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Load config file from a war

I have a Maven project that I'm trying to package as both a war and a jar. As part of my application / servlet initialisation (depending on whether I'm running the jar or the war), I need to read a file called server.ini. I've put the file in src/main/resources/server.ini and am trying to load it like so:
System.class.getResourceAsStream("server.ini");
However, this always results in null. What am I doing wrong?

The server.ini file should be in the root of a resources directory.
By placing it in the webapp you're making the file available via http, but you need it accessible on the classpath, which means that you should place it in the resources directory.

There's a good chance web.xml or context.xml is better suited to what you're trying to do, but...
Try putting server.ini in WEB-INF/classes, or do something like this.

The issue was that I was using the System classloader with an unqualified path, so it was expecting to find my server.ini in the java.lang package.
Since my file is in src/main/resources, I should just use the classloader of my current class, with an absolute path:
getClass().getResourceAsStream("/server.ini")
This works in both the war and the jar.
The "Preferred way of loading resources in Java" question has a great explanation of resource loading.

How to read a directory in webapp folder of Maven web application

I'm working in maven web application. I need to read a directory(For ex: Files) in my webapp folder as follows,
Java.io.File file = new Java.io.File("path");
But I don't know how to specify the path of the directory here.

You shouldn't give local path addresses. Path should be a relative address, e.g. /files/images under your web archive (.war) folder.
To use relative paths properly, I suggest you to add your target folder to the resources definiton of POM.xml, check out these pages
http://www.mkyong.com/maven/how-to-change-maven-resources-folder-location/
http://maven.apache.org/guides/introduction/introduction-to-the-standard-directory-layout.html
You can refer to resources folder easily with something like this:
this.class.getResource("Mydirectory/SubDirectory");

When in doubt how relatives paths work, it's always best to do something like that:
System.out.println(new File("/my/desired/directory").getAbsolutePath());
This will print out the path in which classpath will look for the files.
Assuming:
servlet container webapps dir is located in: /var/lib/tomcat6/webapps
your webapp is called my-webapp.war
You should see the following output: /var/lib/tomcat6/webapps/my-webapp/my/desired/directory
Another pointer: you have mentioned that you are looking for webapp directory. I hope you know that this directory will not end up in *.war - it's contents will.

War files are not always expanded when they are deployed to an app server, so it's possible that a relative path won't exist in a filesystem at all.
Best bets are to use getResource from the class loader, which will return things in the class path (the WEB-INF/lib directory, etc), or to use the getResource() method of ServletContext to find things in the web application itself.

How to change location of static file in WAR archive?

By default static files are located in WEB-INF directory (accessible as /images/logo.png):
foo.war
WEB-INF
web.xml
images
logo.png
I want to change the structure and use this one instead (still accessible as /images/logo.png):
foo.war
WEB-INF
web.xml
static
images
logo.png
How can I do this with web.xml?

The container will repsond with a 404 NOT FOUND error if you directly access the files under WEB-INF using HTTP GET .
But now , you said you can access WEB-INF/images/logo.png by /images/logo.png , so I think your web application most probably achieve this result by some URLRewriteFilter mechainsim or by some Java code in the servlet level (eg a filter) , or by your web application 's framework . I suggest you to check your web application to see what mechanism causes this behvaior now and configurate to your desired result accordingly.

According to http://java.sun.com/j2ee/tutorial/1_3-fcs/doc/WCC3.html,:
A WAR has a specific directory
structure. The top-level directory of
a WAR is the document root of the
application. The document root is
where JSP pages, client-side classes
and archives, and static Web resources
are stored.
The document root contains a
subdirectory called WEB-INF, which
contains the following files and
directories:
web.xml: The Web application
deployment descriptor Tag library
descriptor files (see Tag Library
Descriptors) classes: A directory
that contains server-side classes:
servlets, utility classes, and
JavaBeans components lib: A
directory that contains JAR archives
of libraries (tag libraries and any
utility libraries called by
server-side classes).
You can also create
application-specific subdirectories
(that is, package directories) in
either the document root or the
WEB-INF/classes directory.
So the default behavior is what you're looking for. Is your document root set incorrectly to serve content from WEB-INF?

You may use a filter or URLRewriteFilter to point /images/* to /static/images/*.
If you just want your folder structure to be /static/images for development time organization purposes, but the deployment URL to be /images -- you may need to alter your build script to copy /static/** to /.
I personally would not bother whether my static files are referred as /static/images or /images -- because they would be referred in my code (only), which I have control over.
If you are using these files in CSS and that's why you wanted the path to stay the same... better keep the images under /static/css/images and have the images that are referred in the CSS here. In this way, no matter where you move your CSS folder, you would not bother spoiling your CSS.

directory structure in Tomcat 5(s)

I was wondering if it was possible to maintain a directory structure within the application folder in side webapps folder, i.e. I have created a folder called ITC357, which acts as my application folder which carries all my files, so the directory path is as follows:
C:/Program Files/Tomcat5/webapps/ITC357
I'm doing an assignment and I would like to deploy that ITC357 in a separate folder can I do this? if so how?

It is not clear what you are asking:
If you asking if it is possible to have directories inside C:/Program Files/Tomcat5/webapps/ITC357 then the answer is "Yes".
If you are asking if it is possible to put your webapps file in a separate directory then the answer is "Inadvisable". The tomcat framework looks for certain files within the webapps/<name> tree; e.g. a context.xml file, a web.xml file, classes / JARs, etc. You could code your servlet to look for other things in other places, but this causes various problems with deployment (and undeployment) and security.
If that doesn't cover it, please clarify your question.

If you are writing JSPs, then the URL of the JSP will include any subdirectories that you create. So if under ITC357 you create a subdirectory called "foo", and in that subdirectory you have a JSP called "bar.jsp", and your context name is "plugh", then the URL of that JSP will be "http://whateverserver.com/plugh/foo/bar.jsp".
If you are using servlets, then it is up to your code to decide what to do with any URLs passed to it. You could map "http://whateverserver.com/plugh/foo/twisty.do" to "c:/program files/tomcat5/webapps/ITC357/WEB-INF/classes/foo/twisty.class", or you could map it to someplace totally different. (I prefer to map to a package name that matches the URL unless there's good reason to do otherwise.)

What's the purpose of META-INF?

In Java, you often see a META-INF folder containing some meta files. What is the purpose of this folder and what can I put there?

From the official JAR File Specification (link goes to the Java 7 version, but the text hasn't changed since at least v1.3):
The META-INF directory
The following files/directories in the META-INF directory are recognized and interpreted by the Java 2 Platform to configure applications, extensions, class loaders and services:
MANIFEST.MF
The manifest file that is used to define extension and package related data.
INDEX.LIST
This file is generated by the new "-i" option of the jar tool, which contains location information for packages defined in an application or extension. It is part of the JarIndex implementation and used by class loaders to speed up their class loading process.
x.SF
The signature file for the JAR file. 'x' stands for the base file name.
x.DSA
The signature block file associated with the signature file with the same base file name. This file stores the digital signature of the corresponding signature file.
services/
This directory stores all the service provider configuration files.
New since Java 9 implementing JEP 238 are multi-release JARs. One will see a sub folder versions. This is a feature which allows to package classes which are meant for different Java version in one jar.

Generally speaking, you should not put anything into META-INF yourself. Instead, you should rely upon whatever you use to package up your JAR. This is one of the areas where I think Ant really excels: specifying JAR file manifest attributes. It's very easy to say something like:
<jar ...>
<manifest>
<attribute name="Main-Class" value="MyApplication"/>
</manifest>
</jar>
At least, I think that's easy... :-)
The point is that META-INF should be considered an internal Java meta directory. Don't mess with it! Any files you want to include with your JAR should be placed in some other sub-directory or at the root of the JAR itself.

I've noticed that some Java libraries have started using META-INF as a directory in which to include configuration files that should be packaged and included in the CLASSPATH along with JARs. For example, Spring allows you to import XML Files that are on the classpath using:
<import resource="classpath:/META-INF/cxf/cxf.xml" />
<import resource="classpath:/META-INF/cxf/cxf-extensions-*.xml" />
In this example, I'm quoting straight out of the Apache CXF User Guide. On a project I worked on in which we had to allow multiple levels of configuration via Spring, we followed this convention and put our configuration files in META-INF.
When I reflect on this decision, I don't know what exactly would be wrong with simply including the configuration files in a specific Java package, rather than in META-INF. But it seems to be an emerging de facto standard; either that, or an emerging anti-pattern :-)

The META-INF folder is the home for the MANIFEST.MF file. This file contains meta data about the contents of the JAR. For example, there is an entry called Main-Class that specifies the name of the Java class with the static main() for executable JAR files.

META-INF in Maven
In Maven the META-INF folder is understood because of the Standard Directory Layout, which by name convention package your project resources within JARs: any directories or files placed within the ${basedir}/src/main/resources directory are packaged into your JAR with the exact same structure starting at the base of the JAR.
The Folder ${basedir}/src/main/resources/META-INF usually contains .properties files while in the jar contains a generated MANIFEST.MF, pom.properties, the pom.xml, among other files. Also frameworks like Spring use classpath:/META-INF/resources/ to serve web resources.
For more information see How do I add resources to my Maven Project.

You can also place static resources in there.
In example:
META-INF/resources/button.jpg
and get them in web3.0-container via
http://localhost/myapp/button.jpg
> Read more
The /META-INF/MANIFEST.MF has a special meaning:
If you run a jar using java -jar myjar.jar org.myserver.MyMainClass you can move the main class definition into the jar so you can shrink the call into java -jar myjar.jar.
You can define Metainformations to packages if you use java.lang.Package.getPackage("org.myserver").getImplementationTitle().
You can reference digital certificates you like to use in Applet/Webstart mode.

Adding to the information here, the META-INF is a special folder which the ClassLoader treats differently from other folders in the jar.
Elements nested inside the META-INF folder are not mixed with the elements outside of it.
Think of it like another root. From the Enumerator<URL> ClassLoader#getSystemResources(String path) method et al perspective:
When the given path starts with "META-INF", the method searches for resources that are nested inside the META-INF folders of all the jars in the class path.
When the given path doesn't start with "META-INF", the method searches for resources in all the other folders (outside the META-INF) of all the jars and directories in the class path.
If you know about another folder name that the getSystemResources method treats specially, please comment about it.

Just to add to the information here, in case of a WAR file, the META-INF/MANIFEST.MF file provides the developer a facility to initiate a deploy time check by the container which ensures that the container can find all the classes your application depends on. This ensures that in case you missed a JAR, you don't have to wait till your application blows at runtime to realize that it's missing.

I have been thinking about this issue recently. There really doesn't seem to be any restriction on use of META-INF. There are certain strictures, of course, about the necessity of putting the manifest there, but there don't appear to be any prohibitions about putting other stuff there.
Why is this the case?
The cxf case may be legit. Here's another place where this non-standard is recommended to get around a nasty bug in JBoss-ws that prevents server-side validation against the schema of a wsdl.
http://community.jboss.org/message/570377#570377
But there really don't seem to be any standards, any thou-shalt-nots. Usually these things are very rigorously defined, but for some reason, it seems there are no standards here. Odd. It seems like META-INF has become a catchall place for any needed configuration that can't easily be handled some other way.

If you're using JPA1, you might have to drop a persistence.xml file in there which specifies the name of a persistence-unit you might want to use. A persistence-unit provides a convenient way of specifying a set of metadata files, and classes, and jars that contain all classes to be persisted in a grouping.
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
// ...
EntityManagerFactory emf =
Persistence.createEntityManagerFactory(persistenceUnitName);
See more here:
http://www.datanucleus.org/products/datanucleus/jpa/emf.html

All answers are correct. Meta-inf has many purposes. In addition, here is an example about using tomcat container.
Go to
Tomcat Doc and check
" Standard Implementation > copyXML " attribute.
Description is below.
Set to true if you want a context XML descriptor embedded inside the application (located at /META-INF/context.xml) to be copied to the owning Host's xmlBase when the application is deployed. On subsequent starts, the copied context XML descriptor will be used in preference to any context XML descriptor embedded inside the application even if the descriptor embedded inside the application is more recent. The flag's value defaults to false. Note if the deployXML attribute of the owning Host is false or if the copyXML attribute of the owning Host is true, this attribute will have no effect.

You have MANIFEST.MF file inside your META-INF folder. You can define optional or external dependencies that you must have access to.
Example:
Consider you have deployed your app and your container(at run time) found out that your app requires a newer version of a library which is not inside lib folder, in that case if you have defined the optional newer version in MANIFEST.MF then your app will refer to dependency from there (and will not crash).
Source: Head First Jsp & Servlet

As an addition the META-INF folder is now also used for multi-release jars. This is a feature which allows to package classes which are meant for different Java version in one jar, e.g. include a class for Java 11 with new features offered by Java 11 in a jar also working for Java 8, where a different class for Java 8 with less features in contained. E.g this can be useful if a newer Java version is offering enhanced, different or new API methods which would not work in earlier version due to API violations. One will see a sub folder versions then.