如何从过滤器中查看消息？

Question

我尝试使用 javax.servlet.Filter 来查看消息。

public void doFilter( ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
     BufferedReader reader = request.getReader();
     if ( reader.markSupported() ) {
         reader.mark( contentLen );
     }
     String content = reader.readLine();

     // search some pattern

     if ( reader.markSupported() ) {
         reader.reset();
     }
     chain.doFilter( request, response );
}

最终收到请求的 servlet 会抛出此异常：

java.lang.IllegalStateException: getReader() has already been called for this request

根据 javadoc，这是正确的行为。

我的问题是如何读取输入流的内容？

我还尝试了 ServletInputStream is = request.getInputStream();

Answer 1

未经测试，但您可能可以

• 从请求输入流中读取所有字节并将它们写入字节数组，
• 在此字节数组上构造一个缓冲读取器以读取过滤器中所需的内容，
• 构造一个 HttpServletRequestWrapper 覆盖getInputStream() 通过字节数组返回流，
• 将此包装器传递给过滤器链。

Answer 2

遵循 @JB Nizet 的方法得到了以下代码：

public class HttpServletRequestCopy extends HttpServletRequestWrapper {

    private final byte[]       buffer;

    private ServletInputStream sis;

    private BufferedReader     reader;

    public byte[] getBuffer() {
        return buffer;
    }

    public HttpServletRequestCopy( HttpServletRequest request) throws IOException {
        super( request );
        final ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        copyStream( request.getInputStream(), byteArrayOutputStream );
        buffer = byteArrayOutputStream.toByteArray();
    }

    @Override
    public BufferedReader getReader() throws IOException {
        if ( reader == null ) {
            String characterEncoding = this.getCharacterEncoding();
            if ( characterEncoding == null ) {
                reader = new BufferedReader( new InputStreamReader( this.getInputStream() ) );
            }
            else {
                reader = new BufferedReader( new InputStreamReader( this.getInputStream(), characterEncoding ) );
            }
        }
        return reader;
    }

    @Override
    public ServletInputStream getInputStream() throws IOException {
        if ( sis == null ) {
            final ByteArrayInputStream bais = new ByteArrayInputStream( buffer );
            sis = new ServletInputStream() {
                @Override
                public int read() throws IOException {
                    return bais.read();
                }
            };
        }
        return sis;
    }

    private void copyStream( InputStream input, OutputStream output) throws IOException {
        final byte[] bytes = new byte[ 1024 ];
        int length;
        while ( (length = input.read( bytes )) != -1 ) {
            output.write( bytes, 0, length );
        }
    }
}

Answer 3

ServletRequest.getInputStream() 和 ServletRequest.getReader() 是非此即彼的，因此如果其中一个已经被调用，另一个就会失败。您可以使用简单的 try-catch 来解决此问题：

try {
    request.getInputStream();
} catch (IllegalStateException e) {
    // someone already called getReader(), so use it instead
    request.getReader();
}

注意！没有指定流或读取器应该可重置，因此如果您消耗了其中的任何字节，它们将不再可用到链中进一步的任何过滤器或 servlet。