Java JDBC篇1——初识JDBC

Java DataBase Connectivity Java 数据库连接（Java语言操作数据库）

1、什么是JDBC

其实是官方定义的一套操作所有关系型数据库的规则（接口），各个数据库厂商去实现这套接口，提供数据库驱动jar包，我们使用这套接口（JDBC）编程，真正执行的代码是驱动jar包中的实现类

2、MySql驱动包

官网地址 https://mvnrepository.com/artifact/mysql/mysql-connector-java

mysql-connector-java-5.1.49.jar 百度云：https://pan.baidu.com/s/17J2VfkGS2h44j69eB8TuFA提取码：nhnt

mysql-connector-java-8.0.25.jar 百度云：https://pan.baidu.com/s/1b8n7650uMKJtwidoptOjNQ提取码：wtvn

3、JDBC快速入门

3.1、建表和数据

USE test;
CREATE TABLE USER (id INT PRIMARY KEY AUTO_INCREMENT ,username VARCHAR(50),PASSWORD VARCHAR(50),birthday DATE
);
INSERT INTO USER (username, PASSWORD,birthday)
VALUES('admin1', '123','2000-12-24'),
('admin2','123','2003-12-24'),
('test1', '123','2006-12-24'),
('test2', '123','2005-12-24');

3.2、JDBC

5.x

public class Test {public static void main(String[] args) {Connection connection = null;Statement statement = null;ResultSet resultSet = null;try {// 1、注册驱动Class.forName("com.mysql.jdbc.Driver");// 2、获取连接String url="jdbc:mysql://localhost:3306/test";String username="root";String password="blingbling123.";connection = DriverManager.getConnection(url, username, password);//3、定义sqlString sql="select * from user";//4、获取指定sql对象statement = connection.createStatement();//5、执行sqlresultSet = statement.executeQuery(sql);//6、取出结果while (resultSet.next()){System.out.println(resultSet.getString("username"));}} catch (ClassNotFoundException e) {e.printStackTrace();} catch (SQLException throwables) {throwables.printStackTrace();} finally {//7、关闭连接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();}}}}
}

8.x

public class Test {public static void main(String[] args) {Connection connection = null;Statement statement = null;ResultSet resultSet = null;try {// 1、注册驱动Class.forName("com.mysql.cj.jdbc.Driver");// 2、获取连接String url="jdbc:mysql://localhost:3306/test?serverTimezone=UTC&characterEncoding=utf-8&useSSL=false";String username="root";String password="blingbling123.";connection = DriverManager.getConnection(url, username, password);//3、定义sqlString sql="select * from user";//4、获取指定sql对象statement = connection.createStatement();//5、执行sqlresultSet = statement.executeQuery(sql);//6、取出结果while (resultSet.next()){System.out.println(resultSet.getString("username"));}} catch (ClassNotFoundException e) {e.printStackTrace();} catch (SQLException throwables) {throwables.printStackTrace();} finally {//7、关闭连接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();}}}}
}

4、JDBC对象详解

4.1、Class.forName(“com.mysql.jdbc.Driver”);

查看源码发现：在com.mysql.cj.jdbc.Driver类中存在静态代码块

static {try {java.sql.DriverManager.registerDriver(new Driver());} catch (SQLException E) {throw new RuntimeException("Can't register driver!");}
}

mysql5之后的驱动jar包可以省略注册驱动的步骤

5.x

Class.forName("com.mysql.jdbc.Driver");

8.x

Class.forName("com.mysql.cj.jdbc.Driver");

4.2、DriverManager（数据库连接对象）

方法声明	功能介绍
Connection getConnection(String url, String user, String password)	通过连接字符串和用户名,密码来获取数据库连接对象

5.x url

String url="jdbc:mysql://localhost:3306/test";

8.x url

String url="jdbc:mysql://localhost:3306/test?serverTimezone=UTC&characterEncoding=utf-8&useSSL=false";

4.3、Connection（数据库连接对象）

方法声明	功能介绍
Statement createStatement()	创建 SQL语句执行对象
PreparedStatement prepareStatement(String sql)	创建 SQL语句执行对象（防注入）

4.4、Statement（执行sql对象）

方法声明	功能介绍
boolean execute(String sql)	可以执行任意的sql语句
int executeUpdate(String sql)	执行DML（insert、update、delete）DDL(create，alter、drop)返回值：影响的行数，可以通过这个影响的行数判断DML语句是否执行成功
ResultSet executeQuery(String sql)	执行DQL（select)语句

4.5、ResultSet（结果集对象）

方法声明	功能介绍
boolean next()	游标向下移动一行，判断当前行是否是最后一行末尾(是否有数据)，如果是，则返回false，如果不是则返回true
Xxx getXxx(参数):	获取数据，Xxx：代表数据类型（int：列的编号，String：列名称）

5、抽取JDBC工具类

url=jdbc:mysql://localhost:3306/test
user=root
password=blingbling123.
driver=com.mysql.jdbc.Driver

public class JDBCtool {private static String urls;private static String user;private static String password;private static String driver;static {Properties properties=new Properties();ClassLoader classLoader=JDBCtool.class.getClassLoader();URL url=classLoader.getResource("connection.properties");String path=url.getPath();try {properties.load(new FileReader(path));} catch (IOException e) {e.printStackTrace();}urls=properties.getProperty("url");user=properties.getProperty("user");password=properties.getProperty("password");driver=properties.getProperty("driver");try {Class.forName(driver);} catch (ClassNotFoundException e) {e.printStackTrace();}}public static Connection getconnection() throws SQLException {return DriverManager.getConnection(urls,user,password);}public static void close(Connection connection, PreparedStatement preparedStatement, ResultSet resultSet){if (resultSet!=null){try {resultSet.close();} catch (SQLException e) {e.printStackTrace();}}if (preparedStatement!=null){try {preparedStatement.close();} catch (SQLException e) {e.printStackTrace();}}if (connection!=null){try {connection.close();} catch (SQLException e) {e.printStackTrace();}}}
}

public class Test {public static void main(String[] args) throws SQLException {Connection connection = JDBCtool.getconnection();String sql="select * from user";PreparedStatement preparedStatement = connection.prepareStatement(sql);ResultSet resultSet = preparedStatement.executeQuery(sql);while (resultSet.next()){System.out.println(resultSet.getString("username"));}JDBCtool.close(connection,preparedStatement,resultSet);}
}