We're refactoring our app to allow for multiple database support, mainly MySQL (current) and MongoDB (in dev). For MySQL we have to shade in tomcat jdbc pool code, and for Mongo we shade in the java driver. I need to produce two builds - one for MySQL, one for Mongo.
I'm trying to find a way to do this with maven - only shade tomcat-jdbc or mongo and some internal code needed for that database system. However, I'm not seeing much in the way of multiple builds and have seen several SO answers advising not to use it.
I've also considered separating the database code into different projects entirely - so we can provide the product, and a second jar with either mysql, or mongo code. It's a bit messier for end users, but cleaner for us.
Suggestions?
There is a very important rule in maven (or any other dependency management system):
Different results should always have different coordinates,
or the other way round:
Building from the same sourcecode state should always result in the same artifact, regardless of profiles or target systems.
So, if you want to produce two different results, you need them to have different coordinates. Your two options are:
a) one project creating different classifiers (which is ugly but workable)
b) or create two submodules myproject-mysql and myproject-mongodb (which in turn shade your main code and the respective db-code) (different artifactIds)
There is nothing against shading to create a complete jar, in your case just create two separate jars, which are fully workable by themselves.
Related
While creating a new web application using spring-boot, I wondered about a philosophical question: is the best practice to have only one maven module (and so one jar) for both server-side app and static web content of the client (to generate another jar, maybe?), or is it better to have one maven module for server and another one for client-side?
In other words, is it better to have this maven architecture:
MyProject-parent
- MyProject
or this one ?
MyProject-parent
- MyProject-server
- MyProject-html-client
- MyProject-mobile-client
- ...
As I would like to have a browser client and a mobile one, I would be tempted to say it's a good idea to have separate modules. However, using Spring-boot, it's possible to generate a fat jar, i.e. a jar containing all the other ones. As a consequence, the recommended architecture is, I suppose, only one maven module.
So is there a "better" solution? If yes, can you give me arguments?
I'd prefer the multi module approach for the following reasons:
The project is gonna grow and it gets better organized this way,
which means it would be easier to maintain in future and if you break
the modules properly in the beginning, you are not gonna have to lose
time to refactor and split it into different modules later.
It's better "layered”
It's better for bug fix or make new functionalities, since you can
focus on only one module and run the test only for that one.
As you are using Maven, it helps a lot with the dependencies, you can
build it all with one single maven command and it takes care of the
build order. So I can't see any advantage of using single module for
your case.
You might need to release MyProject-mobile-client without releasing
MyProject-html-client any time in future in case you are planning to
use maven release.
My question is really simple, thought I haven't found anything online related to it.
Is the maven-surefire-plugin able to have a dependency excluded but at class level and not at group-id:artifact-id level?
My problem:
I have a web project, related to a plain java project A. This A project contains hundred of classes that do a variety of things (connects to the database, sends web services, calculates stuff, manages the logs, context, sessions, etc...) and the dependency is quite strong. Since all unit testing on the web project will be hard to do without this A project I need to have it as a dependency even for the testing. But of course I cannot use some of the classes in there (mainly the DB connection and the session stuff). So I thought that instead of mocking them (because there are like a few dozens of them and I want to do different things with the functions (like writing to a file that it tried to connect or read the "session" from an xml file)) I can create a A-test project and include the classes I want from this new project and exclude the classes I don't need from the A project.
I know I can copy/paste all the project and then replace the classes I want, but if something changes in project A, I then have to maintain it in A-test (and I am very lazy and don't like to work twice). I thought that maybe I could have some kind of plugin in maven that will copy all the other classes (the one I am not... let say 'overriding'), every time. But it seems a waste of time if I just can tell the plugin which classes to use during the test step.
Thanks for your help!
We currently have two separate databases/schemas for our application. We have run into data inconsistencies with this setup, so we either need a transaction spanning both databases or to merge the databases. We don't want to use JTA transactions, since we are using a normal Tomcat. So our approach would be to merge the two databases/schemas into one.
Both databases/schemas are currently managed via Liquibase and we would like to maintain two separate ChangeLogs, since one set of entities is from a thirdparty tool and the other set is managed by us. We don't have any name conflicts, other than that liquibase uses its default tablenames.
So my question is, is using the liquibase.databaseChangeLogTableName and liquibase.databaseChangeLogLockTableName properties to define different tablenames for liquibase the best approach for this scenario?
http://forum.liquibase.org/topic/configurable-databasechangelog-table-name
That does look like a reasonable approach - you would have to make sure that when you ran any liquibase commands that you always used the correct liquibase.databaseChangeLogTableName and liquibase.databaseChangeLogLockTableName with the corresponding changelog.
I have some years of experience with maven projects, even with multi modules ones (which has made me hate the multi modules feature of maven (so the disclaimer is now done)) and even if I really like maven there is something I cannot get a clear answer about :
What is a typical usecase of a multi module maven project ? What is the added value of such a structure compared to simple dependencies and parent pom ?
I have seen a lot of configuration of multi module projects but all of them could have clearly been addressed by creating a simple structure of dependency library living their own life as deliverables (even with a parent pom, as a separate deliverable : factorising depedencies and configuration) and I haven't found any usecase where I can clearly see an added value of the multi module structure.
I have always found that this kind of structure brings an overkilling complexity with no real benefit : where am I missing something ? (to be truly honest, I can get that some ear can benefit from this kind of structure but except from that particular usecase, any other real use and benefit ?)
Here's a real life case.
I have a multi-module project (and to your rant... I haven't seen any complications with it.) The end result is a webapp but I have different modules for api, impl, and webapp.
12 months after creating the project I find that I have to integrate with Amazon S3 using a stand-alone process run from a jar. I add a new module which depends on api/impl and write my code for the integration in the new module. I use the assembly plugin (or something like it) to create a runnable jar and now I have a war I can deploy in tomcat and a process I can deploy on another server. I have no web classes in my S3 integration process and I have no Amazon dependencies in my webapp but I can share all the stuff in api and impl.
3 months after that we decide to create a REST webapp. We want to do it as a separate app instead of just new URL mappings in the existing webapp. Simple. One more module, another webapp created as the result of the maven build with no special tinkering. Business logic is shared easily between webapp and rest-webapp and I can deploy them as needed.
The major benefit of multi modules are
one single maven command to build all your modules at once.
and the most important : maven take care of the build order for you.
configuring your CI-server is also very easy: one single jenkins job to build everything.
I already worked in a project with about 30 submodules. Sometimes, you need to change something in more than module, and running one single command and being sure that everything that need to be compiled is compiled in the correct order is a must.
EDIT
Why 30 submodules ?
Huge framework with lot's a features, lot's of developers, separation of features on a module base. It's a real life use case and the separation of the code into module was really meaningful.
I think you are correct in that most project that use multi modules, actually don't need them.
At where I work we use multimodule projects (and I think that for a good reason). We have something similar to a service oriented architecture, so each application
A client module
An interface module (which has shared objects between the client and implementation)
an implementation module
a war module
I agree that putting that implementation and war module in the same actual module would be ok, but the (arguably) benefit of this is that is very clear division between the classes that solve the problem and how the application communicates with the external world.
In previous projects that involved just a web application, I've tried to put everything in the same module, as it made testing easier, given the modules I was using.
Multi modules can help you with re-use your code.
It's one of the best benefits you'll feel in work.
Imagine if you have 3 web projects with a security layer, You'll have to copy paste your code 3 times and trying connect it with each project.
But what if you create a security module a project with a specific job.
It'll be easy to use it by injecting it to your app and then boom it works.
Also as mentioned in #ben75's answer the one maven build command and the correct order of building all your used jars. You'll think no more about which depends on another.
I find maven modules extremely useful for the following reasons:
Architecture layering and boundaries
For example, I make a maven module application-contract which contains the interfaces my presentation layer sees. So I have UI->Presenter-> application-contract <-application-impl <- infrastructure -> domain. This way, I know that my presentation/UI layer will not have access to classes from my Domain/application layers. If domain classes are not in classpath when I code in UI, I cant use them. And I like it this way (utilizing the class path restrictions). Perhaps Java 9 modules can solve this problem too, but (unfortunately) I have work with Java 8.
Running tests in one module each time
When I change code to a layer which is a module (as mentioned previously) I can run its tests only, without re-runing tests from code I did not change. This gives me speed. My presentation layer tests need ~3 seconds (for 300 tests). Every time I change code to a Presenter or whatever below application layer, I don't want my database H2 integration tests to run. Or My Image processing tests to run. Because these do IO and they are slow.
Building
Pretty much the same thing. When I change code to UI, i have only to build and deploy UI stuff (my UI is in Java).
More of a standard practice questions:
Is there any difference in deploying an app as EAR vs WAR? How do you decide? (I know WAR is just a web application may or may not have Java EE features like messaging)
Lets say I have a Spring MVC application stack with Hibernate (MySQL DB), should this be deployed as a War or EAR?
When do we need to worry about JBoss deployment descriptors, if I am not using EJBs. (Just Spring MVC). Lets assume I have JMS as well. Do we need to configure/update/create any other JBoss related config files?
When we package our application EAR/WAR, it include EVERYTHING that we need for our app. Is there a scenario where we need to keep some config / xml files outside of this archive in a specified JBoss folder?
Is it common practice to deploy directly from Eclipse or better to use Ant, etc? Advantage / Disadvantage?
Obviously, I am a newbie :-). Trying to understand this.
1.
This is not always an easy decision, but for beginners and for small projects I would say it's nearly always a WAR. The reason for using an EAR is mainly to isolate a business layer from a UI/Web layer. See this question for more details: How can one isolate logical layers of an Java EE application
2.
I might be mistaken but I think that Spring people typically prefer WARs.
3.
JBoss (vendor) specific deployment descriptors are mostly needed to configure so-called "administered objects" and security. Sometimes they can be used for extra features that are not covered by the Java EE specification (e.g. setting the web root for a WAR). Administered objects are typically data sources (connection to a database) and JMS destinations (queues and topics).
In the traditional Java EE approach these have to be created as far away from the code as possible, which typically means a system admin would create them inside the target AS using some kind of GUI or admin console. In this setup, you as developer would throw a WAR with "unresolved dependencies" over the wall, and a system admin (or "deployer") would then spend days figuring out what those unresolved dependencies should be.
If the communication is relatively good between developers and deployers, the WAR or EAR might be thrown over the wall together with a readme-file, that at least gives some insight into which resources are needed. Depending on the organization the development team might not get any access or feedback about how those "unresolved dependencies" have been resolved. E.g. a data source with a max of 5 connections may have been created, but this may be insufficient if some code does say 10 parallel queries. Without the development team knowing the exact data source configuration, some classes of runtime problems and performance issues may be relatively hard to solve.
To mitigate these problems, some vendors, for some artifacts, offer the developer to create those "unresolved dependencies" instead using proprietary deployment descriptors which are then embedded in the WAR or EAR. For simple local JMS destinations this is then in most cases the end of it, but for data sources there is a little bit more to it. Namely, there has to be a mechanism to switch between data sources for different stages such as Dev, Beta, QA, Production etc. Additionally, it's rarely a good idea to have production passwords in the source code.
If you have a simple app that you want to try out locally, stages and production passwords are not a concern. If you deploy for a (large) company it is.
In Java EE 6 you can define a data source using a standard descriptor (web.xml, ejb-jar.xml or application.xml), and in Java EE 7 you can do the same for JMS destinations. There is no standard way to configure those based on stage, but there is a glimmer of hope that Java EE 8 will address this (see e.g. JAVAEE_SPEC-19). Vendors are not universally happy with those standardized methods, and their main documentation will almost always extensibly tell you how to do those things using their proprietary tools and descriptors, and if you're lucky as a small note tell you there's a standardized way (and then sometimes downplay that or scare you by saying it's not recommended to be used in production).
4.
See answer to 3 mostly. One option to solve the problem of how to switch between stages and keep production passwords out of the WAR/EAR, is to have the full definition of said data source inside the AS (inside JBoss in your case). Every AS installation is tied to a specific server in this setup. If data sources need to be updated, removed or new ones added, you have to communicate with your operations team (if any). As said, depending on your organization this can be anything between trivial and practically impossible.
5.
When developing you most often use your IDE to do a deployment. For production you would never do that. For production you may build with Ant (or Maven) and deploy via something like Jenkins, or e.g Chef.
Check here : .war vs .ear file
If you read the preceeding response, you'd guess that "WAR" it is.
Deployment descriptor are needed to manage the modules of JBoss, if you don't have any conflict or don't need any tweaking, you won't need any deployment descriptor.
You may need to play with some JBoss file if you want to add modules to JBoss, or configure datasources, etc. Read the JBoss documentation for more info.
You can deploy from eclipse during your development phase, but as your other environments (qualification, production, test, etc) should be separeted from your developing one and that they won't have any eclipse installed on them, you should get used to manage your server from the command line and drop your war's in the right directories.
It's a short answer, but I hope it will help.
Read JBoss documentation for more info.