Build project/func on host machine for java-maven

This change introduces a local build step as opposed to the prebuild
step which happens inside a dev container.

fn/langs/java_maven.go

@@ -1,59 +1,31 @@
 package langs
 
-import (
-	"fmt"
-	"os"
-	"os/exec"
-	"path/filepath"
-)
+import "fmt"
 
 // JavaMavenLangHelper provides a set of helper methods for the build lifecycle of Java Maven projects
 type JavaMavenLangHelper struct {
 	BaseHelper
 }
 
-
 // Entrypoint returns the Java runtime Docker entrypoint that will be executed when the function is run
 func (lh *JavaMavenLangHelper) Entrypoint() string {
-	return fmt.Sprintf("java -jar /function/target/function.jar com.example.faas.ExampleFunction::itsOn")
+	// TODO need mechanism to determine the java user function dynamically
+	userFunction := "com.example.faas.ExampleFunction::itsOn"
+	return fmt.Sprintf("java -jar /function/target/function.jar %s", userFunction)
 }
 
-// HasPreBuild returns whether the Java runtime has a pre-build step
-func (lh *JavaMavenLangHelper) HasPreBuild() bool {
+func (lh *JavaMavenLangHelper) HasLocalBuildCmd() bool {
 	return true
 }
 
-// PreBuild runs "mvn clean package" in the root of the project and by default expects a jar at `target/function.jar` as the
-// output.  We mount `$HOME/.m2` in order to get maven the proxy config specified in .m2/settings.xml, but it has the nice
-// side effect of making the users .m2/repository available.  Any new deps downloaded will be owned by root :(
-func (lh *JavaMavenLangHelper) PreBuild() error {
-	wd, err := os.Getwd()
-	if err != nil {
-		return err
+func (lh *JavaMavenLangHelper) LocalBuildCmd() []string {
+	return []string{
+		"mvn clean package",
 	}
-
-	if !exists(filepath.Join(wd, "pom.xml")) {
-		return fmt.Errorf("Could not find pom.xml - are you sure this is a maven project?")
-	}
-
-	cmd := exec.Command(
-		"docker", "run",
-		"--rm",
-		"-v", wd+":/java", "-w", "/java",
-		"-v", os.Getenv("HOME")+"/.m2:/.m2",
-		"maven:3.5-jdk-8-alpine",
-		"/bin/sh", "-c", "mvn -gs /.m2/settings.xml clean package",
-	)
-
-	cmd.Stderr = os.Stderr
-	cmd.Stdout = os.Stdout
-	if err := cmd.Run(); err != nil {
-		return dockerBuildError(err)
-	}
-	return nil
 }
 
-// AfterBuild should remove the (root-owned) target dir.
-func (lh *JavaMavenLangHelper) AfterBuild() error {
-	return nil
-}
+func (lh *JavaMavenLangHelper) HasPreBuild() bool { return false }
+
+func (lh *JavaMavenLangHelper) PreBuild() error { return nil }
+
+func (lh *JavaMavenLangHelper) AfterBuild() error { return nil }