First iteration of support for Java

fn/langs/java.go

@@ -0,0 +1,118 @@
+package langs
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+)
+
+// JavaLangHelper provides a set of helper methods for the build lifecycle of the Java runtime
+type JavaLangHelper struct {
+	BaseHelper
+}
+
+const (
+	mainClass     = "Func"
+	mainClassFile = mainClass + ".java"
+)
+
+// Entrypoint returns the Java runtime Docker entrypoint that will be executed when the function is run
+func (lh *JavaLangHelper) Entrypoint() string {
+	return fmt.Sprintf("java %s", mainClass)
+}
+
+// HasPreBuild returns whether the Java runtime has a pre-build step
+func (lh *JavaLangHelper) HasPreBuild() bool {
+	return true
+}
+
+// PreBuild executes the pre-build step for the Java runtime which involves compiling the relevant classes. It expects
+// the entrypoint to the function, in other words or the class with the main method (not to be confused with the Docker
+// entrypoint from Entrypoint()) to be Function.java
+func (lh *JavaLangHelper) PreBuild() error {
+	wd, err := os.Getwd()
+	if err != nil {
+		return err
+	}
+
+	if !exists(filepath.Join(wd, mainClassFile)) {
+		return fmt.Errorf("could not find function: for Java, class with main method must be "+
+			"called %s", mainClassFile)
+	}
+
+	cmd := exec.Command(
+		"docker", "run",
+		"--rm", "-v", wd+":/java", "-w", "/java",
+		"funcy/java:dev",
+		"/bin/sh", "-c", "javac "+mainClassFile,
+	)
+
+	cmd.Stderr = os.Stderr
+	cmd.Stdout = os.Stdout
+	if err := cmd.Run(); err != nil {
+		return dockerBuildError(err)
+	}
+	return nil
+}
+
+// AfterBuild removes all compiled class files from the host machine
+func (lh *JavaLangHelper) AfterBuild() error {
+	wd, err := os.Getwd()
+	if err != nil {
+		return err
+	}
+
+	files, err := filepath.Glob(filepath.Join(wd, "*.class"))
+	if err != nil {
+		return err
+	}
+
+	for _, file := range files {
+		err = os.Remove(file)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// HasPreBuild returns whether the Java runtime has boilerplate that can be generated.
+func (lh *JavaLangHelper) HasBoilerplate() bool { return true }
+
+const javaFunctionBoilerplate = `import java.io.*;
+
+public class Func {
+
+	/**
+	 * This is the entrypoint to your function. Input will be via STDIN.
+	 * Any output sent to STDOUT will be sent back as the function result.
+	 */
+    public static void main(String[] args) throws IOException {
+        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
+
+        String name = bufferedReader.readLine();
+        name = (name == null) ? "world"  : name;
+
+        System.out.println("Hello, " + name + "!");
+    }
+
+}
+`
+
+// GenerateBoilerplate will generate function boilerplate (Function.java) for java if it does not exist.
+// Returns ErrBoilerplateExists if the function file already exists
+func (lh *JavaLangHelper) GenerateBoilerplate() error {
+	wd, err := os.Getwd()
+	if err != nil {
+		return err
+	}
+
+	pathToFunctionFile := filepath.Join(wd, mainClassFile)
+	if exists(filepath.Join(wd, mainClassFile)) {
+		return ErrBoilerplateExists
+	}
+	return ioutil.WriteFile(pathToFunctionFile, []byte(javaFunctionBoilerplate), os.FileMode(0644))
+}