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 ResultSet
            ResultSet 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ResultSet
            ResultSet 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ResultSet
            ResultSet 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.properties
        InputStream 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。

3.5PreparedStatement接口

PreparedStatement接口是Java中的一个接口，它是用来执行预编译的SQL语句的。PreparedStatement是Statement的子接口，继承了Statement的所有功能。PreparedStatement接口提供了补充占位符变量的方法

Java入坑之数据库编程

一、基础概念

1.1JDBC 步骤

1.2相关类介绍

1.3相关代码

1.3.1查询

1.3.2增删改

1.3.3事务逻辑

1.3.4拼接字符串

1.3.5batch函数

1.3.6ResultSetMetaData类

二、数据库连接池

2.1流程重述

2.2亨元模式

2.3 数据库连接池概念

2.4C3P0连接池

2.4.1配置文件

2.4.2相关代码

2.4.3相关配置

2.4.4 DruidData类

2.4.6配置

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

3.4Statement接口

3.5PreparedStatement接口

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1.3相关代码

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1.3.2增删改

1.3.3事务逻辑

1.3.4拼接字符串

1.3.5batch函数

1.3.6ResultSetMetaData类

二、数据库连接池

2.1流程重述

2.2亨元模式

2.3 数据库连接池概念

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2.4.1配置文件

2.4.2相关代码

2.4.3相关配置

2.4.4 DruidData类

2.4.6配置

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