HttpServletRequestWrapper的应用

　HttpServletRequest中的inputStream是一个基础流，只能读一次被读一次，因此我们有必要通过继承HttpServletRequestWrapper来对这个inputStream进行装饰，使其可以在后续读取中能够多次使用，尤其是项目中在拦截器或者过滤器中又读取入参的需求时，如果不对inputStream进行装饰，则会造成后续controller中通过RequestBody注解封装请求参数是会报stream closed异常，。

public class RequestBodyReaderWrapper extends HttpServletRequestWrapper {

    private final byte[] body;

    public RequestBodyReaderWrapper(HttpServletRequest request) {
        super(request);
        body = getBodyString(request).getBytes();
    }

    public static String getBodyString(HttpServletRequest request) {
        StringBuilder sb = new StringBuilder();
        InputStream inputStream = null;
        BufferedReader reader = null;
        try {
            inputStream = request.getInputStream();
            reader = new BufferedReader(new InputStreamReader(inputStream, Charset.forName("UTF-8")));
            String line = "";
            while ((line = reader.readLine()) != null) {
                sb.append(line);
            }
        } 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();
    }

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

    @Override
    public ServletInputStream getInputStream() {

        final ByteArrayInputStream basis = new ByteArrayInputStream(body);

        return new ServletInputStream() {

            @Override
            public int read() {
                return basis.read();
            }

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

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

            @Override
            public void setReadListener(ReadListener readListener) {

            }
        };
    }
}

@Component
public class RequestBodyMultiReadFilter implements Filter {


    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        ServletRequest requestWrapper = null;
        if(servletRequest instanceof HttpServletRequest) {
            requestWrapper = new RequestBodyReaderWrapper((HttpServletRequest) servletRequest);
        }
        if(requestWrapper == null) {
            filterChain.doFilter(servletRequest, servletResponse);
        } else {
            filterChain.doFilter(requestWrapper, servletResponse);
        }
    }

    @Override
    public void destroy() {

    }
}

　　在使用中注意filter顺序，RequestBodyMultiReadFilter应该放在最前面，这样后续的fliter或者interceptor才能重复读取inputstream