一、基础概念

1.1JDBC 步骤

导入驱动jar包
注册驱动
获取数据库连接对象 Connection
DataSource dSource;
dSource.getConnection();
定义sql语句
String sql = "update account set balance = 500 where id = 1";
获取执行sql语句的对象 Statement
PreparedStatement stmt = conn. prepareStatement(sql)；
执行sql，接受返回结果int count = stmt.executeUpdate(sql);
处理结果 System.out.println(count);
释放资源  stmt.close(); conn.close();

1.2相关类介绍

1.3相关代码

在Maven中声明MySQL的JDBC实现依赖

1.3.1查询

package org.example;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;public class SelectTest {public static void main(String[] args) {// 注册 MySQL 驱动try {Class.forName("com.mysql.cj.jdbc.Driver");System.out.println("注册驱动成功!");} catch (ClassNotFoundException e1) {System.out.println("注册驱动失败!");e1.printStackTrace();return;}String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";Connection conn = null;try {// 构建 Java 和数据库之间的桥梁：URL，用户名，密码conn = DriverManager.getConnection(url, "root", "b123456");System.out.println("连接数据库成功！");// 构建数据库执行者Statement stmt = conn.createStatement();System.out.println("创建 Statement 成功！");// 执行 SQL 语句并返回结果到 ResultSetResultSet rs = stmt.executeQuery("select bookid, bookname, price from book order by bookid");// 开始遍历 ResultSet 数据while (rs.next()) {System.out.println(rs.getInt(1) + "," + rs.getString(2) + "," + rs.getInt("price"));}rs.close();stmt.close();} catch (SQLException e) {e.printStackTrace();} finally {try {if (conn != null) {conn.close();System.out.println("关闭数据库连接成功！");}} catch (SQLException e) {e.printStackTrace();}}}
}

1.3.2增删改

package org.example;import java.sql.*;public class UpdateTest {public static void main(String[] args) {executeUpdate("update book set price = 300 where bookid = 1");executeUpdate("insert into book(bookid, bookname, price) values(4, '编译原理', 90)");executeUpdate("delete from book where bookid = 4");}/*** 执行数据更新操作* @param sql 要执行的 SQL 语句*/public static void executeUpdate(String sql) {// 注册 MySQL 驱动try {Class.forName("com.mysql.cj.jdbc.Driver");System.out.println("注册驱动成功!");} catch (ClassNotFoundException e1) {System.out.println("注册驱动失败!");e1.printStackTrace();}String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";Connection conn = null;try {// 构建 Java 和数据库之间的桥梁：URL，用户名，密码conn = DriverManager.getConnection(url, "root", "b123456");System.out.println("连接数据库成功！");// 构建数据库执行者Statement stmt = conn.createStatement();System.out.println("创建 Statement 成功！");int rs = stmt.executeUpdate(sql);stmt.close();} catch (SQLException e) {e.printStackTrace();} finally {try {if (conn != null) {conn.close();System.out.println("关闭数据库连接成功！");}} catch (SQLException e) {e.printStackTrace();}}}
}

1.3.3事务逻辑

package org.example;import java.sql.*;public class TransactionTest {public static void main(String[] args) throws Exception {// 构建Java和数据库之间的桥梁介质try {Class.forName("com.mysql.cj.jdbc.Driver");System.out.println("注册驱动成功!");} catch (ClassNotFoundException e1) {System.out.println("注册驱动失败!");e1.printStackTrace();}String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";Connection conn = null;try {// 构建Java和数据库之间的桥梁：URL，用户名，密码conn = DriverManager.getConnection(url, "root", "b123456");conn.setAutoCommit(false);insertBook(conn, "insert into book values(101, 'aaaa', 10)");insertBook(conn, "insert into book values(102, 'bbbb', 10)");insertBook(conn, "insert into book values(103, 'cccc', 10)");Savepoint phase1 = conn.setSavepoint(); // 设置一个保存点insertBook(conn, "insert into book values(104, 'cccc', 10)");insertBook(conn, "insert into book values(105, 'cccc', 10)");conn.rollback(phase1); // 回滚到phase1保存点，即上面2行无效conn.commit();System.out.println("操作成功");} catch (SQLException e) {e.printStackTrace();conn.rollback();} finally {if (null != conn) {conn.close();}}}public static void insertBook(Connection conn, String sql) {try {// 构建数据库执行者Statement stmt = conn.createStatement();// 执行SQL语句int result = stmt.executeUpdate(sql);stmt.close();} catch (SQLException e) {e.printStackTrace();}}
}

1.3.4拼接字符串

package org.example;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;public class InsertTest {public static void main(String[] a) {//concatInsertBook();unsafeConcatInsertBook();}public static void concatInsertBook() {// 构建Java和数据库之间的桥梁介质try {Class.forName("com.mysql.cj.jdbc.Driver");System.out.println("注册驱动成功!");} catch (ClassNotFoundException e1) {System.out.println("注册驱动失败!");e1.printStackTrace();}String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";Connection conn = null;try {// 构建Java和数据库之间的桥梁：URL，用户名，密码conn = DriverManager.getConnection(url, "root", "b123456");// 构建数据库执行者Statement stmt = conn.createStatement();System.out.println("创建Statement成功！");// 执行SQL语句int bookid = 11;String bookName = "Effective Java";int price = 50;String sql = "insert into book(bookid,bookname,price) values("+ bookid + ", '" + bookName + "', " + price + ")";int result = stmt.executeUpdate(sql);stmt.close();System.out.println("操作成功");} catch (SQLException e) {e.printStackTrace();} finally {try {if (conn != null) {conn.close();}} catch (SQLException e) {e.printStackTrace();}}}public static void unsafeConcatInsertBook() {// 构建Java和数据库之间的桥梁介质try {Class.forName("com.mysql.cj.jdbc.Driver");System.out.println("注册驱动成功!");} catch (ClassNotFoundException e1) {System.out.println("注册驱动失败!");e1.printStackTrace();}String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";Connection conn = null;try {// 构建Java和数据库之间的桥梁：URL，用户名，密码conn = DriverManager.getConnection(url, "root", "b123456");// 构建数据库执行者Statement stmt = conn.createStatement();System.out.println("创建Statement成功！");// 执行SQL语句int bookid = 13;String bookName = "Effective Java',50);delete from t_book;insert into t_book values(101, 'faked book";int price = 50;String sql = "insert into book(bookid,bookname,price) values("+ bookid + ", '" + bookName + "', " + price + ");";System.out.println(sql);int result = stmt.executeUpdate(sql);stmt.close();System.out.println("操作成功");} catch (SQLException e) {e.printStackTrace();} finally {try {if (conn != null) {conn.close();}} catch (SQLException e) {e.printStackTrace();}}}
}

1.3.5batch函数

package org.example;import java.sql.*;public class InsertTest1 {public static void main(String[] a) {safeInsertBook();batchInsertBook();}public static void safeInsertBook() {Connection conn = null;try {// 注册 MySQL 驱动Class.forName("com.mysql.jdbc.Driver");System.out.println("注册驱动成功!");} catch (ClassNotFoundException e1) {System.out.println("注册驱动失败!");e1.printStackTrace();}String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";try {// 构建Java和数据库之间的桥梁：URL，用户名，密码conn = DriverManager.getConnection(url, "root", "b123456");String sql = "insert into book(bookid,bookname,price) values (?, ?, ?)";// 构建数据库执行者PreparedStatement pstmt = conn.prepareStatement(sql);// 设置参数int bookid = 15;String bookName = "Effective Java',50);delete from t_book;insert into t_book values(101, 'faked book";int price = 50;pstmt.setInt(1, bookid);pstmt.setString(2, bookName);pstmt.setInt(3, price);// 执行SQL语句int result = pstmt.executeUpdate();pstmt.close();System.out.println("操作成功");} catch (SQLException e) {e.printStackTrace();} finally {try {if (conn != null) {conn.close();System.out.println("关闭数据库连接成功！");}} catch (SQLException e) {e.printStackTrace();}}}public static void batchInsertBook() {Connection conn = null;try {// 注册 MySQL 驱动Class.forName("com.mysql.jdbc.Driver");System.out.println("注册驱动成功!");} catch (ClassNotFoundException e1) {System.out.println("注册驱动失败!");e1.printStackTrace();}String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";try {// 构建Java和数据库之间的桥梁：URL，用户名，密码conn = DriverManager.getConnection(url, "root", "b123456");String sql = "insert into book(bookid,bookname,price) values (?,?,?)";// 构建数据库执行者PreparedStatement pstmt = conn.prepareStatement(sql);// 设置参数String bookName = "aaaaaaaaaaaaaaaa";int price;// 执行批量插入操作for (int i = 210; i < 202; i++) {price = 50;pstmt.setInt(1, i);pstmt.setString(2, bookName);pstmt.setInt(3, price);pstmt.addBatch();}pstmt.executeBatch();pstmt.close();System.out.println("操作成功");} catch (SQLException e) {e.printStackTrace();} finally {try {if (conn != null) {conn.close();System.out.println("关闭数据库连接成功！");}} catch (SQLException e) {e.printStackTrace();}}}
}

如果有大量的sq语句，它们结构相同，仅仅差别在具体数值上，那么可以通过addBatch
方法进行批量操作。这样会提高性能，减少数据库负担。

1.3.6ResultSetMetaData类

package org.example;import java.sql.*;public class ResultSetMetaDataTest {public static void main(String[] args) {// 构建Java和数据库之间的桥梁介质try {Class.forName("com.mysql.cj.jdbc.Driver");System.out.println("注册驱动成功!");} catch (ClassNotFoundException e1) {System.out.println("注册驱动失败!");e1.printStackTrace();return;}String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";Connection conn = null;try {// 构建Java和数据库之间的桥梁：URL，用户名，密码conn = DriverManager.getConnection(url, "root", "b123456");// 构建数据库执行者Statement stmt = conn.createStatement();System.out.println("创建Statement成功！");// 执行SQL语句并返回结果到ResultSetResultSet rs = stmt.executeQuery("select bookid, bookname, price from book order by bookid");// 获取结果集的元数据ResultSetMetaData meta = rs.getMetaData();int cols = meta.getColumnCount();for (int i = 1; i <= cols; i++) {System.out.println(meta.getColumnName(i) + "," + meta.getColumnTypeName(i));}rs.close();stmt.close();} catch (SQLException e) {e.printStackTrace();} finally {try {if (conn != null) {conn.close();}} catch (SQLException e) {e.printStackTrace();}}}
}

二、数据库连接池

2.1流程重述

2.2亨元模式

享元模式, Flyweight Pattern
- 经典23个设计模式的一种，属于结构型模式。
- 一个系统中存在大量的相同的对象，由于这类对象的大量使用，会造成系统内存的耗费，可以使用享元模式来减少系统中对象的数量。

2.3 数据库连接池概念

2.4C3P0连接池

2.4.1配置文件

   <!-- https://mvnrepository.com/artifact/com.mchange/c3pθ --><dependency><groupId>com.mchange</groupId><artifactId>c3p0</artifactId><version>0.9.5.2</version></dependency><!-- https://mvnrepository.com/artifact/com.alibaba/druid --><dependency><groupId>com.alibaba</groupId><artifactId>druid</artifactId><version>1.1.10</version></dependency>

2.4.2相关代码

package org.example;import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;public class SelectTest1 {public static void main(String[] args) {Connection conn = null;try {// 从c3p0获取数据库连接conn = C3p0Factory1.getConnection();//conn = C3p0Factory2.getConnection();从Druid获取conn = DruidFactory1.getConnection();//conn = DruidFactory2.getConnection();// 构建数据库执行者Statement stmt = conn.createStatement();System.out.println("创建Statement成功！");// 执行SQL语句并返回结果到ResultSetResultSet rs = stmt.executeQuery("select bookid, bookname, price from book order by bookid");// 开始遍历ResultSet数据while (rs.next()) {System.out.println(rs.getInt(1) + "," + rs.getString(2) + "," + rs.getInt("price"));}rs.close();stmt.close();} catch (Exception e) {e.printStackTrace();} finally {try {if (conn != null) {conn.close();}} catch (SQLException e) {e.printStackTrace();}}}
}

2.4.3相关配置

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config><default-config>    <!--  默认配答 --><property name="driverClass">com.mysql.jdbc.Driver</property><property name="jdbcUrl">jdbc:mysql://localhost:3306/test</property><property name="user">root</property><property name="password">123456</property><property name="initialPoolSize">5</property><property name="maxPoolSize">20</property></default-config>
</c3p0-config>

package org.example;import com.mchange.v2.c3p0.ComboPooledDataSource;
import java.sql.Connection;public class C3p0Factory2 {private static ComboPooledDataSource dataSource = null;public static void init() throws Exception {// 创建 ComboPooledDataSource 实例，会自动加载 c3p0-config.xml 文件的配置dataSource = new ComboPooledDataSource();// 此时 dataSource 是一个完全配置好的可用连接池 DataSource}public static Connection getConnection() throws Exception {if (null == dataSource) {init();}// 返回从连接池获取的数据库连接return dataSource.getConnection();}
}

2.4.4 DruidData类

package org.example;import com.alibaba.druid.pool.DruidDataSource;
import java.sql.Connection;public class DruidFactory1 {private static DruidDataSource dataSource = null;public static void init() throws Exception {dataSource = new DruidDataSource();dataSource.setDriverClassName("com.mysql.jdbc.Driver");dataSource.setUsername("root");dataSource.setPassword("b123456");dataSource.setUrl("jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC");dataSource.setInitialSize(5);dataSource.setMinIdle(1);dataSource.setMaxActive(10);// 启用监控统计功能dataSource.setFilters("stat");}public static Connection getConnection() throws Exception {if (null == dataSource) {init();}return dataSource.getConnection();}
}

2.4.6配置

driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC
username=root
password=b123456
filters=stat
initialSize=2
maxActive=300
maxWait=60000
timeBetweenEvictionRunsMillis=60000
minEvictableIdleTimeMillis=300000
validationQuery=SELECT 1
testWhileIdle=true
testOnBorrow=false
testOnReturn=false
poolPreparedStatements=false
maxPoolPreparedStatementPerConnectionSize=200

package org.example;import com.alibaba.druid.pool.DruidDataSource;
import com.alibaba.druid.pool.DruidDataSourceFactory;import java.io.InputStream;
import java.sql.Connection;
import java.util.Properties;public class DruidFactory2 {private static DruidDataSource dataSource = null;public static void init() throws Exception {Properties properties = new Properties();// 加载属性文件 druid.propertiesInputStream in = DruidFactory2.class.getClassLoader().getResourceAsStream("druid.properties");properties.load(in);// 通过属性创建 Druid 数据源dataSource = (DruidDataSource) DruidDataSourceFactory.createDataSource(properties);in.close();}public static Connection getConnection() throws Exception {if (null == dataSource) {init();}return dataSource.getConnection();}
}

三、基于web的数据库开发

3.1配置DataSource

3.2相关类（driverClassName，驱动类）

3.3Connection接口

java.sql.Connection接口表示与特定数据库的会话。在Connection的上下文中，执行SQL语句并返回结果。Connection接口对于连接到数据库和执行SQL语句至关重要。

3.4Statement接口

Statement接口是Java执行数据库操作的一个重要接口，用于在已经建立数据库连接的基础上，向数据库发送要执行的SQL语句。Statement接口提供了执行语句和获取结果的基本方法。PreparedStatement接口添加了处理IN参数的方法；而CallableStatement添加了处理OUT参数的方法。