JDBC基础

properties的配置

连接数据库的五种方法

增删改的通用操作

查询通用操作

---

properties的配置：

user=root
password=1234
url=jdbc:mysql://localhost:3306/test
driverClass=com.mysql.jdbc.Driver

        连接数据库的五种方法：

import java.io.InputStream;
import java.sql.Connection;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;

import org.junit.Test;

public class ConnectionTest {
	
	private Connection connection;

	//方式一
	@Test
	public void testConnection1() throws SQLException {
		
		Driver driver = new com.mysql.jdbc.Driver();
		
		String url = "jdbc:mysql://localhost:3306/test";
		//将用户名和密码封装在Properties内
		Properties info = new Properties();
		info.setProperty("user", "root");
		info.setProperty("password","1234");
		
		
		
		Connection conn = driver.connect(url, info);
		System.out.println(conn);
	}
	
	//方式二：方式一的迭代(在以下程序中不出现第三方api，有更好的可移植性)
	@Test
	public void testConnection2() throws Exception{
		//获取Driver实现类对象
		Class clazz = Class.forName("com.mysql.jdbc.Driver");
		Driver driver = (Driver) clazz.newInstance();
		
		//提供要连接的数据库
		String url = "jdbc:mysql://localhost:3306/test";
		
		//提供用户密码
		Properties info = new Properties();
		info.setProperty("user", "root");
		info.setProperty("password","1234");
		
		//获取连接
		Connection conn = driver.connect(url, info);
		System.out.println(conn);
	}

	//方式三：使用DriverManager替换Driver
	@Test
	public void testConnection3() throws Exception {
		//获取Driver实现类的对象
		Class clazz = Class.forName("com.mysql.jdbc.Driver");
		Driver driver = (Driver) clazz.newInstance();
		
		//提供另外三个连接的基本信息
		String url = "jdbc:mysql://localhost:3306/test";
		String user = "root";
		String password = "1234";
			
		//注册驱动
		DriverManager.registerDriver(driver);
		
		//获取连接
		Connection conn = DriverManager.getConnection(url,user,password);
		System.out.println(conn);
		
	}
	
	//方式四：可以只加载驱动，不显示注册驱动
		@Test
		public void testConnection4() throws Exception {
			//提供三个连接的基本信息
			String url = "jdbc:mysql://localhost:3306/test";
			String user = "root";
			String password = "1234";
			
			//加载Driver（可省略）
			Class.forName("com.mysql.jdbc.Driver");
			
			//获取连接
			Connection conn = DriverManager.getConnection(url,user,password);
			System.out.println(conn);
			
		}
		

		//方式五：将数据库连接需要的4个基本信息声明在配置文件中，通过读取配置文件的方式连接数据库
		/*
		 * 实现数据与代码的分离，实现了解耦
		 * 
		 */
			@Test
			public void getConnection5() throws Exception {
				
				//读取配置文件中的4个基本信息
				InputStream is = ConnectionTest.class.getClassLoader().getResourceAsStream("jdbc.properties");
				
				Properties pros = new Properties();
				pros.load(is);
				
				String user = pros.getProperty("user");
				String password = pros.getProperty("password");
				String url = pros.getProperty("url");
				String driverClass = pros.getProperty("driverClass");
				
				//加载驱动
				Class.forName(driverClass);
				
				//获取连接
				Connection conn = DriverManager.getConnection(url, user, password);
				System.out.println(conn);
				
				
			}
		
		
		
	
}

       增删改的通用操作：

    @Test
	public void testCommonUpdate() {
		String sql = "delete from customers where id = ?";
		update(sql,3);
	}
	
	//通用的增删改
	public void update(String sql,Object...args){
		
		Connection conn = null;
		PreparedStatement ps = null;
		try {
			//连接数据库
			conn = JDBCUtils.getConnection();
			//预编译数据库
			ps = conn.prepareStatement(sql);
			//填充占位符
			for(int i = 0;i < args.length; i++) {
				ps.setObject(i + 1, args[i]);
			}
			//执行
			ps.execute();
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			//关闭资源
			JDBCUtils.closeResource(conn, ps);
		}
		
	}

        查询通用操作:

    @Test
	public void testGetInstance() {
		String sql = "select id,name,email from customers where id = ?";
		Customer customer = getInstance(Customer.class,sql,12);
		System.out.println(customer);
		
		String sql1 = "select order_id orderId,order_name orderName from `order` where order_id = ?";
		Order order = getInstance(Order.class,sql1,1);
		System.out.println(order);
	}
	
	/*
	 * 针对不同的表的通用的查询操作，返回表中的一条数据
	 */
	public <T> T getInstance(Class<T> clazz,String sql,Object...args) {
		
		Connection conn = null;
		PreparedStatement ps = null;
		ResultSet rs = null;
		try {
			conn = JDBCUtils.getConnection();
			
			ps = conn.prepareStatement(sql);
			for(int i = 0; i < args.length; i++) {
				ps.setObject(i + 1, args[i]);
			}
			
			rs = ps.executeQuery();
			
			//获取结果集的元数据
			ResultSetMetaData rsmd = rs.getMetaData();
			//通过ResultSetMetaData获取结果集中的列数
			int columnCount = rsmd.getColumnCount();
			if(rs.next()) {
				T t = clazz.newInstance();
				
				//处理结果集一行数据中的每一列
				for(int i = 0; i < columnCount; i++) {
					//获取列值
					Object columValue = rs.getObject(i + 1);
					
					//获取每个列的列名
					String columnLabel = rsmd.getColumnLabel(i + 1);
					
					//给t对象指定的属性赋值为value,通过反射
					Field field = clazz.getDeclaredField(columnLabel);
					field.setAccessible(true);
					field.set(t, columValue);
				}
				return t;
			}
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			JDBCUtils.closeResource(conn, ps, rs);
		}
		
		return null;
		
	}

---