JDBCUtil编写心得

详细代码

//操作数据库公共类
public class BaseDao {
    private static String driver;
    private static String username;
    private static String password;
    private static String url;
    private static Connection connection=null;
    private static PreparedStatement preparedStatement=null;
    private static ResultSet resultSet=null;
    //静态代码块，类加载的时候就可以初始化
    static {
        //创建一个配置类
        Properties properties = new Properties();
        //通过类加载器读取配置文件内容转化为流
        InputStream resourceAsStream = BaseDao.class.getClassLoader().getResourceAsStream("db.properties");
        try {
            properties.load(resourceAsStream);//从流中读取信息到properties对象中
        } catch (IOException e) {
            e.printStackTrace();
        }
        driver=properties.getProperty("driver");
        username=properties.getProperty("username");
        password=properties.getProperty("password");
        url=properties.getProperty("url");
    }
    //获取数据库的链接
    public static Connection getConnection(){
        Connection connection=null;
        try {
            Class.forName(driver);//利用反射加载mysql-connector-java驱动
            connection = DriverManager.getConnection(url, username, password);

        } catch (Exception e) {
            e.printStackTrace();
        }
        return connection;
    }
    //编写查询公共类
    public static ResultSet execute(String sql,Object[] params) throws SQLException {
        connection=getConnection();//获取链接
        preparedStatement = connection.prepareStatement(sql);
        for (int i = 0; i < params.length; i++) {
            //setObject占位符从1开始，但是params数组是从0开始的
            preparedStatement.setObject(i+1,params[i]);//根据传入的params参数查询数据，会得到一个包含结果集的resultSet对象如下方所示
        }
        resultSet = preparedStatement.executeQuery();//采用了preparedStatement预编译方式故此处不必传参
        //closeResource(connection,preparedStatement,resultSet);
        return resultSet;
    }

    //编写增删改公共方法
    public static int Upexecute(String sql,Object[] params) throws SQLException {
        connection=getConnection();//获取链接
        preparedStatement = connection.prepareStatement(sql);
        for (int i = 0; i < params.length; i++) {
            //setObject占位符从1开始，但是params数组是从0开始的
            preparedStatement.setObject(i+1,params[i]);//根据出入的params参数插入，更新，或是删除数据，此操作只返回一个int参数
        }
        int UpdateresultSet = preparedStatement.executeUpdate();//采用了preparedStatement预编译方式故此处不必传参
        //closeResource(connection,preparedStatement,resultSet);
        return UpdateresultSet;
    }

    //释放资源
    public static boolean closeResource(){
        boolean flage=true;
        if (resultSet != null) {
            try {
                resultSet.close();
                //GC回收
                resultSet=null;
                System.out.println("rsclose");
            } catch (SQLException e) {
                e.printStackTrace();
                flage=false;
            }
        }
        if (preparedStatement != null) {
            try {
                preparedStatement.close();
                //GC回收
                preparedStatement=null;
                System.out.println("psclose");
            } catch (SQLException e) {
                e.printStackTrace();
                flage=false;
            }
        }
        if (connection != null) {
            try {
                connection.close();
                //GC回收
                connection=null;
                System.out.println("connectionclose");
            } catch (SQLException e) {
                e.printStackTrace();
                flage=false;
            }
        }
        return flage;
    }
}

结论

这种写法存在一个问题，没有考虑到事务的处理，将一些数据库链接的重要环节写死了,直接在方法中开启了数据库链接和预编译操作，不能进行手动开合，

    private static Connection connection=null;
    private static PreparedStatement preparedStatement=null;
    private static ResultSet resultSet=null;

推荐写法

public class BaseDao {

    private static String driver;
    private static String url;
    private static String userName;
    private static String password;

    static {
        Properties properties = new Properties();

        InputStream is = BaseDao.class.getClassLoader().getResourceAsStream("db.properties");

        try {
            properties.load(is);

            driver = properties.getProperty("driver");
            url = properties.getProperty("url");
            userName = properties.getProperty("username");
            password = properties.getProperty("password");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static Connection getConnection() {
        Connection con = null;
        try {
            Class.forName(driver);
            con = DriverManager.getConnection(url, userName, password);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return con;
    }

    public static ResultSet execute(Connection con, PreparedStatement ps, ResultSet rs, String sql, Object[] params) throws SQLException {
        ps = con.prepareStatement(sql);
        for (int i = 0; i < params.length; i++) {
            //setObject 占位符下标从1开始，我们数组是从0开始
            ps.setObject(i + 1, params[i]);
        }
        rs = ps.executeQuery();
        return rs;
    }

    public static int execute(Connection con, PreparedStatement ps, String sql, Object[] params) throws SQLException {
        ps = con.prepareStatement(sql);
        for (int i = 0; i < params.length; i++) {
            //setObject 占位符下标从1开始，我们数组是从0开始
            ps.setObject(i + 1, params[i]);
        }
        return ps.executeUpdate();
    }

    public static boolean closeResource(Connection con, PreparedStatement ps, ResultSet rs) {
        boolean closeFlag = true;
        if (rs != null) {
            try {
                rs.close();
                rs = null;
            } catch (SQLException e) {
                e.printStackTrace();
                closeFlag = false;
            }
        }
        if (ps != null) {
            try {
                ps.close();
                ps = null;
            } catch (SQLException e) {
                e.printStackTrace();
                closeFlag = false;
            }
        }
        if (con != null) {
            try {
                con.close();
                con = null;
            } catch (SQLException e) {
                e.printStackTrace();
                closeFlag = false;
            }
        }
        return closeFlag;
    }

    public static boolean closeResource(Connection con) {
        boolean closeFlag = true;
        if (con != null) {
            try {
                con.close();
                con = null;
            } catch (SQLException e) {
                e.printStackTrace();
                closeFlag = false;
            }
        }
        return closeFlag;
    }

    public static boolean closeResource(PreparedStatement ps, ResultSet rs) {
        boolean closeFlag = true;
        if (rs != null) {
            try {
                rs.close();
                rs = null;
            } catch (SQLException e) {
                e.printStackTrace();
                closeFlag = false;
            }
        }
        if (ps != null) {
            try {
                ps.close();
                ps = null;
            } catch (SQLException e) {
                e.printStackTrace();
                closeFlag = false;
            }
        }
        return closeFlag;
    }
}