如何将不带www的根域名301重定向到带www的主域名

@Override

public void init(FilterConfig filterConfig) throws ServletException {}

@Override

public void doFilter(ServletRequest request, ServletResponse response,

FilterChain chain) throws IOException, ServletException {

HttpServletRequest req = (HttpServletRequest) request;

HttpServletResponse resp= (HttpServletResponse)response;

String tempPathString = req.getRequestURI();

if(req.getRequestURL().indexOf("http://example.com")>=0){ // 不带www，跳转的首页 String queryString = (req.getQueryString() == null ? "" : "?"+req.getQueryString());

resp.setStatus(301);

resp.setHeader( "Location", "http://www.example.com"+tempPathString+queryString);

resp.setHeader( "Connection", "close" );

}

chain.doFilter(request, response);

}

@Override

public void destroy() {}