SpringBoot自定义过滤器读取请求体触发400错误求助

问题根源 #

HttpServletRequest的输入流是一次性读取的，你在过滤器里调用getInputStream()读完请求体后，后续Spring MVC解析请求体（比如绑定到DTO）时，再尝试读取流就会发现流已经被耗尽，直接导致BAD Request错误。

解决方案：包装请求缓存请求体 #

需要自定义一个HttpServletRequestWrapper，把请求体缓存起来，让后续流程可以重复读取请求体，步骤如下：

1. 实现缓存请求体的RequestWrapper

public class CachedBodyHttpServletRequest extends HttpServletRequestWrapper {
    private final byte[] cachedBody;

    public CachedBodyHttpServletRequest(HttpServletRequest request) throws IOException {
        super(request);
        // 读取原始请求体并缓存为字节数组
        InputStream requestInputStream = request.getInputStream();
        this.cachedBody = StreamUtils.copyToByteArray(requestInputStream);
    }

    @Override
    public ServletInputStream getInputStream() throws IOException {
        // 返回可重复读取的缓存流
        return new ServletInputStream() {
            private final ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(cachedBody);

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

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

            @Override
            public void setReadListener(ReadListener readListener) {}

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

    @Override
    public BufferedReader getReader() throws IOException {
        return new BufferedReader(new InputStreamReader(getInputStream()));
    }

    // 提供直接获取缓存请求体字符串的方法
    public String getCachedBody() {
        return new String(this.cachedBody, StandardCharsets.UTF_8);
    }
}

2. 修改过滤器代码，使用包装后的请求

public class PostURLFilter implements Filter {

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) servletRequest;
        // 包装原始请求，缓存请求体
        CachedBodyHttpServletRequest cachedRequest = new CachedBodyHttpServletRequest(req);

        try {
            // 从包装后的请求读取缓存的请求体
            String body = cachedRequest.getCachedBody();
            System.out.println(body + " this is the body");
        } catch (Exception e) {
            e.printStackTrace();
        }

        System.out.println("end");
        // 传递包装后的请求给后续处理链
        filterChain.doFilter(cachedRequest, servletResponse);
    }
}

3. 注意事项

• 注册过滤器时，要确保这个过滤器在Spring MVC的请求解析过滤器之前执行。如果用@WebFilter注解，设置order = -1；如果用配置类注册FilterRegistrationBean，同样设置setOrder(-1)。
• 原代码里的out.println应该是System.out.println（原代码未定义out变量，属于笔误），已修正。

内容的提问来源于stack exchange，提问作者Akil S