class MyDS extends RestDataSource {
 private String extraJSONParameters = "";
    MyDS(LazyResponse result, String gridId, String connectionId) {
        this.setDataFormat(DSDataFormat.JSON);
        this.setDataProtocol(DSProtocol.POSTMESSAGE);
        /*this.setDisableQueuing(true);
        this.setSendMetaData(true);
        this.setCacheAllData(false);
        this.setAutoCacheAllData(false);*/
        this.setDataURL("api/rest/grid");
        /*this.setJsonSuffix("");
        this.setJsonPrefix("");*/

        DataSourceTextField[] fields = new DataSourceTextField[result.getHeaders().size()];
        for (int fieldIndex = 0; fieldIndex < fields.length; fieldIndex++) {
            fields[fieldIndex] = new DataSourceTextField(result.getHeaders().get(fieldIndex));
        }
        this.setFields(fields);

        String PROPERTY_CONNECTIONID = "connection-id";
        String PROPERTY_GRIDID = "grid-id";
        extraJSONParameters = "\"" + PROPERTY_CONNECTIONID + "\": \"" + connectionId
                + "\", \"" + PROPERTY_GRIDID + "\": \"" + gridId + "\"";

        OperationBinding fetchOperation = new OperationBinding();
        fetchOperation.setOperationType(DSOperationType.FETCH);
        fetchOperation.setDataProtocol(DSProtocol.POSTMESSAGE);
        fetchOperation.setDataFormat(DSDataFormat.JSON);
        fetchOperation.setDataURL(this.getDataURL());

        OperationBinding updateOperation = new OperationBinding();
        updateOperation.setOperationType(DSOperationType.UPDATE);
        updateOperation.setDataProtocol(DSProtocol.POSTMESSAGE);
        updateOperation.setDataFormat(DSDataFormat.JSON);
        updateOperation.setDataURL(this.getDataURL());

        OperationBinding addOperation = new OperationBinding();
        addOperation.setOperationType(DSOperationType.ADD);
        addOperation.setDataProtocol(DSProtocol.POSTMESSAGE);
        addOperation.setDataFormat(DSDataFormat.JSON);
        addOperation.setDataURL(this.getDataURL());

        OperationBinding deleteOperation = new OperationBinding();
        addOperation.setOperationType(DSOperationType.REMOVE);
        addOperation.setDataProtocol(DSProtocol.POSTMESSAGE);
        addOperation.setDataFormat(DSDataFormat.JSON);
        addOperation.setDataURL(this.getDataURL());
        this.setOperationBindings(fetchOperation, updateOperation, addOperation,
                deleteOperation);
    }

    @Override
    protected Object transformRequest(DSRequest dsRequest) {
        String message = (String) super.transformRequest(dsRequest);

        message = message.substring(0, message.length() - 1)
                + ", " + extraJSONParameters + " }";

        return message;
    }
}




DataSource ds = new MyDS(result, result.getGridId(), connectionController.getConnectionId());
grid.setDataSource(ds);
grid.fetchData(null, new DSCallback() {
    @Override
    public void execute(DSResponse dsResponse, Object data, DSRequest dsRequest) {
        grid.redraw();
        grid.refreshFields();
        if(grid.getTotalRows() != 0) {
            exportToExcelButton.enable();
        }
    }
});