JDBC connection database reading foreground cannot display data

The phenomenon and background of the problem

Using the druid to connect to the database, the back-end reads the database data to the front-end display Unable to read data and background error

Problem related code , Do not paste screenshots

Entity class

public class Student {    private Integer stuid;    private String stuname;    private Integer age;    private Integer sex;    public Student() {    }    public Student(Integer stuid, String stuname, Integer age, Integer sex) {        this.stuid = stuid;        this.stuname = stuname;        this.age = age;        this.sex = sex;    }    public Integer getStuid() {        return stuid;    }    public void setStuid(Integer stuid) {        this.stuid = stuid;    }    public String getStuname() {        return stuname;    }    public void setStuname(String stuname) {        this.stuname = stuname;    }    public Integer getAge() {        return age;    }    public void setAge(Integer age) {        this.age = age;    }    public Integer getSex() {        return sex;    }    public void setSex(Integer sex) {        this.sex = sex;    }}

dao layer

public class StudentDaoImpl extends DruidUtil implements StudentDao {    @Override    public List<Student> getall() {        List list=new ArrayList();        Connection connection =null;        PreparedStatement preparedStatement=null;        ResultSet resultSet=null;        try {            connection = getConnection();            preparedStatement = connection.prepareStatement("select * from student");            resultSet = preparedStatement.executeQuery();            while(resultSet.next()){                Student student = new Student();                student.setStuid(resultSet.getInt("stuid"));                student.setStuname(resultSet.getString("stuname"));                student.setAge(resultSet.getInt("age"));                student.setSex(resultSet.getInt("sex"));                list.add(student);            }        } catch (SQLException e) {            e.printStackTrace();        } finally {            close(connection,preparedStatement,resultSet);        }        return list;    }}

service

public class StudentServiceImpl implements StudentService {    private StudentDao studentDao = new StudentDaoImpl();    @Override    public List<Student> getall() {        return studentDao.getall();    }}

servlet

@WebServlet(urlPatterns = "/getstus")public class StudentServlet  extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        doPost(req, resp);    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        //1. Receive request parameters         //2. Transfer service Layer method         StudentServiceImpl studentService = new StudentServiceImpl();        List<Student> getall = studentService.getall();        //3. Jump to the page         // The background transfers data to the foreground         req.setAttribute("stulist",getall);        req.getRequestDispatcher("/show.jsp").forward(req,resp);    }}

util

public class DruidUtil {    private static DataSource ds;    static {        try {            Properties ppt = new Properties();            ppt.load(DruidUtil.class.getClassLoader().getResourceAsStream("druid.properties"));            ds = DruidDataSourceFactory.createDataSource(ppt);        } catch (Exception e) {            e.printStackTrace();        }    }    /** *  Take a connection from the connection pool to the user  * * @return */    public static Connection getConnection() throws SQLException {        return ds.getConnection();    }    public static void close(Connection conn, Statement state, ResultSet rs) {        try {            if (rs != null) {                rs.close();            }        } catch (Exception throwables) {            throwables.printStackTrace();        }        try {            if (state != null) {                state.close();            }        } catch (Exception throwables) {            throwables.printStackTrace();        }        try {            if (conn != null) {                conn.close();            }        } catch (Exception throwables) {            throwables.printStackTrace();        }    }} The configuration file ```javaurl=jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf-8username=rootpassword=LYSlys0428driverClassName=com.mysql.jdbc.DriverinitialSize=5maxActive=10minIdle=5maxWait=3000

jsp```java<%@ page contentType="text/html;charset=UTF-8" language="java" %><html><head> <title>$Title$</title></head><body><a href="getstus"> Look up the list of students </a></body></html>

jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %><%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %><html><head> <title>Title</title></head><body><h1>show.jsp</h1><table border="1" width="500px" bgcolor="aqua"> <tr> <td>id</td> <td>name</td> <td>age</td> <td>sex</td> </tr> <c:forEach items="${stulist}" var="stu"> <tr> <td>${stu.stuid}</td> <td>${stu.stuname}</td> <td>${stu.age}</td> <td>${stu.sex==1?" male ":" Woman "}</td> </tr> </c:forEach></table></body></html>

The code structure

Operation results and error reporting contents

My solution ideas and tried methods

Only styles can appear in the foreground , Unable to read data

What I want to achieve

Click hyperlink , Read the database data and display