How to center align the ActionBar title in Android?

To have a centered title in ABS (if you want to have this in the default ActionBar, just remove the "support" in the method names), you could just do this:

In your Activity, in your onCreate() method:

getSupportActionBar().setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM); 
getSupportActionBar().setCustomView(R.layout.abs_layout);

abs_layout:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
        android:layout_gravity="center"
    android:orientation="vertical">

    <android.support.v7.widget.AppCompatTextView
        android:id="@+id/tvTitle"
        style="@style/TextAppearance.AppCompat.Widget.ActionBar.Title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:textColor="#FFFFFF" />

</LinearLayout>

Now you should have an Actionbar with just a title. If you want to set a custom background, set it in the Layout above (but then don't forget to set android:layout_height="match_parent").

or with:

getSupportActionBar().setBackgroundDrawable(getResources().getDrawable(R.drawable.yourimage));

I haven't had much success with the other answers... below is exactly what worked for me on Android 4.4.3 using the ActionBar in the support library v7. I have it set up to show the navigation drawer icon ("burger menu button")

XML

    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="horizontal" >

    <TextView
        android:id="@+id/actionbar_textview"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:maxLines="1"
        android:clickable="false"
        android:focusable="false"
        android:longClickable="false"
        android:textStyle="bold"
        android:textSize="18sp"
        android:textColor="#FFFFFF" />

</LinearLayout>

Java

//Customize the ActionBar
final ActionBar abar = getSupportActionBar();
abar.setBackgroundDrawable(getResources().getDrawable(R.drawable.actionbar_background));//line under the action bar
View viewActionBar = getLayoutInflater().inflate(R.layout.actionbar_titletext_layout, null);
ActionBar.LayoutParams params = new ActionBar.LayoutParams(//Center the textview in the ActionBar !
        ActionBar.LayoutParams.WRAP_CONTENT, 
        ActionBar.LayoutParams.MATCH_PARENT, 
        Gravity.CENTER);
TextView textviewTitle = (TextView) viewActionBar.findViewById(R.id.actionbar_textview);
textviewTitle.setText("Test");
abar.setCustomView(viewActionBar, params);
abar.setDisplayShowCustomEnabled(true);
abar.setDisplayShowTitleEnabled(false);
abar.setDisplayHomeAsUpEnabled(true);
abar.setIcon(R.color.transparent);
abar.setHomeButtonEnabled(true);