【JDBC】CRUD操作

JDBC的CRUD操作

• 向数据库中保存记录
• 修改数据库中的记录
• 删除数据库中的记录
• 查询数据库中的记录

保存代码的实现

package demo1;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

import org.junit.Test;

public class JDBCDemo3 {
    
    @Test
    /**
     * 保存代码的实现
     */
    public void demo3() {
        Connection conn = null;
        Statement stmt = null;
        
        try {
            //注册驱动
            Class.forName("com.mysql.cj.jdbc.Driver");
            //获得连接
            conn = DriverManager.getConnection("jdbc:mysql:///jdbctest?serverTimezone=Hongkong", "root", "1234");
            //获得执行SQL语句的对象
            stmt = conn.createStatement();
            //编写SQL
            String sql = "insert user values(null,'ddd','444','赵六')";
            //执行SQL
            int i = stmt.executeUpdate(sql);
            if(i > 0) {
                System.out.println("保存成功！");
            }
        }catch(Exception e) {
            e.printStackTrace();
        }finally{
            //释放资源
            if(stmt != null) {
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                stmt = null;
            }
            if(conn != null) {
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                conn = null;
            }
        }
    }
}

修改代码的实现

package demo1;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

import org.junit.Test;

public class JDBCDemo3 {
    
    @Test
    /**
     * 修改代码的实现
     */
    public void demo2() {
        Connection conn = null;
        Statement stmt = null;
        
        try {
            //注册驱动
            Class.forName("com.mysql.cj.jdbc.Driver");
            //获得连接
            conn = DriverManager.getConnection("jdbc:mysql:///jdbctest?serverTimezone=Hongkong", "root", "1234");
            //获得执行SQL语句的对象
            stmt = conn.createStatement();
            //编写SQL
            String sql = "update user set username='qqq',password='1234',name='或无言' where uid=4";
            //执行SQL
            int i = stmt.executeUpdate(sql);
            if(i > 0) {
                System.out.println("修改成功！");
            }
        }catch(Exception e) {
            e.printStackTrace();
        }finally{
            //释放资源
            if(stmt != null) {
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                stmt = null;
            }
            if(conn != null) {
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                conn = null;
            }
        }
    }
}

删除代码的实现

package demo1;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

import org.junit.Test;

public class JDBCDemo3 {
    
    @Test
    /**
     * 删除代码的实现
     */
    public void demo1() {
        Connection conn = null;
        Statement stmt = null;
        
        try {
            //注册驱动
            Class.forName("com.mysql.cj.jdbc.Driver");
            //获得连接
            conn = DriverManager.getConnection("jdbc:mysql:///jdbctest?serverTimezone=Hongkong", "root", "1234");
            //获得执行SQL语句的对象
            stmt = conn.createStatement();
            //编写SQL
            String sql = "delete from user where uid=4";
            //执行SQL
            int i = stmt.executeUpdate(sql);
            if(i > 0) {
                System.out.println("删除成功！");
            }
        }catch(Exception e) {
            e.printStackTrace();
        }finally{
            //释放资源
            if(stmt != null) {
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                stmt = null;
            }
            if(conn != null) {
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                conn = null;
            }
        }
    }
}

查询代码的实现

package demo1;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import org.junit.Test;

public class JDBCDemo1 {
    
    @Test
    /**
     * 查询代码的实现
     */
    public void demo1() {
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            //1.加载驱动
            Class.forName("com.mysql.cj.jdbc.Driver");
            
            //2.获得连接
            conn = DriverManager.getConnection("jdbc:mysql:///jdbctest?serverTimezone=Hongkong", "root", "1234");
            
            //3创建执行SQL语句的对象，并且执行SQL
            //3.1创建执行SQL语句的对象
            String sql = "select * from user";
            stmt = conn.createStatement();
            //3.2执行SQL
            rs = stmt.executeQuery(sql);
            while(rs.next()) {
                int uid = rs.getInt("uid");
                String username = rs.getString("username");
                String password = rs.getString("password");
                String name = rs.getString("name");
                
                System.out.println(uid   "-"   username   "-"   password   "-"   name);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            //释放资源
            if(rs != null) {
                try {
                    rs.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                rs = null;
            }
            if(stmt != null) {
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                stmt = null;
            }
            if(conn != null) {
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                conn = null;
            }
        }
    }
}