JDBC<android studio,kotlin>

工具：mysql 5.6.19,mysql-connector-java-5.1.48.jar,android stuido&android studio自带模拟器

1.在mysql数据库中新建表customer,并创建相关字段

SQL命令如下

create table customer(username varchar(20),password varchar(20),email varchar(40));

alter table customer add id int(5) auto_increment primary key;

mysql> insert into customer(username,password,email) values('张三','123456','zhangsan@5429.com');

insert into customer(username,password,email) values('李四','234567','lisi@5429.com');

insert into customer(username,password,email) values('王五','345678','wangwu@5429.com');

insert into customer(username,password,email) values('陈六','456789','chenliu@5429.com');

select * from customer;

 2.JDBC连接数据库

------>页面布局

 ------>设置按钮点击监听

 ------>导入mysql-connector-java-5.1.48.jar包，搜索下载即可

复制粘贴到lib文件下，右键，add as library...

  ------>JDBC连接数据库

（1），添加网络许可<uses-permission android:name="android.permission.INTERNET"/>

（2）Util类代码(待优化)

package com.vocus.jdbctest

import java.lang.Exception
import java.sql.Connection
import java.sql.DriverManager

class Util {
    var conn:Connection?=null
    val driver="com.mysql.jdbc.Drvier"
    val url="jdbc:mysql://10.0.2.2:3306/test"
    val user="root"  //root用户
    val psd="rs123456" //自己的密码
    fun connection():Connection?{
        try{
            Class.forName(driver).newInstance()
        }catch(e:Exception){
            e.printStackTrace()
        }
        try{
            conn=DriverManager.getConnection(url,user,psd)
        }catch (e:Exception){
            e.printStackTrace()
        }
        return conn
    }
}

（3）针对数据库表customer的查询(待优化)

class Customer {
    open val username:String?=null //权宜之计
    open val password:String?=null
    open val email:String?=null

    override fun toString(): String {
        return "Customer(username=$username, password=$password, email=$email)"
    }

}

package com.vocus.jdbctest

import java.lang.Exception

class CustomerForQuery {
    fun query(sql: String, vararg args: Any): Customer?{//sql语句如select username from customer where id=?,args不确定参数

        try {
//            Thread({
                var conn = Util().connection()
                var ps = conn!!.prepareStatement(sql)

                for (i in 0 until args.size) {//设置sql参数
                    ps.setObject(i + 1, args[i])
                }

                var resultSet = ps.executeQuery()//获得查询结果集

                var rsmd = resultSet.getMetaData()
                var columns = rsmd.columnCount //获得结果集列数

                if (resultSet.next()) {
                    var cust = Customer()
                    for (i in 0 until columns) {
                        var value = resultSet.getObject(i + 1)  //获得查询的值
                        var columnsName = rsmd.getColumnName(i + 1) //获得值对应的列名，即字段名
                        //println("查询结果，${value}+${columnsName}")
                        val field = Customer::class.java.getDeclaredField(columnsName)
                        field.setAccessible(true)
                        field.set(cust, value)
                    }
                    println("已执行查询语句...")
                    return cust
                }
//            }).start()
        } catch (e: Exception) {
            e.printStackTrace()
        }
        return null
    }
}

（4）添加按钮点击监听执行

package com.vocus.jdbctest
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
import kotlin.concurrent.thread

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        connBtn.setOnClickListener {
            thread{
                var cust = CustomerForQuery().query("select username from customer where id=?", "3")
                println(cust)
            }
        }
    }

}

 （5）优化关闭连接，引入泛型，实现针对不同表的通用查询等

------>DAO模式

（1）建立DAO抽象类(BaseDAO)

对于数据库的增删改查等基本操作封装在此类中

（2）针对具体的表提供接口(CustomerDAO)

用于说明具体的需求

interface CustomerDAO {
    //查询用户名是否存在
    fun logcheck(username:String,password:String):Boolean
}

（3）实现接口的类（CustomerDAOimpl）

用于需求的实现

class CustomerDAOImpl :BaseDAO(),CustomerDAO {
    override fun logcheck(username: String, password: String): Boolean {
        var cust:Customer?=null
        try{
            cust=query("select password from customer where username=?",username)
        }catch (e:Exception){
            println("用户名不存在...")
            return false
        }
        if(cust!!.password==password){
            return true
        }
        else{
            println("账号和用户名不匹配...")
            return false
        }
    }
}

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        connBtn.setOnClickListener {
            thread{
                //var cust = CustomerForQuery().query("select password from customer where username=?", "张三")
                //println(cust)
                var exist=CustomerDAOImpl().logcheck("张三","123456")
                println("exist?:${exist}")
            }
        }
    }

}

接2.17更新

现在开发后台基本上很少用kotlin，最近尝试做后台，所以用到的jdbc都采用java

实现数据库表的通用查询，以及数据库表通用查询下的返回多条数据，使用到泛型，测试代码如下

->数据库表查询通用方法

public <T> T queryForTable(Class<T> clazz,String sql,Object ...args){
        Connection conn=null;
        PreparedStatement statement=null;
        ResultSet rs=null;
        try{
            conn=JdbcUtil.connection();
            statement=conn.prepareStatement(sql);
            for(int i=0;i<args.length;i++){
                statement.setObject(i+1,args[0]);
            }

            rs=statement.executeQuery();
            //获得结果集原数据
            ResultSetMetaData rsmd=rs.getMetaData();
            int columnCount=rsmd.getColumnCount();
            if(rs.next()){
                T t=clazz.newInstance();
                for(int i=0;i<columnCount;i++){
                    Object columnValue=rs.getObject(i+1);
                    String columnName=rsmd.getColumnName(i+1);
                    //把查询到的每一行数据，映射到java类
                    Field field=clazz.getDeclaredField(columnName);
                    field.setAccessible(true);
                    field.set(t,columnValue);
                }
                return t;

            }

        }catch (Exception e){
            e.printStackTrace();
        }finally {
            new JdbcUtil().closeResource(conn,statement,rs);
        }

        return null;
    }

->返回多条数据

public <T> ArrayList<T> query(Class<T> clazz,String sql,Object ...args) {
        ResultSet rs = null;
        PreparedStatement statement = null;
        Connection conn = new JdbcUtil().connection();
        ArrayList<T> customersList=new ArrayList<T>();//对象列表
        try {

            //String sql = "select * from customer limit 0,10;";
            statement = conn.prepareStatement(sql);
            for(int i=0;i<args.length;i++){
                statement.setObject(i+1,args[i]);
            }

            rs = statement.executeQuery();

            ResultSetMetaData rsmd=rs.getMetaData();
            int columnCount=rsmd.getColumnCount();

            for (int j=0;rs.next();j++) {
                T t=clazz.newInstance();
                for(int i=0;i<columnCount;i++){
                    String columnName=rsmd.getColumnName(i+1);
                    Object columnValue=rs.getObject(i+1);
                    Field field=clazz.getDeclaredField(columnName);
                    field.setAccessible(true);
                    field.set(t,columnValue);
                }
                customersList.add(t);
            }
        } catch (
                SQLException | NoSuchFieldException | IllegalAccessException | InstantiationException e) {
            e.printStackTrace();
        } finally {
            new JdbcUtil().closeResource(conn, statement, rs);
        }
        return customersList;
    }