See the SDK samples for using ServiceInstance with the current user credentials, specifically in VmDataProviderImpl.java:
flex-samples/vsphereviews/vsphere-wssdk-provider/src/main/java/com/vmware/samples/wssdkprovider/VmDataProviderImpl.java
or
html-bridge/samples/vsphereviews/vsphere-wssdk-provider/src/main/java/com/vmware/samples/wssdkprovider/VmDataProviderImpl.java