JDBC全面教程--一篇文行就够了

╰半夏微凉° 2022-02-04 23:15 206阅读 0赞

### 文章目录 ###

*  1.JDBC简介(本文默认mysql数据库)
 *  2.JDBC的基础入门
 *  3. 基础入门示例代码
 *  4. JDBC工具类的构建
 *   *  jdbc工具类代码示例
     *  jdbc工具类代码使用实例
 *  5. 使用单元测试，测试代码
 *  6. Dao模式
 *  7. statement 的安全问题
 *   *  PrepareStatement
 *  8. 全面的通过JDBC增删查改数据库
 *   *  1.jdbc工具类
     *  2.jdbc接口
     *  3.jdbc接口的实现
     *  4.jdbc类的测试

# 1.JDBC简介(本文默认mysql数据库) #

*  Java和数据库之间的访问规则
 *  jdbc在使用前需要导入数据库支持的jar文件

# 2.JDBC的基础入门 #

1.  注册驱动（可省略）
2.  建立连接

`conn = DriverManager.getConnection("jdbc:mysql://localhost/student", "root", "123456");`

*  `url`:协议+访问的数据库
 *  `name`:用户名
 *  `password` ：密码

1.  创建`statement`对象

`Statement st = conn.createStatement();`

1.  执行`sql`得到结果`ResultSet`

String sql = "select * from t_stu";
    ResultSet rs = st.executeQuery(sql);

1.  遍历结果集

while(rs.next()) { 
    				int id = rs.getInt("id");
    				String name = rs.getString("name");
    				int age = rs.getInt("age");
    				
    				System.out.println("id = " + id + ",name = "  + name +",age =" + age);
    			}

1.  释放资源

*  先创建的后释放，后创建的先释放
 *

# 3. 基础入门示例代码 #

import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import java.sql.Statement;
    
    import com.mysql.jdbc.Driver;
    
    
    public class Demo1_JDBC_Main { 
    	private static Statement st;
    	private static ResultSet rs;
    	private static Connection conn;
    
    	public static void main(String[] args) { 
    	
    
    		try { 
    			
    // 1.注册驱动
    // DriverManager.registerDriver(new Driver());
    // 2.建立连接
    			conn = DriverManager.getConnection("jdbc:mysql://localhost/student", "root", "123456");
    // 3.创建statem
    			st = conn.createStatement();
    			
    
    // 4.执行查询
    			String sql = "select * from t_stu";
    			rs = st.executeQuery(sql);
    // 5.遍历结果
    			while(rs.next()) { 
    				int id = rs.getInt("id");
    				String name = rs.getString("name");
    				int age = rs.getInt("age");
    				
    				System.out.println("id = " + id + ",name = "  + name +",age =" + age);
    			}
    			
    			
    // 6.添加数据
    			String sql1 = "insert into t_stu values(6,'bb',99)";
    			int result = st.executeUpdate(sql1);
    			if(result == 1) { 
    				System.out.println("添加成功");
    			}else { 
    				System.out.println("添加失败");
    			}
    			
    			
    			
    		} catch (SQLException e) { 
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}finally { 
    			try { 
    				rs.close();
    			} catch (SQLException e) { 
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    			try { 
    				st.close();
    			} catch (SQLException e) { 
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    			try { 
    				conn.close();
    			} catch (SQLException e) { 
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    		
    			System.out.println("close something");
    		
    		}
    	}
    
    }

**结果**

\[外链图片转存失败(img-hORQfhU4-1564470636901)(C:\\Users\\cds\\AppData\\Roaming\\Typora\\typora-user-images\\1556721242074.png)\]

# 4. JDBC工具类的构建 #

1.  资源释放工作的整合
2.  防止驱动的二次注册
3.  使用`propreties`配置文件

static{ 
    		try { 
    			//1. 创建一个属性配置对象
    			Properties properties = new Properties();
    			InputStream is = new FileInputStream("jdbc.properties"); //对应文件位于工程根目录 
    			//导入输入流。
    			properties.load(is);
    			
    			//读取属性
    			driverClass = properties.getProperty("driverClass");
    			url = properties.getProperty("url");
    			name = properties.getProperty("name");
    			password = properties.getProperty("password");
    			
    		} catch (Exception e) { 
    			e.printStackTrace();
    		}
    	}

## jdbc工具类代码示例 ##

import java.io.FileInputStream;
    import java.io.InputStream;
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import java.sql.Statement;
    import java.util.Properties;
    
    
    
    public class Demo2_JdbcUtil { 
    	
    	//1. 在properties配置文件中读取数据
    	static String driverClass = null;
    	static String url = null;
    	static String name = null;
    	static String password= null;
    	
    	
    	static { 
    		try { 
    			//创建属性配置对象
    			Properties properties = new Properties();
    			//创建输入流
    			InputStream is = new FileInputStream("jdbc.properties");
    			//导入输入流
    			properties.load(is);
    			//读取属性
    			driverClass = properties.getProperty("driverClass");
    			url = properties.getProperty("url");
    			name = properties.getProperty("name");
    			password = properties.getProperty("password");
    			
    			
    		} catch (Exception e) { 
    			e.printStackTrace();
    		}
    	}
    	
    	//获取连接对象
    	public static Connection getConn() { 
    		Connection conn = null;
    		
    		try { 
    			conn = DriverManager.getConnection(url, name, password);
    		} catch (SQLException e) { 
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    		return conn;
    		
    	}
    	
    	
    	//释放资源
    	public static void release(Connection conn , Statement st , ResultSet rs){ 
    		closeRs(rs);
    		closeSt(st);
    		closeConn(conn);
    	}
    	public static void release(Connection conn , Statement st){ 
    		closeSt(st);
    		closeConn(conn);
    	}
    	
    	
    	
    	private static void closeRs(ResultSet rs){ 
    		try { 
    			if(rs != null){ 
    				rs.close();
    			}
    		} catch (SQLException e) { 
    			e.printStackTrace();
    		}finally{ 
    			rs = null;
    		}
    	}
    	
    	private static void closeSt(Statement st){ 
    		try { 
    			if(st != null){ 
    				st.close();
    			}
    		} catch (SQLException e) { 
    			e.printStackTrace();
    		}finally{ 
    			st = null;
    		}
    	}
    	
    	private static void closeConn(Connection conn){ 
    		try { 
    			if(conn != null){ 
    				conn.close();
    			}
    		} catch (SQLException e) { 
    			e.printStackTrace();
    		}finally{ 
    			conn = null;
    		}
    	}
    	
    	
    
    }

## jdbc工具类代码使用实例 ##

import java.sql.Connection;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import java.sql.Statement;
    
    public class Demo3_jdbc_util { 
    	public static void main(String[] args) { 
    		Connection conn = null;
    		Statement st = null;
    		ResultSet rs = null;
    		
    		conn = Demo2_JdbcUtil.getConn();
    		try { 
    			st = conn.createStatement();
    			String sql = "select * from t_stu";
    			rs = st.executeQuery(sql);
    			while(rs.next()) { 
    				int age = rs.getInt("age");
    				int id = rs.getInt("id");
    				String name = rs.getString("name");
    				System.out.println(age + "===" + name + "===" + id);
    			}
    			
    		} catch (SQLException e) { 
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    	}
    
    }

**运行结果**

\[外链图片转存失败(img-5iGYQRjN-1564470636903)(C:\\Users\\cds\\AppData\\Roaming\\Typora\\typora-user-images\\1556721511705.png)\]

# 5. 使用单元测试，测试代码 #

1.  定义一个类，`TestXXX`,在类内定义方法`testXXX`
2.  添加`junit`的支持
    
    1.  右键工程—add Library — Junit5
3.  在方法的上面加上注解，其实就是一个标记
    
        @Test
        public void TestSomething(){
            …………
        }
4.  光标移动到方法的名字上，右键执行单元测试。或者打开outline视图，选择方法右键执行。】

# 6. Dao模式 #

> Date Access Object 数据访问对象

1.  新建一个`dao`借口，在里面声明数据库访问规则

/** * 定义操作数据库的方法 */
    	public interface UserDao { 
    	
    		/** * 查询所有 */
    		void findAll();
    	}

1.  建立一个Dao的实现类，具体实现之前定义的规则

public class UserDaoImpl implements UserDao{ 
    
    	@Override
    	public void findAll() { 
    		Connection conn = null;
    		Statement st = null;
    		ResultSet rs = null;
    		try { 
    			//1. 获取连接对象
    			conn = JDBCUtil.getConn();
    			//2. 创建statement对象
    			st = conn.createStatement();
    			String sql = "select * from t_user";
    			rs = st.executeQuery(sql);
    			
    			while(rs.next()){ 
    				String userName = rs.getString("username");
    				String password = rs.getString("password");
    				
    				System.out.println(userName+"="+password);
    			}
    			
    		} catch (Exception e) { 
    			e.printStackTrace();
    		}finally { 
    			JDBCUtil.release(conn, st, rs);
    		}
    	}
    
    }

1.  直接套用实现

@Test
       	public void testFindAll(){ 
       		UserDao dao = new UserDaoImpl();
       		dao.findAll();
       	}

# 7. statement 的安全问题 #

1.  `Statement`执行的时候，是先拼接sql语句，然后执行的
2.  前面拼接sql语句，如果变量里带有 数据库的关键字，那么一并认为是关键字，不认同为普通字符串

## PrepareStatement ##

> 该对象是用来替换之前的statement对象

1.  相比较以前的statement， 预先处理给定的sql语句，对其执行语法检查。 在sql语句里面使用 ? 占位符来替代后续要传递进来的变量。 后面进来的变量值，将会被看成是字符串，不会产生任何的关键字。

String sql = "insert into t_user values(null , ? , ?)";
    		 ps = conn.prepareStatement(sql);
    		 
    		 //给占位符赋值 从左到右数过来，1 代表第一个问号， 永远你是1开始。
    		 ps.setString(1, userName);
    		 ps.setString(2, password);

# 8. 全面的通过JDBC增删查改数据库 #

## 1.jdbc工具类 ##

package Dmeo_test;
    
    import java.io.FileInputStream;
    import java.io.InputStream;
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import java.sql.Statement;
    import java.util.Properties;
    
    
    
    public class Demo2_JdbcUtil { 
    	
    	//1. 在properties配置文件中读取数据
    	static String driverClass = null;
    	static String url = null;
    	static String name = null;
    	static String password= null;
    	
    	
    	static { 
    		try { 
    			//创建属性配置对象
    			Properties properties = new Properties();
    			//创建输入流
    			InputStream is = new FileInputStream("jdbc.properties");
    			//导入输入流
    			properties.load(is);
    			//读取属性
    			driverClass = properties.getProperty("driverClass");
    			url = properties.getProperty("url");
    			name = properties.getProperty("name");
    			password = properties.getProperty("password");
    			
    			
    		} catch (Exception e) { 
    			e.printStackTrace();
    		}
    	}
    	
    	//获取连接对象
    	public static Connection getConn() { 
    		Connection conn = null;
    		
    		try { 
    			conn = DriverManager.getConnection(url, name, password);
    		} catch (SQLException e) { 
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    		return conn;
    		
    	}
    	
    	
    	
    	public static void release(Connection conn , Statement st , ResultSet rs){ 
    		closeRs(rs);
    		closeSt(st);
    		closeConn(conn);
    	}
    	public static void release(Connection conn , Statement st){ 
    		closeSt(st);
    		closeConn(conn);
    	}
    	
    	
    	
    	private static void closeRs(ResultSet rs){ 
    		try { 
    			if(rs != null){ 
    				rs.close();
    			}
    		} catch (SQLException e) { 
    			e.printStackTrace();
    		}finally{ 
    			rs = null;
    		}
    	}
    	
    	private static void closeSt(Statement st){ 
    		try { 
    			if(st != null){ 
    				st.close();
    			}
    		} catch (SQLException e) { 
    			e.printStackTrace();
    		}finally{ 
    			st = null;
    		}
    	}
    	
    	private static void closeConn(Connection conn){ 
    		try { 
    			if(conn != null){ 
    				conn.close();
    			}
    		} catch (SQLException e) { 
    			e.printStackTrace();
    		}finally{ 
    			conn = null;
    		}
    	}
    	
    	
    
    }

## 2.jdbc接口 ##

package Dmeo_test;
    
    public interface Demo1_InterFace { 
    	void findAll();
    	
    	void delete(String id);
    	
    	void update(String id,String name);
    	
    	void add(String id,String name);
    
    }

## 3.jdbc接口的实现 ##

package Dmeo_test;
    
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    
    import com.mysql.jdbc.Connection;
    
    import 自己训练的代码.Demo2_JdbcUtil;
    
    public class Demo3_Impl implements Demo1_InterFace{ 
    	
    	java.sql.Connection conn = Demo2_JdbcUtil.getConn();
    	PreparedStatement ps  = null;
    	ResultSet rs = null;
    
    	@Override
    	public void findAll() { 
    		// TODO Auto-generated method stub
    		
    		
    		String sql = "select * from t_user";
    		try { 
    			ps = conn.prepareStatement(sql);
    			rs = ps.executeQuery();
    			while(rs.next()) { 
    				String name = rs.getString("name");
    				String id = rs.getString("id");
    				System.out.println(name + "------------" + id);
    			}
    			
    		
    		} catch (SQLException e) { 
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    		
    	}
    	@Override
    	public void delete(String id) { 
    		// TODO Auto-generated method stub
    
    		String sql = "delete from t_user where id = ?";
    		try { 
    			ps = conn.prepareStatement(sql);
    			ps.setString(1, id);
    			int result = ps.executeUpdate();
    			if(result > 0)
    				System.out.println("删除成功");
    			else
    				System.out.println("删除失败");
    		} catch (SQLException e) { 
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    		
    	}
    
    	@Override
    	public void update(String id,String name) { 
    		// TODO Auto-generated method stub
    		String sql = "update t_user set id = ? where name = ?";
    		try { 
    			ps = conn.prepareStatement(sql);
    			ps.setString(1, id);
    			ps.setString(2, name);
    			int result = ps.executeUpdate();
    			if(result > 0)
    				System.out.println("更新成功");
    			else
    				System.out.println("更新失败");
    		} catch (SQLException e) { 
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    		
    	}
    
    	@Override
    	public void add(String id,String name) { 
    		// TODO Auto-generated method stub
    // String sql = "insert into t_user values(?,?)";
    		String sql = "INSERT INTO t_user VALUES(?,?)";
    		try { 
    			ps = conn.prepareStatement(sql);
    			ps.setString(1, id);
    			ps.setString(2, name);
    			int result = ps.executeUpdate();
    			if (result > 0)
    				System.out.println("添加成功");
    			else
    				System.out.println("添加失败");
    		} catch (SQLException e) { 
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    		
    	}
    
    	
    
    }

## 4.jdbc类的测试 ##

package Dmeo_test;
    
    import static org.junit.Assert.*;
    
    import org.junit.Test;
    
    public class Demo3_ImplTest { 
    	Demo3_Impl tao = new Demo3_Impl();
    
    	@Test
    	public void testFindAll() { 
    		tao.findAll();
    	}
    
    	@Test
    	public void testDelete() { 
    		tao.delete("5");
    		
    	}
    
    	@Test
    	public void testUpdate() { 
    		tao.update("13", "cds aixuexi");
    		
    	}
    
    	@Test
    	public void testAdd() { 
    		tao.add("12", "cds aixuexi");
    	}
    
    }