Reduce spacing in bibliography using biblatex

\bibitemsep length between two different entries, preset to \itemsep

\bibnamesep length between two entries of different authors

\bibinitsep length between two entries of authors with different first letter

\documentclass{article}
\usepackage[english]{babel}
\usepackage{blindtext}
\usepackage{biblatex}
\addbibresource{biblatex-examples.bib}% Part of the TeX distribution
\usepackage{setspace}
\onehalfspacing
\begin{document}
\blindtext

\singlespacing\blindtext

\nocite{*}

\begingroup
\setstretch{0.8}
\setlength\bibitemsep{0pt}
\printbibliography
\endgroup

\end{document} 

By the way: I prefer to typeset a bibliography with \RaggedRight (from package ragged2e)

\let\oldbibliography\thebibliography
\renewcommand{\thebibliography}[1]{\oldbibliography{#1}
\setlength{\itemsep}{0pt}} %Reducing spacing in the bibliography.

I had trouble using \singlespace. However I found the .cls file that my tex file referring to had defined an environment singlespace. So my way looks like this

\begin{singlespace}
\setlength\bibitemsep{10pt}   % length between two different entries
\printbibliography
\end{singlespace}
\addcontentsline{toc}{head}{REFERENCES}  % must be after \printbibliography or the page# is wrong