在Java（Servlet）中放置应用程序范围的设置？

Question

In ASP.NET, there is web.config which can hold application-wide settings. Is there a corresponding file (residing outside of the war or jar archive) for a Java EE Servlet?

What I need is some place to point out a configuration file, which currently holds four attributes which in turn, taken together, leads to the database where the rest of the data and configuration is stored. (Server, database, username and password.) These values need to be easy to change without repackaging and redeploying the entire application, hence the configuration file, but hardcoding the path to the configuration file in the application (even if it is as a constant) seems far from optimal.

Any hints? I've tried Google but found very little that seemed relevant - and what I did find appeared hideously over-engineered for my needs.

Answer 1

In ASP.NET, there is web.config which can hold application-wide settings. Is there a corresponding file (residing outside of the war or jar archive) for a Java EE Servlet?

That's the web.xml . You can define settings as <context-param> entries.

<context-param>
    <param-name>foo</param-name>
    <param-value>bar</param-value>
</context-param>

It's available by ServletContext#getInitParameter() . The ServletContext is in turn available anywhere.

String foo = getServletContext().getInitParameter("foo"); // Contains "bar"

You can also access it by EL.

#{initParam.foo} <!-- prints "bar" -->

What I need is some place to point out a configuration file, which currently holds four attributes which in turn, taken together, leads to the database where the rest of the data and configuration is stored. (Server, database, username and password.) These values need to be easy to change without repackaging and redeploying the entire application , hence the configuration file, but hardcoding the path to the configuration file in the application (even if it is as a constant) seems far from optimal.

As per the emphasis, I'd use a properties file for this particular purpose which is then placed in a path outside the WAR. You just need to add this path to the Java runtime classpath. Then you can obtain it as classpath resource:

Properties properties = new Properties();
properties.load(Thread.currentThread().getContextClassLoader().getResourceAsStream("filename.properties"));
// ...

However, with the particular sole purpose to serve a DB connection, you're indeed better off with a servletcontainer-managed datasource as answered by Qwerky. All you possibly would need to configure is then just the datasource name.

Answer 2

If this is a web app then you'd be better served configuring the database connection as a resource on the server, then getting your app to retrieve it using JNDI. Your app server will have documentation on how to do this, its a basic task.

99% of serious web apps do this, the other 1% should.

Answer 3

You can have your application load an arbitrary external file by simply passing the path as a command-line parameter (to the servlet container startup script). Then store the values in the ServletContext