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+ * 1 数据库相关的操作，使用封装的工具类
+
+ * 2 编写四个servlet，使用注解指定相关的访问路径，分别对应查询，修改，删除，添加的操作
+
+ * 3 从浏览器中，访问这中个路径，显示响应的信息，查询显示结果，其它的显示成功或是失败
+
+   ```java
+   package 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.sql.*;
+   
+   //使用注解，给这个类绑定一个访问的路径
+   @WebServlet("/select")
+   public class StudentServlet extends HttpServlet {
+       @Override
+       protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+           req.setCharacterEncoding("utf-8");
+           resp.setContentType("text/html;charset=utf-8");
+           try {
+               Class.forName("com.mysql.jdbc.Driver");
+               Connection conn = DriverManager.getConnection("jdbc:mysql://localhost/student_db?useSSL=false&useUnicode=true&characterEncoding=utf8","root","root");
+               String sql="select * from student";
+               PreparedStatement pst = conn.prepareStatement(sql);
+               ResultSet rs = pst.executeQuery(sql);
+               while (rs.next()){
+                   //结果集取值方式，结果集对象名.getXxx(索引,or 字段名)  Xxx是数据类型
+                   int id = rs.getInt("id");
+                   String name = rs.getString("name");
+                   String sex = rs.getString("sex");
+                   resp.getWriter().write(id+name+sex+"</br>");
+               }
+               rs.close();
+               pst.close();
+               conn.close();
+           } catch (ClassNotFoundException e) {
+               throw new RuntimeException(e);
+           } catch (SQLException e) {
+               throw new RuntimeException(e);
+           }
+       }
+   
+       @Override
+       protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+           super.doPost(req, resp);
+       }
+   }
+   
+   ```
+
+   浏览器
+
+```java
+<?xml version="1.0" encoding="UTF-8"?>
+<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
+         version="4.0">
+
+
+    <servlet>
+        <servlet-name>servlet</servlet-name>
+        <servlet-class>servlet.StudentServlet</servlet-class>
+    </servlet>
+    <servlet-mapping>
+        <servlet-name>servlet</servlet-name>
+        <url-pattern>/let</url-pattern>
+    </servlet-mapping>
+</web-app>
+```
+
+更新
+
+```java
+package 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.sql.*;
+
+@WebServlet("/update")
+public class StudentServlet0 extends HttpServlet {
+    @Override
+    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        req.setCharacterEncoding("utf-8");
+        resp.setContentType("text/html;charset=utf-8");
+        try {
+            Class.forName("com.mysql.jdbc.Driver");
+            Connection conn = DriverManager.getConnection("jdbc:mysql://localhost/student_db?useSSL=false&useUnicode=true&characterEncoding=utf8","root","root");
+            String sql="update student set name=? where id=? ";
+            PreparedStatement pst = conn.prepareStatement(sql);
+            ResultSet rs = pst.executeQuery(sql);
+            while (rs.next()){
+                //结果集取值方式，结果集对象名.getXxx(索引,or 字段名)  Xxx是数据类型
+                int id = rs.getInt("id");
+                String name = rs.getString("name");
+                String sex = rs.getString("sex");
+                resp.getWriter().write(id+name+sex+"</br>");
+            }
+            int i=pst.executeUpdate(sql);
+            rs.close();
+            pst.close();
+            conn.close();
+            if(i>0){
+                System.out.println("更新成功");
+            }else
+                System.out.println("更新失败");
+        } catch (ClassNotFoundException e) {
+            throw new RuntimeException(e);
+        } catch (SQLException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    @Override
+    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        super.doPost(req, resp);
+    }
+}
+
+```
+
+删除
+
+```java
+package 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.sql.*;
+
+@WebServlet("/update")
+public class StudentServlet0 extends HttpServlet {
+    @Override
+    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        req.setCharacterEncoding("utf-8");
+        resp.setContentType("text/html;charset=utf-8");
+        try {
+            Class.forName("com.mysql.jdbc.Driver");
+            Connection conn = DriverManager.getConnection("jdbc:mysql://localhost/student_db?useSSL=false&useUnicode=true&characterEncoding=utf8","root","root");
+            String sql="delete from math where id=2 ";
+            PreparedStatement pst = conn.prepareStatement(sql);
+            ResultSet rs = pst.executeQuery(sql);
+            while (rs.next()){
+                //结果集取值方式，结果集对象名.getXxx(索引,or 字段名)  Xxx是数据类型
+                int id = rs.getInt("id");
+                String name = rs.getString("name");
+                String sex = rs.getString("sex");
+                resp.getWriter().write(id+name+sex+"</br>");
+            }
+            int i=pst.executeUpdate(sql);
+            rs.close();
+            pst.close();
+            conn.close();
+            if(i>0){
+                System.out.println("删除成功");
+            }else
+                System.out.println("删除失败");
+        } catch (ClassNotFoundException e) {
+            throw new RuntimeException(e);
+        } catch (SQLException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    @Override
+    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        super.doPost(req, resp);
+    }
+}
+
+```
+
+添加
+
+```java
+package 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.sql.*;
+
+@WebServlet("/update")
+public class StudentServlet0 extends HttpServlet {
+    @Override
+    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        req.setCharacterEncoding("utf-8");
+        resp.setContentType("text/html;charset=utf-8");
+        try {
+            Class.forName("com.mysql.jdbc.Driver");
+            Connection conn = DriverManager.getConnection("jdbc:mysql://localhost/student_db?useSSL=false&useUnicode=true&characterEncoding=utf8","root","root");
+            String sql="insert into math values (19,'朱元璋',34455) ";
+            PreparedStatement pst = conn.prepareStatement(sql);
+            ResultSet rs = pst.executeQuery(sql);
+            while (rs.next()){
+                //结果集取值方式，结果集对象名.getXxx(索引,or 字段名)  Xxx是数据类型
+                int id = rs.getInt("id");
+                String name = rs.getString("name");
+                String sex = rs.getString("sex");
+                resp.getWriter().write(id+name+sex+"</br>");
+            }
+            int i=pst.executeUpdate(sql);
+            rs.close();
+            pst.close();
+            conn.close();
+            if(i>0){
+                System.out.println("添加成功");
+            }else
+                System.out.println("添加失败");
+        } catch (ClassNotFoundException e) {
+            throw new RuntimeException(e);
+        } catch (SQLException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    @Override
+    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        super.doPost(req, resp);
+    }
+}
+
+```
+