Java与数据库学习总结

1、连接数据库

package utils;

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

public class JDBCUtils {
    private JDBCUtils() {
    }

    private static Connection con;
    static {
        try {
            // 注册驱动
            Class.forName("com.mysql.jdbc.Driver");
            // 获得连接 对象
            String url = "jdbc:mysql://localhost:3306/day35";
            // 账号密码
            String username = "root";
            String password = "root";
            // 连接数据库
            con = DriverManager.getConnection(url, username, password);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 定义静态方法 返回数据库的连接
    public static Connection getConnection() {
        return con;
    }

    // 关资源
    public static void close(Connection con, Statement stat) {
        if (stat != null) {
            try {
                stat.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
            if (con != null) {
                try {
                    con.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public static void close(Connection con, Statement stat, ResultSet rs) {
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {

                e.printStackTrace();
            }
            if (stat != null) {
                try {
                    stat.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                if (con != null) {
                    try {
                        con.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }
}

还可以通过配置文件方式连接数据库

配置文件(database.properties)：

driverClass=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/day35
username=root
password=root

Java：

package utils;

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

public class JDBCUtilsConfig {
    private static Connection con;
    private static String driverClass;
    private static String url;
    private static String username;
    private static String password;
    static {
        try {
            readConfig();
            Class.forName(driverClass);
            con = DriverManager.getConnection(url, username, password);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 读配置文件
    private static void readConfig() throws Exception {
        // 类加载器
        InputStream in = JDBCUtilsConfig.class.getClassLoader().getResourceAsStream("database.properties");
        Properties p = new Properties();
        p.load(in);
        driverClass = p.getProperty("driverClass");
        url = p.getProperty("url");
        username = p.getProperty("username");
        password = p.getProperty("password");
    }

    public static Connection getConnection() {
        return con;
    }
}

2、访问数据库

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

public class JDBCDemo {   
    public static void main(String[] args) throws ClassNotFoundException, SQLException {
        Class.forName("com.mysql.jdbc.Driver");
        String url = "jdbc:mysql://localhost:3306/day35";
        String uname = "root";
        String pwd = "root";
        Connection con = DriverManager.getConnection(url, uname, pwd);
        //获得语句执行平台
        Statement sta = con.createStatement();
        sta.executeUpdate("insert into money (name) values ('we232')");
        sta.close();
        con.close();
    }
}

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

//  查询
public class JDBCDemo1 {

    public static void main(String[] args) throws ClassNotFoundException, SQLException {
        // 1 注册驱动
        Class.forName("com.mysql.jdbc.Driver");
        // 2获得连接 对象
        String url = "jdbc:mysql://localhost:3306/day35";
        String username = "root";
        String password = "root";
        Connection con = DriverManager.getConnection(url, username, password);
        // 3 获取执行sql语句对象
        Statement stat = con.createStatement();// 有注入攻击风险，不建议使用，可以用另一种平台
        // 4 调用执行者对象的方法
        String sql = "SELECT * FROM sort";
        ResultSet rs = stat.executeQuery(sql);
        // 5 rs结果集 ResultSet 方法 bollean next(); 返回true 有结果返回false 没有
        while (rs.next()) {
            // 获取每一列数据 ResultSet getxxx方法
            System.out.println(rs.getInt("sid") + "  " + rs.getDouble("sprice") + "   " + rs.getString("sdesc"));
        }
        // 5 关资源
        rs.close();
        stat.close();
        con.close();
    }
}

另一种语句执行平台

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

public class JDBCDemo2 {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {
        // 1 注册驱动
        Class.forName("com.mysql.jdbc.Driver");
        // 2获得连接 对象
        String url = "jdbc:mysql://localhost:3306/day35";
        String username = "root";
        String password = "root";
        Connection con = DriverManager.getConnection(url, username, password);
        // 3 获得执行对象 换执行平台对象 prepareStatement
        String sql = "UPDATE sort SET sname=?,sprice=? WHERE sid=?";
        PreparedStatement pst = con.prepareStatement(sql);
        // pst 有方法 setxxx(占位符的位置，值)
        pst.setObject(1, "饭缸");
        pst.setObject(2, "20000");
        pst.setObject(3, 1);
        int s = pst.executeUpdate();
        System.out.println(s);
        // 4 关
        pst.close();
        con.close();
    }
}

3、使用第三方工具包访问数据库

import java.sql.Connection;
import java.sql.SQLException;

import org.apache.commons.dbutils.DbUtils;
import org.apache.commons.dbutils.QueryRunner;

public class Demo2 {
    private static Connection con = JDBCUtilsConfig.getConnection();

    public static void main(String[] args) throws SQLException {
        insert();
        update();
        delete();
    }

    public static void insert() throws SQLException {
        QueryRunner qr = new QueryRunner();
        String sql = "insert into sort (sname,sprice,sdesc) values (?,?,?)";
        Object[] param = { "猫", 555, "小橘猫" };
        qr.update(con, sql, param);
        DbUtils.close(con);
    }

    public static void update() throws SQLException {
        QueryRunner qr = new QueryRunner();
        String sql = "update sort set sname = ?,sprice = ?,sdesc = ? where id = ?";
        Object[] param = { "qy95", 40, "AAA", 6 };
        qr.update(con, sql, param);
        DbUtils.close(con);
    }

    public static void delete() throws SQLException {
        QueryRunner qr = new QueryRunner();
        String sql = "delete from sort where id = ?";
        qr.update(con, sql, 9);
        DbUtils.close(con);
    }
}

4、第三方包8种结果集处理方式

package cn.zlh.Demo;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.List;
import java.util.Map;

import javax.management.Query;

import org.apache.commons.dbutils.DbUtils;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.ArrayHandler;
import org.apache.commons.dbutils.handlers.ArrayListHandler;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.apache.commons.dbutils.handlers.ColumnListHandler;
import org.apache.commons.dbutils.handlers.MapHandler;
import org.apache.commons.dbutils.handlers.MapListHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;

import cn.zlh.domain.Sort;
import cn.zlh.utils.JDBCUtilsConfig;

// 8种结果集处理
public class Demo3 {
    private static Connection con = JDBCUtilsConfig.getConnection();

    public static void main(String[] args) throws SQLException {
        arrayHandler();
        arrayListHandler();
        beanHandler();
        beanListHandler();
        columnListHandler();
        scalarHandler();
        mapHandler();
        mapListHandler();
    }

    // 将每一条数据都以key-value的形式放在Map集合中，再把这些Map放到一个List集合中
    public static void mapListHandler() throws SQLException {
        QueryRunner qr = new QueryRunner();
        String sql = "select * from sort";
        List<Map<String, Object>> query = qr.query(con, sql, new MapListHandler());
        DbUtils.close(con);
        for (Map<String, Object> map : query) {
            for (String key : map.keySet()) {
                System.out.print(key + ":" + map.get(key));
            }
            System.out.println();
        }
    }

    // 将第一天数据以key-value的形式放在Map集合中
    public static void mapHandler() throws SQLException {
        QueryRunner qr = new QueryRunner();
        String sql = "select * from sort";
        Map<String, Object> query = qr.query(con, sql, new MapHandler());
        DbUtils.close(con);
        for (String key : query.keySet()) {
            System.out.println(key + ":" + query.get(key));
        }
    }

    // 可以使用聚合函数统计数据
    public static void scalarHandler() throws SQLException {
        QueryRunner qr = new QueryRunner();
        String sql = "select count(*) from sort";
        Long query = qr.query(con, sql, new ScalarHandler<Long>());
        DbUtils.close(con);
        System.out.println(query);
    }

    // 将所有数据中某一列的值放到一个List集合中
    public static void columnListHandler() throws SQLException {
        QueryRunner qr = new QueryRunner();
        String sql = "select * from sort";
        List<Object> query = qr.query(con, sql, new ColumnListHandler<Object>("sprice"));
        DbUtils.close(con);
        for (Object o : query) {
            System.out.println(o);
        }
    }

    // 将每一条数据各自封装成一个对象，再把这些对象放到一个List集合里
    public static void beanListHandler() throws SQLException {
        QueryRunner qr = new QueryRunner();
        String sql = "select * from sort";
        List<Sort> query = qr.query(con, sql, new BeanListHandler<Sort>(Sort.class));
        DbUtils.close(con);
        for (Sort s : query) {
            System.out.println(s);
        }
    }

    // 将第一条数据封装成一个对象
    public static void beanHandler() throws SQLException {
        QueryRunner qr = new QueryRunner();
        String sql = "select * from sort";
        Sort query = qr.query(con, sql, new BeanHandler<>(Sort.class));
        DbUtils.close(con);
        System.out.println(query);
    }

    // 将每一条数据各自放到一个数组里，再把这些数组放到一个List集合里
    public static void arrayListHandler() throws SQLException {
        QueryRunner qr = new QueryRunner();
        String sql = "select * from sort";
        List<Object[]> query = qr.query(con, sql, new ArrayListHandler());
        DbUtils.close(con);
        for (Object[] o : query) {
            for (Object obj : o) {
                System.out.print(obj + ",");
            }
            System.out.println();
        }
    }

    // 将第一条数据放到数组里
    public static void arrayHandler() throws SQLException {
        QueryRunner qr = new QueryRunner();
        String sql = "select * from sort";
        Object[] query = qr.query(con, sql, new ArrayHandler());
        DbUtils.close(con);
        for (Object o : query) {
            System.out.println(o);
        }
    }
}