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经常会遇到需要处理http请求以及响应body的场景。而这里比较大的一个问题是servlet的requestBody或responseBody流一旦被读取了。就无法二次读取了。针对这个问题，spring本身提供了解决方案，即ContentCachingRequestWrapper/ContentCachingResponseWrapper。

我们编写一个过滤器:

public abstract class HttpBodyRecorderFilter extends OncePerRequestFilter {
    private static final int DEFAULT_MAX_PAYLOAD_LENGTH = 1024 * 512;
    private int maxPayloadLength = DEFAULT_MAX_PAYLOAD_LENGTH;
    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)            throws ServletException, IOException {
        boolean isFirstRequest = !isAsyncDispatch(request);
        HttpServletRequest requestToUse = request;
        if (isFirstRequest
                && !(request instanceof ContentCachingRequestWrapper)
                && (request.getMethod().equals(HttpMethod.PUT.name())                        || request.getMethod().equals(HttpMethod.POST.name()))) {
            requestToUse = new ContentCachingRequestWrapper(request);
        }
        HttpServletResponse responseToUse = response;
        if (!(response instanceof ContentCachingResponseWrapper)
                && (request.getMethod().equals(HttpMethod.PUT.name())                        || request.getMethod().equals(HttpMethod.POST.name()))) {
            responseToUse = new ContentCachingResponseWrapper(response);
        }
        boolean hasException = false;
        try {
            filterChain.doFilter(requestToUse, responseToUse);
        } catch (final Exception e) {
            hasException = true;
            throw e;
        } finally {
            int code = hasException ? 500 : response.getStatus();
            if (!isAsyncStarted(requestToUse)
                    && (this.codeMatched(code, AdvancedHunterConfigManager.recordCode()))) {
                recordBody(createRequest(requestToUse), createResponse(responseToUse));
            } else {
                writeResponseBack(responseToUse);
            }
        }
    }
    protected String createRequest(HttpServletRequest request) {
        String payload = "";
        ContentCachingRequestWrapper wrapper =
                WebUtils.getNativeRequest(request, ContentCachingRequestWrapper.class);
        if (wrapper != null) {
            byte[] buf = wrapper.getContentAsByteArray();
            payload = genPayload(payload, buf, wrapper.getCharacterEncoding());
        }
        return payload;
    }
    protected String createResponse(HttpServletResponse resp) {
        String response = "";
        ContentCachingResponseWrapper wrapper = WebUtils.getNativeResponse(resp, ContentCachingResponseWrapper.class);
        if (wrapper != null) {
            byte[] buf = wrapper.getContentAsByteArray();
            try {
                wrapper.copyBodyToResponse();
            } catch (IOException e) {
                e.printStackTrace();
            }
            response = genPayload(response, buf, wrapper.getCharacterEncoding());
        }
        return response;
    }
    protected void writeResponseBack(HttpServletResponse resp) {
        ContentCachingResponseWrapper wrapper = WebUtils.getNativeResponse(resp, ContentCachingResponseWrapper.class);
        if (wrapper != null) {
            try {
                wrapper.copyBodyToResponse();
            } catch (IOException e) {
                LOG.error("Fail to write response body back", e);
            }
        }
    }
    private String genPayload(String payload, byte[] buf, String characterEncoding) {
        if (buf.length > 0 && buf.length < getMaxPayloadLength()) {
            try {
                payload = new String(buf, 0, buf.length, characterEncoding);
            } catch (UnsupportedEncodingException ex) {
                payload = "[unknown]";
            }
        }
        return payload;
    }
    public int getMaxPayloadLength() {
        return maxPayloadLength;
    }
    private boolean codeMatched(int responseStatus, String statusCode) {
        if (statusCode.matches("^[0-9,]*$")) {
            String[] filteredCode = statusCode.split(",");
            return Stream.of(filteredCode).map(Integer::parseInt).collect(Collectors.toList()).contains(responseStatus);
        } else {
            return false;
        }
    }
    protected abstract void recordBody(String payload, String response);
    protected abstract String recordCode();
}

这样自定义一个filter继承HttpBodyRecorderFilter，重写recordBody方法就能自定义自己的处理逻辑了。另外，recordCode方法可用于定义在请求响应码为多少的时候才会去记录body，例如可以定义为只有遇到400或500时才记录body，用于错误侦测。

过滤器的匹配规则比较简单，如果想要像springmvc那样进行匹配，我们可以使用AntPathMatcher。

class PatternMappingFilterProxy implements Filter {
    private final Filter delegate;
    private final List pathUrlPatterns = new ArrayList();
    private PathMatcher pathMatcher;
    public PatternMappingFilterProxy(Filter delegate, String... urlPatterns) {
        Assert.notNull(delegate, "A delegate Filter is required");
        this.delegate = delegate;
        int length = urlPatterns.length;
        pathMatcher = new AntPathMatcher();
        for (int index = 0; index < length; ++index) {
            String urlPattern = urlPatterns[index];
            this.pathUrlPatterns.add(urlPattern);
        }
    }
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)            throws IOException, ServletException {
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        String path = httpRequest.getRequestURI();
        if (this.matches(path)) {
            this.delegate.doFilter(request, response, filterChain);
        } else {
            filterChain.doFilter(request, response);
        }
    }
    private boolean matches(String requestPath) {
        for (String pattern : pathUrlPatterns) {
            if (pathMatcher.match(pattern, requestPath)) {
                return true;
            }
        }
        return false;
    }
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        this.delegate.init(filterConfig);
    }
    @Override
    public void destroy() {
        this.delegate.destroy();
    }
    public List getPathUrlPatterns() {
        return pathUrlPatterns;
    }
    public void setPathUrlPatterns(List urlPatterns) {
        pathUrlPatterns.clear();
        pathUrlPatterns.addAll(urlPatterns);
    }
}

这样子，PatternMappingFilterProxy装饰了真正的HttpBodyRecorderFilter，支持传入urlPatterns，从而实现像springmvc那样的ant style的匹配。例如对于以下接口：


 @PostMapping("/test/{id}")
 public Object test(@PathVariable(value =  "id",required =  true)  final Integer index)  {
 //do something
 }

可以设置urlPattern为/test/{id:[0-9]+}。

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作者：fredalxin
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