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。
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ArrayLis
t 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