Google Application Engine開發筆記

GAE (1.7.4):

1. 取得上傳日期

String applicationVersion = SystemProperty.applicationVersion.get();
Date uploadDate = new Date(Long.parseLong(applicationVersion.substring(applicationVersion.lastIndexOf(‌​".")+1))/ (2 << 27) * 1000);

Ref: SystemProperty

JPA 2

限制：

1. Simple Join
2. Entity Group Transaction
   An entity’s parent, parent’s parent, and so on recursively, are its ancestors; its children, children’s children, and so on, are its descendants. An entity and its descendants are said to belong to the same **entity group**_._
   一般我們常常在一個transaction內大量修改同一類型物件，例如修改多個User的資料，這就算 Cross Group Transaction操作，最多不能超過5個entity group。

參考資料：

• Google App Engine JPA test case
• simple join works on unowned one-to-many relationship.
• limitation: Problem with query : Joins can only be sorted by the join column in ascending order (in this case
  ‘attendeeList’)
• 開發GAE會遇到的問題

Maven

若使用JPA，datanucleus plugin 的設定官方文件未提及，不方便，很容易跟project 依賴的版本不合。我參考
http://www.loop81.com/2013/02/gae-google-app-engine-jpa2-maven-and.html
https://code.google.com/p/datanucleus-appengine/source/browse/trunk/pom.xml
https://code.google.com/p/datanucleus-appengine/wiki/Compatibility
使用 GAE Maven plugin時，在eclipse debug mode下執行時
http://stackoverflow.com/questions/13924990/how-do-i-make-eclipse-and-mvn-appenginedevserver-talk-to-each-other

Jersey (1.18)

• NoClassDefFoundError: misc.sun.Unsafe on Google App Engine Jerset 2.x 因有已知的bug無法run 在GAE 上，
• java.lang.IncompatibleClassChangeError: Implementing class
  因為Jersey 1.18依賴 asm 3.1, 但GAE倚賴asm 4所造成。
  有兩個解決辦法：
  
  1. 改用asm 3
  2. 寫一個class 繼承javax.ws.rs.core.Application 去指定annotated class