核心：javax.servlet.http.HttpServletRequestWrapper

WebMvcConfig：

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new MyInterceptor()).addPathPatterns("/**");
    }
    @Bean
    public FilterRegistrationBean<MyFilter> filterRegistrationBean() {
        FilterRegistrationBean<MyFilter> registration = new FilterRegistrationBean<>();
        registration.setFilter(new MyFilter());
        registration.addUrlPatterns("/*");
        registration.setName("MyFilter");
        registration.setOrder(1);
        return registration;
    }
}

MyController：

@RestController("/")
public class MyController {
    @PostMapping("/")
    public String index(@RequestBody String json) {
        System.out.println(json);
        return json;
    }
}

MyInterceptor：

public class MyInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        if ("POST".equalsIgnoreCase(request.getMethod())) {
            RequestWrapper myRequestWrapper = new RequestWrapper(request);
            String body = myRequestWrapper.getBody();
            System.out.println("拦截器拦截到的请求体： " + body);
        }
        return true;
    }
}

RequestWrapper：

public class RequestWrapper extends HttpServletRequestWrapper {
    private final String body;
    public RequestWrapper(HttpServletRequest request) throws IOException {
        super(request);
        StringBuilder stringBuilder = new StringBuilder();
        BufferedReader bufferedReader = null;
        try {
            InputStream inputStream = request.getInputStream();
            if (inputStream != null) {
                bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
                char[] charBuffer = new char[128];
                int bytesRead;
                while ((bytesRead = bufferedReader.read(charBuffer)) > 0) {
                    stringBuilder.append(charBuffer, 0, bytesRead);
                }
            }
        } finally {
            if (bufferedReader != null) {
                bufferedReader.close();
            }
        }
        body = stringBuilder.toString();
    }
    @Override
    public ServletInputStream getInputStream() {
        final ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(body.getBytes());
        return new ServletInputStream() {
            @Override
            public boolean isFinished() {
                return false;
            }
            @Override
            public boolean isReady() {
                return false;
            }
            @Override
            public void setReadListener(ReadListener readListener) {
            }
            @Override
            public int read() {
                return byteArrayInputStream.read();
            }
        };
    }
    @Override
    public BufferedReader getReader() {
        return new BufferedReader(new InputStreamReader(this.getInputStream()));
    }
    public String getBody() {
        return this.body;
    }
}

MyFilter：

public class MyFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        Filter.super.init(filterConfig);
    }
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        ServletRequest requestWrapper = null;
        if(request instanceof HttpServletRequest) {
            requestWrapper = new RequestWrapper((HttpServletRequest) request);
        }
        if(requestWrapper == null) {
            chain.doFilter(request, response);
        } else {
            chain.doFilter(requestWrapper, response);
        }
    }
}