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Java web project, property file not updated properly and missed some position in the loop [duplicate]

In my web application I have to send email to set of predefined users like finance#xyz.example, so I wish to add that to a .properties file and access it when required. Is this a correct procedure, if so then where should I place this file? I am using Netbeans IDE which is having two separate folders for source and JSP files.

It's your choice. There are basically three ways in a Java web application archive (WAR):
1. Put it in classpath
So that you can load it by ClassLoader#getResourceAsStream() with a classpath-relative path:
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
InputStream input = classLoader.getResourceAsStream("foo.properties");
// ...
Properties properties = new Properties();
properties.load(input);
Here foo.properties is supposed to be placed in one of the roots which are covered by the default classpath of a webapp, e.g. webapp's /WEB-INF/lib and /WEB-INF/classes, server's /lib, or JDK/JRE's /lib. If the propertiesfile is webapp-specific, best is to place it in /WEB-INF/classes. If you're developing a standard WAR project in an IDE, drop it in src folder (the project's source folder). If you're using a Maven project, drop it in /main/resources folder.
You can alternatively also put it somewhere outside the default classpath and add its path to the classpath of the appserver. In for example Tomcat you can configure it as shared.loader property of Tomcat/conf/catalina.properties.
If you have placed the foo.properties it in a Java package structure like com.example, then you need to load it as below
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
InputStream input = classLoader.getResourceAsStream("com/example/foo.properties");
// ...
Note that this path of a context class loader should not start with a /. Only when you're using a "relative" class loader such as SomeClass.class.getClassLoader(), then you indeed need to start it with a /.
ClassLoader classLoader = getClass().getClassLoader();
InputStream input = classLoader.getResourceAsStream("/com/example/foo.properties");
// ...
However, the visibility of the properties file depends then on the class loader in question. It's only visible to the same class loader as the one which loaded the class. So, if the class is loaded by e.g. server common classloader instead of webapp classloader, and the properties file is inside webapp itself, then it's invisible. The context class loader is your safest bet so you can place the properties file "everywhere" in the classpath and/or you intend to be able to override a server-provided one from the webapp on.
2. Put it in webcontent
So that you can load it by ServletContext#getResourceAsStream() with a webcontent-relative path:
InputStream input = getServletContext().getResourceAsStream("/WEB-INF/foo.properties");
// ...
Note that I have demonstrated to place the file in /WEB-INF folder, otherwise it would have been public accessible by any webbrowser. Also note that the ServletContext is in any HttpServlet class just accessible by the inherited GenericServlet#getServletContext() and in Filter by FilterConfig#getServletContext(). In case you're not in a servlet class, it's usually just injectable via #Inject.
3. Put it in local disk file system
So that you can load it the usual java.io way with an absolute local disk file system path:
InputStream input = new FileInputStream("/absolute/path/to/foo.properties");
// ...
Note the importance of using an absolute path. Relative local disk file system paths are an absolute no-go in a Java EE web application. See also the first "See also" link below.
Which to choose?
Just weigh the advantages/disadvantages in your own opinion of maintainability.
If the properties files are "static" and never needs to change during runtime, then you could keep them in the WAR.
If you prefer being able to edit properties files from outside the web application without the need to rebuild and redeploy the WAR every time, then put it in the classpath outside the project (if necessary add the directory to the classpath).
If you prefer being able to edit properties files programmatically from inside the web application using Properties#store() method, put it outside the web application. As the Properties#store() requires a Writer, you can't go around using a disk file system path. That path can in turn be passed to the web application as a VM argument or system property. As a precaution, never use getRealPath(). All changes in deploy folder will get lost on a redeploy for the simple reason that the changes are not reflected back in original WAR file.
See also:
getResourceAsStream() vs FileInputStream
Adding a directory to tomcat classpath
Accessing properties file in a JSF application programmatically

Word of warning: if you put config files in your WEB-INF/classes folder, and your IDE, say Eclipse, does a clean/rebuild, it will nuke your conf files unless they were in the Java source directory. BalusC's great answer alludes to that in option 1 but I wanted to add emphasis.
I learned the hard way that if you "copy" a web project in Eclipse, it does a clean/rebuild from any source folders. In my case I had added a "linked source dir" from our POJO java library, it would compile to the WEB-INF/classes folder. Doing a clean/rebuild in that project (not the web app project) caused the same problem.
I thought about putting my confs in the POJO src folder, but these confs are all for 3rd party libs (like Quartz or URLRewrite) that are in the WEB-INF/lib folder, so that didn't make sense. I plan to test putting it in the web projects "src" folder when i get around to it, but that folder is currently empty and having conf files in it seems inelegant.
So I vote for putting conf files in WEB-INF/commonConfFolder/filename.properties, next to the classes folder, which is Balus option 2.

Ex: In web.xml file the tag
<context-param>
<param-name>chatpropertyfile</param-name>
<!-- Name of the chat properties file. It contains the name and description of rooms.-->
<param-value>chat.properties</param-value>
</context-param>
And chat.properties you can declare your properties like this
For Ex :
Jsp = Discussion about JSP can be made here.
Java = Talk about java and related technologies like J2EE.
ASP = Discuss about Active Server Pages related technologies like VBScript and JScript etc.
Web_Designing = Any discussion related to HTML, JavaScript, DHTML etc.
StartUp = Startup chat room. Chatter is added to this after he logs in.

It just needs to be in the classpath (aka make sure it ends up under /WEB-INF/classes in the .war as part of the build).

You can you with your source folder so whenever you build, those files are automatically copied to the classes directory.
Instead of using properties file, use XML file.
If the data is too small, you can even use web.xml for accessing the properties.
Please note that any of these approach will require app server restart for changes to be reflected.

Assume your code is looking for the file say app.properties. Copy this file to any dir and add this dir to classpath, by creating a setenv.sh in the bin dir of tomcat.
In your setenv.sh of tomcat( if this file is not existing, create one , tomcat will load this setenv.sh file.
#!/bin/sh
CLASSPATH="$CLASSPATH:/home/user/config_my_prod/"
You should not have your properties files in ./webapps//WEB-INF/classes/app.properties
Tomcat class loader will override the with the one from WEB-INF/classes/
A good read:
https://tomcat.apache.org/tomcat-8.0-doc/class-loader-howto.html

What's Thymeleaf "prefix" relative to?

I'm just starting using Thymeleaf and I'm trying to understand the setPrefix() method in the template resolver. There are cases that I understand, like setPrefix("classpath:/com/package") or setPrefix("file:folder") (relative to working directory).
But I still don't understand what, for example, setPrefix("/views/") refers to. Where Thymeleaf expects the views folder to be? Does the / at the beginning means that is an absolute path? If so, where's the 'root'?
Does it depends of the specific TemplateResolver? In my instance, I'm using the SpringResourceTemplateResolver.

If you are using SpringResourceTemplateResolver, the prefix is relative to the root of the war file (or the web-app base directory when unpacked).
When using Maven as build system, the source folder for this is src/main/webapp. For example, if you setPrefix("/views/") your templates should be put in src/main/webapp/views/.
Hint: Use WEB-INF directory to protect from end-users retrieving the templates directly.

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.