How to collect information of all esx hosts connected to vCenter server using vSphere API and Java?

I am collecting information of esx systems using vSphere API. By using this API, I am able to collect information of esx hosts by giving IP.

try{
ServiceInstance si =newServiceInstance(new URL(url), user, pass,true);
   System.out.println("host :"+host+"---"+si.getAboutInfo().getFullName());

System.out.println(" Version is .. "+si.getAboutInfo().version);
System.out.println(" os type is .. "+si.getAboutInfo().osType);
System.out.println("Vendor is .. "+ si.getAboutInfo().vendor);
System.out.println("name is"+ si.getAboutInfo().name);

ManagedEntity[] managedEntities =newInventoryNavigator(
  si.getRootFolder()).searchManagedEntities("VirtualMachine");
   ManagedEntity[] hostmanagedEntities =newInventoryNavigator(
  si.getRootFolder()).searchManagedEntities("HostSystem");

for(ManagedEntity hostmanagedEntity : hostmanagedEntities){
   HostSystem hostsys =(HostSystem) hostmanagedEntity;

   StringESXhostname= hostsys.getName();

   HostListSummary hls = hostsys.getSummary();
   HostHardwareSummary hosthwi = hls.getHardware();
   HostListSummaryQuickStats hqs = hls.getQuickStats();
   Datastore[] HDS = hostsys.getDatastores();
   StringBuilder DS =newStringBuilder();
   for(int i=0;i <HDS.length;i++){
   DatastoreSummary dsm =HDS[i].getSummary();

  DS.append(dsm.name+":"+dsm.capacity+":"+dsm.freeSpace+"-");
   }

   int MEM=hqs.overallMemoryUsage;
   int UPT=hqs.getUptime();
   Integer CPU=hqs.getOverallCpuUsage();  

   String esxkey ="ESXRealInfo";
   String esxvalue ="ESXhostname-"+ESXhostname
   +";CPU Usage-"+ CPU +";MEM Usage-"
   + MEM +";UPTIME-"+ UPT+"; Datastores -"+DS;
   }


}
catch(Exception e){ e.printStackTrace();}

By using this code and manipulating managedentities object I can extract information of each host and vm working on each host.

Now instead of collecting information from different hosts, I want to collect information from vcenter server. vCenter server also contains all details about hosts and their VMs.

I want to get this information by using vCenter server instead of visiting each host. Is it possible to get this information? how?