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Java EE容器不允许使用Java SE conccurency API(Java EE containers don't allow using Java SE conccurency API)

 在Arun Gupta“Java EE 7 Essentials”一书中，我发现了这个：  
 诸如EJB或Web容器之类的Java EE容器不允许直接使用常见的Java SE并发API，例如java.util.concurrent.ThreadPoolExecutor，java.lang.Thread或java.util.Timer。  
 什么意思是“不允许”？ 我不明白容器如何禁止我创建新线程或使用标准的ExecutorService。 我的标准线程会发生什么？ 任何人都可以解释这些吗？  
 一些评论。 我理解为什么使用ManagedExecutorService而不是ExecutorService可以提高效率，我不明白如果我使用SE会出现什么问题 

In the book of Arun Gupta "Java EE 7 Essentials" I found this: 
Java EE containers such as the EJB or web container do not allow using common Java SE concurrency APIs such as java.util.concurrent.ThreadPoolExecutor, java.lang.Thread, or java.util.Timer directly. 
What does mean "do not allow"? I don't understand how container can forbid me create new thread or use standard ExecutorService. What will happen with my standard threads? Can anybody explain these? 
Some remark. I understand why use ManagedExecutorService instead of ExecutorService for example can be mor efficient, I don't understand what problems can occur if I'll use SE

原文：https://stackoverflow.com/questions/34514750

更新时间：2023-05-06 15:05

最满意答案

 你非常接近 - 但由于<emailTo>是一个元素 （不是属性），你需要使用：  
select 
T.id, 
T.xml_data.value('(SSRSReport/email/emailTo)[1]', 'varchar(50)') as PropertyName 
 
 使用/emailTo （不是/@emailTo ）作为XPath表达式的最后一部分。  
 此外， .exist()函数只能检查是否存在XML元素（或属性），因此您可以检查<emailTo>元素是否存在（或不存在），但是您无法与值进行比较。 所以你的WHERE子句无效 - 你可能想要：  
where 
   T.xml_data.value('(SSRSReport/email/emailTo)[1]', 'varchar(50)') = 'xyz.com' 

You're pretty close - but since <emailTo> is an element (not an attribute), you need to use: 
select 
T.id, 
T.xml_data.value('(SSRSReport/email/emailTo)[1]', 'varchar(50)') as PropertyName 
 
Use /emailTo (not /@emailTo) as the last part of your XPath expression. 
Also, the .exist() function can only check for the presence of a XML element (or attribute), so you could check to see if a <emailTo> element exists (or does not exist), but you cannot compare to a value. So your WHERE clause is invalid - you probably wanted: 
where 
   T.xml_data.value('(SSRSReport/email/emailTo)[1]', 'varchar(50)') = 'xyz.com'

Java EE容器不允许使用Java SE conccurency API(Java EE containers don't allow using Java SE conccurency API)

最满意答案

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