初学JDBC

2303_Alpha2025-08-26 10:31

JDBCDemo

java 复制代码 
package study;

import com.easy.web.pojo.Student;
import org.junit.Test;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class JDBCDemo {

    @Test
    public void test1(){


        try {
            //1、加载驱动Class.forName("");    （不需要背，能看懂就行）
            Class.forName("com.mysql.cj.jdbc.Driver");
            //2、获得连接对象Connection    （不需要背，能看懂就行）(jdbc:mysql（协议）://localhost（找到本机）:3306（访问mysql）/study?（数据库的名字）后面是一些属性设置)
            Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/study?useSSL=false&useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2b8", "root", "1234");
            //3、写sql语句
            String sql = "SELECT id,name,age,gender FROM student";
            //4、创建Statement(一艘船)     （用连接（connection）创建）
            Statement statement = connection.createStatement();  //（后面用PreparedStatement代替Statement）
            //5、执行sql语句              （statement执行）
            //        (1) 更新类（更改了表里面数据）：delete/update/insert          executeUpdate()
            //    返回值：int，表示你影响的行数
            //        (2)查询（没有改变表里面数据）:  select                        executeQuery()
            //    返回值：结果集ResultSet
            ResultSet resultSet = statement.executeQuery(sql);
            //（创建一个列表保存Student）
            List<Student> list = new ArrayList<>();
            //判断下一个还有没有，有返回true，没有返回false
            while (resultSet.next()){
                //while循环每遍历一次，就把这一行的字段值全拿出来，封装成一个Student
                int id = resultSet.getInt("id");
                String name = resultSet.getString("name");
                int age = resultSet.getInt("age");
                String gender = resultSet.getString("gender");
                //封装Student
                Student student = new Student(id,name,age,gender);
                //将封装完成的Student存入list集合中
                list.add(student);
            }
            for (Student student : list) {
                System.out.println(student);
            }
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        } catch (SQLException e) {
            throw new RuntimeException(e);
        } finally{
            //6、关闭连接
        }
    }

    @Test
    //用PreparedStatement代替Statement,效率更高且可以防止sql注入，Statement不能防止sql注入
    //sql注入：不规范输入影响了代码结构，使代码逻辑出错，执行非预期操作
    public void test2() {

        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/study?useSSL=false&useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2b8", "root", "1234");
            String sql = "SELECT id,name,age,gender FROM student";
            //4、创建PreparedStatement(一艘船)     （用连接（connection）创建）
            PreparedStatement preparedStatement = connection.prepareStatement(sql);  //可以直接用sql进行预编译，执行的时候就不需要传sql，效率更高
            ResultSet resultSet = preparedStatement.executeQuery(); //不用传入sql作为参数
            List<Student> list = new ArrayList<>();
            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 (ClassNotFoundException e) {
            throw new RuntimeException(e);
        } catch (SQLException e) {
            throw new RuntimeException(e);
        } finally {
            //6、关闭连接
        }
    }

    @Test
    //关闭连接
    public void test3() {
        //提前声明扩大作用域
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            //上面已经声明过了，不需要再声明
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/study?useSSL=false&useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2b8", "root", "1234");
            String sql = "SELECT id,name,age,gender FROM student";
            //与connection同理
            preparedStatement = connection.prepareStatement(sql);
            resultSet = preparedStatement.executeQuery();
            List<Student> list = new ArrayList<>();
            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 (ClassNotFoundException e) {
            throw new RuntimeException(e);
        } catch (SQLException e) {
            throw new RuntimeException(e);
        } finally {
            //6、关闭连接
            //需要关闭的有connection、preparedStatement、resultSet，
            //但是在Test2的结构中，在finally这里拿不到这三个变量，所以需要将这三个变量声明在最前面
            //后打开先关闭
            if(resultSet != null){
                try {
                    resultSet.close();
                } catch (SQLException e) {
                    throw new RuntimeException(e);
                }
            }

            if(preparedStatement != null){
                try {
                    preparedStatement.close();
                } catch (SQLException e) {
                    throw new RuntimeException(e);
                }
            }

            if(connection != null){
                try {
                    connection.close();
                } catch (SQLException e) {
                    throw new RuntimeException(e);
                }
            }
        }
    }

    @Test
    //将重复的内容抽取为工具类
    public void test4() {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            //利用工具类方法获取连接
            connection = JDBCUtil.getConnection();
            String sql = "SELECT id,name,age,gender FROM student";
            preparedStatement = connection.prepareStatement(sql);
            resultSet = preparedStatement.executeQuery();
            List<Student> list = new ArrayList<>();
            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);
            }
        }
        //ClassNotFoundException在JDBCUtil静态代码块中已被捕获，所以不需要在这里再捕获了
        catch (SQLException e) {
            throw new RuntimeException(e);
        } finally {
            JDBCUtil.close(connection, preparedStatement, resultSet);
        }
    }

    @Test
    public void testInsert(){
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        //不是查询类，没有结果集

        try {
            connection = JDBCUtil2.getConnection();
            String sql = "INSERT INTO student(id,name,age,gender) VALUES(?,?,?,?)";
            //一个一个填补括号中的"？"
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setInt(1,10);
            preparedStatement.setString(2,"张三11");
            preparedStatement.setInt(3,23);
            preparedStatement.setString(4,"男");
            //打印出来，显示在执行什么语句（非必须）
            System.out.println(preparedStatement);

            //返回影响行数
            int count = preparedStatement.executeUpdate();
            System.out.println("count: " + count);

        } catch (SQLException e) {
            throw new RuntimeException(e);
        } finally {
            JDBCUtil2.close(connection,preparedStatement,null);
        }
    }


    @Test
    public void testDelete(){
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        //不是查询类，没有结果集

        try {
            connection = JDBCUtil2.getConnection();
            String sql = "DELETE FROM student WHERE id=?";
            //一个一个填补括号中的"？"
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setInt(1,10);
            //打印出来，显示在执行什么语句（非必须）
            System.out.println(preparedStatement);

            //返回影响行数
            int count = preparedStatement.executeUpdate();
            System.out.println("count: " + count);

        } catch (SQLException e) {
            throw new RuntimeException(e);
        } finally {
            JDBCUtil2.close(connection,preparedStatement,null);
        }
    }


    @Test
    public void testUpdate(){
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        //不是查询类，没有结果集

        try {
            connection = JDBCUtil2.getConnection();
            String sql = "UPDATE student SET name=?,age=?,gender=? WHERE id=?";
            //一个一个填补括号中的"？"
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1,"李四11");
            preparedStatement.setInt(2,24);
            preparedStatement.setString(3,"男");
            preparedStatement.setInt(4,9);
            //打印出来，显示在执行什么语句（非必须）
            System.out.println(preparedStatement);

            //返回影响行数
            int count = preparedStatement.executeUpdate();
            System.out.println("count: " + count);

        } catch (SQLException e) {
            throw new RuntimeException(e);
        } finally {
            JDBCUtil2.close(connection,preparedStatement,null);
        }
    }

    //模糊查找
    @Test
    public void testLike() {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            connection = JDBCUtil.getConnection();
            String sql = "SELECT id,name,age,gender FROM student WHERE name LIKE ?";
            preparedStatement = connection.prepareStatement(sql);
            //填补"？"
            preparedStatement.setString(1,"%张%");
            System.out.println(preparedStatement);
            resultSet = preparedStatement.executeQuery();
            List<Student> list = new ArrayList<>();
            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 e) {
            throw new RuntimeException(e);
        } finally {
            JDBCUtil.close(connection, preparedStatement, resultSet);
        }
    }
}

JDBCUtil

java 复制代码 
package study;

import java.sql.*;

//将重复代码块封装为Util工具类
public class JDBCUtil {

    //因为驱动只需要加载一次，如果放在下面的方法当中，每次调用方法都会加载驱动，
    //利用静态代码块保证驱动只加载一次
    static {
        //1、加载驱动Class.forName("");    （不需要背，能看懂就行）
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }

    //需要有一个方法获取连接
    //返回值类型为Connection
    public static Connection getConnection() throws SQLException {       //（抛出getConnection的异常，调用时catch一下即可，在这里直接try catch也可以）
        //2、获得连接对象Connection    （不需要背，能看懂就行）(jdbc:mysql（协议）://localhost（找到本机）:3306（访问mysql）/study?（数据库的名字）后面是一些属性设置)
        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/study?useSSL=false&useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2b8", "root", "1234");
        return connection;
    }

    public static void close(Connection connection, PreparedStatement preparedStatement, ResultSet resultSet){
        if(resultSet != null){
            try {
                resultSet.close();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }

        if(preparedStatement != null){
            try {
                preparedStatement.close();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }

        if(connection != null){
            try {
                connection.close();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }
    }
}

JDBCUtil2

java 复制代码 
package study;

import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;

//当把driver、url、username、password放在代码中时，因为都是写死的，不容易进行修改
//所以也将这些东西单独拿出来作为Util的一部分，代码中直接获取即可
public class JDBCUtil2 {
    private static String driver;
    private static String url;
    private static String username;
    private static String password;

    static {
        //加载文件（与加载驱动分开）
        try {
            //1.通过当前类获取类加载器
            ClassLoader classLoader = JDBCUtil2.class.getClassLoader();
            //2.通过类加载器获取输入流
            //参数传入properties文件名（放在resources文件夹中）
            InputStream inputStream = classLoader.getResourceAsStream("db.properties");
            //3.创建一个properties对象加载输入流
            Properties properties = new Properties();
            properties.load(inputStream);
            //4.根据key获取配置文件中对应的value值
            driver = properties.getProperty("driver");
            url = properties.getProperty("url");
            username = properties.getProperty("username");
            password = properties.getProperty("password");
        } catch (IOException e) {
            throw new RuntimeException(e);
        }

        //加载驱动
        try {
            Class.forName(driver);
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }

    }

    public static Connection getConnection() throws SQLException {       //（抛出getConnection的异常，调用时catch一下即可，在这里直接try catch也可以）
        Connection connection = DriverManager.getConnection(url, username, password);
        return connection;
    }

    public static void close(Connection connection, PreparedStatement preparedStatement, ResultSet resultSet){
        if(resultSet != null){
            try {
                resultSet.close();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }

        if(preparedStatement != null){
            try {
                preparedStatement.close();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }

        if(connection != null){
            try {
                connection.close();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }
    }
}

Student类

java 复制代码 
package com.easy.web.pojo;

import java.io.Serializable;

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

    public Student() {
    }

    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 + '\'' +
                '}';
    }
}
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