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服务器之家 - 编程语言 - Java教程 - 详细说明关于Java的数据库连接(JDBC)

详细说明关于Java的数据库连接(JDBC)

2021-12-21 13:29谁砍了我的二叉树 Java教程

这篇文章主要介绍了详细说明关于Java的数据库连接JDBC,JDBC是用Java语言向数据库发送SQL语句,需要的朋友可以参考下面文章内容

Java的数据库连接(JDBC)

1、什么是JDBC

JDBC(JavaDataBase Connectivity) 就是Java数据库连接,说白了就是用Java语言来操作数据库。原来我们操作数据库是在控制台使用SQL语句来操作数据库,JDBC是用Java语言向数据库发送SQL语句。

2、JDBC的原理

早期SUN公司的天才们想编写一套可以连接天下所有数据库的API,但是当他们刚刚开始时就发现这是不可完成的任务,因为各个厂商的数据库服务器差异太大了。后来SUN开始与数据库厂商们讨论,最终得出的结论是,由SUN提供一套访问数据库的规范(就是一组接口),并提供连接数据库的协议标准,然后各个数据库厂商会遵循SUN的规范提供一套访问自己公司的数据库服务器的API出现。SUN提供的规范命名为JDBC,而各个厂商提供的,遵循了JDBC规范的,可以访问自己数据库的API被称之为驱动!JDBC是接口,而JDBC驱动才是接口的实现,没有驱动无法完成数据库连接!每个数据库厂商都有自己的驱动,用来连接自己公司的数据库。

详细说明关于Java的数据库连接(JDBC)

3、演示JDBC的使用

通过下载MySQL的驱动jar文件,将其添加到项目中间,在注册驱动时要指定为已经下载好的驱动。

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package jdbc;
 
import com.mysql.jdbc.Driver;  //这是我们驱动的路径
 
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;
public class Jdbc01 {
    public static void main(String[] args) throws SQLException {
 
        //1.注册驱动
        Driver driver = new Driver();
 
        //2.得到连接
        //jdbc:mysql:// 规定好的协议  localhost 连接的地址  3306 监听的端口 test_table 连接的数据库
        String url = "jdbc:mysql://localhost:3306/test_table";
        Properties properties = new Properties();
        //user和password 规定好的不能随意改
        properties.setProperty("user", "root");//
        properties.setProperty("password", "161142");
        Connection connect = driver.connect(url, properties); //相当于网络连接
 
        //3.执行sql语句
        //String sql = "insert into actor values(null,'syj','女','2000-05-26','110')";
        String sql = "update actor set name = 'xhj' where id =  2";
        Statement statement = connect.createStatement();
        int rows = statement.executeUpdate(sql);    //返回影响的行数
        if (rows > 0) System.out.println("添加成功");
        else System.out.println("添加失败");
 
        //4.关闭连接资源
        statement.close();
        connect.close();
    }
}

4、数据库连接方式

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public class JdbcConn {
    @Test    /* 第一种 */
    public void testConn01() throws SQLException {
        //获取Driver实现类对象
        Driver driver = new Driver();
 
        String url = "jdbc:mysql://localhost:3306/test_table";
        Properties properties = new Properties();
        properties.setProperty("user", "root");
        properties.setProperty("password", "161142");
        Connection connect = driver.connect(url, properties);
        System.out.println(connect);
    }
    
    @Test    /* 第二种 */
    public void testConn02() throws Exception{
        //使用反射加载Driver类,动态加载,可以通过配置文件灵活使用各种数据库
        Class<?> aClass = Class.forName("com.mysql.jdbc.Driver");
        Driver driver = (Driver) aClass.getDeclaredConstructor().newInstance();
 
        String url = "jdbc:mysql://localhost:3306/test_table";
        Properties properties = new Properties();
        properties.setProperty("user", "root");
        properties.setProperty("password", "161142");
        Connection connect = driver.connect(url, properties);
        System.out.println(connect);
    }
    
    @Test    /* 第三种 */
    //DriverManager统一来管理Driver
    public void testConn03() throws Exception{
        //使用反射加载Driver类
        Class<?> aClass = Class.forName("com.mysql.jdbc.Driver");
        Driver driver = (Driver) aClass.getDeclaredConstructor().newInstance();
 
        //创建url和user和password
        String url = "jdbc:mysql://localhost:3306/test_table";
        String user = "root";
        String password = "161142";
 
        DriverManager.registerDriver(driver);   //注册Driver驱动
 
        Connection connection = DriverManager.getConnection(url, user, password);
        System.out.println(connection);
    }
    
    @Test    /* 第四种 */
    public void testConn04() throws Exception{
        //使用反射加载Driver类
        Class.forName("com.mysql.jdbc.Driver");
        /* Class.forName("com.mysql.jdbc.Driver")在底层加载Driver时自动完成注册驱动,简化代码
            //在底层加载Driver时会自动加载静态代码块
            static {
                try {
                    DriverManager.registerDriver(new Driver());
                } catch (SQLException var1) {
                    throw new RuntimeException("Can't register driver!");
                }
            }
        */
        //Class.forName("com.mysql.jdbc.Driver");
        /*  Class.forName("com.mysql.jdbc.Driver");这句话也可以去掉
            mysql驱动5.1.6可以无需CLass.forName(“com.mysql.jdbc.Driver");
            从jdk1.5以后使用了jdbc4,不再需要显示调用class.forName()注册驱动而是自动调用驱动
            jar包下META-INF\services\java.sqI.Driver文本中的类名称去注册
            建议还是写上,更加明确
        */
        //创建url和user和password
        String url = "jdbc:mysql://localhost:3306/test_table";
        String user = "root";
        String password = "161142";
 
        Connection connection = DriverManager.getConnection(url, user, password);
        System.out.println(connection);
    }
    
    @Test    /* 第五种(推荐使用) */
    public void testConn05() throws Exception{
        //在方式4的情况下,将信息放到配置文件里,利于后续可持续操作
        //获取配置文件信息
        Properties properties = new Properties();
        properties.load(new FileInputStream("src\\mysql.properties"));
        //获取相关信息
        String user = properties.getProperty("user");
        String password = properties.getProperty("password");
        String url = properties.getProperty("url");
        String driver = properties.getProperty("driver");
 
        Class.forName(driver);  //加载Driver类,建议加上
 
        Connection connection = DriverManager.getConnection(url, user, password);
        System.out.println(connection);
    }
}

5、JDBC的查询

使用ResultSet 记录查询结果
ResultSet: 底层使用ArrayList 存放每一行数据(二维字节数组,每一维表示一行中的一个数据)
Resultment: 用于执行静态SQL语句并返回其生成的结果的对象,是一个接口,需要各个数据库厂家来实现。(实际中我们一般不用这个)

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public class jdbc03 {
    public static void main(String[] args) throws Exception {
        Properties properties = new Properties();
        properties.load(new FileInputStream("src\\mysql.properties"));
        String user = properties.getProperty("user");
        String password = properties.getProperty("password");
        String url = properties.getProperty("url");
        String driver = properties.getProperty("driver");
        Class.forName(driver);
        Connection connection = DriverManager.getConnection(url, user, password);
        Statement statement = connection.createStatement();
 
        ResultSet resultSet = statement.executeQuery("select id,`name`,sex,borndate from actor;");
 
        while (resultSet.next()){ //resultSet.previous();//向上移动一行
            int id = resultSet.getInt(1);
            //int id = resultSet.getInt("id"); //也可以按照列明来获取
            String name = resultSet.getString(2);
            String sex = resultSet.getString(3);
            Date date = resultSet.getDate(4);
            //Object object = resultSet.getObject(索引|列明); //对象形式操作(分情况考虑)
            System.out.println(id + "\t" + name + "\t" + sex + "\t" + date);
        }
 
        statement.close();
        connection.close();
    }
}

6、SQL注入

SQL注入: 是利用某些系统没有对用户输入的数据进行充分的检查,而在用户输入数据中注入非法的SQL语句段或命令,恶意攻击数据库。
例如下列代码实现了注入问题(而Statement就存在这个问题,所以实际开发过程中不用它)

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create table admit(name varchar(32),password varchar(32));
insert into admit values('tom','1234');
select * from admit where name = 'tom' and password = '1234'; # 输出 tom 1234
# 如果有人输入 name 为 1' or   password 为  or '1' = '1
# 那么select 就变成
select * from admit where name = '1' or ' and password = ' or '1' = '1'; # 其中'1' = '1'永远成立

7、预处理查询

使用PreparedStatement代替Statement就避免了注入问题,通过传入**?** 代替拼接 (PreparedStatement接口继承了Statement接口)

PreparedStatement的好处

  • 不再使用+拼接sql语句,减少语法错误
  • 有效的解决了sql注入问题!
  • 大大减少了编译次数,效率较高

7.1 查询 已解决注入问题

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public class jdbc04 {
    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入用户名:");
        String name = scanner.nextLine();
        System.out.print("请输入密码:");
        String pwd = scanner.nextLine();
 
        Properties properties = new Properties();
        properties.load(new FileInputStream("src\\mysql.properties"));
        String user = properties.getProperty("user");
        String password = properties.getProperty("password");
        String url = properties.getProperty("url");
        String driver = properties.getProperty("driver");
        Class.forName(driver);
        Connection connection = DriverManager.getConnection(url, user, password);
 
        //Statement statement = connection.createStatement();
        //preparedStatement是PreparedStatement实现类的对象
        PreparedStatement preparedStatement = connection.prepareStatement("select `name` ,`password` " +
                "from admit where name = ? and password = ?");
        preparedStatement.setString(1,name);    //?号下标从1开始
        preparedStatement.setString(2,pwd);
 
        ResultSet resultSet = preparedStatement.executeQuery();
        if (resultSet.next()) System.out.println("登录成功");
        else System.out.println("登陆失败");
 
        preparedStatement.close();
        connection.close();
    }
}

7.2 插入,更新,删除

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public class jdbc05 {
    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入用户名:");
        String name = scanner.nextLine();
        System.out.print("请输入密码:");
        String pwd = scanner.nextLine();
 
        Properties properties = new Properties();
        properties.load(new FileInputStream("src\\mysql.properties"));
        String user = properties.getProperty("user");
        String password = properties.getProperty("password");
        String url = properties.getProperty("url");
        String driver = properties.getProperty("driver");
        Class.forName(driver);
        Connection connection = DriverManager.getConnection(url, user, password);
 
        //添加
        String sql1 = "insert into admit values(?,?)";
        //修改
        String sql2 = "update admit set name = ? where name = ? and password = ?";
        //删除
        String sql3 = "delete from admit where name = ? and password = ?";
        PreparedStatement preparedStatement = connection.prepareStatement(sql3);
        //preparedStatement.setString(1,name+"plas");    //?号下标从1开始
        //preparedStatement.setString(2,name);
        //preparedStatement.setString(3,pwd);
 
        preparedStatement.setString(1,name);
        preparedStatement.setString(2,pwd);
 
        int rows = preparedStatement.executeUpdate();
        if (rows > 0) System.out.println("操作成功");
        else System.out.println("操作失败");
 
        preparedStatement.close();
        connection.close();
    }
}

8、工具类开发

由于在进行数据库操作时,有些步骤是重复的,如连接,关闭资源等操作。
工具类

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package utils;
import java.sql.*;
import java.io.FileInputStream;
import java.util.Properties;
public class JDBCUtils {
    private static String user;     //用户名
    private static String password; //密码
    private static String url;      //连接数据库的url
    private static String driver;   //驱动
    
    //静态代码块进行行初始化
    static {
        try {
            Properties properties = new Properties();
            properties.load(new FileInputStream("src\\mysql.properties"));
            user = properties.getProperty("user");
            password = properties.getProperty("password");
            url = properties.getProperty("url");
            driver = properties.getProperty("driver");
        } catch (Exception e) {
            //实际开发过程中(将编译异常,改成运行异常,用户可以捕获异常,也可以默认处理该异常)
            throw new RuntimeException(e);
        }
    }
    //连接
    public static Connection getConnection(){
        try {
            return DriverManager.getConnection(url,user,password);
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }
    //关闭资源
    public static void close(ResultSet set, Statement statement,Connection connection){
        try {
            if (set != null) set.close();
            if (statement != null)statement.close();
            if (connection != null)connection.close();
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }
}

应用:

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public class JdbcUtilsTest {
    @Test  //测试select操作
    public void testSelect() {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
 
        try {
            //得到连接
            connection = JDBCUtils.getConnection();
 
            //设置sql
            String sql = "select * from actor where id = ?";
 
            //创建PreparedStatement
            preparedStatement = connection.prepareStatement(sql);
 
            //占位赋值
            preparedStatement.setInt(1,2);
 
            //执行
            resultSet = preparedStatement.executeQuery();
            while (resultSet.next()) {
                /* 也可以这样写
                int id = resultSet.getInt("id");
                String name = resultSet.getString("name");
                String sex = resultSet.getString("sex");
                Date date = resultSet.getDate("borndate");
                String phone = resultSet.getString("phone");
                 */
                int id = resultSet.getInt(1);
                String name = resultSet.getString(2);
                String sex = resultSet.getString(3);
                Date date = resultSet.getDate(4);
                String phone = resultSet.getString(5);
                System.out.println(id + "\t" + name + "\t" + sex + "\t" + date + "\t" + phone);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(resultSet, preparedStatement, connection);
        }
    }
 
    @Test  //测试DML操作
    public void testDML() {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
 
        try {
            //得到连接
            connection = JDBCUtils.getConnection();
 
            //设置sql
            String sql = "update actor set name = ?,sex = ? where id = ?";
 
            //创建PreparedStatement
            preparedStatement = connection.prepareStatement(sql);
 
            //占位符赋值
            preparedStatement.setString(1, "sxy");
            preparedStatement.setString(2, "男");
            preparedStatement.setInt(3, 2);
 
            //执行
            preparedStatement.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(null, preparedStatement, connection);
        }
    }
}

9、JDBC事务

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public class Jdbc06 {
    public static void main(String[] args) {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try {
            connection = JDBCUtils.getConnection();
            connection.setAutoCommit(false);//关闭自动提交(开启事务)
 
            //第一个动作
            String sql = "update actor set phone = phone - 10 where id = 2";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.executeUpdate();
 
            //int i = 1/0;  异常
 
            //第二个动作
            sql = "update actor set phone = phone + 10 where id = 1";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.executeUpdate();
 
            //提交事务
            connection.commit();
 
        } catch (Exception e) {
            System.out.println("有异常存在,撤销sql服务");
            try {
                connection.rollback();  //回滚到事务开始的地方
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
            e.printStackTrace();
        } finally {
            JDBCUtils.close(null, preparedStatement, connection);
        }
 
    }
}

10、批处理

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public class Jdbc07 {
    @Test   //普通处理5000条插入数据   执行时间169839
    public void test01() {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try {
            connection = JDBCUtils.getConnection();
            String sql = "insert into actor(id,`name`,sex) values (?,?,'男')";
            preparedStatement = connection.prepareStatement(sql);
            long begin = System.currentTimeMillis();
            for (int i = 0; i < 5000; i++) {
                preparedStatement.setString(1, 3 + i + "");
                preparedStatement.setString(2, "sxy" + (i + 1));
                preparedStatement.executeUpdate();
            }
            long end = System.currentTimeMillis();
            System.out.println(end - begin);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(null, preparedStatement, connection);
        }
    }
 
    @Test   //批处理   执行时间429
    public void test02() {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try {
            connection = JDBCUtils.getConnection();
            String sql = "insert into actor(id,`name`,sex) values (?,?,'男')";
            preparedStatement = connection.prepareStatement(sql);
            long begin = System.currentTimeMillis();
            for (int i = 0; i < 5000; i++) {
                preparedStatement.setString(1, 3 + i + "");
                preparedStatement.setString(2, "sxy" + (i + 1));
                
                //将sql语句加入批处理包中
                preparedStatement.addBatch();
                /*
                    preparedStatement.addBatch()在底层把每一条数据加入到ArrayList
                    执行过程:检查本条sql中的语法问题 -> 把本条sql语句加入到ArrayList -> 每1000条执行一次
                    批处理优点:减少了编译次数,又减少了运行次数,效率大大提高
                    还需要在properties配置文件中将url加上?rewriteBatchedStatements=true
                    url=jdbc:mysql://localhost:3306/test_table?rewriteBatchedStatements=true
                */
                
                //当有1000条时,在进行处理
                if ((i + 1) % 1000 == 0) {
                    preparedStatement.executeBatch();
                    //清空批处理包
                    preparedStatement.clearBatch();
                }
            }
            long end = System.currentTimeMillis();
            System.out.println(end - begin);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(null, preparedStatement, connection);
        }
    }
}

11、数据库连接池

由于有很多用户连接数据库,而数据库连接数量又是有限制的,而且就算连接并且关闭也是很耗时,所以就有了引入了数据库连接池可以很好的来解决这个问题。下面是普通连接数据库连接并且关闭5000次所耗时间6249毫秒,可以发下时间相对很长。

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public class ConQuestion {
    public static void main(String[] args) {
        //看看连接-关闭 connection 会耗用多久
        long start = System.currentTimeMillis();
        System.out.println("开始连接.....");
        for (int i = 0; i < 5000; i++) {
            //使用传统的jdbc方式,得到连接
            Connection connection = JDBCUtils.getConnection();
            //做一些工作,比如得到PreparedStatement ,发送sql
            //..........
            //关闭
            JDBCUtils.close(null, null, connection);
 
        }
        long end = System.currentTimeMillis();
        System.out.println("传统方式5000次 耗时=" + (end - start));//传统方式5000次 耗时=6249
    }
}

11.1 数据库连接池基本介绍

  • 预先在缓冲池中放入一定数量的连接,当需要建立数据库连接时,只需从“缓冲池”中取出一个,使用完毕之后再放回去。
  • 数据库连接池负责分配,管理和释放数据库连接,它允许应用程序重复使用一个现有的数据库连接,而不是重新建立一个。
  • 当应用程序向连接池请求的连接数超过最大连接数量时,这些请求将被加入到等待队列中。

11.2 JDBC的数据库连接池使用

JDBC的数据库连接池使用javax.sql.DataSource来表示,DataSource只是一个接口,该接口通常由第三方提供实现。

11.3 数据库连接池的种类

  • C3P0 数据库连接池,速度相对较慢,稳定性不错(hibernate,spring)。(用的较多)
  • DBCP数据库连接池,速度相对c3p0较快,但不稳定。
  • Proxool数据库连接池,有监控连接池状态的功能,稳定性较c3p0差一点。
  • BoneCP 数据库连接池,速度快。
  • Druid (德鲁伊)是阿里提供的数据库连接池,集DBCP,C3P0,Proxool优点于身的数据库连接池。(应用最广)

11.4 C3P0连接池

利用C3P0连接池再次尝试连接5000次数据库 可以发现耗时方式一仅仅花了456毫秒,第二种通过配置文件操作也是花了419毫秒差不多的时间,值得说的是这个连接池连接配置文件不能是我们自己写,官方有给定的模板(c3p0.config.xml)。

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public class C3P0_ {
    @Test   //方式一: 相关参数,在程序中指定user,url,password
    public void testC3P0_1() throws Exception {
        //创建一个数据源对象
        ComboPooledDataSource comboPooledDataSource = new ComboPooledDataSource();
 
        //通过配合文件获取相关连接信息
        Properties properties = new Properties();
        properties.load(new FileInputStream("src\\mysql.properties"));
        String user = properties.getProperty("user");
        String password = properties.getProperty("password");
        String url = properties.getProperty("url");
        String driver = properties.getProperty("driver");
 
        //给数据源(comboPooledDataSource)设置相关参数
        //连接管理是由comboPooledDataSource(连接池)来管理的
        comboPooledDataSource.setDriverClass(driver);   //设置驱动
        comboPooledDataSource.setJdbcUrl(url);
        comboPooledDataSource.setUser(user);
        comboPooledDataSource.setPassword(password);
 
        //初始化数据源的连接数
        comboPooledDataSource.setInitialPoolSize(10);
        //数据库连接池最大容量,如果还有连接请求,那么就会将该请求放入等待队列中
        comboPooledDataSource.setMaxPoolSize(50);
 
        //测试连接池的效率, 测试对mysql 5000次操作
        long start = System.currentTimeMillis();
        for (int i = 0; i < 5000; i++) {
            //getConnection()这个方法就是重写了DataSource接口的方法
            Connection connection = comboPooledDataSource.getConnection();
            connection.close();
        }
        long end = System.currentTimeMillis();
        //c3p0 5000连接mysql 耗时=456
        System.out.println("c3p0 5000连接mysql 耗时=" + (end - start));
        comboPooledDataSource.close();
    }
    
    
    //第二种方式 使用配置文件模板来完成
    //将C3P0 提供的 c3p0.config.xml 拷贝到 src目录下
    //该文件指定了连接数据库和连接池的相关参数
    @Test
    public void testC3P0_02() throws SQLException {
        ComboPooledDataSource comboPooledDataSource = new ComboPooledDataSource("sxy");
        //测试5000次连接mysql
        long start = System.currentTimeMillis();
        for (int i = 0; i < 5000; i++) {
            Connection connection = comboPooledDataSource.getConnection();
            connection.close();
        }
        long end = System.currentTimeMillis();
        //c3p0的第二种方式(5000) 耗时=419
        System.out.println("c3p0的第二种方式(5000) 耗时=" + (end - start));
 
    }
}

11.5 Druid连接池

在使用Druid连接池连接数据库500000次耗时643毫秒,而C3P0500000次连接耗时2373毫秒,很显然Druid连接速度更快。

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public class Druid_ {
    @Test
    public void testDruid() throws Exception {
        //1.加入Druid jar包
        //2.加入 配置文件 druid.properties 放到src目录下
        //3.创建Properties对象
        Properties properties = new Properties();
        properties.load(new FileInputStream("src\\druid.properties"));
 
        //4.创建一个指定参数的数据库连接池
        DataSource dataSource = DruidDataSourceFactory.createDataSource(properties);
 
        long start = System.currentTimeMillis();
        for (int i = 0; i < 500000; i++) {
            Connection connection = dataSource.getConnection();
            connection.close();
        }
        long end = System.currentTimeMillis();
        //Druid的500000次创建 耗时=643
        System.out.println("Druid的500000次创建 耗时=" + (end - start));
    }
}

对应的工具类

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public class JDBCUtilsByDruid {
    private static DataSource ds;
 
    //在静态代码块完成 ds初始化
    static {
        Properties properties = new Properties();
        try {
            properties.load(new FileInputStream("src\\druid.properties"));
            ds = DruidDataSourceFactory.createDataSource(properties);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
 
    //编写getConnection方法
    public static Connection getConnection() throws SQLException {
        return ds.getConnection();
    }
 
    //关闭连接:在数据库连接池技术中,close不是真的断掉连接,而是把使用的Connection对象放回连接池
    public static void close(ResultSet resultSet, Statement statement, Connection connection) {
        try {
            if (resultSet != null) resultSet.close();
            if (statement != null) statement.close();
            if (connection != null) connection.close();
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }
}

使用工具类:

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public class TestUtilsByDruid {
    @Test
    public void testSelect() {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            //得到连接
            connection = JDBCUtilsByDruid.getConnection();
            System.out.println(connection.getClass());
            //connection 的运行类型 class com.alibaba.druid.pool.DruidPooledConnection
            //设置sql
            String sql = "select * from actor where id = ?";
            //创建PreparedStatement
            preparedStatement = connection.prepareStatement(sql);
            //占位赋值
            preparedStatement.setInt(1, 2);
            //执行
            resultSet = preparedStatement.executeQuery();
            while (resultSet.next()) {
                int id = resultSet.getInt(1);
                String name = resultSet.getString(2);
                String sex = resultSet.getString(3);
                Date date = resultSet.getDate(4);
                String phone = resultSet.getString(5);
                System.out.println(id + "\t" + name + "\t" + sex + "\t" + date + "\t" + phone);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            JDBCUtilsByDruid.close(resultSet, preparedStatement, connection);
        }
    }
}

12、Apache-DBUtils

由于resultSet存放数据集合,在connection关闭时,resultSet结果集无法使用。所以为了使用这些数据,也有JDBC官方提供的文件Apache-DBUtils来存放数据。

12.1 ArrayList模拟

ArrayList模拟Apache-DBUtils

Actor类 用来保存Actor表中的数据用的。

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public class Actor { //Javabean, POJO, Domain对象
    private Integer id;
    private String name;
    private String sex;
    private Date borndate;
    private String phone;
    public Actor() { //一定要给一个无参构造器[反射需要]
    }
 
    public Actor(Integer id, String name, String sex, Date borndate, String phone) {
        this.id = id;
        this.name = name;
        this.sex = sex;
        this.borndate = borndate;
        this.phone = phone;
    }
 
    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 String getSex() { return sex; }
    public void setSex(String sex) { this.sex = sex; }
    public Date getBorndate() { return borndate; }
    public void setBorndate(Date borndate) { this.borndate = borndate; }
    public String getPhone() { return phone; }
    public void setPhone(String phone) { this.phone = phone; }
 
    @Override
    public String toString() {
        return "\nActor{" + "id=" + id + ", name='" + name + '\'' +
                ", sex='" + sex + '\'' + ", borndate=" + borndate +
                ", phone='" + phone + '\'' + '}';
    }
}

用ArrayList来存放数据

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public class LikeApDB {
 
    @Test
    public /*也可以返回ArrayList<Actor>*/void testSelectToArrayList() {
        Connection connection = null;
        String sql = "select * from actor where id >= ?";
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        ArrayList<Actor> list = new ArrayList<>();
        try {
            connection = JDBCUtilsByDruid.getConnection();
            System.out.println(connection.getClass());
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setInt(1, 1);
            resultSet = preparedStatement.executeQuery();
            while (resultSet.next()) {
                int id = resultSet.getInt("id");
                String name = resultSet.getString("name");//getName()
                String sex = resultSet.getString("sex");//getSex()
                Date borndate = resultSet.getDate("borndate");
                String phone = resultSet.getString("phone");
                //把得到的 resultSet 的记录,封装到 Actor对象,放入到list集合
                list.add(new Actor(id, name, sex, borndate, phone));
            }
 
            System.out.println("list集合数据=" + list);
            for(Actor actor : list) {
                System.out.println("id=" + actor.getId() + "\t" + actor.getName());
            }
 
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            //关闭资源
            JDBCUtilsByDruid.close(resultSet, preparedStatement, connection);
        }
        //因为ArrayList 和 connection 没有任何关联,所以该集合可以复用.
        //return  list;
    }
}

12.2 Apache-DBUtils 

 基本介绍

commons-dbutils是 Apache组织提供的一个开源JDBC工具类库,它是对JDBC的封装,使用dbutils能极大简化jdbc编码的工作量。

DbUtils类

  • QueryRunner类:该类封装了SQL的执行,是线程安全的。可以实现增,删,改,查,批处理
  • 使用QueryRunner类实现查询。
  • ResultSetHandler接口:该接口用于处理 java.sql.ResultSet,将数据按要求转换为另一种形式

应用实例

使用Apache-DBUtils工具+数据库连接池(Druid)方式,完成对一个表的增删改查。

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package datasourse;
 
import ApDB.Actor;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;
import org.junit.jupiter.api.Test;
 
import java.sql.Connection;
import java.sql.SQLException;
import java.util.List;
public class DBUtils_Use {
    @Test       //查询多条数据
    public void testQueryMany() throws Exception {
        //1.得到连接(Druid)
        Connection connection = JDBCUtilsByDruid.getConnection();
        //2.使用 DBUtils 类和接口,先引入 DBUtils jar文件 ,放到src目录下
        //3.创建QueryRunner
        QueryRunner queryRunner = new QueryRunner();
        //4.执行相应的方法,返回ArrayList结果集
        String sql = "select * from actor where id >= ?";
        //String sql = "select id,`name` from actor where id >= ?";
        /*
        (1) query 方法就是执行sql 语句,得到resultSet ---封装到 --> ArrayList 集合中
        (2) 返回集合
        (3) connection: 连接
        (4) sql : 执行的sql语句
        (5) new BeanListHandler<>(Actor.class): 在将resultSet -> Actor 对象 -> 封装到 ArrayList
            底层使用反射机制 去获取Actor 类的属性,然后进行封装
        (6) 1 就是给 sql 语句中的? 赋值,可以有多个值,因为是可变参数Object... params
        (7) 底层得到的resultSet ,会在query 关闭, 关闭PreparedStatement
         */
        List<Actor> query =
                queryRunner.query(connection, sql, new BeanListHandler<>(Actor.class), 1);
        /**
         * 分析 queryRunner.query方法源码分析
         * public <T> T query(Connection conn, String sql, ResultSetHandler<T> rsh, Object... params) throws SQLException {
         *         PreparedStatement stmt = null;//定义PreparedStatement
         *         ResultSet rs = null;//接收返回的 ResultSet
         *         Object result = null;//返回ArrayList
         *
         *         try {
         *             stmt = this.prepareStatement(conn, sql);//创建PreparedStatement
         *             this.fillStatement(stmt, params);//对sql 进行 ? 赋值
         *             rs = this.wrap(stmt.executeQuery());//执行sql,返回resultset
         *             result = rsh.handle(rs);//返回的resultset --> arrayList[result] [使用到反射,对传入class对象处理]
         *         } catch (SQLException var33) {
         *             this.rethrow(var33, sql, params);
         *         } finally {
         *             try {
         *                 this.close(rs);//关闭resultset
         *             } finally {
         *                 this.close((Statement)stmt);//关闭preparedstatement对象
         *             }
         *         }
         *
         *         return result;
         *     }
         */
        for (Actor actor : query) {
            System.out.print(actor);
        }
        JDBCUtilsByDruid.close(null,null,connection);
    }
 
    @Test               //查询单条记录
    public void testQuerySingle() throws SQLException {
        Connection connection = JDBCUtilsByDruid.getConnection();
        QueryRunner queryRunner = new QueryRunner();
        String sql = "select * from actor where id = ?";
        //已知查询的是单行,所以就用BeanHandler,返回一个对应的对象
        Actor query = queryRunner.query(connection, sql, new BeanHandler<>(Actor.class), 2);
        System.out.print(query);
        JDBCUtilsByDruid.close(null,null,connection);
    }
 
    @Test               //查询单行单列(某个信息)  返回一个Object对象
    public void testQuerySingleObject() throws SQLException {
        Connection connection = JDBCUtilsByDruid.getConnection();
        QueryRunner queryRunner = new QueryRunner();
        String sql = "select `name` from actor where id = ?";
        //已知查询的是单行单列,所以就用BeanHandler,返回一个Object
        Object query = queryRunner.query(connection, sql, new ScalarHandler(), 1);
        System.out.println(query);
        JDBCUtilsByDruid.close(null,null,connection);
    }
 
    @Test       //演示DML操作(insert,update,delete)
    public void testDML() throws SQLException {
        Connection connection = JDBCUtilsByDruid.getConnection();
        QueryRunner queryRunner = new QueryRunner();
 
        //String sql = "update actor set phone = ? where id = ?";
        //int affectedRow = queryRunner.update(connection, sql, "110", 2);
 
        String sql = "insert into actor values(?,?,?,?,?)";
        int affectedRow = queryRunner.update(connection, sql, 3, "xhj", "女", "2000-05-26", "110");
 
        //String sql = "delete from actor where id = ?";
        //int affectedRow = queryRunner.update(connection, sql, 5004);
 
        System.out.println(affectedRow > 0 ? "OK" : "NO");
        JDBCUtilsByDruid.close(null,null,connection);
    }
}

13、BasicDao

引入问题

  • SQL语句是固定,不能通过参数传入,通用性不好,需要进行改进,更方便执行增删改查
  • 对于select 操作,如果有返回值,返回类型不能固定,需要使用泛型
  • 将来的表很多,业务需求复杂,不可能只靠一个JAVA类完成。

所以在实际开发中,也有解决办法 —BasicDao

13.1 BasicDAO类

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public class BasicDAO<T> {  //泛型指定具体的类型
    private QueryRunner queryRunner = new QueryRunner();
 
    //开发通用的DML,针对任意表
    public int update(String sql,Object... parameter){
        Connection connection = null;
        try {
            connection = JDBCUtilsByDruid.getConnection();
            return queryRunner.update(connection, sql, parameter);
        } catch (SQLException e) {
            throw new RuntimeException(e);//将编译异常转化成运行异常,可以被捕获,也可以被抛出
        }finally {
            JDBCUtilsByDruid.close(null,null,connection);
        }
    }
 
    /**                     返回多个对象(多行结果)
     *
     * @param sql       sql语句,可以存在?
     * @param clazz     传入一个类的class对象   例如Actor.class
     * @param parameter 传入?号具体的值,可以有多个
     * @return          根据类似Actor.class类型,返回对应的ArrayList集合
     */
    public List<T> QueryMultiply(String sql,Class<T> clazz, Object... parameter){
        Connection connection = null;
        try {
            connection = JDBCUtilsByDruid.getConnection();
            return queryRunner.query(connection,sql,new BeanListHandler<T>(clazz),parameter);
        } catch (SQLException e) {
            throw new RuntimeException(e);//将编译异常转化成运行异常,可以被捕获,也可以被抛出
        }finally {
            JDBCUtilsByDruid.close(null,null,connection);
        }
    }
    //返回单个对象(单行数据)
    public T querySingle(String sql,Class<T> clazz,Object... parameter){
        Connection connection = null;
        try {
            connection = JDBCUtilsByDruid.getConnection();
            return queryRunner.query(connection,sql,new BeanHandler<T>(clazz),parameter);
        } catch (SQLException e) {
            throw new RuntimeException(e);//将编译异常转化成运行异常,可以被捕获,也可以被抛出
        }finally {
            JDBCUtilsByDruid.close(null,null,connection);
        }
    }
    //返回单个对象的单个属性(单行中的单列)
    public Object queryScalar(String sql,Object... parameter){
        Connection connection = null;
        try {
            connection = JDBCUtilsByDruid.getConnection();
            return queryRunner.query(connection,sql,new ScalarHandler(),parameter);
        } catch (SQLException e) {
            throw new RuntimeException(e);//将编译异常转化成运行异常,可以被捕获,也可以被抛出
        }finally {
            JDBCUtilsByDruid.close(null,null,connection);
        }
    }
}

13.2 domain中的类

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public class Actor { //Javabean, POJO, Domain对象
    private Integer id;
    private String name;
    private String sex;
    private Date borndate;
    private String phone;
    public Actor() { //一定要给一个无参构造器[反射需要]
    }
 
    public Actor(Integer id, String name, String sex, Date borndate, String phone) {
        this.id = id;
        this.name = name;
        this.sex = sex;
        this.borndate = borndate;
        this.phone = phone;
    }
 
    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 String getSex() { return sex; }
    public void setSex(String sex) { this.sex = sex; }
    public Date getBorndate() { return borndate; }
    public void setBorndate(Date borndate) { this.borndate = borndate; }
    public String getPhone() { return phone; }
    public void setPhone(String phone) { this.phone = phone; }
 
    @Override
    public String toString() {
        return "\nActor{" + "id=" + id + ", name='" + name + '\'' +
                ", sex='" + sex + '\'' + ", borndate=" + borndate +
                ", phone='" + phone + '\'' + '}';
    }
}

ActorDAO类继承BasicDAO类,这样的类可以有很多。

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public class ActorDAO extends BasicDAO<Actor> {
}

13.3 测试类

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public class TestDAO {
    @Test//测试ActorDAO对actor表的操作
    public void testActorDAO() {
        ActorDAO actorDAO = new ActorDAO();
        //1.查询多行
        List<Actor> actors = actorDAO.QueryMultiply("select * from actor where id >= ?", Actor.class, 1);
        System.out.println(actors);
 
        //2.查询单行
        Actor actor = actorDAO.querySingle("select * from actor where id = ?", Actor.class, 1);
        System.out.println(actor);
 
        //3.查询单行单个数据
        Object o = actorDAO.queryScalar("select name from actor where id = ?", 1);
        System.out.println(o);
 
        //4.DML操作   当前演示update
        int affectedRow = actorDAO.update("update actor set phone = ? where id = ?", "120", 3);
        System.out.println(affectedRow > 0 ? "OK" : "NO");
    }
}

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原文链接:https://blog.csdn.net/weixin_46687179/article/details/120105398

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