Android, Development

AndroidAutoAlerts – Simple alerts app for Android Auto

AndroidAutoAlerts is a very simple app for Android Auto I have developed to test my Android Auto unit. Please read through the article to check it out!

What it does and how it works

As I said, the app is very simple and at the moment it has only one functionality: it will notify the driver if the speed limit is exceeded. Wow!

The driver can set the maximum speed limit through the app’s settings (you can also choose the name of your virtual assistant!)

androidautoalerts settings

Then, go back to the main screen and start the notification service. A service will run (and will keep running in the foreground using a system notification when you exit the app or attach your device to your Android Auto unit).

androidautoalerts mainscreenandroidautoalerts foreground notification

So, now, using the speed taken from the GPS sensor, when the app catches you going faster a notification will be displayed on your Android Auto unit from your virtual assistant! Tap it and listen to what it has to say to you! Please slow down, you have exceeded your speed limit!!

androidautoalerts notification


Where to get it

At the moment, the app is not following all of the Android Auto requirements (see them here) and Google only allows music and messaging Android Auto apps. For this reason I had to create the notification like a messaging app, like you are going to reply to it, even if you are not. Furthermore, I’m not going to publish it on Google Play at the moment (till apps of this kink will be accepted on it), but you can check its source code which I shared here on github.

Future development

Let’s wait for Google to accept other kinds of apps on the Android Auto platform and let’s hope this platform will become more and more interactive, full of useful apps (maybe some which can control car’s features, would be amazing!) and used by more and more people! I already love it, can’t live without it!

Development, Java, Spring

Using Spring Data to persist a Set of Enums in a Many-To-Many relationship

Usually, when we write a Many-To-Many relationship it is between 2 entities. Sometimes, it could happen that we have an entity which has a field which is a set of enum. In this case, we need to approach the problem differently and Spring comes to help.

Let’s see an example where we have two classes: Person and Skill (e.g. swimming, running, etc).

Many-To-Many between entities example

The following code shows what the situation is when Person and Skill are both entities.

public class Person {
  private Long id;
  private String name;
  @ManyToMany(fetch = FetchType.LAZY)
  @JoinTable(name = "person_skill", joinColumns = {
            @JoinColumn(name = "person_id")}, inverseJoinColumns = {
            @JoinColumn(name = "skill_id")})
  private Set<Skill> skillSet;

public class Skill {
  private Long id;
  private String name;

To use this mapping, you would have 3 tables. You can create them with the following SQL code.

CREATE TABLE `person` (
  `name` VARCHAR(45) NOT NULL,
  PRIMARY KEY (`id`));

CREATE TABLE `skill` (
  `name` VARCHAR(45) NOT NULL,
  PRIMARY KEY (`id`));

CREATE TABLE `person_skill` (
  `person_id` BIGINT(20) NOT NULL,
  `skill_id` BIGINT(20) NOT NULL,
  PRIMARY KEY (`person_id`, `skill_id`),
  INDEX `skill_fk_idx` (`skill_id` ASC),
  CONSTRAINT `person_fk`
    FOREIGN KEY (`person_id`)
    REFERENCES `person` (`id`)
  CONSTRAINT `skill_fk`
    FOREIGN KEY (`skill_id`)
    REFERENCES `skill` (`id`)


Many-To-Many between entity and enum example

The following code shows what the situation is when Person is an entity and Skill is an enum.

public class Person { 
  private Long id; 
  private String name; 
  @ElementCollection(targetClass = Skill.class)
  @CollectionTable(name = "person_skill",
            joinColumns = @JoinColumn(name = "person_id"))
  @Column(name = "skill_id")
  private Set<Skill> skillSet;

public enum Skill {

To use this mapping, you would have only 2 tables, because Skill is not an entity and would not have its own table. You can create them with the following SQL code.

CREATE TABLE `person` (
  `name` VARCHAR(45) NOT NULL,
  PRIMARY KEY (`id`));

CREATE TABLE `person_skill` (
  `person_id` BIGINT(20) NOT NULL,
  `skill_name` VARCHAR(45) NOT NULL,
  PRIMARY KEY (`person_id`, `skill_name`),
  CONSTRAINT `person_fk`
    FOREIGN KEY (`person_id`)
    REFERENCES `person` (`id`)

As you can see here, you don’t have the table skill because Skill is not an entity but only an enum; you only have to create the table which represents the relationship between Person and Skill. Furthermore, since we added the annotation @Enumerated(EnumType.STRING) Spring Data will save the name of the entity in the database (look, we put a VARCHAR column). If you prefer, you could use EnumType.ORDINAL and Spring Data will save the ordinal value of the entity (1,2,3,etc..), so change the column to accept a numeric value.

That’s it!

Android, Development

Android Contextual Action Bar

In this post you will learn how to implement a Contextual Action Bar (CAB) which will be useful to do actions on multiple items you have selected in a RecyclerView.

The Contextual Action Mode represents a contextual mode of the user interface and focuses user interaction toward performing contextual actions. In the case of a RecyclerView which shows a list of item, Contextual Action Mode is triggered after a long press on one of this items: this causes the Contextual Action Bar to appear at the top of the screen so then the user can interact with its actions.

Let’s follow these steps!

Initial setup

First of all, create a RecyclerView and its adapter in the usual way you do it. Here in this example I will use a RecyclerView which shows Authentication items (it is a class I made for a project, it doesn’t matter for the purpose of the example, use whatever you want, and change the names accordingly).

Theme changes

Open your styles.xml file and add the following lines:

<!--  It should be true otherwise action mode will not overlay toolbar -->
       <item name="windowActionModeOverlay">true</item>
       <!--  For Custom Action Mode Background Color/Drawable -->
       <item name="actionModeBackground">@color/colorAccent</item>

Comments should be self-explanatory.

Menu file

We need a menu file which contains the available actions for that RecyclerView. Let’s create a file into the res/menu directory like the following:

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android=""

        app:showAsAction="always" />


We added a delete action that will be shown on the CAB.

Adapter changes

Our adapter we created in the first step needs to be able to keep trace of the elements we select. To do this, let’s modify our adapter and create a new field

private final SparseBooleanArray selectedItemsIds;

and initialize it in our constructor

selectedItemsIds = new SparseBooleanArray();

Now, let’s create an Interface which will be useful for all the Adapters which need the CAB, and make our Adapter implements it. Please note this is a generic interface, so adapt it to the model you are displaying in your adapter.

public interface ActionModeAdapterCallbacks<T> {

    void toggleSelection(int position);

    void clearSelections();

    int getSelectedCount();

    List<T> getSelectedItems();

This is what the implementation should look like:

public void toggleSelection(final int position) {
    if (selectedItemsIds.get(position)) {
    } else {
        selectedItemsIds.put(position, true);

public void clearSelections() {

public int getSelectedCount() {
    return selectedItemsIds.size();

public List<Authentication> getSelectedItems() {
    final List<Authentication> selectedItemList = new LinkedList<>();
    for (int i = 0; i < selectedItemsIds.size(); i++) {
    return selectedItemList;

Now, we also need the Adapter to change the view state when an item gets selected to show the user a visual feedback. To do this we can use a StateListDrawable and in the onBindViewHolder() method add this line.


Create a new xml file inside the res/drawable directory:

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="">
    <item android:drawable="@color/colorPrimaryDark" android:state_activated="true" />
    <item android:drawable="@android:color/transparent" />

and assign it to the root view element of the layout file which represents your adapter’s row item:


Doing so, each time an item is selected or deselected, the adapter will change its color accordingly.

Fragment/Activity changes

Now, we need to make our Fragment/Activity class aware that we can trigger the Contextual Action Mode. To do so, let’s create an interface and call it ActionModeViewCallbacks.

public interface ActionModeViewCallbacks {

    void onListItemSelect(final int position);

    void onDestroyActionMode();


This interface has 2 methods:

  • onListItemSelect(final int position): to be used after a long click on an item to trigger the Action Mode (or after a single click on an item, if Action Mode was already triggered, to select this new item, too);
  • onDestroyActionMode(): reset actionMode variable to null;

Now, let’s create another interface which extends from this one:

public interface ListAuthenticationActionModeViewCallbacks extends ActionModeViewCallbacks {

    void onDeleteActionClicked();


This new interface has another method, onDeleteActionClicked(), which is where the presenter gets called (check MVP if you are not aware what MVP and a Presenter are) and asked to delete the items the user has selected (if you have more than a single action, you need to create more methods, each for any action you have).

This interface must be implemented by the Fragment/Activity which wants to use the Contextual Action Mode. The implementation looks like this:

    public void onListItemSelect(final int position) {

        final boolean hasCheckedItems = listAuthenticationAdapter.getSelectedCount() > 0;

        if (hasCheckedItems && actionMode == null) {
            // there are some selected items, start the actionMode
            actionMode = ((AppCompatActivity) getActivity()).startSupportActionMode(new ListAuthenticationToolbarActionModeCallback(this, this, listAuthenticationAdapter));
        } else if (!hasCheckedItems && actionMode != null) {
            // there no selected items, finish the actionMode

       if (actionMode != null) {
            //set action mode title on item selection
            actionMode.setTitle(getString(R.string.cab_selected, listAuthenticationAdapter.getSelectedCount()));

    public void onDestroyActionMode() 
        actionMode = null;

public void onDeleteActionClicked() {

where R.string.cab_selected is

<string name="cab_selected">%1$d selected</string>

In doing startSupportActionMode() we need to pass a ActionMode.Callback item that I haven’t explained yet. Let’s create another class which implements that interface.

public class ListAuthenticationToolbarActionModeCallback implements ActionMode.Callback {

    private final ActionModeViewCallbacks actionModeViewCallbacks;
    private final ListAuthenticationAdapter listAuthenticationAdapter;

    public ListAuthenticationToolbarActionModeCallback(final ActionModeViewCallbacks actionModeViewCallbacks, final ListAuthenticationAdapter listAuthenticationAdapter) {
        this.actionModeViewCallbacks = actionModeViewCallbacks;
        this.listAuthenticationAdapter = listAuthenticationAdapter;

    public boolean onCreateActionMode(final ActionMode mode, final Menu menu) {
        mode.getMenuInflater().inflate(, menu);
        return true;

    public boolean onPrepareActionMode(final ActionMode mode, final Menu menu) {
        return true;

    public boolean onActionItemClicked(final ActionMode mode, final MenuItem item) {
        switch (item.getItemId()) {
                return true;
        return false;

    public void onDestroyActionMode(final ActionMode mode) {

Please have a look on the official documentation here to understand how ActionMode.Callback works.


See the following screenshots:

  • first one shows the initial situation before Action Mode is triggered;
  • second one shows the situation after Action Mode was triggered by long press an item;
  • third one shows the final situation after the item “Auth 2” was deleted.

contextual action bar first contextual action bar selected contextual action bar after delete


Your Contextual Action Mode should work now! I suggest you to create different menu files, Fragment/ActivityToolbarActionModeCallback and Fragment/ActivityActionModeViewCallbacks to keep everything separated.

Please note: if you rotate the device, Contextual Action Mode is lost, you need to save its state and restore it. Another post will follow, hopefully soon!

Development, Java

Java concurrency: a few examples

Sometimes we write very high level code, sometimes we don’t. I want to put here a link to a simple project which shows how to deal with concurrency in Java with a few examples.

The project is available on Github here

Goal of the project is to retrieve the details and the balance of a player and show them at the same time: until you have collected both of them you have to wait before showing the user the information.

There are two different packages: in the first, Futures and Callables are being used, in the other, Threads/Runnables and a CountDownLatch are.

Futures and Callables are the best option when you need to run a task which has a return value. I also made it in a different way using Threads/Runnables, a CountDownLatch and some listeners but these classes are usually used when you have tasks which won’t return any value.

Use the two Main classes to run the examples. Have fun!

Android, Development

Android NoteApp with Dagger and Retrofit

Today I show a simple Android project I wrote which shows the use of Dagger, Retrofit and some other stuff.

The full source code of the project is available for you here

The project’s main purposes are the following:

  • Show Dagger2 dependency injection;
  • Show MVP architecture (made through Dagger2)
  • Show the repository pattern used to cache server data
  • Show the creation and use of a CustomView

Furthermore, I have used ButterKnife to remove the boilerplate code needed to bind classes/views, and GreenDao to automatically create the SQLite repository/model classes.

This project is based on the Google Android Architecture samples which are available here


ApplicationContextException using SpringBoot with Gradle and IntelliJ IDEA

In my spare time I decided to have a better look to SpringBoot and in doing so I decided to leave back Maven and Eclipse and to move to Gradle and IntelliJ, which I already use to develop Android applications.

During the first phase of my development I encountered a strange issue: it seems that IntelliJ IDEA will add wrong dependencies to your SpringBoot project which will cause it to crash at runtime.

This was the exception thrown and the full stack trace:

org.springframework.context.ApplicationContextException: Unable to start embedded container; nested exception is org.springframework.context.ApplicationContextException: Unable to start EmbeddedWebApplicationContext due to missing EmbeddedServletContainerFactory bean.
	at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.onRefresh( ~[spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE]
	at ~[spring-context-4.2.5.RELEASE.jar:4.2.5.RELEASE]
	at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh( ~[spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE]
	at org.springframework.boot.SpringApplication.refresh( [spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE]
	at org.springframework.boot.SpringApplication.createAndRefreshContext( [spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE]
	at [spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE]
	at [spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE]
	at [spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE]
	at com.sampleapp.SampleAppApplication.main( [main/:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_72]
	at sun.reflect.NativeMethodAccessorImpl.invoke( ~[na:1.8.0_72]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke( ~[na:1.8.0_72]
	at java.lang.reflect.Method.invoke( ~[na:1.8.0_72]
	at com.intellij.rt.execution.application.AppMain.main( [idea_rt.jar:na]
Caused by: org.springframework.context.ApplicationContextException: Unable to start EmbeddedWebApplicationContext due to missing EmbeddedServletContainerFactory bean.
	at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.getEmbeddedServletContainerFactory( ~[spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE]
	at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.createEmbeddedServletContainer( ~[spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE]
	at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.onRefresh( ~[spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE]
	... 13 common frames omitted

This stacktrace is related to SpringBoot v1.3.3 but I experienced the same issue even with SpringBoot v1.4.0.

In the end I found that IntelliJ was putting this line in the build.gradle file:


After removing that line, the project ran without issues.
So if you are experiencing an ApplicationContextException and you couldn’t find its cause, try to have a look at your build.gradle file.