java - 如何从 POST 请求获取 XML 并在 Servlet Filter 中修改它？

Question

我目前正在处理一个需求，在请求到达 Spring Controller 之前，我需要在 servlet 过滤器中获取 XML(来自 POST 请求)，然后我需要处理 XML(切断一些空节点/元素) ) 在过滤器中，然后调用应该继续进行。

我尝试了下面的代码(仅附加代码片段)，我能够获取请求正文(XML)并能够设置修改后的响应。

    HttpServletRequest httpRequest = (HttpServletRequest) request;
    HttpServletResponse httpResponse = (HttpServletResponse) response;
    if (httpRequest.getMethod().equalsIgnoreCase("POST")) {
      extractDataFromRequest(httpRequest);
      httpResponse.getWriter().write("<root><root>");
    }
    chain.doFilter(request, wrappedResponse);

   public static String extractDataFromRequest(HttpServletRequest request) throws IOException {

    String line;
    StringBuilder builder = new StringBuilder();
    BufferedReader reader = request.getReader();
    while ((line = reader.readLine()) != null) {
      builder.append(line);
    }
    return builder.toString();
  }

但是，spring 失败并出现以下异常。

Severe: java.lang.IllegalStateException: PWC3997: getReader() has already been called for this request
    at org.apache.catalina.connector.Request.getInputStream(Request.java:1178)
    at org.apache.catalina.connector.RequestFacade.getInputStream(RequestFacade.java:407)
    at org.springframework.http.server.ServletServerHttpRequest.getBody(ServletServerHttpRequest.java:165)
    at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.readWithMessageConverters(RequestResponseBodyMethodProcessor.java:120)
    at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.resolveArgument(RequestResponseBodyMethodProcessor.java:100)

我正在寻找专家针对此要求的具体实现。

Answer 1

您不能使用InputStream两次，您需要创建一个包装类来保留InputStream的可重复副本。

public class ReadTwiceHttpServletRequestWrapper extends HttpServletRequestWrapper {

private ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

public ReadTwiceHttpServletRequestWrapper(HttpServletRequest request) {
    super(request);
    try {
        IOUtils.copy(request.getInputStream(), outputStream);
    } catch (IOException e) {
        e.printStackTrace();
    }
}

@Override
public BufferedReader getReader() throws IOException {
    return new BufferedReader(new InputStreamReader(new ByteArrayInputStream(outputStream.toByteArray())));
}

@Override
public ServletInputStream getInputStream() throws IOException {
    final ByteArrayInputStream inputStream = new ByteArrayInputStream(outputStream.toByteArray());
    return new ServletInputStream() {

        @Override
        public int readLine(byte[] b, int off, int len) throws IOException {
            return inputStream.read(b, off, len);
        }

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

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

        @Override
        public void setReadListener(ReadListener arg0) {
            // TODO Auto-generated method stub
        }

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

public void setBody(String body) {
    outputStream = new ByteArrayOutputStream();
    try {
        outputStream.write(body.getBytes());
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

public String getBody() {
    return new String(outputStream.toByteArray());
}

}

然后您需要使用链中第一个过滤器对其进行初始化。

public class ReadTwiceFilter implements Filter {

@Override
public void destroy() {
}

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

    ReadTwiceHttpServletRequestWrapper readTwiceHttpServletRequestWrapper = new ReadTwiceHttpServletRequestWrapper(
            (HttpServletRequest) request);

    String newBody = readTwiceHttpServletRequestWrapper.getBody().replace("<soap:studentId>1</soap:studentId>", "<soap:studentId>2</soap:studentId>");
    readTwiceHttpServletRequestWrapper.setBody(newBody);

    chain.doFilter(readTwiceHttpServletRequestWrapper, response);
}

@Override
public void init(FilterConfig arg0) throws ServletException {
}

}