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Why doesn't Eclipse m2e automatically add generated source folder to classpath?

I'm using 2018-12 with Java 8, but I'm running Eclipse itself with Java 11.
I have version "1.10.0.20181127-2120" of the m2e plugin.
I have a bunch of projects with similar characteristics. Maven projects run with Spring Boot. They are all stored in git.
For some reason, one of those projects was somewhat brain-damaged this morning. It still would build fine from the command line. Eclipse still knew it was a maven project, but it had no source folders. The .classpath file wasn't empty, it was just very minimal.
I got this particular problem resolved by simply copying the .classpath file from a similar project into this project. That fixed most of the problems, but I remembered that this one project uses a code generator plugin along with the "build-helper-maven-plugin" to indicate where the source is being generated. I found that Eclipse didn't have the generated sources folder as a source folder. I thought adding the "build-helper-maven-plugin" reference was what I needed to do to make Eclipse M2E to automatically detect this, but it doesn't appear to be working.
Once I manually added the generated sources folder as a source folder, that cleaned out the last compile errors.
This is a hopefully relevant excerpt from my pom:
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>build-helper-maven-plugin</artifactId>
<executions>
<execution>
<phase>generate-sources</phase>
<goals>
<goal>add-source</goal>
</goals>
<configuration>
<sources>
<source>${project.build.directory}/java-gen</source>
</sources>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.jsonschema2pojo</groupId>
<artifactId>jsonschema2pojo-maven-plugin</artifactId>
<version>0.4.34</version>
<configuration>
<sourcePaths>
<sourcePath>${basedir}/src/main/schema/...</sourcePath>
<sourcePath>${basedir}/src/main/schema/...</sourcePath>
</sourcePaths>
<targetPackage>...</targetPackage>
<annotationStyle>jackson2</annotationStyle>
<useCommonsLang3>true</useCommonsLang3>
<useDoubleNumbers>true</useDoubleNumbers>
<includeAccessors>true</includeAccessors>
<includeAdditionalProperties>true</includeAdditionalProperties>
<sourceType>jsonschema</sourceType>
<generateBuilders>true</generateBuilders>
<includeJsr303Annotations>true</includeJsr303Annotations>
</configuration>
<executions>
<execution>
<goals>
<goal>generate</goal>
</goals>
</execution>
</executions>
</plugin>
Update:
Deleting the Eclipse project and reimporting from git made no difference. Same result.

Put libraries for spring boot application in extra lib dir

I am currently building my spring boot application as a fat jar. But because I am also building a docker image from these, I have to pull the jar with all its dependencies every time I change some of my code. So my question is: How would I have to change my gradle files to get a task called 'buildWithExternalLibs' that has all dependencies in a lib folder, but can still be started using java -jar ... as long as the lib folder is right next to the jar?

I have done it in maven project. You can use same logic in gradle too.
When you will clean install, it will copy your jar file too.
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-install-plugin</artifactId>
<executions>
<execution>
<phase>install</phase>
<id>install-jar-lib</id>
<goals>
<goal>install-file</goal>
</goals>
<configuration>
<groupId>com.***.*</groupId>
<artifactId>abc-library</artifactId>
<version>*.*.*</version>
<packaging>jar</packaging>
<file>${project.basedir}/src/lib/***.jar</file>
</configuration>
</execution>
</executions>
<inherited>false</inherited>
</plugin>

How to copy war file to multiple folders?

It's possible to change the target build path where the war file is placed on mvn package by:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<configuration>
<outputDirectory>my\target\folder</outputDirectory>
</configuration>
</plugin>
Question: how can I create the war file in the default /target, folder, but additionally copy the war file to one (or multiple) other destinations after build?

A simple way to do that would be to bind an execution of the maven-antrun-plugin to the package phase. The advantage is that you don't need to re-execute the maven-war-plugin like mentioned in this answer.
This execution would copy the main artifact to the folder /path/to/folder.
<plugin>
<artifactId>maven-antrun-plugin</artifactId>
<version>1.8</version>
<executions>
<execution>
<phase>package</phase>
<configuration>
<target>
<copy file="${project.build.directory}/${project.build.finalName}.war"
todir="/path/to/folder" />
</target>
</configuration>
<goals>
<goal>run</goal>
</goals>
</execution>
</executions>
</plugin>
(This snippet must be placed inside the <build><plugins> element).
Running mvn clean install (or "Run As... > Maven Install" in Eclipse), Maven will do what you want. ${project.build.directory}/${project.build.finalName}.war refers to the main WAR artifact present in the build directory (which is target by default).

Maven: jar-with-dependencies include external jar [duplicate]

I want to build a .jar file with dependencies in maven. Unfortunately I have to include some external .jars in my buildpath. When I now try to build this project with maven package I will get an error that those external .jars are not found.
How to adapt my pom file to add those jars?
current:
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.3.2</version>
<configuration>
<source>1.6</source>
<target>1.6</target>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<executions>
<execution>
<id>copy-dependencies</id>
<phase>prepare-package</phase>
<goals>
<goal>copy-dependencies</goal>
</goals>
<configuration>
<outputDirectory>${project.build.directory}/classes/lib</outputDirectory>
<overWriteReleases>false</overWriteReleases>
<overWriteSnapshots>false</overWriteSnapshots>
<overWriteIfNewer>true</overWriteIfNewer>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.2-beta-4</version>
<configuration>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>

You can include the external jars in your build path as dependency with <scope>system</scope>
.
Check this link

You need use below command to add external jar into .m2 folder
mvn install:install-file -Dfile=[JAR] -DgroupId=[some.group] -DartifactId=[Some Id] -Dversion=1.0.0 -Dpackaging=jar
This will add the given jar in to your .m2 folder. After that go to pom.xm and just add the dependency with given group id, artifact id and version.

A simple solution for this is to add it into local maven repository
One way to do is via mvn install commands as suggested in previous post .
Another easy way is,
In your eclipse ide right click on project select Maven option.
Select Install or deploy an artifact to a maven repository option and click on next.
Click on browse next to the Artifact file checkbox & select your jar file.
Enter the GroupId and ArtifactId and version ensure generate pom & create checksum are checked & packaging is jar
Click on finish, Wallah!!! your job is done the jar is added in your local repository which you can define in setting.xml or m2 directory.
Now just add the simple maven dependency as per the GroupId,ArtifactId & jar version that you have entered as per the import and that's it your external jar will be packaged by maven.

Maven dependencies not being compiled

I have been trying for the last hour or so to get my Maven project to include source files from its dependencies, but for some reason, it isn't. I have followed the steps provided by the following link, but when I compile and run the plugin, I get a ClassNotFoundException:
https://github.com/mkremins/fanciful
I have made sure to include the dependencies and the repository from the link above into my pom.xml file, but when I compile, they don't get added to my .jar file.
I am fairly new to using Maven, and like it so far, albeit that it can be a pain to solve issues like this.
I am building the project by doing the following:
Right click project -> Run As -> Maven Build -> Goal: clean install
EDIT -
With a little more searching around, I figured it wasn't as easy as I thought so. I added the following to my pom.xml build section:
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>2.1</version>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
<configuration>
<createDependencyReducedPom>false</createDependencyReducedPom>
<minimizeJar>true</minimizeJar>
<artifactSet>
<includes>
<include>mkremins:fanciful</include>
<include>org.json:json</include>
</includes>
</artifactSet>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
The only problem with this is that I needed to also manually include the dependencies of the main library I wanted to use - mkremins:fanciful; is there flag or option to automatically copy dependencies from the one file I need, rather than also including <include>org.json:json</include>?

Well, if you want to have your dependencies copied to your target jar, you need to tell maven to do so! Maven doesn't know if the artifact of your project is meant to be self-sufficient executable jar, jar to be executed inside a container or just a dependency or library for another project.
You might want to use copy-dependencies task from maven-dependency-plugin
For example:
<build>
<plugins>
<plugin>
<artifactId>maven-dependency-plugin</artifactId>
<executions>
<execution>
<id>copy-dependencies</id>
<phase>package</phase>
<goals>
<goal>copy-dependencies</goal>
</goals>
<configuration>
<includeScope>runtime</includeScope>
<outputDirectory>${project.build.directory}</outputDirectory>
<excludeTransitive>false</excludeTransitive>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
For more tweaking you might also want to play with jar plugin and assembly plugin. On more about creating executable jars:
http://www.ibm.com/developerworks/java/library/j-5things13/index.html?ca=dat-

You have mistaken the idea of Maven. Maven is intended to use dependencies which are located in Maven Central. It's idea is not to compile dependencies. I recommend you to read about Maven and learn how it works.