjsxt.service.impl.UserLoginServiceImpl.userLogin(UserLoginServiceImpl.java:13)
	at com.bjsxt.web.servlet.UserLoginServlet.doPost(UserLoginServlet.java:29)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1590)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:745)

控制台报错如上，是不是和数据库的链接还有出现了问题？还有空指针异常？如下出现错误指向的代，请老师帮忙看一下，谢谢！

jdbc.driver=com.mysql.jdbc.Driver 
jdbc.url=jdbc:mysql://localhost:3306/bjsxt?useUnicode=true&characterEncoding=utf8 
jdbc.username=root 
jdbc.password=root

package com.bjsxt.commons;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.ResourceBundle;

public class JdbcUtils {
    private static String driver;
    private static String url;
    private static String username;
    private static String password;
    static {
        try{
            ResourceBundle bundle = ResourceBundle.getBundle("db");
            driver = bundle.getString("jdbc.driver");
            url = bundle.getString("jdbc.url");
            username = bundle.getString("jdbc.username");
            password = bundle.getString("jdbc.password");
            Class.forName(driver);
        }catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    //获取连接方法
    public static Connection getConnection(){
        Connection conn = null;
        try{
            conn = DriverManager.getConnection(url,username,password);
        }catch(Exception e){
            e.printStackTrace();
        }
        return conn;
    }

    //关闭连接
    public  static void closeConnection (Connection conn){
        try{
            conn.close();
        }catch (SQLException e){
            e.printStackTrace();
        }
    }
}

package com.bjsxt.dao.impl;

import com.bjsxt.commons.JdbcUtils;
import com.bjsxt.dao.UserLoginDao;
import com.bjsxt.pojo.Users;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class UserLoginDaoImpl implements UserLoginDao {
    @Override
    public Users selectUsersByUserNameAndUserPwd(String username, String userpwd) {
        Users user = null;
        Connection conn = null;
        try{
            conn = JdbcUtils.getConnection();
            PreparedStatement ps = conn.prepareStatement("select * from users where username = ? and userpwd = ?");
            ps.setString(1,username);
            ps.setString(2,userpwd);
            ResultSet resultSet = ps.executeQuery();
            while(resultSet.next()){
                user = new Users();
                user.setUsersex(resultSet.getString("usersex"));
                user.setUserpwd(resultSet.getString("userpwd"));
                user.setUsername(resultSet.getString("username"));
                user.setUserid(resultSet.getInt("userid"));
                user.setPhonenumber(resultSet.getString("phonenumber"));
                user.setQqnumber(resultSet.getString("qqnumber"));
            }

        }catch (Exception e){
            e.printStackTrace();
        }finally {

        }
        return user;
    }
}

JAVA 全系列/第五阶段：JavaWeb开发/Web实战案例 1222楼

得到了Cookie可以实现免密码登录，，

JAVA 全系列/第五阶段：JavaWeb开发/Servlet技术详解（旧） 1223楼

老师，我这个遍历values值的方法看着没问题吧？为什么结果取不到值呢？

package com.bjsxt.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.*;

/**
 * 获取请求数据
 */
public class GetRequestDateServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("username");
        String[] hobbies = req.getParameterValues("hobby");
        List<String> strings = Arrays.asList(hobbies);
        Enumeration<String> parameterNames = req.getParameterNames();
        List<String> keys = new ArrayList<>();
        while(parameterNames.hasMoreElements()){
            keys.add(parameterNames.nextElement());
        }
        Map<String, String[]> parameterMap = req.getParameterMap();
        PrintWriter out = resp.getWriter(); //将请求信息返回给客户端浏览器，使用IO流PrintWriter做输出
        out.println("<!DOCTYPE HTML PUBLIC \'-//W3C//DTD HTML 4.0 Transitional//EN\'>");
        out.println("<HTML>");
        out.println("<HEAD><TITLE>A Servlet</TITLE></HEAD>");
        out.println("<BODY>");
        out.println("Username:"+username+"<br/>");
        out.println("Hobbies:"+strings+"<br/>");
        out.println("Keys:"+keys+"<br/>");
        Iterator<Map.Entry<String,String[]>> iterator = parameterMap.entrySet().iterator();
        while (iterator.hasNext()){
            Map.Entry<String,String[]> entry = iterator.next();
            out.println("Keys:"+entry.getKey()+" Value:"+Arrays.asList(entry.getValue()+"<br/>"));
        }
        out.println("</BODY>");
        out.println("</HTML>");
        out.flush();
        out.close();
    }
}