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详细说明关于Java的数据库连接(JDBC)

转载 作者：qq735679552 更新时间：2022-09-27 22:32:09 31 4
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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 等
     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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