问题
For the past couple of days, every time I try to run my web application, Error - 503 has been showing up. This happens even when I try to go to the admin page. Is this a problem with Google?
回答1:
It's important when creating a GAE project that any .class that extends HttpServlet and are used as entry point to your Google App are mapped in web.xml found in war/WEB-INF as pictured below.
Java Servlets you create that extend HttpServlet must be mapped in the web.xml like the following:-
In this Test GAE project ecipse generated sample code that created a Java Servlet called TestServlet.class that extends HttpServlet and is appropriately mapped.
To run your app you need to include the url mapped to the TestServlet.class found in the web.xml (In this case /test) in your index.html. (In the case of generated project sample code created by eclipse this will already have been done).
Once your Java Servlets are correctly mapped in the web.xml and included in your index.html the mapped url that is clicked will invoke the appropriate Servlet and run your app.
This will eliminate common 503 errors in terms of new project setup.
来源：https://stackoverflow.com/questions/9347725/google-app-engine-error-503-service-unavailable