How to work around the stricter Java 8 Javadoc when using Maven

Question

You'll quickly realize that JDK8 is a lot more strict (by default) when it comes to Javadoc. (link - see last bullet point)

If you never generate any Javadoc then of course you'll not experience any problems but things like Maven release process and possibly your CI builds will suddenly fail where they worked just fine with JDK7. Anything that checks the exit value of the Javadoc tool will now fail. JDK8 Javadoc is probably also more verbose in terms of warnings compared to JDK7 but that's not the scope here. We are talking about errors!

This question exist to collect proposals on what to do about it. What is the best approach ? Should these errors be fixed once and for all in the source code files? If you have a huge code base this might be a lot of work. What other options exist ?

You are also welcome to comment with stories of what now fails that would previously pass.

Horror stories of what now fails

wsimport tools

wsimport tool is a code generator for creating web service consumers. It is included in the JDK. Even if you use the wsimport tool from JDK8 it will nevertheless produce source code that cannot be compiled with the javadoc compiler from JDK8.

@author tag

I'm opening up source code files 3-4 years old and see this:

/**
 * My very best class
 * @author John <[email protected]> 
 */

This now fails because of the < character. Strictly speaking this is justified, but not very forgiving.

HTML tables

HTML Tables in your Javadoc? Consider this valid HTML:

/**
 *
 * <table>
 *   <tr>
 *      <td>Col1</td><td>Col2</td><td>Col3</td>
 *   </tr>
 * </table>
 */

This now fails with error message no summary or caption for table. One quick fix is to do like this:

/**
 *
 * <table summary="">
 *   <tr>
 *      <td>Col1</td><td>Col2</td><td>Col3</td>
 *   </tr>
 * </table>
 */

but why this has to be a stop-the-world error from Javadoc tool beats me??

Things that now fail for more obvious reasons

1. Invalid links, e.g. {@link notexist}
2. Malformed HTML, e.g. always returns <code>true<code> if ...

UPDATE

Links:

Excellent blog on the subject by Stephen Colebourne.

Solution 1

For now, the easiest way I know to work around the stricter Java 8 Javadoc when using Maven is deactivating it.

Since the parameter -Xdoclint:none only exists in Java 8, defining this parameter breaks the build for any other Java. To prevent this, we can create a profile that will be active only for Java 8, making sure our solution works regardless of the Java version.

<profiles>
    <profile>
        <id>disable-java8-doclint</id>
        <activation>
            <jdk>[1.8,)</jdk>
        </activation>
        <properties>
            <additionalparam>-Xdoclint:none</additionalparam>
        </properties>
    </profile>
</profiles>

Just add that to your POM and you're good to go.

---

For maven-javadoc-plugin 3.0.0 users:

Replace

<additionalparam>-Xdoclint:none</additionalparam>

by

<doclint>none</doclint>

Thanks @banterCZ!

Solution 2

If you are using the maven javadoc plugin, you can use the failOnError option to prevent it from stopping if it finds any html errors:

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-javadoc-plugin</artifactId>
  <configuration>
    <failOnError>false</failOnError>
  </configuration>
</plugin>

Or you can deactivate the strict html options completely with:

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-javadoc-plugin</artifactId>
    <configuration>
      <additionalparam>-Xdoclint:none</additionalparam>
    </configuration>
  </plugin>
</plugins>

For more info.

Solution 3

Since version 3.0.0 of maven-javadoc-plugin the doclint is configured via the dedicated XML tag

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-javadoc-plugin</artifactId>
    <version>3.0.0</version>
    <configuration>
       <doclint>none</doclint>
    </configuration>
</plugin>

Solution 4

Note that for the error no summary or caption for table, using <table summary=""> won't work anymore. If that's your situation, add a <caption> element to your table, like this:

<table>
    <caption>Examples</caption>
    ...
</table>

Hope this helps someone out there. It took me a while until I found this out.

Solution 5

I like @ThiagoPorciúncula's solution but it didn't quite go far enough for me.

I typically already have javadoc plugin additionalparam set which were not being overridden by the profile. Because of this I had to:

• Set a disableDoclint property to be empty by default.
• If in java >= 8, set the disableDoclint property to be -Xdoclint:none
• The use ${disableDoclint} in theadditionalparamsection of themaven-javadoc-plugin`.

This seems to work well albeit verbose.

<properties>
    <!-- set empty property -->
    <disableDoclint></disableDoclint>
</properties>
<profiles>
    <profile>
        <id>disable-java8-doclint</id>
        <activation>
            <jdk>[1.8,)</jdk>
        </activation>
        <properties>
            <!-- set property if >= java 8 -->
            <disableDoclint>-Xdoclint:none</disableDoclint>
        </properties>
    </profile>
    ...
</profiles>

Then down below I could use the optional ${disableDoclint} variable in the additionalparam section that I had already defined.

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-javadoc-plugin</artifactId>
    <executions>
        <execution>
            <goals>
                <goal>jar</goal>
            </goals>
            <configuration>
                <showPackage>false</showPackage>
                <additionalparam>-tag inheritDoc:X ${disableDoclint}</additionalparam>
            </configuration>
        </execution>
    </executions>
    <configuration>
        <showPackage>false</showPackage>
        <bottom>This documentation content is licensed...</bottom>
        <additionalparam>-tag inheritDoc:X ${disableDoclint}</additionalparam>
    </configuration>
</plugin>

This works under java 8 but doesn't cause syntax errors under java 7. Woo hoo!

View more solutions

Comments

[peterh]

Hmm. The problem with these solutions is that if you think of it with JDK8 Javadoc you would want not to fail on errors whereas with JDK7 Javadoc you do. So for this reason I like best the -Xdoclint option. The hope is it will be silently ignored if executed with a JDK7 Javadoc ?

[Donal Fellows]

You could apply the option conditionally via a maven profile keyed on the Java version…?

[Giovanni Toraldo]

Nope, with JDK7 it fail with javadoc: error - invalid flag: -Xdoclint:none (nice job Oracle).

[peterh]

I'll accept this as the most likely solution that most of us will implement. I like the <activation> part. But I wish someone would come up with a tool that could go through those many source files and aid the developer in fixing the errors ... rather than just turning off DocLint.

[mwhs]

Beware using this solution if you rely on another profile being active by default at the same time (using activeByDefault=true).

[Daniel Hári]

@peterh: There is no meaning of documenting fully everything, that is a useless duplicated work, by clean code principles it is recommended to document only what is not obvious, and the public API.

[Mehrad Sadegh]

This does not work with maven-javadoc-plugin version 3.0.0. I had to go back to version 3.0.0-M1 for making -Xdoclint:none work.

[banterCZ]

@MehradSadegh For maven-javadoc-plugin version 3.0.0 just replace <additionalparam>-Xdoclint:none</additionalparam> by <doclint>none</doclint>

[amanzoor]

As off maven-javadoc-plugin version 3.0.0 you can use additionalJOption property to pass options to javadoc, it will be <additionalJOption>-Xdoclint:none</additionalJOption> property in this case.

[Saurabhcdt]

Yes, Adding JDK 8 related profile & setting <doclint>none</doclint> resolves the issue. It generates javadoc jar same as it was generating in JDK 7. Thanks.

[old-monk]

<doclint>none</doclint> finally helped after searching stackoverflows for a while.. thanks!!!

[peterh]

What version of the JDK? For sure the <table summary=""> trick still works on JDK8. (just tested on jdk1.8.0_201)

[Jeronimo Backes]

@peterh I used jdk 11.

[kap]

This is the up-to-date answer. summary="..." attribute is not supported with HTML5 (the default output for JDK 11 javadoc) any more. It is also supported in JDK 8.