ServletRequest中getReader()和getInputStream()只能调用一次的解决办法

最近使用spring mvc做项目，数据格式是json，有一个功能是实现记录请求的参数，而请求的参数是整个RequestBody，Controller里是用过@RequestBody获取的。实现方法是通过一个Filter读取整个RequestBody并记录。但是这时就遇到一个问题，ServletRequest的getReader()和getInputStream()两个方法只能被调用一次，而且不能两个都调用。那么如果Filter中调用了一次，在Controller里面就不能再调用了。查看了下ServletRequest的说明，如下：

    /**
     * Retrieves the body of the request as binary data using
     * a {@link ServletInputStream}.  Either this method or 
     * {@link #getReader} may be called to read the body, not both.
     *
     * @return			a {@link ServletInputStream} object containing
     * 				the body of the request
     *
     * @exception IllegalStateException  if the {@link #getReader} method
     * 					 has already been called for this request
     *
     * @exception IOException    	if an input or output exception occurred
     *
     */

    public ServletInputStream getInputStream() throws IOException; 

    /**
     * Retrieves the body of the request as character data using
     * a <code>BufferedReader</code>.  The reader translates the character
     * data according to the character encoding used on the body.
     * Either this method or {@link #getInputStream} may be called to read the
     * body, not both.
     * 
     *
     * @return					a <code>BufferedReader</code>
     *						containing the body of the request	
     *
     * @exception UnsupportedEncodingException 	if the character set encoding
     * 						used is not supported and the 
     *						text cannot be decoded
     *
     * @exception IllegalStateException   	if {@link #getInputStream} method
     * 						has been called on this request
     *
     * @exception IOException  			if an input or output exception occurred
     *
     * @see 					#getInputStream
     *
     */

    public BufferedReader getReader() throws IOException;

两个方法都注明方法只能被调用一次，由于RequestBody是流的形式读取，那么流读了一次就没有了，所以只能被调用一次。既然是因为流只能读一次的原因，那么只要将流的内容保存下来，就可以实现反复读取了。

实现方法：先将RequestBody保存为一个byte数组，然后通过Servlet自带的HttpServletRequestWrapper类覆盖getReader()和getInputStream()方法，使流从保存的byte数组读取。然后再Filter中将ServletRequest替换为ServletRequestWrapper。代码如下：

BodyReaderHttpServletRequestWrapper类包装ServletRequest，将流保存为byte[]，然后将getReader()和getInputStream()方法的流的读取指向byte[]

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStreamReader;

import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

import jodd.JoddDefault;
import jodd.io.StreamUtil;

public class BodyReaderHttpServletRequestWrapper extends HttpServletRequestWrapper {

	private final byte[] body;
	
	public BodyReaderHttpServletRequestWrapper(HttpServletRequest request) 
throws IOException {
		super(request);
		body = StreamUtil.readBytes(request.getReader(), JoddDefault.encoding);
	}

	@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();
			}
		};
	}

}

在Filter中将ServletRequest替换为ServletRequestWrapper

public class HttpServletRequestReplacedFilter implements Filter {

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
		//Do nothing
	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		ServletRequest requestWrapper = null;
		if(request instanceof HttpServletRequest) {
			requestWrapper = new BodyReaderHttpServletRequestWrapper((HttpServletRequest) request);
		}
		if(null == requestWrapper) {
			chain.doFilter(request, response);
		} else {
			chain.doFilter(requestWrapper, response);
		}
		
	}

	@Override
	public void destroy() {
		//Do nothing
	}

}