Add maven helper file; use maven wrapper if available instead of global 'mvn' executable

ale_linters/java/javac.vim

@@ -9,13 +9,7 @@ call ale#Set('java_javac_classpath', '')
 call ale#Set('java_javac_sourcepath', '')
 
 function! ale_linters#java#javac#RunWithImportPaths(buffer) abort
-    let l:command = ''
-    let l:pom_path = ale#path#FindNearestFile(a:buffer, 'pom.xml')
-
-    if !empty(l:pom_path) && executable('mvn')
-        let l:command = ale#path#CdString(fnamemodify(l:pom_path, ':h'))
-        \ . 'mvn dependency:build-classpath'
-    endif
+    let l:command = ale#maven#BuildClasspathCommand(a:buffer)
 
     " Try to use Gradle if Maven isn't available.
     if empty(l:command)

autoload/ale/maven.vim

@@ -0,0 +1,51 @@
+" Description: Functions for working with Maven projects.
+"
+" Given a buffer number, find a Maven project root.
+function! ale#maven#FindProjectRoot(buffer) abort
+    let l:wrapper_path = ale#path#FindNearestFile(a:buffer, 'mvnw')
+
+    if !empty(l:wrapper_path)
+        return fnamemodify(l:wrapper_path, ':h')
+    endif
+
+    let l:pom_path = ale#path#FindNearestFile(a:buffer, 'pom.xml')
+
+    if !empty(l:pom_path)
+        return fnamemodify(l:pom_path, ':h')
+    endif
+
+    return ''
+endfunction
+
+
+" Given a buffer number, find the path to the executable.
+" First search on the path for 'mvnw' (mvnw.cmd on Windows), if nothing is found,
+" try the global command. Returns an empty string if cannot find the executable.
+function! ale#maven#FindExecutable(buffer) abort
+    let l:wrapper_cmd = has('unix') ? 'mvnw' : 'mvnw.cmd'
+    let l:wrapper_path = ale#path#FindNearestFile(a:buffer, l:wrapper_cmd)
+
+    if executable(l:wrapper_path)
+        return l:wrapper_path
+    endif
+
+    if executable('mvn')
+        return 'mvn'
+    endif
+
+    return ''
+endfunction
+
+" Given a buffer number, build a command to print the classpath of the root
+" project. Returns an empty string if cannot build the command.
+function! ale#maven#BuildClasspathCommand(buffer) abort
+    let l:executable = ale#maven#FindExecutable(a:buffer)
+    let l:project_root = ale#maven#FindProjectRoot(a:buffer)
+
+    if !empty(l:executable) && !empty(l:project_root)
+        return ale#path#CdString(l:project_root)
+        \ . l:executable . ' dependency:build-classpath'
+    endif
+
+    return ''
+endfunction