change datasource via rest service

HttpRequestBase httpReq = new HttpPut();
     BasicHttpEntity reqEntity = new BasicHttpEntity();
     String requestXml="<resourceDescriptor name='TestUdc1' wsType='reportUnit' " +
                       "uriString='/reports/test/TestUdc' isNew='false'>" +
                       " <label>Bar Unit</label> " +
                       "<description>This is a test</description> " ;
 
     String requestXml2="<resourceDescriptor name='' wsType='datasource' uriString='/reports/test/TestUdc' isNew='false'>"+
                        "<label> Test </label>"+
                        "<resourceProperty name='PROP_REFERENCE_URI'>"+
                        "<value>/datasources/PilocDS</value>"+
                        "</resourceProperty>"+
                        "<resourceProperty name='PROP_IS_REFERENCE'>"+
                        "<value>true</value>"+
                        "</resourceProperty>"+
                        "</resourceDescriptor>"+
                        "</resourceDescriptor>";
 
     requestXml=requestXml+requestXml2;
     reqEntity.setContent(new ByteArrayInputStream(requestXml.getBytes()));
     ((HttpEntityEnclosingRequestBase) httpReq).setEntity(reqEntity);
 
     URI uri = createURI("/report/reports/test/TestUdc?RUN_OUTPUT_FORMAT=HTML", null, false);            
     httpReq.setURI(uri);
     httpRes = httpClient.execute(httpReq, httpContext);
     System.out.println("Response status line:"+httpRes.getStatusLine());
 
     String responseReportRD = EntityUtils.toString(httpRes.getEntity());
 
     DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
     DocumentBuilder builder = domFactory.newDocumentBuilder();
     StringReader sr = new StringReader(responseReportRD);
     InputSource is = new InputSource(sr);
     Document xmlDoc = builder.parse(is);
 
     //Extracting the report's UUID
     NodeList nodes = xmlDoc.getElementsByTagName("uuid");
     String reportUuid = nodes.item(0).getTextContent();
     System.out.println("-----ReportUUid:"+reportUuid);