Realize simple database query (incomplete)

Realize simple database query

JS The main points of ：

• JS： Explanatory language .（ The code is interpreted and executed by the browser , No precompiling .）
• JS Don't differentiate between single and double quotes .
• Direct embedding HTML page .

Direct measurement ( Constant ) ： Also known as “ Literal ”, Just see something , It's what it is .

• for example ：alert(886) and alert(“886”) The results are the same ;//886 It's a number, so you don't need quotation marks ,"886" Is string .
  

Variable ：（ All use var Definition ） example ：var a=100; var b=“abc”;

Variable names are case sensitive , Allow letters 、 Numbers 、 Dollar symbol ($) And the underline , But the first character is not allowed to be a number , Spaces and other punctuation marks are not allowed .

DOM Introduce ：

dom Technology in JS Internal function ：JS Language and Html/Xml A bridge between labels .

For convenience javascript Language passing dom operation html It's more convenient ,
hold html The content of the tag is divided into various nodes ：

• Document nodes (document)
• Element nodes It's also called a label getElementsByTagName
• Text node
• Attribute node type=”text” name=”username”
• Comment node

---

documnet： Is the built-in object in the page , The built-in object is simply understood as already new A good object , The name of the object is document.

• Acquisition of element nodes ：
  document.getElementById( id Property value );
• document.getElementsByTagName(“ Tag name ”);

---

Relational operator ：

• Congruence ：===
• Incongruence ：!==

---

toggle case

• str.toLowerCase();
• str.toUpperCase();

---

Query the index of the specified string

• str.indexOf(findstr, index);
• str.indexOf(findstr)
• str.indexOf(findstr,index)
• str.lastIndexOf(findstr, index);

---

• split() Method is used to split a string into an array of strings .

---

• innerText Show it directly as a string ;innerHtml Think of content as html Parsing

---

JSP Script for :（ A script is a piece of code ）

• grammar ：<%java Code %>
• effect ： perform java Code

JSP expression :

• grammar ：<%= Variable or expression %>
• effect ： Output the value of a variable or the result of an expression calculation to the browser

1. establish Project (Module)

After creation ：

2. establish lib file

Pictured ： Put in mysql drive

3. Create a static resource package （static）, Put in the required static resources

Put the file below , Self taking ：

link ：https://pan.baidu.com/s/1v6W11ZOcYOtjwf6f_gZN0g
Extraction code ：call

Write code ：

1. establish pojo package , Put in Student class ：

package com.situ.web.pojo;

public class Student {
    
    private Integer id;
    private String name;
    private Integer age;
    private String gender;

    public Student(Integer id, String name, Integer age, String gender) {
    
        this.id = id;
        this.name = name;
        this.age = age;
        this.gender = gender;
    }

    public Integer getId() {
    
        return id;
    }

    public void setId(Integer id) {
    
        this.id = id;
    }

    public String getName() {
    
        return name;
    }

    public void setName(String name) {
    
        this.name = name;
    }

    public Integer getAge() {
    
        return age;
    }

    public void setAge(Integer age) {
    
        this.age = age;
    }

    public String getGender() {
    
        return gender;
    }

    public void setGender(String gender) {
    
        this.gender = gender;
    }

    @Override
    public String toString() {
    
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", gender='" + gender + '\'' +
                '}';
    }
}

2. For easy connection , Will be part of JDBC Operation encapsulation is JDBCUtil class ：

package com.situ.web.util;

import java.sql.*;

public class JDBCUtil {
    
 
    private final static String URL = "jdbc:mysql://localhost:3306/java2207?useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC";
    private final static String USER = "root";
    private final static String PASSWORD = "root";
    
    // Private constructors prevent instantiation 
    private JDBCUtil() {
    
    }

    // The load driver （static Execute once when the class is loaded ）
    static {
    
        try {
    
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
    
            e.printStackTrace();
        }
    }
    // Establishing a connection 
    public static Connection getConnection() throws SQLException {
    
        Connection connection = DriverManager.getConnection(URL,USER,PASSWORD);
        return connection;
    }
    // encapsulation close Method , According to the principle of establishing before closing （ Similar to stack , The order of creation is connection,preparedStatement,resultSet, So the order of closing is as follows ）
    public static void close(Connection connection, PreparedStatement preparedStatement, ResultSet resultSet){
    
        if (resultSet != null) {
    
            try {
    
                resultSet.close();
            } catch (SQLException throwables) {
    
                throwables.printStackTrace();
            }
        }
        if (preparedStatement != null) {
    
            try {
    
                preparedStatement.close();
            } catch (SQLException throwables) {
    
                throwables.printStackTrace();
            }
        }
        if (connection != null) {
    
            try {
    
                connection.close();
            } catch (SQLException throwables) {
    
                throwables.printStackTrace();
            }
        }
    }
}

3.index.jsp quote layui style （ Only use the student management part ）

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <!DOCTYPE html> <html> <head> <title> Home page </title> <link rel="stylesheet" type="text/css" href="static/layui/css/layui.css"/> </head> <body class="layui-layout-body"> <div class="layui-layout layui-layout-admin"> <div class="layui-header"> <div class="layui-logo">JAVA-0000</div> <ul class="layui-nav layui-layout-left"> </ul> <ul class="layui-nav layui-layout-right"> <li class="layui-nav-item"> <a href="javascript:;"> <%-- <img src="<%=path%>/img/fei.png" --%> <!-- class="layui-nav-img"/> -->  user ${
    user.name}
          <%-- [${
    user.name}] --%>
        </a>
        <dl class="layui-nav-child">
          <dd>
            <a href="javascript:openUser()"> Basic information </a>
          </dd>
          <dd>
            <a href="javascript:openPass()"> Change Password </a>
          </dd>
          <dd>
            <a href="javascript:openPic()"> Modify the head image </a>
          </dd>
        </dl>
      </li>
      <li class="layui-nav-item">
        <a href="javascript:logout()"> Cancellation </a>
      </li>
    </ul>
  </div>
  <div class="layui-side layui-bg-black">
    <div class="layui-side-scroll">
      <!--  Left navigation area （ Compatible layui Existing vertical navigation ） -->
      <ul class="layui-nav layui-nav-tree" >
        <li class="layui-nav-item layui-nav-itemed">
          <a href="javascript:;"> Information maintenance </a>
          <dl class="layui-nav-child">
            <dd>
              <a href="javascript:;"
                 data-url="${pageContext.request.contextPath}/user"
                 class="site-demo-active"> Administrator management </a>
            </dd>
            <dd>
              <a href="javascript:;"
                 data-url="<%=request.getContextPath()%>/student"
                 class="site-demo-active"> Student management </a>
            </dd>
            <dd>
              <a href="javascript:;"
                 data-url="<%=request.getContextPath()%>/teacher"
                 class="site-demo-active"> Teacher management </a>
            </dd>
            <dd>
              <a href="javascript:;"
                 data-url="${path}/echarts.jsp"
                 class="site-demo-active"> Statistical charts </a>
            </dd>

          </dl>
        </li>
        <li class="layui-nav-item">
          <a href="javascript:;"> Basic configuration </a>
          <dl class="layui-nav-child">
            <dd>
              <a href="javascript:;"
                 class="site-demo-active"
                 data-url="/web/page/dict/dictlist.jsp">
                 Basic data maintenance </a>
            </dd>
            <dd>
              <a href="javascript:;" class="site-demo-active"
                 data-url="/web/404.jsp">404-1</a>
            </dd>
          </dl>
        </li>
      </ul>
    </div>
  </div>
  <div class="layui-body"><!--  Content subject area  -->
    <iframe name="rightframe" width="99%" height="97%" src="/echarts/getEChartsPage"></iframe>
  </div>
  <div class="layui-footer"> JAVA -  Bottom fixed area </div>
</div>
<script src="static/layui/layui.js"></script>
<script type="text/javascript">
  var $ = layui.jquery;
  var layer = layui.layer;
  var element = layui.element;
  $('.site-demo-active').click(function() {
    
    window.open($(this).data('url'), "rightframe");
  });
  element.render();// element.init();
  function openURL(url){
    
    window.open(url, "rightframe");
  }

  function logout() {
    
    layer.confirm( ' Are you sure you want to exit ',
            {
    icon:3}, function() {
    
              location.href = '${
    path}/user?method=logout'
            }
    );
  }

</script>
</body>
</html>

3. rewrite service Method , Set up the server （tomcat） Put our code in tomcat Execute share to browser .

What is? Servlet？

servlet yes java Write a server-side program , Running on the web Server
effect :

• Receive the request from the client
• Call other java Program to process requests Will deal with the result , Return to the server

@WebServlet("/student")
public class StudentServlet extends HttpServlet {
    
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        //request Request unified coding .
        req.setCharacterEncoding("utf-8");
        
        String method = req.getParameter("method");
        if(method == null || method.equals("")){
    
            method = "selectAll";
        }
        switch(method){
    
            case "selectAll":
                selectAll(req,resp);
                break;
            case "deleteById":
                delete(req,resp);
                break;
            case "add":
                add(req,resp);
                break;
            case "update":
                update(req,resp);
                break;
            case "getStudentUpdatePage":
                getStudentById(req,resp);
                break;
        }

    }

    private void getStudentById(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        String id = req.getParameter("id");
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        Student student = null;
        List<Student> list = new ArrayList<>();
        try {
    
            connection = JDBCUtil.getConnection();
            String sql = "select name,age,gender from student where id=?";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setInt(1,Integer.parseInt(id));
            resultSet = preparedStatement.executeQuery();
            if(resultSet.next()){
    
                String name = resultSet.getString("name");
                int age = resultSet.getInt("age");
                String gender = resultSet.getString("gender");
                student = new Student(Integer.parseInt(id),name,age,gender);
            }
        } catch (SQLException throwables) {
    
            throwables.printStackTrace();
        }finally {
    
            JDBCUtil.close(connection,preparedStatement,resultSet);
        }
        req.setAttribute("student",student);
        req.getRequestDispatcher("student_update.jsp").forward(req,resp);
    }

    private void update(HttpServletRequest req, HttpServletResponse resp) throws IOException {
    
        System.out.println("StudentServlet.update");
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        Integer id = Integer.parseInt(req.getParameter("id"));
        String name = req.getParameter("name");
        Integer age = Integer.parseInt(req.getParameter("age"));
        String gender = req.getParameter("gender");
        try {
    
            connection = JDBCUtil.getConnection();
            String sql = "update student set name=?,age=?,gender=? where id=?";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1,name);
            preparedStatement.setInt(2,age);
            preparedStatement.setString(3,gender);
            preparedStatement.setInt(4,id);
            System.out.println(preparedStatement);
            int count = preparedStatement.executeUpdate();
            System.out.println(count);
        } catch (SQLException throwables) {
    
            throwables.printStackTrace();
        }finally {
    
            JDBCUtil.close(connection,preparedStatement,null);
        }
        resp.sendRedirect(req.getContextPath() + "/student?method=selectAll");
    }

    private void add(HttpServletRequest req, HttpServletResponse resp) throws IOException {
    

        String name = req.getParameter("name");
        String age = req.getParameter("age");
        String gender = req.getParameter("gender");
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try {
    
            connection = JDBCUtil.getConnection();
            String sql = "insert into student(name,age,gender) values (?,?,?)";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1,name);
            preparedStatement.setInt(2, Integer.parseInt(age));
            preparedStatement.setString(3,gender);
            System.out.println(preparedStatement);
            int count = preparedStatement.executeUpdate();
            System.out.println(count);
        } catch (SQLException throwables) {
    
            throwables.printStackTrace();
        }finally {
    
            JDBCUtil.close(connection,preparedStatement,null);
        }
        resp.sendRedirect(req.getContextPath() + "/student?method=selectAll");
    }

    private void delete(HttpServletRequest req, HttpServletResponse resp) throws IOException {
    
        String id = req.getParameter("id");
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try {
    
            connection = JDBCUtil.getConnection();
            String sql = "delete from student where id=?";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setInt(1,Integer.parseInt(id));
            System.out.println(preparedStatement);
            int count = preparedStatement.executeUpdate();
            System.out.println(count);
        } catch (SQLException throwables) {
    
            throwables.printStackTrace();
        }finally {
    
            JDBCUtil.close(connection,preparedStatement,null);
        }
        // Redirect 
        resp.sendRedirect(req.getContextPath() + "/student");
    }

    private void selectAll(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        List<Student> list = new ArrayList<>();
        try {
    
            connection = JDBCUtil.getConnection();
            String sql = "select id,name,age,gender from student";
            preparedStatement = connection.prepareStatement(sql);
            resultSet = preparedStatement.executeQuery();
            while(resultSet.next()){
    
                int id = resultSet.getInt("id");
                String name = resultSet.getString("name");
                int age = resultSet.getInt("age");
                String gender = resultSet.getString("gender");
                Student student = new Student(id,name,age,gender);
                list.add(student);
            }
            for (Student student : list) {
    
                System.out.println(student);
            }
        } catch (SQLException throwables) {
    
            throwables.printStackTrace();
        }finally {
    
            JDBCUtil.close(connection,preparedStatement,resultSet);
        }
        resp.setContentType("text/html;charset=utf-8");
        req.setAttribute("list",list);
        req.getRequestDispatcher("student_list.jsp").forward(req,resp);
    }
}

4. To write student_list.jsp

JSP：
Servlet The role of ： be used for java Language development technology of dynamic resources ！！
JSP The role of ： use java Language + html Language , Technology for developing dynamic resources ！！
JSP Namely servlet！！！

JSP Script for :（ A script is a piece of code ）
grammar ：<%java Code %>
effect ： perform java Code

JSP expression :
grammar ：<%= Variable or expression %>
effect ： Output the value of a variable or the result of an expression calculation to the browser

%@ page import="java.util.List" %>
<%@ page import="com.situ.web.pojo.Student" %>
<%@ page import="java.util.List" %>
<%@ page import="java.util.ArrayList" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
    <link rel="stylesheet" type="text/css" href="static/bootstrap-3.4.1-dist/css/bootstrap.css"/>
</head>
<body>
${
    list}
<%
    List<Student> list = (List<Student>) request.getAttribute("list");
%>
<table class="table table-striped table-bordered table-hover table-condensed">
    <tr>
        <th>ID</th>
        <th> full name </th>
        <th> Age </th>
        <th> Gender </th>
    </tr>
    <%
        for (Student student:list) {
    
    %>
        <tr>
            <td><%=student.getId()%></td>
            <td><%=student.getName()%></td>
            <td><%=student.getAge()%></td>
            <td><%=student.getGender()%></td>
            <td><a href=""> Delete </a></td>
        </tr>
    <%
        }
    %>

</table>
</body>
</html>