app_build.gradle

...

apply plugin: 'findbugs'

...

task findbugs(type: FindBugs, dependsOn: assembleDebug) {
    excludeFilter file("${project.rootDir}/config/findbugs/exclude.xml")
    classes = fileTree('build/intermediates/classes/debug/')  // Varies based on your app build configs and flavors...
    source = fileTree('src/main/java/')
    classpath = files()
    effort = 'max'
    reports {
        xml.enabled = false
        html.enabled = true
    }
}

config_findbugs_exclude.xml

<?xml version="1.0" encoding="UTF-8"?>
<FindBugsFilter>
    <!-- http://stackoverflow.com/questions/7568579/eclipsefindbugs-exclude-filter-files-doesnt-work -->
    <Match>
        <Class name="~.*\.R\$.*"/>
    </Match>
    <Match>
        <Class name="~.*\.Manifest\$.*"/>
    </Match>
    <!-- All bugs in test classes, except for JUnit-specific bugs -->
    <Match>
        <Class name="~.*\.*Test" />
        <Not>
            <Bug code="IJU" />
        </Not>
    </Match>
</FindBugsFilter>

example.md

./gradlew app:findbugs