![](https://csdnimg.cn/release/download_crawler_static/3479144/bg11.jpg)
1 Introduction
more. In fact, internally, the front-end programs VirtualBox and VBoxManage use nothing but
this API as well – there are no hidden backdoors into the virtualization engine for our own front-
ends. This ensures the entire Main API is both well-documented and well-tested. (The same
applies to VBoxHeadless, which is not shown in the image.)
1.2 Two guises of the same “Main API”: the web service or
COM/XPCOM
There are several ways in which the Main API can be called by other code:
1. VirtualBox comes with a web service that maps nearly the entire Main API. The web ser-
vice ships in a stand-alone executable (vboxwebsrv) that, when running, acts as an HTTP
server, accepts SOAP connections and processes them.
Since the entire web service API is publicly described in a web service description file (in
WSDL format), you can write client programs that call the web service in any language with
a toolkit that understands WSDL. These days, that includes most programming languages
that are available: Java, C++, .NET, PHP, Python, Perl and probably many more.
All of this is explained in detail in subsequent chapters of this book.
There are two ways in which you can write client code that uses the web service:
a) For Java as well as Python, the SDK contains easy-to-use classes that allow you to use
the web service in an object-oriented, straightforward manner. We shall refer to this
as the “object-oriented web service (OOWS)“.
The OO bindings for Java are described in chapter 10, Using Java API, page 294, those
for Python in chapter 2.1.2, The object-oriented web service for Python, page 24.
b) Alternatively, you can use the web service directly, without the object-oriented client
layer. We shall refer to this as the “raw web service”.
You will then have neither native object orientation nor full type safety, since web
services are neither object-oriented nor stateful. However, in this way, you can write
client code even in languages for which we do not ship object-oriented client code; all
you need is a programming language with a toolkit that can parse WSDL and generate
client wrapper code from it.
We describe this further in chapter 2.2, Using the raw web service with any language,
page 25, with samples for Java and Perl.
2. Internally, for portability and easier maintenance, the Main API is implemented using the
Component Object Model (COM), an interprocess mechanism for software components
originally introduced by Microsoft for Microsoft Windows. On a Windows host, VirtualBox
will use Microsoft COM; on other hosts where COM is not present, it ships with XPCOM,
a free software implementation of COM originally created by the Mozilla project for their
browsers.
So, if you are familiar with COM and the C++ programming language (or with any other
programming language that can handle COM/XPCOM objects, such as Java, Visual Basic or
C#), then you can use the COM/XPCOM API directly. VirtualBox comes with all necessary
files and documentation to build fully functional COM applications. For an introduction,
please see chapter 2.3, Using COM/XPCOM directly, page 31 below.
The VirtualBox front-ends (the graphical user interfaces as well as the command line),
which are all written in C++, use COM/XPCOM to call the Main API. Technically, the web
service is another front-end to this COM API, mapping almost all of it to SOAP clients.
If you wonder which way to choose, here are a few comparisons:
17