我们从事项目开发，和数据库打交道是必不可少的环节。今天为大家分享Java中连接数据库（本文演示使用的是MySQL数据库,其他关系型数据库类似）常用的5种方式，读者可以自行比较优缺点，在实际项目开发或学习研究中采用其中一种即可！
首先，需要导入相关jar包。 这里是5种连接方式jar包的总和，按项目实际需要添加即可。截图如下：
一、直接代码连接
测试代码如下：
public class TestConnByJDBC {
public static void main(String[] args) throws SQLException {
Connection conn = null;
String driver = "com.mysql.cj.jdbc.Driver";
String url = "jdbc:mysql://localhost:3306/test?serverTimezone=UTC";
String username = "root";
String password = "root";
try {
Class.forName(driver);
conn = DriverManager.getConnection(url, username, password);
System.out.println("TestConnectionByJDBC success");
conn.close();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
效果图：
二、读取属性文件
在src下新建属性文件jdbc.properties,并加入以下内容：
driver =com.mysql.cj.jdbc.Driver
url =jdbc:mysql://localhost:3306/test?serverTimezone=UTC
username =root
password =root
测试代码如下：
public class TestConnByPropertiesFile {
public static void main(String[] args) throws IOException, ClassNotFoundException {
InputStream in = TestConnByPropertiesFile.class.getClassLoader().getResourceAsStream("jdbc.properties");
Properties pt = new Properties();
pt.load(in);
String driver = pt.getProperty("driver");
String url = pt.getProperty("url");
String username = pt.getProperty("username");
String password = pt.getProperty("password");
Connection conn = null;
Class.forName(driver);
try {
conn = DriverManager.getConnection(url, username, password);
System.out.println("TestConnectionByPropertiesFile success");
conn.close();
}
catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
效果图：
三、C3p0配置
在src下新建配置文件c3p0-config.xml，并加入以下内容：
<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>
<named-config name="myTest">
<property name="user">root</property>
<property name="password">root</property>
<property name="jdbcUrl">jdbc:mysql://localhost:3306/test?serverTimezone=UTC</property>
<property name="driverClass">com.mysql.cj.jdbc.Driver</property>
<property name="acquireIncrement">5</property>
<property name="initialPoolSize">20</property>
<property name="maxPoolSize">25</property>
<property name="minPoolSize">5</property>
</named-config>
</c3p0-config>
测试代码如下：
public class TestConnByC3P0Conf {
private static ComboPooledDataSource cpds;
static {
cpds = new ComboPooledDataSource("myTest");
}
public static DataSource getDataSource() {
return cpds;
}
public static Connection getConnection() throws SQLException {
return cpds.getConnection();
}
public static void main(String[] args) throws Exception{
Connection connection = TestConnByC3P0Conf.getConnection();
System.out.println(connection);
}
}
效果图：
四、使用MyBatis
在src下新建配置文件MyBatisconfig.xml，并加入如下内容：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="com.mysql.cj.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/test?serverTimezone=UTC" />
<property name="username" value="root" />
<property name="password" value="root" />
</dataSource>
</environment>
</environments>
</configuration>
测试代码如下：
public class TestConnByMyBatis {
public static void main(String[] args) {
String resource = "./src/MyBatisconfig.xml";
InputStream is = null;
try {
is = new FileInputStream(resource);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
SqlSession session = sessionFactory.openSession();
System.out.println(session.getConnection());
}
}
效果图：
五、使用Hibernate
在src下新建配置文件hibernate.cfg.xml，并加入如下内容：
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="connection.driver_class">com.mysql.cj.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost:3306/test?serverTimezone=UTC</property>
<property name="connection.username">root</property>
<property name="connection.password">root</property>
<property name="connection.pool_size">2</property>
<property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
<property name="show_sql">true</property>
<property name="hbm2ddl.auto">create</property>
</session-factory>
</hibernate-configuration>
测试代码如下：
public class TestConnByHibernate {
public static void main(String[] args) {
Configuration configure = new Configuration().configure();
SessionFactory factory = configure.buildSessionFactory();
Session session = factory.openSession();
System.out.println(session.connection());
}
}
效果图：
至此，我们学会了连接数据库的各种方式！