cmd/gomobile: call System.loadLibrary for .aar

Change-Id: I3fd099910cfb1fe112ded4386905d370acfea002
Reviewed-on: https://go-review.googlesource.com/11816
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

bind/java/Seq.java

@@ -15,6 +15,14 @@ import java.util.concurrent.Executors;
 // Used by automatically generated language bindings to talk to Go.
 public class Seq {
 	static {
+		// Look for the shim class auto-generated by gomobile bind.
+		// Its only purpose is to call System.loadLibrary.
+		try {
+			Class.forName("go.LoadJNI");
+		} catch (ClassNotFoundException e) {
+			// Ignore, assume the user will load JNI for it.
+		}
+
 		initSeq();
 		new Thread("GoSeq") {
 			public void run() { Seq.receive(); }

bind/java/SeqTest.java

@@ -15,7 +15,6 @@ import go.testpkg.Testpkg;
 
 public class SeqTest extends AndroidTestCase {
   public SeqTest() {
-    System.loadLibrary("gojni");
   }
 
   public void testAdd() {

cmd/gomobile/bind.go

@@ -150,8 +150,13 @@ func runBind(cmd *command) error {
 		return err
 	}
 
+	dst := filepath.Join(androidDir, "src/main/java/go/LoadJNI.java")
+	if err := ioutil.WriteFile(dst, []byte(loadSrc), 0664); err != nil {
+		return err
+	}
+
 	src := filepath.Join(repo, "bind/java/Seq.java")
-	dst := filepath.Join(androidDir, "src/main/java/go/Seq.java")
+	dst = filepath.Join(androidDir, "src/main/java/go/Seq.java")
 	rm(dst)
 	if err := symlink(src, dst); err != nil {
 		return err
@@ -160,6 +165,15 @@ func runBind(cmd *command) error {
 	return buildAAR(androidDir, bindPkg)
 }
 
+var loadSrc = `package go;
+
+public class LoadJNI {
+	static {
+		System.loadLibrary("gojni");
+	}
+}
+`
+
 type binder struct {
 	files []*ast.File
 	fset  *token.FileSet