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Spring, Maven: Correct the classpath of your application

I am trying to create a maven version of the gradle-based treehouse 'unit-testing-a-spring-application' project used in this course. See course code here.
After not being able to build initially, I ended up adding dependency versions specified in the original gradle build file. Maven will build fine, but running the app gives this:
The following method did not exist:
org.springframework.data.repository.config.RepositoryConfigurationSource.getAttribute(Ljava/lang/String;)
Ljava/lang/String;
The method's class, org.springframework.data.repository.config.RepositoryConfigurationSource, is
available from the following locations:
jar:file:/C:/Users/home/.m2/repository/org/springframework/data/spring-data-
commons/2.1.6.RELEASE/spring-data-commons-2.1.6.RELEASE.jar!/org/springframework/data/repository/config/RepositoryConfigurationSource.class
It was loaded from the following location:
file:/C:/Users/home/.m2/repository/org/springframework/data/spring-data-commons/2.1.6.RELEASE/spring-
data-commons-2.1.6.RELEASE.jar
Action
Correct the classpath of your application so that it contains a single, compatible version of
org.springframework.data.repository.config.RepositoryConfigurationSource.
Several similar problems are solved here on S.O. by changing the version of some related dependency. I have tried various versions of the following to no avail (I stick normally with spring-boot-starter-parent v2.1.4 cause it works all the time with my projects):
spring-data-commons
spring-boot-starter-parent
I see the needed class below listed in my project Dependencies directory, but what dependency versions will work in this case? How can I solve this otherwise?
org/springframework/data/repository/config/RepositoryConfigurationSource.class

I looked at your code and found some mistakes. Since your project is a spring-boot one, you mustn't add direct spring dependencies in your pom file. Instead try to use spring-boot based dependencies. For instance, instead of having such this dependency:
<dependency>
<groupId>org.springframework.data</groupId>
<artifactId>spring-data-jpa</artifactId>
<version>1.9.2.RELEASE</version>
</dependency>
You must have the following one in your pom file.
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

Maven - "Package from transitive module dependency referenced, declare a direct dependency to fix."

I never worked with Maven before, but after having a lot of problems with mockito dependencies in my Netbeans module, I decided to create a new one using Maven and move everything to this new project. After some time doing so, I managed to get the module running just ok.
The problem is that when I use some functionalities that require the Netbeans API I get an exception.
My guess is that the problem is in the dependencies declared in pom.xml. In some of the imports that I use in my application, I get the following message:
Package from transitive module dependency referenced, declare a
direct dependency to fix.
When I clean and build or run mvn clean install in the root directory I get this error:
Project uses classes from transitive module
org.netbeans.api:org-netbeans-modules-projectapi:jar:RELEASE73 which
will not be accessible at runtime.
To fix the problem, add this module as direct dependency. For OSGi bundles that are supposed to be wrapped in NetBeans modules, use the
useOSGiDependencies=false parameter
In the org.codehaus.mojo plugin declaration (which was the only one that had the useOSGiDependencies tag) I tried to change useOSGiDependencies=true to useOSGiDependencies=false but that didn't work. I also tried to change RELEASE73 to RELEASE82, since I am using Netbeans 8.2 but that didn't work as well. I also tried a bunch of other possible solutions that I found on google, but none seemed to work for me.
These are the Netbeans api dependencies that I have in my pom.xml file:
<dependencies>
<dependency>
<groupId>org.netbeans.api</groupId>
<artifactId>org-netbeans-modules-project-libraries</artifactId>
<version>RELEASE73</version>
</dependency>
<dependency>
<groupId>org.netbeans.api</groupId>
<artifactId>org-netbeans-api-annotations-common</artifactId>
<version>RELEASE82</version>
</dependency>
<dependency>
<groupId>org.netbeans.api</groupId>
<artifactId>org-openide-util</artifactId>
<version>RELEASE82</version>
</dependency>
<dependency>
<groupId>org.netbeans.api</groupId>
<artifactId>org-openide-awt</artifactId>
<version>RELEASE82</version>
</dependency>
<dependency>
<groupId>org.netbeans.modules</groupId>
<artifactId>org-netbeans-core</artifactId>
<version>RELEASE73</version>
</dependency>
<!-- ... -->
</dependencies>
I looked everywhere but couldn't find a straightforward answer on how to declare a direct dependency.
Can anyone explain to me what am I doing wrong here?

After digging a bit more, I found that I had to add all the dependencies manually. This answer helped me a lot.
I just lack experience with maven. Basically I googled org-netbeans-modules-projectapi:jar:RELEASE73 maven entered the first link and added the needed dependency to my project.

Jetty wants Jersey, but I'm not using it

Building a relatively simple jetty app, following the instructions here:
http://www.eclipse.org/jetty/documentation/9.4.x/maven-and-jetty.html
I'm not using Jersey, but mvn jetty:run complains about
Provider com.sun.jersey.server.impl.container.servlet.JerseyServletContainerInitializer not found
My pom.xml does not include any reference to Jersey. In fact, it is quite simple:
<dependency>
<groupId>org.eclipse.jetty</groupId>
<artifactId>jetty-server</artifactId>
<version>${jettyVersion}</version>
</dependency>
<dependency>
<groupId>org.apache.solr</groupId>
<artifactId>solr-solrj</artifactId>
<version>6.0.1</version>
</dependency>
What is making jetty look for Jersey?

Search all of your dependencies for META-INF/services/javax.servlet.ServletContainerInitializer files.
The one that has the entry for com.sun.jersey.server.impl.container.servlet.JerseyServletContainerInitializer is the one causing you problems.
Look at your project dependencies (aka <project><dependencies>) and your project's configuration of jetty-maven-plugin to see if that <plugin> has any extra dependencies added to it (aka <plugin><dependencies>).

Well, after much machination, and gnashing of teeth, I think I stumbled about the answer. Whilst learning about maven, I was playing with shaded uber-jars. I had compiled one of the packages as an uper-jar, and installed it. When maven put it all together, it added a bit too much and broke my dependencies. Removing the shaded jar for local installation and just using it for distribution worked just fine.

Maven dependency for Google Spreadsheet

Added the following dependency in pom.xml.
<dependency>
<groupId>com.google.api.client</groupId>
<artifactId>google-api-data-spreadsheet-v3</artifactId>
<version>1.0.10-alpha</version>
</dependency>
But it doesn't seem to work. It doesn't contain any of the required classes. For example, SpreadsheetService, SpreadsheetFeed, SpreadsheetEntryetc.
Is there any other maven repository for Google Spreadsheet?
Also, in this documentation, they haven't mentioned any maven repository. So, do I have to manually download the required JARs and add them to my project?

After some searching and experimentation, I finally found the dependency which contains the required classes to work with Google Spreadsheets. Here it is -
<dependency>
<groupId>com.google.gdata</groupId>
<artifactId>core</artifactId>
<version>1.47.1</version>
</dependency>
To test this, I used the code given here.
As far as getting authorization is concerned, look at this answer.

How to add Spring libs using Maven

I learned Spring via Spring In Action 3 few month ago. I downloaded Spring libraries from official site (list was like in SIA3(aop, asm, aspects, beans ...)), added them to my project and everything worked fine. Now I want to use Maven, but I am getting a lot of errors and sinking in searching what library to add.
I am newby, dont know all Spring dependencies(within it libs) and the question is not about my errors, but about the way to add all Spring libraries to my project via Maven. How do you usually add Spring libs using Maven?

You don't have to download the libraries themselves anymore. That is what Maven is for. (and quite some more, of course)
set up Maven properly
set up Maven in the IDE tool you have (like this)
edit the pom.xml to include what you need, adding the dependencies in the in the dependencies tag.
Maven takes care of resolving the dependencies of the specified packages. If a package depends on other packages, it will do it for you. You only have to specify the packages you directly need
For example
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring</artifactId>
<version>2.5.6</version>
</dependency>
You can easily find the packages using Google, and searching for "maven repository "
Avoiding version clashes
Also, as Bart mentioned, the common way of having Spring in the pom.xml - as it has way too many versions, and clashes can occur - is through a common property specifying the version for all Spring components. (Based on this answer)
Specify the property in the properties tag:
<properties>
<spring.version>3.0.5.RELEASE</spring.version>
</properties>
Then use it in the dependencies like this:
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>${spring.version}</version>
</dependency>
Be careful to use it for ALL components to avoid version clashes. (of course, issues mught still occur, bz having different libraries reference spring too, but that is another story in its own.)
Side note
Keep in mind note that Maven projects use specific directory layout. When I first started using maven for my own projects, first I created a new blank one, and played around with it, before I began migrating my older projects to use maven. Believe me, it pays off.

Add spring artifacts to your pom.xml file. For example
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-beans</artifactId>
<version>3.2.4.RELEASE</version>
You can find more artifact info here
http://mvnrepository.com/

HERE you can find the dependencies as per your requirement. Just click on the dependency and inside click on the latest release, scroll down there is your code inside the <dependencies> Your required dependency and version</dependencies>.
Just copy the XML code and paste it in your pom.xml file.