DBUtils 学习笔记 , 简简单单了解,简简单单用用

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++++++++++++++++++++++++   DBUtils    +++++++++++++++++++++++++
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    DBUtils 框架是一款简化JDBC代码的强大工具  ,  底层依赖反射
//实体类创建尽可能用包装类,基本类型会和许多的库不兼容 ,如Redis.
    DBUtil在传入Javabean的时候,对象必须符合bean的封装要求
    DBUtil是根据无参构造方法实例化对象的...
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---->        gender.equals("")
---->         "".equals(gender)          二者相比

                                        前者更具有稳定性.

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 使用步骤:
        1/ 导入包
        2/ 使用其提供的工具类 , 创建 QueryRunner 对象
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            QueryRunner queryRunner = new QueryRunner();
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        3/ 通过工具类调用方法 ,实现CRUD操作
           a/ 创建工具类    ---->      笔记末尾提供工具类代码块儿
           b/ 测试CRUD操作
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                    //增加 :
            public void insertOne() throws SQLException {
                   queryRunner.update(connection , "INSERT INTO persons SET  name = '赵老三' ,idcard = '10003' , gender = '1' , address = '山东蓝翔'; ");
               }
                    //增加    传入对象数组..
           public static int  insertOneByObj(Object[] objects) throws SQLException {
                        return queryRunner.update(connection , "INSERT INTO persons SET  name = ? ,idcard = ? , gender = ? , address = ? ",objects);
               }
                    //更新
            public void updataOne() throws SQLException {
                  queryRunner.update(connection , "UPDATE persons SET `name` = 'updata' WHERE id =5; ");
              }
                    //查找:  DBUtil 返回一个封装好的map , 值得注意的值这里的第三个参数是 MapHandler  ==> 返回类型是map
            public void selectOne() throws SQLException {
                   Map map =queryRunner.query(connection,"SELECT * FROM persons WHERE id = 1;",new MapHandler());
               }
           }
                    //查找:   返回实体类               第三个参数是  BeanHandler   返回一个实体类型
            public void selectOne1() throws  Exception {
                  Persons persons  =queryRunner.query(connection,"SELECT * FROM persons WHERE id = 1;",new BeanHandler(Persons.class));
                   System.out.println(persons);
               }
                    //查找    返回实体类集合      第三个参数是  BeanListHandler   返回一个实体类型集合
            public void selectOnelist() throws  Exception {
                  List list = queryRunner.query(connection,"SELECT * FROM persons",new BeanListHandler(Persons.class));
              }
                     //查找    返回实体类集合      第三个参数是  MapListHandler   返回一个实体类型集合
            public void selectOnemap() throws  Exception {
                   List> list = queryRunner.query(connection,"SELECT * FROM persons",new MapListHandler());
               }
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            public class JdbcUtil {
                private static String driver = null;// 驱动

                private static String url = null;// 连接地址

                private static String username = null;// 用户名

                private static String password = null;// 密码

                static {
                    try {
                        Properties props = new Properties();
                        InputStream ins = JdbcUtil.class.getClassLoader().getResourceAsStream("database.properties");
                        props.load(ins);
                        driver = props.getProperty("jdbc.driverClassName");
                        url = props.getProperty("jdbc.url");
                        username = props.getProperty("jdbc.username");
                        password = props.getProperty("jdbc.password");
                        Class.forName(driver);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }


                /**
                 *
                 * Description: 获取数据库连接

                 */
                public static Connection getConnection() throws Exception {
                    return DriverManager.getConnection(url, username, password);// 硬编码
                }

                /**
                 * Description: 释放数据库资源

                 */
                public static void close(ResultSet rs, Statement st, Connection conn) throws Exception {
                    if (rs != null)
                        rs.close();
                    if (st != null)
                        st.close();
                    if (conn != null)
                        conn.close();
                }
            }
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