详细说明关于Java的数据库连接(JDBC)
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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。
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。
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
public class JdbcConn {
@Test
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
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
//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
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");
//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
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("class="lazy" data-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)
public class jdbc03 {
public static void main(String[] args) throws Exception {
Properties properties = new Properties();
properties.load(new FileInputStream("class="lazy" data-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)
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
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("class="lazy" data-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
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("class="lazy" data-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
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("class="lazy" data-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:
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()) {
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
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
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();
//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。
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)。
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("class="lazy" data-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 class="lazy" data-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。
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class="lazy" data-src目录下
//3.创建Properties对象
Properties properties = new Properties();
properties.load(new FileInputStream("class="lazy" data-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
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("class="lazy" data-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：
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。
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
public class LikeApDB {
@Test
public 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。
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class="lazy" data-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 >= ?";
List<Actor> query =
queryRunner.query(connection, sql, new BeanListHandler<>(Actor.class), 1);
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
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);
}
}
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
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。
public class ActorDAO extends BasicDAO<Actor> {
}
13.3 测试类
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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