HttpServletRequestWrapperFilter

作用其实很简单就是 在HttpServletRequest对象在包装一次，让其支持getUserPrincipal，getRemoteUser方法来获取登录的用户信息。

  public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

       //从session或者request中取得AttributePrincipal，其实Assertion的一个principal属性

        AttributePrincipal principal = this.retrievePrincipalFromSessionOrRequest(servletRequest);

       //对request进行包装，并处理后面的过滤器，使其后面的过滤器或者servlert能够在reqeust能够在request.getRemoteUser()或者request.getUserPrincipal

        filterChain.doFilter(new HttpServletRequestWrapperFilter.CasHttpServletRequestWrapper((HttpServletRequest)servletRequest, principal), servletResponse);

    }

    protected AttributePrincipal retrievePrincipalFromSessionOrRequest(ServletRequest servletRequest) {

        HttpServletRequest request = (HttpServletRequest)servletRequest;

        HttpSession session = request.getSession(false);

        Assertion assertion = (Assertion)((Assertion)(session == null?request.getAttribute("_const_cas_assertion_"):session.getAttribute("_const_cas_assertion_")));

        return assertion == null?null:assertion.getPrincipal();

    }

    实现起来也比较简单，这个里面使用一个内部类CasHttpServletRequestWrapper，其继承HttpServletRequestWrapper，

    通过给定Assertion对象中取得AttributePrincipal对象来组装CasHttpServletRequestWrapper。

    final class CasHttpServletRequestWrapper extends HttpServletRequestWrapper {

        private final AttributePrincipal principal;

        CasHttpServletRequestWrapper(HttpServletRequest request, AttributePrincipal principal) {

            super(request);

            this.principal = principal;

        }

        public Principal getUserPrincipal() {

            return this.principal;

        }

        public String getRemoteUser() {

            return this.principal != null?this.principal.getName():null;

        }

        public boolean isUserInRole(String role) {

            if(CommonUtils.isBlank(role)) {

                HttpServletRequestWrapperFilter.this.logger.debug("No valid role provided.  Returning false.");

                return false;

            } else if(this.principal == null) {

                HttpServletRequestWrapperFilter.this.logger.debug("No Principal in Request.  Returning false.");

                return false;

            } else if(CommonUtils.isBlank(HttpServletRequestWrapperFilter.this.roleAttribute)) {

                HttpServletRequestWrapperFilter.this.logger.debug("No Role Attribute Configured. Returning false.");

                return false;

            } else {

                Object value = this.principal.getAttributes().get(HttpServletRequestWrapperFilter.this.roleAttribute);

                if(value instanceof Collection) {

                    Iterator isMember = ((Collection)value).iterator();

                    while(isMember.hasNext()) {

                        Object o = isMember.next();

                        if(this.rolesEqual(role, o)) {

                            HttpServletRequestWrapperFilter.this.logger.debug("User [{}] is in role [{}]: true", this.getRemoteUser(), role);

                            return true;

                        }

                    }

                }

                boolean isMember1 = this.rolesEqual(role, value);

                HttpServletRequestWrapperFilter.this.logger.debug("User [{}] is in role [{}]: {}", new Object[]{this.getRemoteUser(), role, Boolean.valueOf(isMember1)});

                return isMember1;

            }

        }

        private boolean rolesEqual(String given, Object candidate) {

            return HttpServletRequestWrapperFilter.this.ignoreCase?given.equalsIgnoreCase(candidate.toString()):given.equals(candidate);

        }

    }