How to make javadoc doclava doclet works with gradle

I am building a project with gradle using java plugin and I want also to build javadoc using doclava doclet

Here is the relevant part of the module's build.gradle

apply plugin: 'java'
javadoc {
    source = sourceSets.main.allJava

    ...

    exclude "com/mobaires/sdk/api/debug/**"

    options.windowTitle = "SDK"
    options.docTitle = "SDK"

    options.doclet = "com.google.doclava.Doclava"
    options.docletpath = [file("libs/doclava-1.0.5.jar")]    
}

When I run ./gradlew javadoc I get this error

16:24:46.030 [LIFECYCLE] [class org.gradle.TaskExecutionLogger] :javadoc FAILED
16:24:46.035 [DEBUG] [org.gradle.execution.taskgraph.AbstractTaskPlanExecutor] Task worker [Thread[main,5,main]] finished, busy: 0.695 secs, idle: 0.0040 secs
16:24:46.044 [ERROR] [org.gradle.BuildExceptionReporter] 
16:24:46.045 [ERROR] [org.gradle.BuildExceptionReporter] FAILURE: Build failed with an exception.
16:24:46.045 [ERROR] [org.gradle.BuildExceptionReporter] 
16:24:46.046 [ERROR] [org.gradle.BuildExceptionReporter] * What went wrong:
16:24:46.046 [ERROR] [org.gradle.BuildExceptionReporter] Execution failed for task ':javadoc'.
16:24:46.047 [ERROR] [org.gradle.BuildExceptionReporter] > Javadoc generation failed. Generated Javadoc options file (useful for troubleshooting): '.../build/tmp/javadoc/javadoc.options'
16:24:46.048 [ERROR] [org.gradle.BuildExceptionReporter] 
16:24:46.048 [ERROR] [org.gradle.BuildExceptionReporter] * Try:
16:24:46.049 [ERROR] [org.gradle.BuildExceptionReporter] Run with --stacktrace option to get the stack trace. 
16:24:46.055 [LIFECYCLE] [org.gradle.BuildResultLogger] 
16:24:46.058 [LIFECYCLE] [org.gradle.BuildResultLogger] BUILD FAILED
16:24:46.059 [LIFECYCLE] [org.gradle.BuildResultLogger] 
16:24:46.060 [LIFECYCLE] [org.gradle.BuildResultLogger] Total time: 9.297 secs

Could anybody make it work doclava with Gradle?

Solution

After taking a look to the javadoc.options that is mentioned in the error log it says

-classpath '... all the classpath here ...'
-d '.../build/docs/javadoc'
-doclet 'com.google.doclava.Doclava'
-docletpath '../libs/doclava-1.0.5.jar'
-doctitle 'XXXX'
-quiet 
-windowtitle 'XXXX'
'... classes to get javadoc'

The problem is that gradle is passing doctitle and windowtitle as arguments to javadoc command which are NOT supported by doclava doclet.

Diving into org.gradle.api.tasks.javadoc.Javadoc code I found a workaround that worked. I have simply added title = null to the javadoc task in build.gradle file

javadoc {
    source = sourceSets.main.allJava
    ...
    exclude "com/mobaires/sdk/api/debug/**"

    title = null

    options.doclet = "com.google.doclava.Doclava"
    options.docletpath = [file("libs/doclava-1.0.5.jar")]    
}

I hope it helps others :)