记录一次Filter中读取request body参数调试（getReader() has already been called、request body is missing）

现象

filter中获取HttpServletRequest 请求Body中的数据后，报错：getReader() has already been called、request body is missing。

根本原因

ServletRequest输入流只可以获取一次：stream对应数据，数据存储在内存或者部分存储在内存中，在对stream操作时，每read一次mark一次当前位置，第二次read留时就从mark的位置继续读数据（从内存中copy），因此stream读取一次后再次读取为空。

如何避免？更改stream中mark的位置即pos改为0。Java中reset()方法可以重置streammark位置为其实位置，注意：并不是所有的stream都可以调用reset()方法，ServletInputStream恰恰不可以调用reset方法，因此ServletRequest中流只可以调取一次。

解决方案

新建类继承HttpServletRequestWrapper,类中新建对象存储body数据。filter中使用时，使用新建对象类：

public class BodyReaderHttpServletRequestWrapper extends HttpServletRequestWrapper {
    private final byte[] body;
    private String bodyStr;

    public BodyReaderHttpServletRequestWrapper(HttpServletRequest request) throws IOException {
        super(request);
        String bodyString = getBodyString(request);
        body = bodyString.getBytes(Charset.forName("UTF-8"));
        bodyStr=bodyString;
    }

    public String getBodyStr() {
        return bodyStr;
    }

    @Override
    public ServletInputStream getInputStream() throws IOException {
        final ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(body);

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

            @Override
            public boolean isFinished() {
                return false;
            }

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

            @Override
            public void setReadListener(ReadListener readListener) {
            }
        };
    }


    public  String getBodyString(HttpServletRequest request) throws IOException {
        StringBuilder sb = new StringBuilder();
        InputStream inputStream = null;
        BufferedReader reader = null;
        try {
            inputStream = request.getInputStream();
            reader = new BufferedReader(
                    new InputStreamReader(inputStream, Charset.forName("UTF-8")));

            char[] bodyCharBuffer = new char[1024];
            int len = 0;
            while ((len = reader.read(bodyCharBuffer)) != -1) {
                sb.append(new String(bodyCharBuffer, 0, len));
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return sb.toString();
    }
}

Filter中使用

public class filter extends OncePerRequestFilter{
    ...
    
    protected void doFilterInternal(HttpServletRequest request,HttpServletResponse respnose,FilterChain filterChain) throws ServletException,IOException{
        BodyReaderHttpServletRequestWrapper wrapper = new BodyReaderHttpServletRequestWrapper(request);
        wrapper.getBodyStr();//获取body json字符串
        filterChain.doFilter(wrapper,response);
    }

    ...
}