解决流不能重复使用

在InputStream读取的时候，会有一个pos指针，他指示每次读取之后下一次要读取的起始位置，当读到最后一个字符的时候，pos指针不会重置。” 
，就是说InputStream的读取是单向的。但是并不是所有的InputStream实现类都是这样的实现方式。
可以换存到byte数组。


public class BodyReaderHttpServletRequestWrapper extends HttpServletRequestWrapper {

    private final byte[] body;

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

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

    @Override
    public ServletInputStream getInputStream() throws IOException {

        final ByteArrayInputStream bais = new ByteArrayInputStream(body);

        return new ServletInputStream() {

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

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

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

            @Override
            public void setReadListener(ReadListener readListener) {

            }
        };
    }

}

HttpHelper.java
/**
 * 获取请求Body
 *
 * @param request
 * @return
 */
public static String getBodyString(ServletRequest 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();
}

Filter.Java
@Override
protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
        throws ServletException, IOException {
            
    // 防止流读取一次后就没有了, 所以需要将流继续写出去
    ServletRequest requestWrapper = new BodyReaderHttpServletRequestWrapper(request);
    String json = HttpHelper.getBodyString(requestWrapper);
            
    System.out.println(json);

    filterChain.doFilter(requestWrapper, response);