转载

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
正文到此结束
Loading...