Http Servlet请求在读取一次后从POST正文中丢失参数

Answer 1

顺便说一句，解决这个问题的另一种方法是不使用过滤器链，而是构建自己的拦截器组件，也许使用方面，它可以对解析的请求体进行操作。由于只将请求InputStream转换为您自己的模型对象一次，因此它可能会更高效。

然而，我仍然认为希望多次读取请求主体是合理的，特别是当请求通过筛选器链时。我通常会对某些操作使用过滤器链，这些操作希望保留在HTTP层，与服务组件解耦。

正如Will Hartung所建议的，我通过扩展HttpServletRequestWrapper、使用请求InputStream和缓存字节来实现了这一点。

public class MultiReadHttpServletRequest extends HttpServletRequestWrapper {
  private ByteArrayOutputStream cachedBytes;

  public MultiReadHttpServletRequest(HttpServletRequest request) {
    super(request);
  }

  @Override
  public ServletInputStream getInputStream() throws IOException {
    if (cachedBytes == null)
      cacheInputStream();

      return new CachedServletInputStream();
  }

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

  private void cacheInputStream() throws IOException {
    /* Cache the inputstream in order to read it multiple times. For
     * convenience, I use apache.commons IOUtils
     */
    cachedBytes = new ByteArrayOutputStream();
    IOUtils.copy(super.getInputStream(), cachedBytes);
  }

  /* An inputstream which reads the cached request body */
  public class CachedServletInputStream extends ServletInputStream {
    private ByteArrayInputStream input;

    public CachedServletInputStream() {
      /* create a new input stream from the cached request body */
      input = new ByteArrayInputStream(cachedBytes.toByteArray());
    }

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

现在，通过在通过筛选器链之前包装原始请求，可以多次读取请求主体：

public class MyFilter implements Filter {
  @Override
  public void doFilter(ServletRequest request, ServletResponse response,
        FilterChain chain) throws IOException, ServletException {

    /* wrap the request in order to read the inputstream multiple times */
    MultiReadHttpServletRequest multiReadRequest = new MultiReadHttpServletRequest((HttpServletRequest) request);

    /* here I read the inputstream and do my thing with it; when I pass the
     * wrapped request through the filter chain, the rest of the filters, and
     * request handlers may read the cached inputstream
     */
    doMyThing(multiReadRequest.getInputStream());
    //OR
    anotherUsage(multiReadRequest.getReader());
    chain.doFilter(multiReadRequest, response);
  }
}

此解决方案还允许您通过GetParameterXXX方法多次读取请求主体，因为底层调用是GetInputStream()，它当然将读取缓存的请求InputStream。