Java API bindings
The Java bindings make use of JNA to expose the C API in a Java friendly way. The bindings are based on work initiated by Toth Istvan.
Content
The bindings are articulated around a few classes in the
org/libvirt
package, notably the Connect
,
Domain
and Network
ones. Functions in the
C API taking
virConnectPtr
, virDomainPtr
or
virNetworkPtr
as their first argument usually become
methods for the classes, their name is just stripped from the
virConnect or virDomain(Get) prefix and the first letter gets
converted to lower case, for example the C functions:
int virConnectNumOfDomains (virConnectPtr conn); int virDomainSetMaxMemory (virDomainPtr domain, unsigned long memory);
become
virConn.numOfDomains() virDomain.setMaxMemory(long memory)
There is of course some functions where the mapping is less direct and using extra classes to map complex arguments. The Javadoc is available online or as part of a separate libvirt-java-javadoc package.
So let's look at a simple example inspired from the
test.java
test found in src
in the source
tree:
import org.libvirt.*; public class minitest { public static void main(String[] args) { Connect conn=null; try{ conn = new Connect("test:///default", true); } catch (LibvirtException e) { System.out.println("exception caught:"+e); System.out.println(e.getError()); } try{ Domain testDomain=conn.domainLookupByName("test"); System.out.println("Domain:" + testDomain.getName() + " id " + testDomain.getID() + " running " + testDomain.getOSType()); } catch (LibvirtException e) { System.out.println("exception caught:"+e); System.out.println(e.getError()); } } }
There is not much to comment about it, it really is a straight mapping from the C API, the only points to notice are:
-
the import of the modules in the
org.libvirt
package -
getting a connection to the hypervisor, in that case using the readonly access to the default test hypervisor.
-
getting an object representing the test domain using
lookupByName
-
if the domain is not found a LibvirtError exception will be raised
-
extracting and printing some information about the domain using various methods associated to the Domain class.