skaffold init supports Java/Buildpacks projects (#4318)

* `skaffold init` supports Java/Buildpacks projects

Signed-off-by: David Gageot <david@gageot.net>

* Test all buildpacks samples

Signed-off-by: David Gageot <david@gageot.net>

integration/examples/buildpacks-java/README.md

@@ -0,0 +1,7 @@
+### Example: buildpacks (Java)
+
+This is an example demonstrating:
+
+* **building** a Java app built with [Cloud Native Buildpacks](https://buildpacks.io/)
+* **tagging** using the default tagPolicy (`gitCommit`)
+* **deploying** a single container pod using `kubectl`

integration/examples/buildpacks-java/k8s/web.yaml

@@ -0,0 +1,30 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: web
+spec:
+  ports:
+  - port: 8080
+    name: http
+  type: LoadBalancer
+  selector:
+    app: web
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: web
+spec:
+  selector:
+    matchLabels:
+      app: web
+  template:
+    metadata:
+      labels:
+        app: web
+    spec:
+      containers:
+      - name: web
+        image: skaffold-buildpacks
+        ports:
+          - containerPort: 8080

integration/examples/buildpacks-java/pom.xml

@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>org.skaffold</groupId>
+    <artifactId>hello-spring-boot</artifactId>
+    <version>0.1.0</version>
+    <description>Spring Boot</description>
+
+    <properties>
+        <java.version>1.8</java.version>
+    </properties>
+
+    <parent>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-starter-parent</artifactId>
+        <version>2.0.5.RELEASE</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>hello</finalName>
+        <plugins>
+            <plugin>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-maven-plugin</artifactId>
+            </plugin>
+        </plugins>
+    </build>
+</project>

integration/examples/buildpacks-java/skaffold.yaml

@@ -0,0 +1,15 @@
+apiVersion: skaffold/v2beta5
+kind: Config
+build:
+  artifacts:
+  - image: skaffold-buildpacks
+    buildpacks:
+      builder: "gcr.io/buildpacks/builder:v1"
+      env:
+      - GOOGLE_RUNTIME_VERSION=8
+    sync:
+      auto: {}
+profiles:
+- name: gcb
+  build:
+    googleCloudBuild: {}

integration/examples/buildpacks-java/src/main/java/hello/Application.java

@@ -0,0 +1,11 @@
+package hello;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class Application {
+    public static void main(String[] args) {
+        SpringApplication.run(Application.class, args);
+    }
+}

integration/examples/buildpacks-java/src/main/java/hello/HelloController.java

@@ -0,0 +1,12 @@
+package hello;
+
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.bind.annotation.RequestMapping;
+
+@RestController
+public class HelloController {
+    @RequestMapping("/")
+    public String index() {
+        return "Hello, World!";
+    }
+}

integration/run_test.go

@@ -94,10 +94,25 @@ func TestRun(t *testing.T) {
 			pods:        []string{"getting-started"},
 		},
 		{
-			description: "buildpacks",
+			description: "buildpacks Go",
 			dir:         "examples/buildpacks",
 			deployments: []string{"web"},
 		},
+		{
+			description: "buildpacks NodeJS",
+			dir:         "examples/buildpacks-node",
+			deployments: []string{"web"},
+		},
+		{
+			description: "buildpacks Python",
+			dir:         "examples/buildpacks-python",
+			deployments: []string{"web"},
+		},
+		{
+			description: "buildpacks Java",
+			dir:         "examples/buildpacks-java",
+			deployments: []string{"web"},
+		},
 		{
 			description: "kustomize",
 			dir:         "examples/getting-started-kustomize",

pkg/skaffold/build/buildpacks/init.go

@@ -73,24 +73,27 @@ func (c ArtifactConfig) Path() string {
 func validate(path string) bool {
 	valid := false
 
-	file := filepath.Base(path)
-	switch {
+	switch filepath.Base(path) {
 	// Buildpacks project descriptor.
-	case file == "project.toml":
+	case "project.toml":
 		valid = true
 
 	// NodeJS.
-	case file == "package.json":
+	case "package.json":
 		valid = true
 
 	// Go.
-	case file == "go.mod":
+	case "go.mod":
+		valid = true
+
+	// Java.
+	case "pom.xml", "build.gradle", "build.gradle.kts":
 		valid = true
 
 	// Python.
 	// TODO(dgageot): When the Procfile is missing, we might want to inform the user
 	// that this still might be a valid python project.
-	case file == "requirements.txt":
+	case "requirements.txt":
 		if _, err := os.Stat(filepath.Join(filepath.Dir(path), "Procfile")); err == nil {
 			valid = true
 		}

pkg/skaffold/build/buildpacks/init_test.go

@@ -72,6 +72,21 @@ func TestValidate(t *testing.T) {
 			},
 			expectedValid: true,
 		},
+		{
+			description:   "Java Maven",
+			path:          filepath.Join("path", "to", "pom.xml"),
+			expectedValid: true,
+		},
+		{
+			description:   "Java Gradle",
+			path:          filepath.Join("path", "to", "build.gradle"),
+			expectedValid: true,
+		},
+		{
+			description:   "Java Gradle Kotlin",
+			path:          filepath.Join("path", "to", "build.gradle.kts"),
+			expectedValid: true,
+		},
 		{
 			description:   "Buildpacks",
 			path:          "project.toml",