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JDBC

一 JDBC简介

Java DataBase Connectivity Java语言连接数据库

官方(Sun公司)定义的一套操作所有关系型数据库的规则(接口) 各个数据库厂商去实现这套接口提供数据库驱动JAR包可以使用这套接口(JDBC)编程真正执行的代码是驱动JAR包中的实现类

JDBC

二 JDBC初体验

1. 新建一个Maven项目

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.hy.jdbc</groupId>
    <artifactId>jdbc-demo</artifactId>
    <version>1.0-SNAPSHOT</version>

    <!-- 定义依赖版本号 -->
    <properties>
        <junit.version>4.12</junit.version>
        <mysql-connector-java.version>8.0.11</mysql-connector-java.version>
        <druid.version>1.1.10</druid.version>
    </properties>

    <!-- 管理jar版本号 -->
    <dependencyManagement>
        <dependencies>
            <!-- junit -->
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>${junit.version}</version>
            </dependency>
            <!-- mysql -->
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>${mysql-connector-java.version}</version>
            </dependency>
            <dependency>
                <groupId>com.alibaba</groupId>
                <artifactId>druid</artifactId>
                <version>${druid.version}</version>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <!-- junit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
        </dependency>
        <!-- mysql -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
        </dependency>
    </dependencies>
</project>

sql

CREATE TABLE account (
    aid INT PRIMARY KEY,
    aname VARCHAR(100),
    amoney DOUBLE
);

2. 插入

@Test
public void test01() {
    Connection connection = null;
    PreparedStatement statement = null;
    try {
        // 注册驱动 MySQL5之后的驱动JAR包可以省略该步骤
        Class.forName("com.mysql.cj.jdbc.Driver");
        // 获取数据库连接对象 Connection
        connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/demo_hy", "root", "root");
        // 开启事务
        connection.setAutoCommit(false);
        // 定义SQL
        String sql = "insert into account values(?, ?, ?)";
        // 获取执行SQL的对象 PreparedStatement
        statement = connection.prepareStatement(sql);
        // 设置参数
        statement.setInt(1, 1); //'?' 位置的编号 从1开始
        statement.setString(2, "No1"); //'?' 位置的编号 从1开始
        statement.setDouble(3, 2000); //'?' 位置的编号 从1开始
        // 执行SQL 返回受影响的行数
        int count = statement.executeUpdate();
        // 提交事务
        connection.commit();
        // 处理结果
        System.out.println("count = " + count);

    } catch (Exception e) {
        e.printStackTrace();
        // 回滚事务
        if (null != connection) {
            try {
                connection.rollback();
            } catch (SQLException exception) {
                exception.printStackTrace();
            }
        }

    } finally {
        // 释放资源
        if (null != statement) {
            try {
                statement.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (null != connection) {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

3. 删除

@Test
public void test02() {
    Connection connection = null;
    PreparedStatement statement = null;
    try {
        // 注册驱动 MySQL5之后的驱动JAR包可以省略该步骤
        //Class.forName("com.mysql.cj.jdbc.Driver");
        // 获取数据库连接对象 Connection
        connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/demo_hy", "root", "root");
        // 开启事务
        connection.setAutoCommit(false);
        // 定义SQL
        String sql = "delete from account where aid = ?";
        // 获取执行SQL的对象 PreparedStatement
        statement = connection.prepareStatement(sql);
        // 设置参数
        statement.setInt(1, 1); //'?' 位置的编号 从1开始
        // 执行SQL 返回受影响的行数
        int count = statement.executeUpdate();
        // 提交事务
        connection.commit();
        // 处理结果
        System.out.println("count = " + count);

    } catch (Exception e) {
        e.printStackTrace();
        // 回滚事务
        if (null != connection) {
            try {
                connection.rollback();
            } catch (SQLException exception) {
                exception.printStackTrace();
            }
        }

    } finally {
        // 释放资源
        if (null != statement) {
            try {
                statement.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (null != connection) {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

4. 修改

@Test
public void test03() {
    Connection connection = null;
    PreparedStatement statement1 = null;
    PreparedStatement statement2 = null;
    try {
        // 注册驱动 MySQL5之后的驱动JAR包可以省略该步骤
        Class.forName("com.mysql.cj.jdbc.Driver");
        // 获取数据库连接对象 Connection
        connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/demo_hy", "root", "root");
        // 开启事务
        connection.setAutoCommit(false);
        // 定义SQL
        String sql1 = "update account set amoney = amoney + ? where aid = ?";
        String sql2 = "update account set amoney = amoney - ? where aid = ?";
        // 获取执行SQL的对象 PreparedStatement
        statement1 = connection.prepareStatement(sql1);
        statement2 = connection.prepareStatement(sql2);
        // 设置参数
        statement1.setDouble(1, 500); //'?' 位置的编号 从1开始
        statement1.setInt(2, 1); //'?' 位置的编号 从1开始
        statement2.setDouble(1, 500); //'?' 位置的编号 从1开始
        statement2.setInt(2, 2); //'?' 位置的编号 从1开始
        // 执行SQL 返回受影响的行数
        statement1.executeUpdate();
        int i = 3 / 0; //模拟异常
        statement2.executeUpdate();
        // 提交事务
        connection.commit();

    } catch (Exception e) {
        e.printStackTrace();
        // 回滚事务
        if (null != connection) {
            try {
                connection.rollback();
            } catch (SQLException exception) {
                exception.printStackTrace();
            }
        }

    } finally {
        // 释放资源
        if (null != statement2) {
            try {
                statement2.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (null != statement1) {
            try {
                statement1.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (null != connection) {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

5. 查询

@Test
public void test04() {
    Connection connection = null;
    PreparedStatement statement = null;
    ResultSet resultSet = null;
    try {
        // 注册驱动 MySQL5之后的驱动JAR包可以省略该步骤
        Class.forName("com.mysql.cj.jdbc.Driver");
        // 获取数据库连接对象 Connection
        connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/demo_hy", "root", "root");
        // 开启事务
        connection.setAutoCommit(false);
        // 定义SQL
        String sql = "select * from account";
        // 获取执行SQL的对象 PreparedStatement
        statement = connection.prepareStatement(sql);
        // 执行SQL 返回结果集
        resultSet = statement.executeQuery();
        // 提交事务
        connection.commit();
        // 处理结果
        while (resultSet.next()) {
            int id = resultSet.getInt(1); //代表列的编号 从1开始
            String name = resultSet.getString("aname"); //代表列的名称
            double money = resultSet.getDouble(3); //代表列的编号 从1开始
            System.out.println(id + "---" + name + "---" + money);
        }

    } catch (Exception e) {
        e.printStackTrace();
        // 回滚事务
        if (null != connection) {
            try {
                connection.rollback();
            } catch (SQLException exception) {
                exception.printStackTrace();
            }
        }

    } finally {
        // 释放资源
        if (null != resultSet) {
            try {
                resultSet.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (null != statement) {
            try {
                statement.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (null != connection) {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

三数据库连接池

一个存放数据库连接的容器

当系统初始化后容器被创建容器中会申请一些连接对象当用户访问数据库时从容器中获取连接对象用户访问完之后会将连接对象归还给容器这样可以节约资源提高访问效率

常见的数据库连接池有 Druid C3P0...

Druid初体验

druid.properties

url=jdbc:mysql://localhost:3306/demo_hy
driverClassName=com.mysql.cj.jdbc.Driver
username=root
password=root
maxActive=10
minIdle=5

XTest.java

@Test
public void test05() {
    InputStream stream = null;
    Connection connection = null;
    PreparedStatement statement = null;
    ResultSet resultSet = null;
    try {
        // 加载配置文件
        Properties properties = new Properties();
        stream = XTest.class.getClassLoader().getResourceAsStream("druid.properties");
        properties.load(stream);
        // 获取连接池对象
        DataSource dataSource = DruidDataSourceFactory.createDataSource(properties);
        // 获取数据库连接对象 Connection
        connection = dataSource.getConnection();
        // 开启事务
        connection.setAutoCommit(false);
        // 定义SQL
        String sql = "select * from account";
        // 获取执行SQL的对象 PreparedStatement
        statement = connection.prepareStatement(sql);
        // 执行SQL 返回结果集
        resultSet = statement.executeQuery();
        // 提交事务
        connection.commit();
        // 处理结果
        while (resultSet.next()) {
            int id = resultSet.getInt(1); //代表列的编号 从1开始
            String name = resultSet.getString("aname"); //代表列的名称
            double money = resultSet.getDouble(3); //代表列的编号 从1开始
            System.out.println(id + "---" + name + "---" + money);
        }

    } catch (Exception e) {
        e.printStackTrace();
        // 回滚事务
        if (null != connection) {
            try {
                connection.rollback();
            } catch (SQLException exception) {
                exception.printStackTrace();
            }
        }

    } finally {
        // 释放资源
        if (null != resultSet) {
            try {
                resultSet.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (null != statement) {
            try {
                statement.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (null != connection) {
            try {
                connection.close(); //归还连接
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (null != stream) {
            try {
                stream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

原文 https://www.maiyewang.com/archives/103130

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