【Spring】使用Filter过滤请求

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原文：http://liujiajia.me/#/blog/details/spring-filter-request-with-filter

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public class CustomizedFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        //Do nothing
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        // 验证请求
        if (!validate(request)) {
            HttpServletResponse httpResponse = (HttpServletResponse) response;
            httpResponse.setCharacterEncoding("UTF-8");
            httpResponse.setContentType("application/json;charset=UTF-8");
            httpResponse.setStatus(HttpServletResponse.SC_OK);

            Result result = new Result();
            result.setCode(ErrorCode.UNHANDLEDEXCEPTION); // 错误号
            result.setMsg("error message"); // 错误信息
            httpResponse.setHeader("Access-Control-Allow-Origin", "*");
            httpResponse.getWriter().write(JSONObject.fromObject(result).toString());

            return;
        }

        chain.doFilter(request, response);
    }

    private boolean validate(ServletRequest request) {
        // do some validation
        return true;
    }

    @Override
    public void destroy() {
        //Do nothing
    }
}