Creating Data View Extensions

When you create data view extensions for the vSphere Client user interface layer, follow these general recommendations:

You do not need to change the Data Adapter services running in the service layer.
You can use the generic DataAccessController Java class provided with each generated plug-in project to handle HTTP JSON GET data requests.
You must access data through the vSphere Client server and avoid calling directly your back end services or database.

Common Data Access Pattern

You can use the pattern demonstrated in the html-sample in the SDK to access data from the vCenter Server system from your plug-ins:

The Ajax GET request created in your JavaScript code has the following format:
```
/plugin_context_path/rest/data/properties/objectId?properties=properties-list
```
, where objectId is the object ID of the currently selected vSphere object, and properties-list is the comma-separated list of properties that must be retrieved for that object.
The web.xml deployment descriptor located in the WEB-INF folder of the UI bundle of your plug-in contains the <servlet-mapping> element that defines the /rest/* URL pattern for invoking the springServlet servlet.
```
   <servlet-mapping>
      <servlet-name>springServlet</servlet-name>
      <url-pattern>/rest/*</url-pattern>
   </servlet-mapping>
```
The bundle-context.xml file located in the WEB-INF\spring folder declares the dataAccessController bean for the DataAccessController class that is available in the Java service bundle of your plug-in.
```
<bean name="dataAccessController" 
     class="com.vmware.samples.vspherewssdk.mvc.DataAccessController" />
```

The DataAccessController class included in the Java service bundle of your plug-in has the @RequestMapping annotation set to process the HTTP JSON GET for the /data endpoint. The getProperties() generic method has the @RequestMapping annotation set to the /properties/{objectId} value to handle the Ajax GET requests created in your JavaScript code.

    ...
@Controller
@RequestMapping(value = "/data", method = RequestMethod.GET)
public class DataAccessController {

    ...

   @RequestMapping(value = "/properties/{objectId}")
   @ResponseBody
   public Map<String, Object> getProperties(
            @PathVariable("objectId") String encodedObjectId,
            @RequestParam(value = "properties", required = true) String properties)

    ...

The getProperties() generic method uses the QueryUtil class to create a Data Service query for the requested list of vSphere object properties. The query results are returned to the Web browser as JSON data.

     ...
      Object ref = getDecodedReference(encodedObjectId);
      String objectId = _objectReferenceService.getUid(ref);

      String[] props = properties.split(",");
      PropertyValue[] pvs = QueryUtil.getProperties(_dataService, ref, props);
      Map<String, Object> propsMap = new HashMap<String, Object>();
      propsMap.put(OBJECT_ID, objectId);
      for (PropertyValue pv : pvs) {
         propsMap.put(pv.propertyName, pv.value);
      }
      return propsMap;
   }

The JavaScript code can display the data returned by the Ajax GET request as needed.