java中过滤器的使用

public final class EntranceFilter implements Filter {private static final String JSONP_CALLBACK = "callback";private static final String JSONP_UPLOAD_CALLBACK = "uploadcallback";private static final String HTTP_AJAX_TYPE = "ajax";@SuppressWarnings("unchecked")public void doFilter(ServletRequest req, ServletResponse respon, FilterChain chain) throws IOException, ServletException {HttpServletRequest request = (HttpServletRequest) req;HttpServletResponse response = (HttpServletResponse) respon;//请求类型  如果是ajax请求响应头会有，x-requested-with；if (request.getHeader("x-requested-with") != null&& request.getHeader("x-requested-with").equalsIgnoreCase("XMLHttpRequest")) {TempleConfigContext.setCurrentRequestType(TempleConfigContext.AJAX_REQUEST_TYPE);}//跨域请求if(request.getParameter(JSONP_CALLBACK) != null || request.getParameter(JSONP_UPLOAD_CALLBACK) != null){TempleConfigContext.setCurrentRequestType(TempleConfigContext.AJAX_REQUEST_TYPE);}if(request.getParameter(HTTP_AJAX_TYPE) != null){TempleConfigContext.setCurrentRequestType(TempleConfigContext.AJAX_REQUEST_TYPE);}//请求是ajax请求if(TempleConfigContext.getCurrentRequestType() == TempleConfigContext.AJAX_REQUEST_TYPE){ByteResponseWrapper brw = new ByteResponseWrapper(response);chain.doFilter(request, brw);String out = new String(brw.getBytes());//ajax矫正if(TempleConfigContext.getCurrentRequestType() == TempleConfigContext.AJAX_REQUEST_TYPE){Map<String, Object> map = null;try {map = JsonTool.getMap4Json(out);} catch (JSONException ex) {map = new HashMap<String, Object>();map.put(Constant.MESSAGE, out);}int status = brw.getStatus();response.setStatus(HttpStatus.OK.value());if (status >= 200 && status < 300 || status == 304) {if (status == 304) {response.setStatus(HttpStatus.NOT_MODIFIED.value());}map.put(Constant.STATUS, Constant.SUCCESS);} else {map.put(Constant.STATUS, Constant.FAILURE);}out = JSONObject.fromObject(map).toString();}//System.out.println(out);if (request.getParameter(JSONP_CALLBACK) != null) {out = request.getParameter(JSONP_CALLBACK) + "(" + out + ");";response.setCharacterEncoding("utf8");response.setContentType("application/json;charset=" + Constant.ENCODING);response.setContentLength(out.getBytes().length);response.getOutputStream().write(out.getBytes());response.getOutputStream().flush();}else if(request.getParameter(JSONP_UPLOAD_CALLBACK) != null){out = URLEncoder.encode(out, Constant.ENCODING); response.setCharacterEncoding(Constant.ENCODING);response.setContentType("text/html;charset=" + Constant.ENCODING);response.setHeader("Cache-Control", "no-cache");response.addHeader("Access-Control-Allow-Origin", "*");response.addHeader("Access-Control-Allow-Headers", "x-requested-with");response.addHeader("Location", Constant.FRONT_DOMAIN_NAME + "/deal_callback.html?" + request.getParameter(JSONP_UPLOAD_CALLBACK) + "(" + out + ")");response.sendRedirect(Constant.FRONT_DOMAIN_NAME + "/deal_callback.html?" + request.getParameter(JSONP_UPLOAD_CALLBACK) + "(" + out + ")");}else {response.getOutputStream().write(out.getBytes());response.getOutputStream().flush();}}else {chain.doFilter(request, respon);}TempleConfigContext.removeContext();}public void destroy() {}public void init(FilterConfig filterConfig) {}static class ByteResponseWrapper extends HttpServletResponseWrapper {private PrintWriter writer;private ByteOutputStream output;private int code = 200;public byte[] getBytes() {writer.flush();return output.getBytes();}public ByteResponseWrapper(HttpServletResponse response) {super(response);output = new ByteOutputStream();writer = new PrintWriter(output);}@Overridepublic PrintWriter getWriter() {return writer;}@Overridepublic ServletOutputStream getOutputStream() throws IOException {return output;}public int getStatus() {return code;}public void sendRedirect(String location) throws IOException {code = HttpStatus.MOVED_TEMPORARILY.value();super.sendRedirect(location);}@Overridepublic void setStatus(int sc) {this.code = sc;}@Overridepublic void setStatus(int sc, String message) {this.code = sc;}@Overridepublic void sendError(int sc) throws IOException {this.code = sc;}@Overridepublic void sendError(int sc, String msg) throws IOException {this.code = sc;}}static class ByteOutputStream extends ServletOutputStream {private ByteArrayOutputStream bos = new ByteArrayOutputStream();@Overridepublic void write(int b) throws IOException {bos.write(b);}public byte[] getBytes() {return bos.toByteArray();}}private static class JsonTool {@SuppressWarnings({ "unchecked", "rawtypes" })public static Map getMap4Json(String jsonString) {JSONObject jsonObject = JSONObject.fromObject(jsonString);Iterator keyIter = jsonObject.keys();String key;Object value;Map valueMap = new HashMap();while (keyIter.hasNext()) {key = (String) keyIter.next();value = jsonObject.get(key);valueMap.put(key, value);}return valueMap;}}}

如果请求是跨域的则请求会带一个callback的参数 进入过滤器并设置请求类型是AJAX_REQUEST_TYPE

当准备响应给浏览器时 再次进入过滤器将返回的字符串转化为JSON对象 这里controller的返回类型必须是对象类型 比如Map<String, Object>或者bean 不能是JSONArray对象或者直接是List对象 因为JsonTool.getMap4Json转化json的时候JSONObject.fromObject()这句的限制只能转化Object