Improve FindBugs Gradle task

Based on https://github.com/square/sqlbrite/blob/master/gradle/android-findbugs.gradle

gradle/plugins/findbugs-android.gradle

@@ -1,14 +1,29 @@
 apply plugin: 'findbugs'
 
-check.dependsOn 'findbugs'
-task findbugs(type: FindBugs, dependsOn: ['compileDebugJava', 'compileDebugTestJava']) {
-    ignoreFailures = true
-    classes = fileTree('build/intermediates/classes/debug/') +
-            fileTree('build/intermediates/classes/test/debug/')
-    source = project.android.sourceSets.main.java.getSrcDirs() +
-            project.android.sourceSets.androidTest.java.getSrcDirs()
-    classpath = files()
-    effort = 'max'
-    includeFilter = file("$rootProject.projectDir/config/findbugs/include_filter.xml")
-    excludeFilter = file("$rootProject.projectDir/config/findbugs/exclude_filter.xml")
+afterEvaluate {
+    def variants = plugins.hasPlugin('com.android.application') ?
+            android.applicationVariants : android.libraryVariants
+
+    variants.each { variant ->
+        def task = project.task("findBugs${variant.name.capitalize()}", type: FindBugs) {
+            group = 'verification'
+            description = "Run FindBugs for the ${variant.description}."
+
+            effort = 'max'
+            ignoreFailures = true
+
+            includeFilter = file("$rootProject.projectDir/config/findbugs/include_filter.xml")
+            excludeFilter = file("$rootProject.projectDir/config/findbugs/exclude_filter.xml")
+
+            def variantCompile = variant.javaCompile
+
+            classes = fileTree(variantCompile.destinationDir)
+            source = variantCompile.source
+            classpath = variantCompile.classpath.plus(project.files(android.bootClasspath))
+
+            dependsOn(variantCompile)
+        }
+
+        tasks.getByName('check').dependsOn(task)
+    }
 }