JDBC增删改查案例

​ 为了支持各大编程语言能够操纵数据库，完成对数据库的增删改查。各大厂商各自编写了连接自己数据库的JDBC实现程序。这个JDBC接口模板则由Java程序的设计者提供，由数据库厂商自己完成逻辑编写。对于最早的平台服务应用，由于没有各大ORM框架，我么基本所有的数据库操作都需要程序员自己编写，最底层就是对JDBC程序的封装。现在由于ORM框架的兴起，程序编写者只用更加注重业务逻辑的编写，对于数据库的连接管理基本都是框架自动完成，大大方便了程序编写者。

这里探究JDBC的应用，使用JDBC操纵MySQL数据库完成简单的增删改查逻辑。

这里以员工（employee） 和部门（emp）表为例进行操作。

create table emp(
	id int primary key auto_increment,
	empname varchar(60)
);
create table employee(
	id int primary key auto_increment comment '员工id',
	ename employeevarchar(60) comment '员工名称',
	gender varchar(1) comment '员工性别',
	empid int comment '部门id'
);
alter table employee add foreign key(empid) references emp(id);
insert into emp values(1,'广告部');
insert into emp values(2,'开发部');
insert into employee values(1,'tom','M',2);

创建简单的maven工程即可，导入mysql连接依赖包

        
            mysql
            mysql-connector-java
            5.1.37
        

我们将连接进行封装，可以快速获取连接，避免重复造轮子，提高开发效率。

package cn.jdbccase.demo.utils;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;

public class JDBCUtils {
    
    public static Properties getdbproperties(){
        Properties properties = new Properties();
        // 获取类加载器
        ClassLoader classLoader = JDBCUtils.class.getClassLoader();
        try {
            properties.load(classLoader.getResourceAsStream("db.properties"));
        } catch (IOException e) {
            e.printStackTrace();
        }
        return properties;
    }

    // 获取连接
    public static Connection getCon(){
        Properties properties = getdbproperties();

        String url = properties.getProperty("jdbc.url");

        String user = properties.getProperty("jdbc.user");

        String password = properties.getProperty("jdbc.password");

        String driver = properties.getProperty("jdbc.driver");

        Connection con = null;
        try {
            // 注册驱动
            Class.forName(driver);
            // 获取连接
            con = DriverManager.getConnection(url, user, password);
        } catch (SQLException | ClassNotFoundException throwables) {
            throwables.printStackTrace();
        }
        return con;
    }
    // 关闭资源
    public static void closeResource(Connection con, Statement st) {
        if (st != null) {
            try {
                st.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (con != null) {
            try {
                con.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

db.properties文件：

jdbc.url=jdbc:mysql://localhost:3306/jdbc_db
jdbc.user=root
jdbc.password=123456
jdbc.driver=com.mysql.jdbc.Driver

package cn.jdbccase.demo;
import cn.jdbccase.demo.utils.JDBCUtils;
import java.sql.*;
public class demo1 {
    public static void main(String[] args) throws  SQLException {
        Connection con = JDBCUtils.getCon();

        Statement statement = con.createStatement();

        ResultSet res = statement.executeQuery("select * from employee");

        while (res.next()){
            int id = res.getInt("id");
            String ename = res.getString("ename");
            String gender = res.getString("gender");
            int empid = res.getInt("empid");
            System.out.println(id + "t" + ename + "t" + gender + "t" + empid);
        }
        res.close();
        JDBCUtils.closeResource(con,statement);
    }
}

结果：

get 和 set方法省略

public class employee {
    private Integer id;
    private String ename;
    private String gender;
    private Integer empid;
	....get and set 方法
}

public class Emp {
    private Integer id;
    private String empname;
	....get and set 方法
}

package cn.jdbccase.demo.dao;
import cn.jdbccase.demo.utils.JDBCUtils;
import java.lang.reflect.Field;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;


public abstract class baseDao {

    
    public int update(Connection conn, String sql, Object... params) {
        int count = 0;
        try {
            PreparedStatement ps = conn.prepareStatement(sql);
            // 添加参数
            for (int i = 0; i < params.length; i++) {
                ps.setObject(i+1,params[i]);
            }
            //执行sql语句
            count = ps.executeUpdate();
            // 关闭资源
            JDBCUtils.closeResource(null,ps);
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return count;
    }

    
    public  T getInstance(Connection conn, Class cla, String sql, Object... args) {
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            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
            ResultSetmetaData rsmd = rs.getmetaData();
            // 通过ResultSetmetaData获取结果集中的列数
            int columnCount = rsmd.getColumnCount();

            //利用反射封装对象
            if (rs.next()) {
                T t = cla.newInstance();
                for (int i = 0; i < columnCount; i++) {
                    Object columValue = rs.getObject(i + 1);
                    String columnLabel = rsmd.getColumnLabel(i + 1);
                    Field field = cla.getDeclaredField(columnLabel);
                    field.setAccessible(true);
                    field.set(t, columValue);
                }
                return t;
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.closeResource(null, ps, rs);
        }

        return null;
    }

    // 查询一批数据
    public  List getForList(Connection conn, Class clazz, String sql, Object... args) {
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            ps = conn.prepareStatement(sql);
            for (int i = 0; i < args.length; i++) {
                ps.setObject(i + 1, args[i]);
            }
            rs = ps.executeQuery();
            ResultSetmetaData rsmd = rs.getmetaData();
            int columnCount = rsmd.getColumnCount();
            ArrayList list = new ArrayList();
            while (rs.next()) {
                T t = clazz.newInstance();
                for (int i = 0; i < columnCount; i++) {
                    Object columValue = rs.getObject(i + 1);
                    String columnLabel = rsmd.getColumnLabel(i + 1);
                    Field field = clazz.getDeclaredField(columnLabel);
                    field.setAccessible(true);
                    field.set(t, columValue);
                }
                list.add(t);
            }
            return list;
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.closeResource(null, ps, rs);
        }
        return null;
    }
}

baseDao类里面使用了反射来封装查询结果，这里理解比较抽象，需要先理解反射机制。通过反射来分装结果集，可以令方法变的通用，更加的灵活。

根据面向接口编程的思想，若需要编写Employee层的逻辑，我们需要先定义操作接口。

package cn.jdbccase.demo.dao;

import cn.jdbccase.demo.domain.employee;

import java.sql.Connection;

public interface EmployeeDao {
    // 添加员工
    public Integer addEmployee(employee em, Connection con);

    // 根据id删除员工
    public Integer delEmployById(Integer id, Connection con);

    // 根据id修改员工
    public Integer updateEmployById(employee e, Connection con);

    // 根据id查询某个员工
    public employee getEmployById(Integer id, Connection con);
}

实现类的编写：

package cn.jdbccase.demo.dao;

import cn.jdbccase.demo.domain.employee;

import java.sql.Connection;

public class EmployeeDaoImpl extends baseDao implements EmployeeDao{

    @Override
    public Integer addEmployee(employee em, Connection con) {
        String sql = "insert into employee(ename,gender,empid) values(?,?,?)";

        int count = update(con,sql, em.getEname(), em.getGender(), em.getEmpid());

        return count;
    }

    @Override
    public Integer delEmployById(Integer id, Connection con) {

        String sql = "delete from employee where id = ?";

        int count = update(con,sql, id);

        return count;
    }

    @Override
    public Integer updateEmployById(employee e, Connection con) {
        String sql = "update employee set ename = ?,gender = ?,empid = ? where id = ?";

        int count = update(con,sql,e.getEname(),e.getGender(),e.getEmpid(),e.getId());

        return count;
    }

    @Override
    public employee getEmployById(Integer id, Connection con) {

        String sql = "select * from employee where id = ?";

        employee instance = (employee) getInstance(con, employee.class, sql, id);

        return instance;
    }
}

package cn.jdbccase.demo.test;
import cn.jdbccase.demo.dao.EmployeeDao;
import cn.jdbccase.demo.dao.EmployeeDaoImpl;
import cn.jdbccase.demo.domain.employee;
import cn.jdbccase.demo.utils.JDBCUtils;
import org.junit.Before;
import org.junit.Test;
import java.sql.Connection;

public class DaoTest {

    EmployeeDao empdao = null;

    @Before
    public void init(){
        empdao = new EmployeeDaoImpl();
    }

    @Test
    public void testadd(){
        Connection con = JDBCUtils.getConnection();
        employee employee = new employee();
        employee.setEname("Bob");
        employee.setGender("M");
        employee.setEmpid(2);
        Integer count = empdao.addEmployee(employee, con);
        System.out.println(count);
        JDBCUtils.closeResource(con,null);
    }

    @Test
    public void testdel(){
        Connection con = JDBCUtils.getConnection();

        Integer count = empdao.delEmployById(4, con);
        System.out.println(count);
        JDBCUtils.closeResource(con,null);
    }

    @Test
    public void testupdate(){
        Connection con = JDBCUtils.getConnection();
        employee employee = new employee();
        employee.setId(1);
        employee.setEname("tom");
        employee.setGender("F");
        employee.setEmpid(1);
        Integer count = empdao.updateEmployById(employee,con);
        System.out.println(count);
        JDBCUtils.closeResource(con,null);
    }

    @Test
    public void testselect(){

        Connection con = JDBCUtils.getConnection();

        employee employ = empdao.getEmployById(1,con);

        System.out.println(employ);

        JDBCUtils.closeResource(con,null);
    }
}

完成简单的增删改查