Web 应用程序无法建立与数据库的连接

Question

My application, when running on Tomcat, is not able to connect to my database when deployed as a.war in the webapps folder, but it can connect when I am running it through Eclipse directly. The code is exactly the same in both cases. In addition, other apps in the webapps folder, which originally could connect to the database, can no longer do so. The jdbc code is correct as I have tested it with offline applications or when running it through eclipse, but not when I access it on, say, Chrome, using localhost. What has happened to my tomcat server?

Note: the JDBC driver is the MS Access one.

Answer 1

The code is exactly the same in both cases.

No it's not; if it were exactly the same you'd be connecting properly.

but it can connect when I am running it through Eclipse directly

Does this mean that you have a main method that drives the code that connects properly? The way you do it is usually different from a web app - you know that, right?

If you could post an exception or log message it would help a great deal.

I'm guessing it could be any one of the following; guessing is necessary because you haven't provided enough information for a solid answer:

1. The JDBC driver JAR is not available when you run under one configuration; you'll see a ClassNotFoundException in that case.
2. You haven't configured a JNDI data source properly in Tomcat.
3. You didn't put the JDBC driver JAR in the Tomcat /lib directory.

Could be other possibilities.

UPDATE:

Since you're using Access, and providing no other information, I'm guessing that you're using a relative file path to get to the Access .mdb file. Your command line app that runs successfully in Eclipse works because you give a relative file path that is correct relative to the project root. When you deploy to Tomcat, that relative path is no longer correct, so your application can't find the database anymore.

Sounds like you aren't printing the stack trace for errors, so you're losing out on information that might help you figure this out.

Microsoft Access is not a multi-user database. A web based application running on Tomcat is certainly multi-threaded. You should not be using Access for a web application. I'd consider switching to another database.

Answer 2

First, you need to verify the path to your database file. In fact, I believe it has to be an absolute path for tomcat to work correctly. The simplest thing to do is to put your database file in C:\data or similar and then hard code the path in your code. Of course, the file will be outside of your war and thus not portable (ie, deployable to a remote server).

Second, you do need to make sure that the JDBC driver is available. If you use Class.forName in your code to load the driver, you will only need to make sure that the jar containing the driver is in the tomcat classpath (which would include the lib directory of your webapp). If you use the -Djdbc.drivers JVM flag approach, you will need to add it to the tomcat startup scripts.