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
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>4.0.0modelVersion>
<groupId>com.hy.jdbcgroupId>
<artifactId>jdbc-demoartifactId>
<version>1.0-SNAPSHOTversion>
<properties>
<junit.version>4.12junit.version>
<mysql-connector-java.version>8.0.11mysql-connector-java.version>
<druid.version>1.1.10druid.version>
properties>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>junitgroupId>
<artifactId>junitartifactId>
<version>${junit.version}version>
dependency>
<dependency>
<groupId>mysqlgroupId>
<artifactId>mysql-connector-javaartifactId>
<version>${mysql-connector-java.version}version>
dependency>
<dependency>
<groupId>com.alibabagroupId>
<artifactId>druidartifactId>
<version>${druid.version}version>
dependency>
dependencies>
dependencyManagement>
<dependencies>
<dependency>
<groupId>junitgroupId>
<artifactId>junitartifactId>
dependency>
<dependency>
<groupId>mysqlgroupId>
<artifactId>mysql-connector-javaartifactId>
dependency>
<dependency>
<groupId>com.alibabagroupId>
<artifactId>druidartifactId>
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?characterEncoding=utf8&useSSL=false", "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?characterEncoding=utf8&useSSL=false", "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?characterEncoding=utf8&useSSL=false", "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?characterEncoding=utf8&useSSL=false", "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?characterEncoding=utf8&useSSL=false 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(); } } } }