JGit in short example

JGit is the great java library, that provides functionality to perform basic git operations. I used it when I decided to implement release cutting helper for my team. One of the requirements was to make this tool cross-platform (part of the team uses Windows PCs, and another one - Macs), that's why I decided to use java.

The very first search in google pointed me to JGit as "one of the best solutions to work with git from java".

Despite its popularity, it was hard to find some useful code examples for beginners, instead I've found a lot of general descriptions of how cool this library is.

Finally I've got some working examples in stackoverflow, that allowed me to start building my tool.

So trying to fix that situation - listing basic git operations using JGit:

public class GitUtils {
    private Git git;

    public GitUtils(String localPath) throws Exception {
        if(!localPath.endsWith(File.separator)){
            localPath += File.separator;
        }
        git = new Git(new FileRepository(localPath + ".git"));
    }

    public void pull() throws Exception {
        String currentBranch = git.getRepository().getBranch();
        StoredConfig config = git.getRepository().getConfig();
        if(config.getString("branch", currentBranch, "remote") == null){
            config.setString("branch", currentBranch, "remote", "origin");
            config.setString("branch", currentBranch, "merge", "refs/heads/" + currentBranch);
        }
        git.pull().call();
    }

    public void commit(String message) throws Exception {
        git.commit()
                .setMessage(message)
                .setAll(true)
                .call();
    }

    public void push() throws Exception{
        git.push().call();
    }

    public void checkout(String branchName, String sourceBranchName, boolean createNew) throws Exception {
        CheckoutCommand command = git.checkout()
                .setName(branchName)
                //.setUpstreamMode(CreateBranchCommand.SetupUpstreamMode.TRACK)
                .setForce(true)
                .setCreateBranch(createNew);
        if(StringUtils.isNotBlank(sourceBranchName)){
            command = command.setStartPoint(sourceBranchName);
        }
        command.call();
    }
}

Enjoy coding!

Google Guava: missing cache entries

Recently I had to create new caching layer for our web applications. Nothing fancy, just usual multi-level read-through cache. I used Cache from Google Guava library for one of the caching levels, and faced interesting issue. Some tests intermittently failed b/c of the cache data misses, even despite that data was loaded into the cache during test data initialization.

Playing with different cache configurations I found out that data misses happens in a case of full cache population.

Below are the test that demonstrates the issue. It creates Cache, populates it with the random data, then reads the data from the cache and and counts number of misses (google guava v. 14).

public class GuavaTest {

    public static void main(String[] args){

        for(int i = 1000; i <= 50000; i += 1000){
            System.out.println(MessageFormat.format("count = {0} missCount = {1}", i, String.valueOf(test(i))));
        }

    }

    public static int test(final int cacheSize){

        String[] urls = new String[cacheSize];
        com.google.common.cache.Cache<Object, Object> cache = CacheBuilder.newBuilder()
                .maximumSize(cacheSize)
                .build();

        for(int i = 0; i < cacheSize; i++){
            urls[i] = UUID.randomUUID().toString();
            cache.put(urls[i], new Object());
        }

        int missCount = 0;

        for(int i = 0; i < cacheSize; i++){
            Object o = cache.getIfPresent(urls[i]);
            if(o == null){
                ++missCount;
            }
        }

        return missCount;
    }
}

Below are results I've got (they're slightly different every time, but trend and range are approx. the same):

I was really surprised with results. Maybe that's the price for some kind of optimization or something. I'm still using guava cache, it is great tool, but always keep in mind that I have to reserve a bit more slots than required number to avoid data loss.

"I hate Android!" or my first android app

Despite having development experience for different mobile platforms, I have never worked with Android (so shame!). However last month good candidate for my first android app was found!

The company where I'm working has started using 2-step authentication. So every time any employee wants to connect to f.e. VPN, he/she has to:

• sign-in using username and password
• if credentials are valid, system calls to the employee's cellphone and asks to press pound ("#") sign to complete authentication.

This second step is a bit annoying - you have to search your phone every time you want to login. Especially it annoys at home, where my phone usually hides from me in different places. Also if you forgot your phone somewhere (in the car, at home etc.) it is hard to connect to corporate network.

"It's time for Android development"- I have decided to create android app, that should:

1. Pick up the phone
2. Press pound key
3. Hang up
4. Bring the beer (joking :) )

Sounds not very scary (huh, if I knew!), simple enough for the first app. Let's rock!

Before start

Development Tools

I tried to use pre-released version of AndroidStudio, but for some reasons  it didn't work on my OS X 10.8.5. So I fall back to "standard" ADT Bundle. Unfortunately its built-in Eclipse-based IDE has disappointed me - it is slow thing with "bugged" debugger, that often disconnects from emulator without any obvious reasons. I'm not saying it is ugly, but that is definitely worst dev tool for mobile platforms I've ever tried (I'm comparing with dev tools I used for development for iPhone, BlackBerry and Nokia). Looking forward to trying release version of AndroidStudio - I hope guys from JetBrains won't break good tradition and will deliver high-quality product soon.

Documentation and tutorials

Opposite to the toolkit, documentation is very good. Here some good resources for beginners:

• Android Development Tutorial - good overview of android platform, provides basic understanding of android's app and its components.
• UI Overview - must read - provides overview of the main UI components and recommendations how to use them to improve apps' usability.
• Devices and Displays, Metrics and Grids, Iconography - basics about different UI interface aspects.
• Best practices for Performance, Best UX - highly recommended to read.
• Firs app - if you're building your first app
• Android Performance Case Study - very good post about performance of android's apps - even if you do not try to profile your app, article provides basic understanding of the apps' performance and ways for optimization.
• SDK Samples, Google I/O App, photup - learn best practices by reading source code.

Huh, finally - development!!!

Preferences Screen

I didn't want that my app intercept every call, only from some certain number. I also would like to have ability to turn application off. So I started building my preferences view from scratch, but then I realized that there is mechanism building standard preferences screens. I won't pay a lot of attention of how to work with preferences, it is well described here. All that added to it is displaying preference value in the preferences main screen:

    @Override
    protected void onPause() {
        super.onPause();
        // Unregister the listener whenever a key changes
        getPreferenceScreen().getSharedPreferences()
                .unregisterOnSharedPreferenceChangeListener(this);
    }
 
    @Override
    protected void onResume() {
        super.onResume();
        //update phone preference summary with actual value
        SharedPreferences preferences = getPreferenceScreen().getSharedPreferences();
        phoneNumberPreference.setSummary(preferences.getString(PHONE_NUMBER_PREFERENCE, getResources().getString(R.string.phone_number_desc)));
        preferences.registerOnSharedPreferenceChangeListener(this);
    }

    @Override
    public void onSharedPreferenceChanged(SharedPreferences preferences, String key) {
        //update phone preference summary with actual value
        if(key.equals(PHONE_NUMBER_PREFERENCE)){
            phoneNumberPreference.setSummary(preferences.getString(key, getResources().getString(R.string.phone_number_desc)));
        }
    }

Pick up the phone

Surprise - there is no easy way to do it in Android. Traditional approach - use hidden ITelephony API via reflection does not work in v. 2.3+ (details here and here). Finally (after spending many hours trying to find solution) I applied approach used in this great application - I just send bluetooth keypressed event, and it works even if there is no bluetooth headset installed! Magic!

    // Simulate a press of the headset button to pick up the call
    Log.d("AuthenticatorAutoAnswerIntentService.pickUp", "Intent.ACTION_MEDIA_BUTTON Down");
    Intent buttonDown = new Intent(Intent.ACTION_MEDIA_BUTTON);
    buttonDown.putExtra(Intent.EXTRA_KEY_EVENT, new KeyEvent(KeyEvent.ACTION_DOWN, KeyEvent.KEYCODE_HEADSETHOOK));
    context.sendOrderedBroadcast(buttonDown, "android.permission.CALL_PRIVILEGED");

    // trigger on buttonUp instead of buttonDown
    Log.d("AuthenticatorAutoAnswerIntentService.pickUp", "Intent.ACTION_MEDIA_BUTTON Up");
    Intent buttonUp = new Intent(Intent.ACTION_MEDIA_BUTTON);
    buttonUp.putExtra(Intent.EXTRA_KEY_EVENT, new KeyEvent(KeyEvent.ACTION_UP, KeyEvent.KEYCODE_HEADSETHOOK));
    context.sendOrderedBroadcast(buttonUp, "android.permission.CALL_PRIVILEGED");

Press pound key

I was not able to do it programmatically. There is no API to do it. There is open issue to provide it, but it is still open. Here what I tried:

• Send "#" pressed event - no luck (good overview of different ways how to do it is here)
• Use hidden android.telephony.Phone class (as suggested here)
• Call the "#" number using intent (recipe from here)
• During experiments I've found out, that when I put my android device close enough to the powerful sound speaker that plays"#" tone (300ms long), it was recognized by caller as "#" keypress. But when I tried to play "#" DTMF tone (using ToneGenerator) by android audio system (after my application picks up the phone), it didn't work. I think that my phone's sound is just not powerful enough.  However when my app makes android audio to play long DTMF beep (5 seconds instead 300ms), caller hangs up - so it "hears" long beeps, but ignores short ones (again - in a case of external sound source, short DTMF beeps worked well - magic!).

I was not able to make my app send "#" DTMF to the caller, and left "beeps" variant as "almost work" one.

Hang up

The most easy case - that was done by using ITelephony hack, which (in this particular case) for some unbelievable reasons does not need android.permission.MODIFY_PHONE_STATE permission.

Dessert - notification

In addition, application shows notification in the status bar when auto-answer is activated. I found that very useful.

Project Structure

Project lives here

• SettingsActivity - main settings screen
• AuthenticatorAutoAnswerNotifier - main guy who takes care about apps' notifications in the status bar
• AuthenticatorAutoAnswerBootReceiver - starts on device boot complete, all that it does - just calls AuthenticatorAutoAnswerNotifier to update notification
• AuthenticatorAutoAnswerReceiver - receiver that activates on incomming call, checks settings, and in case if app is activated and it is "authenticator" phone number, initiates async call to the auto-answer service.
• AuthenticatorAutoAnswerIntentService - service that does all the "auto-answer and authenticate" work. All process takes several seconds, so we cannot perform it in AuthenticatorAutoAnswerReceiver, which is running in main application thread.