首页
\
问答
\
为什么在包含Servlet和Java中的“worker”线程的web-app中使用ServletContext对象(Why use the ServletContext object in a web-app containing servlets and “worker” threads in Java)
为什么在包含Servlet和Java中的“worker”线程的web-app中使用ServletContext对象(Why use the ServletContext object in a web-app containing servlets and “worker” threads in Java)
我目前有一个Web应用程序，我有Servlet读取和写入
ServletContext属性，我有“工作”线程（守护进程线程），它们在启动时初始化并且当前保持为ServletContext对象的成员。 出于几个原因，我正在考虑转而使用“实现Runnable”，而且我很困惑这样一个事实，即我需要一个公共资源，servlet和非servlet可以用来相互交流，我觉得我有点卡在整个ServletContext范例中。 我会很感激，如果有人可以提供点为什么要使用ServletContext（我的方式或另一种方式），我也想只使用一个单身类，将在启动时初始化，将是线程安全的，我会只需通过它传递servlet和非servlet的所有通信。 你怎么看？谢谢
I currently have a web-app where I have Servlets reading and writing to the
ServletContextattributes and I have "working" Threads (Daemon threads) which get initialized on startup and currently hold as a member theServletContextobject. For a couple of reasons I'm thinking of moving to "implementRunnable" instead and I'm kind of stuck with the fact that I need a common resource that servlets and non-servlets can use to talk with each other and I feel I'm a bit stuck in the wholeServletContextparadigm. I'd appreciate it if someone could provide points on why to use theServletContext(my way or another way) and also I'm thinking to just use a singleton class which will be initialized on startup and will be thread safe and I'll just route all communication of the servlets and non-servlets through it. What do you think?Thanks
原文：https://stackoverflow.com/questions/1517420
更新时间：2023-12-21 16:12
最满意答案
select name, MIN(ID) from aCertainTable group by nameselect name, MIN(ID) from aCertainTable group by name
相关问答
更多-
select name, MIN(ID) from aCertainTable group by name select name, MIN(ID) from aCertainTable group by name
-
SELECT name, color FROM new_dogs EXCEPT SELECT name, color FROM name_color_pairs 要么 SELECT name, color FROM new_dogs nd WHERE NOT EXISTS (SELECT name, color FROM name_color_pairs ncp WHERE (ncp.name = nd.name) AND (ncp.color = nd.color)) 或者最后（应该到处工作）： SE ...
-
SELECT INTO查询(SELECT INTO query)[2022-11-13]
SELECT history_number = IDENTITY(INT,1,1), ... etc... INTO NewTable FROM ExistingTable WHERE ... 您可以使用ROW_NUMBER而不是身份，即ROW_NUMBER（）OVER（ORDER BY） SELECT history_number = IDENTITY(INT,1,1), ... etc... INTO NewTable FROM ExistingTable WHERE ... You ... -
我如何编写这个SQL查询？(How do I write this SQL query?)[2022-07-17]
这可以做到这一点： SELECT * FROM MyTable WHERE parentId = '001' AND childId = (SELECT MAX(childId) FROM MyTable WHERE parentId = '001') This aught to do it: SELECT * FROM MyTable WHERE parentId = '001' AND childId = (SELECT MAX(childId) FROM MyTable WHERE parentId ... -
使用subquery ： select * from table t where event_timestamp = (select max(event_timestamp) from table where event_name = t.event_name); 而且，一般来说最有效的方法是使用排名函数（如果支持） select * from ( select *, ...
-
需要帮助编写SQL查询？(Need help to write a SQL query?)[2021-09-22]
使用Arnold Fribble在这个帖子中回答的分割函数 Create FUNCTION dbo.Split (@sep char(1), @s varchar(512)) RETURNS table AS RETURN ( WITH Pieces(pn, start, stop) AS ( SELECT 1, 1, CHARINDEX(@sep, @s) UNION ALL SELECT pn + 1, stop + 1, CHARINDEX(@sep, @s ... -
您应该使用用于聚合的子查询来编写此查询： select p.*, c.car_brands, m.mobile_brands from person p left join (select c.person_id, array_agg(cd.car_brand) as car_brands from car_details c group by c.person_id ) c on c.person_id = p.id left join (s ...
-
多对多的选择查询(many to many select query)[2023-12-04]
这应该是相当接近你正在寻找 SELECT product.* FROM product JOIN ProductCategory ON ProductCategory.ProductID = Product.product_id JOIN #my_temp ON #my_temp.category_id = ProductCategory.CategoryID 编辑 正如在评论中指出的那样，这将产生出现在多个类别中的产品的重复。 若要更正此问题，请在列列表前指定DISTINCT 。 我已将所有 ... -
如何编写高效的sql查询来从多个表中进行选择？(How to write efficient sql query to select from multiple tables?)[2022-12-16]
尝试 select p.Title, stuff((select ', ' + i.ImageName from Images i where i.ListingID = p.ListingID for xml path('')),1,2,'') as Images, stuff((select ', ' + t.Tag from Tags t where t.ListingID = p.ListingID for xml path('')),1,2,'') as Tags from Listing p ... -
如果您尝试更新集合中的所有记录，则可以编写如下查询： UPDATE message_queue mq INNER JOIN ( SELECT NULL AS msg_id, NULL AS total, NULL AS found FROM dual WHERE ( @total :=0 OR @found :=0 ) UNION SELECT msg_id, @total AS total, @found :=1 ...