有些场景，比如验签，需要在拦截器中读取 Request Body 进行校验的操作。如果通过 HttpServletRequest#getInputStream() 方法读取，会导致后续的读取操作都失败。因为它只能读取一次，第二次读取会抛出异常。最常见的问题就是 @RequestBody 注解失效。

接下来我们通过包装 HttpServletRequest 和 Filter 来处理这个问题。

包装 HttpServletRequest

通过 body 字节数组进行缓存。

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public class ContentCachingHttpServletRequestWrapper extends HttpServletRequestWrapper {

    private byte[] body;

    private BufferedReader reader;

    private ServletInputStream inputStream;

    /**
     * Constructs a request object wrapping the given request.
     *
     * @param request the {@link HttpServletRequest} to be wrapped.
     * @throws IllegalArgumentException if the request is null
     */
    public ContentCachingHttpServletRequestWrapper(HttpServletRequest request) throws IOException {
        super(request);
        loadBody(request);
    }

    private void loadBody(HttpServletRequest request) throws IOException {
        body = IOUtils.toByteArray(request.getInputStream());
        inputStream = new RequestCachingInputStream(body);
    }

    public byte[] getBody() {
        return body;
    }

    @Override
    public ServletInputStream getInputStream() throws IOException {
        if (inputStream != null) {
            return inputStream;
        }
        return super.getInputStream();
    }

    @Override
    public BufferedReader getReader() throws IOException {
        if (reader == null) {
            reader = new BufferedReader(new InputStreamReader(inputStream, getCharacterEncoding()));
        }
        return reader;
    }

    private static class RequestCachingInputStream extends ServletInputStream {

        private final ByteArrayInputStream inputStream;

        public RequestCachingInputStream(byte[] bytes) {
            inputStream = new ByteArrayInputStream(bytes);
        }

        @Override
        public int read() throws IOException {
            return inputStream.read();
        }

        @Override
        public boolean isFinished() {
            return inputStream.available() == 0;
        }

        @Override
        public boolean isReady() {
            return true;
        }

        @Override
        public void setReadListener(ReadListener readlistener) {
        }

    }
}

Filter 实现

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@Component
public class RequestBodyRetrieveFilter implements Filter {



    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest httpServletRequest = (HttpServletRequest) request;
        String contentType = httpServletRequest.getContentType();
        if (contentType != null && contentType.startsWith("multipart/")) {
            chain.doFilter(request, response);
            return;
        }
        String requestURI = httpServletRequest.getRequestURI();
        if (requestURI.contains("/druid")) {
            chain.doFilter(request, response);
            return;
        }
        ContentCachingHttpServletRequestWrapper requestWrapper = new ContentCachingHttpServletRequestWrapper((HttpServletRequest) request);
        chain.doFilter(requestWrapper, response);
    }


}

Interceptor 中使用

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@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    String requestBody =  "";
    if (request instanceof ContentCachingRequestWrapper) {
        requestBody = new String(((ContentCachingRequestWrapper) request).getBody(), request.getCharacterEncoding());
    }
}

至此，即可完成 Request Body 的重复读取。