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

原文地址：http://liwx2000.iteye.com/blog/1542431

原文作者：liwx2000

为了提高项目安全性，拦截非法访问，要给项目增加了一个过滤器，拦截所有的请求，校验是否有不安全因素。

这个过程就遇到了一个问题：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。没办法，就去网上搜罗了一通，发现了一个超赞的解决方法。为了记录备案，无耻的转了过来，原文地址在上，内容在下。

1. 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。byte数组允许被多次读取，而不会丢失内容。下面使用byte数组将流的内容保存下来。

2.  工具方法：

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);  
　　　　 // 因为http协议默认传输的编码就是iso-8859-1,如果使用utf-8转码乱码的话，可以尝试使用iso-8859-1
　　　　 body = StreamUtil.readBytes(request.getReader(), "iso-8859-1");
    }  

    @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();
            }
        };
    }  

}  

3. 在Filter中的使用：

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
    }  

}