I just learned that I could retrieve parameters and other stuff from "ServletContext" (i.e. by overriding contextInitialized).
Reading tomcats context doc reveals that I could set parameters via web.xml (used as default values) and then overwrite them with an [context].xml file.
First question: is this a good way to set default properties and let server administrators overwrite them?
First is there an overview that shows all kinds of attributes/parameters that are available with it's tag used in tomcats context xml, the tag used in web xml, how the retrieve it from within java and a use case / example for what kind of stuff a parameter should be used?
By toying around with it I am facing the following problem: If I deploy the web app via tomcats web interface the [context].xml is completly ignored (console states that it is deployed but 2nd is null)
To cut a long story short: how to properly use web.xml and [context].xml - the link below isn't much help.
Well first off, declaring (servlet/application) context attributes via web.xml is better, as this is the official Java EE supported way, so if you declare them like this they will work when you deploy your app in other App Servers other than Tomcat.
Second, I believe the Tomcat rule for overriding param values is:
if you have a $CATALINA_BASE/conf/context.xml and you have the same attribute declared in it and in web.xml, the one in web.xml will have priority
if you have a $CATALINA_BASE/conf/context.xml as well as a context.xml file inside your application (in the META-INF directory) both with the same parameter, the one in the META-INF/context.xml will have priority.
Finally, if you have all three files decalring the same parameter, the one in the web.xml will have priority.
Related
There's a web application and a number of environments in which it works. In each environment it has different settings like DB connection and SOAP ends-points that in their turn are defined in properties-files and accessed in the following way:
config.load(AppProp.class.getClassLoader().getResourceAsStream(
PROPERTIES_FILE_PATH + PROPERTIES_FILE_NAME));
Thus the WAR-files are different for every environment.
What we need is to build a unified WAR-file that doesn't contain any configuration and works in any environment (for now, Tomcat instance) getting its configuration from outside its WAR-file.
The answer Java Web Application Configuration Patterns, to my mind, gives the full set of common approaches but with just few examples. The most attractive way is configuring JNDI lookup mechanism. As I can guess it allows to separately configure web-applications by their context paths. But couldn't find a simple (step-by-step) instructions in both the Internet and the Tomcat's docs. Unfortunately cannot spend much time on studying this complicated stuff in order to just meet so seemingly simple and natural demand :(
Would appreciate your links at the relevant descriptions or any alternative suggestion on the problem.
If its a case of simply deploying your WAR on different environment (executed by different OS user), then you can put all your config files in the user's home folder and load them as:
config.load(new FileInputStream(System.getProperty("user.home") + PROPERTIES_FILE_NAME));
This gives you the isolation and security and makes your WAR completely portable. Ideally though, you should still provide built-in default configuration if that makes sense in your case.
The approach we've taken is based on our existing deployment method, namely to put the WAR files in the filesystem next to the Tomcat, and deploy a context.xml pointing to the WAR file to Tomcat.
The context descriptor allows for providing init parameters which is easily accessible in a servlet. We've also done some work on making this work with CDI (for Glassfish and TomEE dependency injection).
If you only have a single WAR file deployed to this Tomcat instance, you can also add init parameters to the default global context XML. These will be global and you can then deploy the WAR file directly. This is very useful during development.
I have a webservice that uses Java, REST, Jersey and runs on Tomcat8. The webservice requires access to a database. Depending on where we are in the process the we may be using a testdatabase, production database or something else. Ideally we would like to be able to set which database to use without requiring a code change and recompile.
The approach we have tried is to have a properties file defining the database parameters and use an environment variable to point to the file. This has proved troublesome, first we've had a hard time defining system properties on the Tomcat server that we can read from the application, also it seems like all the files will have to be defined on the classpath, i.e already configured ahead of time and part of the codebase.
This seems like fairly common scenario, so I'm sure there is a recommended way to handle situations like this?
Zack Macomber has a point here. Don't enable your app/service to look up its settings dynamically.
Make your build process dynamic instead.
Maven, Gradle and friends all provide simple ways to modify output depending on build parameters and or tasks/profiles.
In your code always link to the same file (name). The actual file will then be included based on your task and/or build environment. Test config for tests. Production config for production.
In many cases a complete recompilation is not necessary and will therefore be skipped (this depends on your tool, of course).
No code changes at all. Moreover the code will be dumb as hell as it does not need to know anything about context.
Especially when working on something with multiple people this approach provides the most stable long-term-solution. Customizable for those who need some special, local config and most important transparent for all who don't need or don't want to know about runtime environment requirements!
We have a similar case. We have created a second web service on the same endpoint (/admin) which we call to set a few configuration parameters. We also have a DB for persisting the configuration once set. To make life easier, we also created a simple UI to set these values. The user configures the values in the UI, the UI calls the /admin web service, and the /admin service sets the configuration in memory (as properties) as well as in the DB. The main web service uses the properties as dynamic configuration.
Note: we use JWT based authorization to prevent unauthorized access to /admin. But depending upon your need you can keep it unsecure, use basic HTTP auth or go with something more detailed.
Not sure if in this particular case it is wise, but it is possible indeed to create a .properties file anywhere on the filesystem - and link it into your application by means of a Resources element.
https://tomcat.apache.org/tomcat-8.0-doc/config/resources.html
The Resources element represents all the resources available to the web application. This includes classes, JAR files, HTML, JSPs and any other files that contribute to the web application. Implementations are provided to use directories, JAR files and WARs as the source of these resources and the resources implementation may be extended to provide support for files stored in other forms such as in a database or a versioned repository.
You would need a PreResources element here, linking to a folder, the contents of which will be made available to the application at /WEB-INF/classes.
<Context antiResourceLocking="false" privileged="true" docBase="${catalina.home}/webapps/myapp">
<Resources className="org.apache.catalina.webresources.StandardRoot">
<!-- external res folder (contains settings.properties) -->
<PreResources className="org.apache.catalina.webresources.DirResourceSet"
base="/home/whatever/path/config/"
webAppMount="/WEB-INF/classes" />
</Resources>
</Context>
Your application now 'sees' the files in /home/whatever/path/config/ as if they were located at /WEB-INF/classes.
Typically, the Resources element is put inside a Context element. The Context element must be put in a file located at:
$CATALINA_BASE/conf/[enginename]/[hostname]/ROOT.xml
See https://tomcat.apache.org/tomcat-8.0-doc/config/context.html#Defining_a_context
I got a situation that I must serve files from different folders then the one of the context my web app is running. As an example, suppose my web app is running in a servlet context on "/opt/tomcat/webapps/ROOT/" and I must serve files existent in "/opt/my_other_folder/". These folders can be changed in runtime by the client, so I can't simply add a new context pointing to these directories. I would like a solution that I wouldn't have to rewrite a web server only for that. Also, the product I work on is generic, so I can't have a solution specific to some servlet container.
Thanks!
If you're only serving files, I would consider fronting your servlet container with something like Apache HTTP Server, where you could simply use its various directives to provide a "virtual directory" pointing to an easily configured location.
Otherwise, you could write and configure a standard Java servlet that would do essentially the same thing - storing the actual path in a Java properties file that would be read by the servlet. But while this isn't a lot of work, it would be significantly more work that the above Apache HTTP Server solution. This would be very similar to several of the answers posted at Servlet for serving static content . Specifically, you could either use or extend upon Apache Tomcat's DefaultServlet. (There are some Tomcat-specific classes used in here, but they could be easily replaced with generic equivalents.) http://balusc.blogspot.com/2009/02/fileservlet-supporting-resume-and.html looks even closer to what you'd be looking for, and it is completely generic - while still having some additional, significant features.
Either of these options would be very generic, and not specific to any particular servlet container.
I am trying to figure out what the following url does.
http://server/abc/testmodule/runtest.do?action=edit&id=123
I am new to jboss/jsp but I am very familiar with .net.
When I see this url, I expect to see the physical folder called "abc" and subfolder called "testmodule" and a physical file "runtest". am i wrong? what does runtest.do? is "runtest" class and "do" is a method within it?
It could be anything--URLs can map to arbitrary resources. It might be a Struts action, it might be a servlet, it might be a Spring controller, etc.
You'd need to check your web.xml file and/or any framework configuration files, or provide more information.
(Also, JBoss isn't a framework, it's a Java EE container :)
The /abc entry is the name of the context in which the application is running. If it's a web app, deployed in a WAR file, that would be the name of the WAR that's deployed (abc.war).
The .do extension suggests a Struts or JSF action mapping.
There are two parameters passed in the GET: action, with value edit, and id, with value 123. Looks like a REST-ful API to me.
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.
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.
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.
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