DBUtils常用方法

DBUtils是JDBC的簡化開發工具包，需要使用連接池，SQL語句。開發中常用的查詢方法使用 BeanListHandler、BeanHandler、ScalarHandler的情況較多，需要牢牢掌握。

public void queryById() {
        QueryRunner queryRunner = new QueryRunner(C3P0Utils.getDataSource());
        String sql = "select * from user where uid=?";
        Object[] params = { 6 };
        try {
            User user = queryRunner.query(sql, new BeanHandler<>(User.class), params);
            System.out.println(user);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

public void queryAll() {
        try {
            QueryRunner queryRunner = new QueryRunner(C3P0Utils.getDataSource());
            String sql = "select * from user";
            List<User> users = queryRunner.query(sql, new BeanListHandler<User>(User.class));
            users.stream().forEach(user -> System.out.println(user));
            List<Map<String, Object>> list = queryRunner.query(sql, new MapListHandler());
            list.stream().forEach(map->System.out.println(map));
            List<Object> query = queryRunner.query(sql, new ColumnListHandler("uname"));
            query.stream().forEach(obj->System.out.println(obj));
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }

public void testCount() {
        QueryRunner queryRunner = new QueryRunner(C3P0Utils.getDataSource());
        String sql = "select count(*) from user";
        try {
            long count = (long) queryRunner.query(sql, new ScalarHandler());
            System.out.println(count);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }