更新自@MrEngineer13的回答:要在任何情况下对齐标题中心，包括汉堡图标，选项菜单，你可以在工具栏中添加一个框架布局，像这样:

   <android.support.v7.widget.Toolbar
    android:id="@+id/toolbar_top"
    android:layout_height="wrap_content"
    android:layout_width="match_parent"
    android:minHeight="?attr/actionBarSize"
    android:background="@color/action_bar_bkgnd"
    app:theme="@style/ToolBarTheme" >

         <FrameLayout android:layout_width="match_parent"
                    android:layout_height="match_parent">

              <TextView
               android:layout_width="wrap_content"
               android:layout_height="wrap_content"
               android:text="Toolbar Title"
               android:layout_gravity="center"
               style="@style/TextAppearance.AppCompat.Widget.ActionBar.Title"
               android:id="@+id/toolbar_title" />

        </FrameLayout>

   </android.support.v7.widget.Toolbar>

对于自定义字体在工具栏，你可以覆盖textView字体的风格，然后每个textView在你的应用程序也工具栏标题字体自动改变 我在android studio 3.1.3中进行了测试

在风格上这样做:

<style name="defaultTextViewStyle" parent="android:Widget.TextView">
        <item name="android:fontFamily">@font/your_custom_font</item>
</style>

然后在你的主题中使用这个:

<item name="android:textViewStyle">@style/defaultTextViewStyle</item>

private void makeTitleCenter(String title, Toolbar toolbar) {
    if (title != null && !TextUtils.isEmpty(title.trim())) {
        final String tag = " ";
        if (getSupportActionBar() != null) {
            getSupportActionBar().setTitle(tag);
        }
        TextView titleTv = null;
        View leftBtn = null;
        for (int i = 0; i < toolbar.getChildCount(); i++) {
            View view = toolbar.getChildAt(i);
            CharSequence text = null;
            if (view instanceof TextView && (text = ((TextView) view).getText()) != null && text.equals(tag)) {
                titleTv = (TextView) view;
            } else if (view instanceof ImageButton) {
                leftBtn = view;
            }
        }
        if (titleTv != null) {
            final TextView fTitleTv = titleTv;
            final View fLeftBtn = leftBtn;
            fTitleTv.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
                @Override
                public void onGlobalLayout() {
                    fTitleTv.getViewTreeObserver().removeOnGlobalLayoutListener(this);
                    int leftWidgetWidth = fLeftBtn != null ? fLeftBtn.getWidth() : 0;
                    fTitleTv.setPadding(DimenUtil.getResources().getDisplayMetrics().widthPixels / 2 - leftWidgetWidth - fTitleTv.getWidth() / 2, 0, 0, 0);
                    fTitleTv.requestLayout();
                }
            });
        }
    }
}

我用这个问题的解决方案:

 public static void applyFontForToolbarTitle(Activity a){
        Toolbar toolbar = (Toolbar) a.findViewById(R.id.app_bar);
        for(int i = 0; i < toolbar.getChildCount(); i++){
            View view = toolbar.getChildAt(i);
            if(view instanceof TextView){
                TextView tv = (TextView) view;
                if(tv.getText().equals(a.getTitle())){
                    tv.setTypeface(getRuneTypefaceBold(a));
                    break;
                }
            }
        }
    }

对于重心，我认为有必要将布局参数水平更改为match_parent，然后:

tv.setGravity(Gravity.CENTER);

这里是标题文本依赖的方法，从工具栏找到TextView实例。

  public static TextView getToolbarTitleView(ActionBarActivity activity, Toolbar toolbar){
    ActionBar actionBar = activity.getSupportActionBar();
    CharSequence actionbarTitle = null;
    if(actionBar != null)
        actionbarTitle = actionBar.getTitle();
    actionbarTitle = TextUtils.isEmpty(actionbarTitle) ? toolbar.getTitle() : actionbarTitle;
    if(TextUtils.isEmpty(actionbarTitle)) return null;
    // can't find if title not set
    for(int i= 0; i < toolbar.getChildCount(); i++){
        View v = toolbar.getChildAt(i);
        if(v != null && v instanceof TextView){
            TextView t = (TextView) v;
            CharSequence title = t.getText();
            if(!TextUtils.isEmpty(title) && actionbarTitle.equals(title) && t.getId() == View.NO_ID){
                //Toolbar does not assign id to views with layout params SYSTEM, hence getId() == View.NO_ID
                //in same manner subtitle TextView can be obtained.
                return t;
            }
        }
    }
    return null;
}

要在工具栏中使用自定义标题，您可以添加一个自定义标题，如:

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    android:background="?attr/colorPrimary"
    android:elevation="5dp"
    app:contentInsetLeft="0dp"
    app:contentInsetStart="0dp"
    app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
    app:theme="@style/ThemeOverlay.AppCompat.Dark">


        <LinearLayout
            android:id="@+id/lnrTitle"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center_horizontal"
            android:orientation="vertical">

            <TextView
                android:id="@+id/txvHeader"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center_horizontal|center"
                android:gravity="center"
                android:ellipsize="end"
                android:maxLines="1"
                android:text="Header"
                android:textColor="@color/white"
                android:textSize="18sp" />


        </LinearLayout>


</android.support.v7.widget.Toolbar>

Java代码:

Toolbar toolbar = findViewById(R.id.toolbar);

setSupportActionBar(toolbar);

if (getSupportActionBar() == null)
    return;

getSupportActionBar().setTitle("Title");

getSupportActionBar().setDisplayHomeAsUpEnabled(true);