JDBC

2024-02-18 19:20:40

● 简介

● JDBC 的常⽤类和接⼝

● JDBC开发步骤：

● JDBC接口核心的API

● PreparedStatement（预编译） vs Statement：

● 加载mysql-connector-java-5.1.7-bin.jar

● 使用JDBCUtil

●删除、增加、修改

● 简介：

（java DateBase Connective）java 数据连接技术，是由 java 提供的⼀个与平台⽆关的数据库操作标准（是⼀组接⼝的组成），数据库属于资源操作，所以所有的数据库操作最后必须要关闭数据库的连接。

● JDBC 的常⽤类和接⼝：

驱动管理器获得数据连接：public class DriverManager extends Object
数据库连接接⼝：public interface Connection extends Wrapper, AutoCloseable
⽤来操作静态 SQL 语句：public interface Statement extends Wrapper, AutoCloseable
⽤来操作动态 SQL 语句：public interface PreparedStatement extends Statement
⽤来调⽤储存过程的语句：public interface CallableStatement extends PreparedStatement
结果结合接⼝：public interface ResultSet extends Wrapper, AutoCloseable
结果集元数据：public interface ResultSetMetaData extends Wrapper
数据元数据：public interface DatabaseMetaData extends Wrapper

● JDBC开发步骤：

1、加载驱动Class.forName("");

2、获得连接对象Connection

3、写sql语句

4、创建Statement(一艘船)

5、执行sql语句

(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

6、关闭连接

● JDBC接口核心的API

|- DriverManager类：驱动管理器类，用于管理所有注册的驱动程序

|-registerDriver(driver) : 注册驱动类对象

|-Connection getConnection(url,user,password); 获取连接对象

|- Connection接口：表示java程序和数据库的连接对象。

|- Statement createStatement() ：创建Statement对象

|- PreparedStatement prepareStatement(String sql) 创建PreparedStatement对象

|- CallableStatement prepareCall(String sql) 创建CallableStatement对象(调用写好的存储过程)

|- Statement接口：用于执行静态的sql语句

|- int executeUpdate(String sql) ：执行静态的更新sql语句

|- ResultSet executeQuery(String sql) ：执行的静态的查询sql语句

|-PreparedStatement接口：用于执行预编译sql语句

|- int executeUpdate() ：执行预编译的更新sql语句

|-ResultSet executeQuery() ：执行预编译的查询sql语句

|- ResultSet接口：用于封装查询出来的数据

|- boolean next() ：将光标移动到下一行

|-getXX() : 获取列的值

● PreparedStatement（预编译） vs Statement：

1、语法不同：

PreparedStatement可以使用预编译的sql，只需要发送一次sql语句，后面只要发送参数即可，公用一个sql语句。

Statement只能使用静态的sql。 delete from student where id=1;

2、效率不同：PreparedStatement使用了sql缓冲区，效率要比Statement高。

3、安全性不同：PreparedStatement可以有效的防止sql注入，而Statement不能防止sql注入。

     @Test
    public void test1() {
        try {
            // 1、加载驱动Class.forName("");
            Class.forName("com.mysql.jdbc.Driver");
            // 2、获得连接对象Connection
            Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/java?useUnicode=true&characterEncoding=UTF-8", "root", "1234");
            // 3、写sql语句
            String sql = "SELECT id,`name`,age,gender FROM student";
            // 4、创建Statement(一艘船)
            Statement statement = connection.createStatement();
            // 5、执行sql语句
            //         (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);
            ArrayList<Student> list = new ArrayList<>();
            // next()方法判断下一行有没有，如果有指向下一行
            while (resultSet.next()) {
                // 每遍历一次循环，就拿出数据库查询结果里面的一行记录，就是一个学生的信息,
                // 就可以封装成一个Student对象
                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);
            }
            // 6、关闭连接
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }finally {
            // 先打开的后关闭
            if (resultSet != null) {
                try {
                    resultSet.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }
            if (statement != null) {
                try {
                    statement.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }
            if (connection != null) {
                try {
                    connection.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }

        // SELECT id,`name`,age,gender FROM student
        // ArrayList<Student> list
    } 


 @Test
    public void test2() {
        int selectId =15;
        Connection connection = null;
        PreparedStatement statement = null;
        ResultSet resultSet = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb?useUnicode=true&characterEncoding=UTF-8", "root", "123456");
            String sql = "SELECT id,`name`,age,gender FROM student WHERE id >= ?";
            // PreparedStatement 使用预编译的sql
            statement = connection.prepareStatement(sql);
            // 填上？占位符的值
            statement.setInt(1, selectId);
            System.out.println(statement);
            resultSet = statement.executeQuery();
            ArrayList<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) {
            e.printStackTrace();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            // 先打开的后关闭
            if (resultSet != null) {
                try {
                    resultSet.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }
            if (statement != null) {
                try {
                    statement.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }
            if (connection != null) {
                try {
                    connection.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }
        }
    }

● 加载mysql-connector-java-5.1.7-bin.jar

● 使用JDBCUtil

public class JDBCUtil {

    private JDBCUtil() {
    }

    // 静态代码块  只执行一次，保证这个驱动只加载一次
    static {
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    public static  Connection getConnection() throws SQLException {
        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/java?useUnicode=true&characterEncoding=UTF-8", "root", "1234");
        return connection;
    }

    public static void close(Connection connection, PreparedStatement statement, ResultSet resultSet) {
        // 先打开的后关闭
        if (resultSet != null) {
            try {
                resultSet.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
        if (statement != null) {
            try {
                statement.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
        if (connection != null) {
            try {
                connection.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }



}

  @Test
    public void test3() {
        int selectId =15;
        Connection connection = null;
        PreparedStatement statement = null;
        ResultSet resultSet = null;
        try {
            connection = JDBCUtil.getConnection();
            String sql = "SELECT id,`name`,age,gender FROM student WHERE id >= ?";
            // PreparedStatement 使用预编译的sql
            statement = connection.prepareStatement(sql);
            // 填上？占位符的值
            statement.setInt(1, selectId);
            System.out.println(statement);
            resultSet = statement.executeQuery();
            ArrayList<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 throwables) {
            throwables.printStackTrace();
        } finally {
            JDBCUtil.close(connection, statement, resultSet);
        }
    }

●删除、增加、修改

//删除
 @Test
    public void testDelete() {
        Connection connection = null;
        PreparedStatement statement = null;
        try {
            connection = JDBCUtil.getConnection();
            String sql = "DELETE FROM student WHERE id=?";
            statement = connection.prepareStatement(sql);
            statement.setInt(1, 15);
            System.out.println(statement);
            int count = statement.executeUpdate();
            System.out.println("count: " + count);
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            JDBCUtil.close(connection, statement, null);
        }
    }

//增加
    @Test
    public void testInsert() {
        Connection connection = null;
        PreparedStatement statement = null;
        try {
            connection = JDBCUtil.getConnection();
            String sql = "INSERT INTO student(name,age,gender) VALUES (?,?,?)";
            statement = connection.prepareStatement(sql);
            statement.setString(1, "小张");
            statement.setInt(2, 21);
            statement.setString(3, "男");
            System.out.println(statement);
            int count = statement.executeUpdate();
            System.out.println("count: " + count);
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            JDBCUtil.close(connection, statement, null);
        }
    }

//修改    
    @Test
    public void testUpdate() {
        Connection connection = null;
        PreparedStatement statement = null;
        try {
            connection = JDBCUtil.getConnection();
            String sql = "UPDATE student SET name=?,age=?,gender=? WHERE id=?";
            statement = connection.prepareStatement(sql);
            statement.setString(1, "小王");
            statement.setInt(2, 20);
            statement.setString(3, "女");
            statement.setInt(4, 16);
            System.out.println(statement);
            int count = statement.executeUpdate();
            System.out.println("count: " + count);
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            JDBCUtil.close(connection, statement, null);
        }
    }

码农公寓

● 简介：

● JDBC 的常⽤类和接⼝：​​​​​​​

● JDBC开发步骤：​​​​​​​

● JDBC接口核心的API

● PreparedStatement（预编译） vs Statement：

● 加载mysql-connector-java-5.1.7-bin.jar

● 使用JDBCUtil

●删除、增加、修改

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