has already been called for this request

java.lang.IllegalStateException: getReader() has already been called for this request
	at org.apache.catalina.connector.Request.getInputStream(Request.java:1056)
	at org.apache.catalina.connector.RequestFacade.getInputStream(RequestFacade.java:365)
	at javax.servlet.ServletRequestWrapper.getInputStream(ServletRequestWrapper.java:149)
	at org.springframework.http.server.ServletServerHttpRequest.getBody(ServletServerHttpRequest.java:212)
	at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver$EmptyBodyCheckingHttpInputMessage.<init>(AbstractMessageConverterMethodArgumentResolver.java:317)

HttpServletRequest的 getReader()和getInputStream()只能调用一次，Request body是流方式请求，读取一次之后，就不能再用了，看下源码：

@Override
    public BufferedReader getReader() throws IOException {

        if (usingInputStream) {
            throw new IllegalStateException(sm.getString("coyoteRequest.getReader.ise"));
        }

        // InputBuffer has no easily accessible reference chain to the Context
        // to check for a default request character encoding at the Context.
        // Therefore, if a Context default should be used, it is set explicitly
        // here. Need to do this before setting usingReader.
        if (coyoteRequest.getCharacterEncoding() == null) {
            // Nothing currently set explicitly.
            // Check the content
            Context context = getContext();
            if (context != null) {
                String enc = context.getRequestCharacterEncoding();
                if (enc != null) {
                    // Explicitly set the context default so it is visible to
                    // InputBuffer when creating the Reader.
                    setCharacterEncoding(enc);
                }
            }
        }

        usingReader = true;

        inputBuffer.checkConverter();
        if (reader == null) {
            reader = new CoyoteReader(inputBuffer);
        }
        return reader;
    }

@Override
    public ServletInputStream getInputStream() throws IOException {

        if (usingReader) {
            throw new IllegalStateException(sm.getString("coyoteRequest.getInputStream.ise"));
        }

        usingInputStream = true;
        if (inputStream == null) {
            inputStream = new CoyoteInputStream(inputBuffer);
        }
        return inputStream;

    }

可以看到Request.java调用getReader()方法后，usingReader被设置为true，getInputStream()方法会读取usingReader变量，如果为true就会报错