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maven-javadoc-plugin fails on jdk 11 when compiling for jdk 8 [duplicate]

Exit code: 1 - javadoc: error - The code being documented uses packages in the unnamed module, but the packages defined in https://docs.oracle.com/en/java/javase/11/docs/api/ are in named modules.
Has anyone been able to make javadoc work without having to change the source version to 1.8 (as suggested in other forums)? I'm using JDK v11.0.5 and the issue still present (also with JDK 12+).
Edit: This error originated from maven and thrown by the maven-javadoc-plugin. I have not been able to make it work for JDK 11+ even with the <source>8</source> configuration.

As suggested in OpenJDK issue tracker this can be worked around with defining source on Javadoc plugin:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-javadoc-plugin</artifactId>
<configuration>
<source>8</source>
</configuration>
</plugin>

Adding <detectJavaApiLink>false</detectJavaApiLink> to the Maven javadoc pluging configuration fix the error

I needed the bit from Carlos Santos to make this really work. The complete config that incorporates his answer is:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-javadoc-plugin</artifactId>
<configuration>
<source>8</source>
<detectJavaApiLink>false</detectJavaApiLink>
</configuration>
</plugin>

javadoc produces links to packages you use, e.g. to classes documented in .../javase/11/docs/api. While your comments are in an unnamed module, the targets are not, and javadoc can't combine those two. It produces either a package-list or an element-list file, so you can't mix unnamed modules (packages) with named modules.
I didn't find a way to limit the links that javadoc tries to produce; so you may have to use modules for your own project. This seems ridiculous to me, just to make javadoc happy. I guess this is just one of the reasons that so many people stick to Java 8.

I was able to get my own project to work by using a new version of the compiler plugin and setting the release property to 8.
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
</plugin>
<properties>
<maven.compiler.release>8</maven.compiler.release>
</properties>

I was facing the same issue. I was using Java 11.0.3 and org.apache.maven.plugins:maven-javadoc-plugin:2.10.4:jar. Updating the maven-javadoc-plugin version to 3.2.0 worked perfectly for me.

We can use <detectOfflineLinks>false</detectOfflineLinks> in the configuration.

Maven 3.0.4 - execute annotation processors after compile

I would like to run the following basic procedure within my Maven 3.0.4 project. I have all the basics in place and haven't had any issues but am running into problems on step #3. For some reason the basic solution is eluding me, since it seems like something that should be very obvious.
Run a basic clean/install (without annotation processing)
Request that a site build be run
Before the site build kicks off, run annotation processing on the compiled classes using an annotation processor class that was compiled in the initial steps
I tried setting up the annotation processing goal as follows:
<plugin>
<groupId>org.bsc.maven</groupId>
<artifactId>maven-processor-plugin</artifactId>
<executions>
<execution>
<id>process</id>
<goals>
<goal>process</goal>
</goals>
<phase>pre-site</phase>
<configuration>
<outputDirectory>${basedir}/target/generated-documentation</outputDirectory>
<processors>
<processor>com.mydomain.MyFancyAnnotationProcessor</processor>
</processors>
</configuration>
</execution>
</executions>
</plugin>
For some reason this doesn't seem to be working.
I feel like I'm doing something very, very silly that is preventing it from working.
I am using the Maven Annotation Plugin instead of the basic, Mojo Apt Plugin. I don't mind switching if someone has a working solution with that one. I tried both without any immediate signs of success. Again, it feels like it's just something obvious that I'm overlooking.
Error received:
[INFO] diagnostic error: Annotation processor 'com.mydomain.MyFancyAnnotationProcessor' not found
[ERROR] error on execute: error during compilation

My guess would be that the plugin is not including the current project itself in its classpath. The best solution would be to separate the annotation processor into its own (sub-)module if possible. If you can't do that, you may be able to just add this project itself as a dependency of the plugin (using a <dependencies> section under the plugin node).
As a diagnostic note, you can run maven with the '-X' argument to see detailed info about the build. This should show you exactly what is on the classpath when the plugin is executed.

Maven example of annotation preprocessing and generation of classes in same compile process?

Does anyone have a clean example of a maven project preprocessing class annotations at compile time with subsequent generation of classes to be compiled in the same compilation process?
Does anyone have a step-by-step procedure to implement such a project?

After navigating a lot in existing documentation on the net, I came up with the following:
What needs to be clarified:
In order to process annotations on a given project P, you first need an annotation processor compiled in a separate library S. P should have a dependency on S.
Implementing annotation processing in Java 5 is absolutely not the same thing as in Java 6.
Java 5 relies on a separate execution of apt. The corresponding tutorials here and here help understanding the basics of annotation processing and implementation in Java 5. Good reading for newbies.
Implementing annotation processing in Java 5 with Maven is tricky. One needs to add a local dependency to tools.jar to access the API described in these tutorials. Not clean. Some third-party plugins calling the apt are available, but not well documented.
Those using Java 6 should not jump-start implementing their processors according to the above tutorials.
Annotation Processing in Java 6 with Maven
A new package has been delivered in Java 6 to process annotations: the Pluggable Annotation Processing.
To implement a processor, create a separate Maven project. The above tutorial or this one explains how to proceed. This is our library S.
Then, create your project P and add a Maven dependency on S.
There is currently an issue with the maven-compiler-plugin, but a workaround is available here. Use it to compile your generated code as part of existing annotated code.
...and code generation
A great Java code generation library called CodeModel is available from Maven central. A good tutorial is available here. The javax annotation processing package offers some tools to generate output too.

maven-processor-plugin can do that...
https://code.google.com/p/maven-annotation-plugin/
Example from documentation:
<build> <plugins>
<!-- Run annotation processors on src/main/java sources -->
<plugin>
<groupId>org.bsc.maven</groupId>
<artifactId>maven-processor-plugin</artifactId>
<executions>
<execution>
<id>process</id>
<goals>
<goal>process</goal>
</goals>
<phase>generate-sources</phase>
</execution>
</executions>
</plugin>
<!-- Disable annotation processors during normal compilation -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<compilerArgument>-proc:none</compilerArgument>
</configuration>
</plugin>
</plugins> </build>

The Maven-Antlr-Plugin exactly does this. It generates Java classes from a grammar and the compile plugin compiles the generated classes. May it might be usefull the maven-annotation-plugin

Moving to Maven from GNUMake

I've been a long time user of the Make build system, but I have decided to begin learning the Maven build system. While I've read through most of the online docs, none seem to give me the analogies I'm looking for. I understand the system's lifecycle, but I have not see one reference to compile step dependencies. For example, I want to generate a JFlex grammar as part of the compile lifecycle step. Currently, I see no way of making that step a pre-compile phase step. Documentation seems to be limited on this. In general, the concept of step dependencies seem to be baked into Maven and require a plugin for any alteration. Is this the case? What am I missing, because currently the Maven build system seems very limited in how you can setup compilation steps.

You can do anything in Maven. It generally has a default way to do each thing, and then you can hook in and override if you want to do something special. Sometimes it takes a lot of Stack Overflowing and head scratching to figure it out.
There is even an official JFlex Maven plugin.
Whenever possible, find someone who has made a Maven plugin do what you want. Even if it isn't 100% right, it may at least give you an idea on how to make maven do something.
Minimal configuration
This configuration generates java code of a parser for all grammar files (.jflex , *.jlex , *.lex , .flex ) found in src/main/jflex/ and its sub-directories. The name and package of the generated Java source code are the ones defined in the grammar. The generated Java source code is placed in target/generated-source/jflex , in sub-directories following the Java convention on package names.
pom.xml
<project>
<!-- ... -->
<build>
<plugins>
<plugin>
<groupId>de.jflex</groupId>
<artifactId>jflex-maven-plugin</artifactId>
<version>1.6.0</version>
<executions>
<execution>
<goals>
<goal>generate</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
<!-- ... -->
</build>
<!-- ... -->
</project>
This feels like the maven way to do things. Put your stuff in the right folders (src/main/flex), and this plugin will automatically build it into your project. If you want to do fancier custom stuff, there are some options. but Maven is all about favoring convention over configuration.

To be frank I think that your current mindset maps much better to ant than to maven, and I would suggest starting with that.

Organize imports with Maven2, Eclipse-style?

I'm a lone Emacs user in a group that's hung up on Eclipse. Time and again, code diffs are made larger by imports that have been "organized" or "cleaned up" by Eclipse.
I don't have a strong opinion on the subject of import style in Java, but I do want to minimize our diffs. What can I do?
We use Maven2 for builds; is there a plugin that can help me? Can a piece of Eclipse be abstracted out & turned into a Maven plugin? I currently use ImportScrubber and have encountered a few other stand-alone pieces that do the same thing. What I'm really looking for is a Maven plugin that can integrate with the build.
Barring the above, I'll put an ImportScrubber invocation into my .git/hooks/post-commit.

The Hybridlabs beautifier which is used internally in the openArchitectureWare project (an open source generator framework) is doing what you're looking for. As explained in this blog entry, the beautifier is available as a Google Code project and its documentation describes a maven 2 plugin:
<plugin>
<groupId>org.hybridlabs</groupId>
<artifactId>maven-beautifier-plugin</artifactId>
<executions>
<execution>
<goals>
<goal>beautify-imports</goal>
</goals>
</execution>
</executions>
<configuration>
<!-- Recursively scan for *.java and beautifies imports -->
<inputDirectory>${pom.basedir}/..</inputDirectory>
<!--outputDirectory>${pom.basedir}/..</outputDirectory>
<runBeautifier>true/runBeautifier>
<runJalopy>false</runJalopy-->
</configuration>
</plugin>
There is indeed a mojo in the source tree but it doesn't match the groupId mentioned above (this is a bit confusing) and I've not been able to find the plugin in maven's public repository.
Maybe you'll be more lucky with the version available in AndroMDA plugin repository as documented in this thread (the plugin is indeed present in http://team.andromda.org/maven2/).
The plugin is under
org.apache.maven.plugins.maven-beautifier-plugin.
It can be run with the short form:
mvn beautifier:beautify-imports. It
can also be run as part of a project
pom by adding the plugin declaration
under <build><plugins>:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-beautifier-plugin</artifactId>
<version>1.0</version>
<executions>
<execution>
<goals>
<goal>beautify-imports</goal>
</goals>
</execution>
</executions>
<configuration>
<inputDirectory>${pom.basedir}/target/src</inputDirectory>
</configuration>
</plugin>
Or contact the project's author (e.g. through twitter or by mail).

I think all of you (Eclipse, Emacs or whatever users) should use something like Jalopy which supports both Eclipse and Maven. This way it becomes irrelevant where the code was modified as long as it has been run through pretty-printer as part of checking code in. Said that - I'm not sure if Jalopy supports organizing imports beyond sorting these up

I have also found an ImportScrubber plugin. Can't as of yet attest to its quality.

Does your shop have code standards for how imports should be organized? If so then you are out of luck. Minimizing diffs is a small sacrifice to make towards incremental code improvement.