Spring-web源码解析之Filter-AbstractRequestLoggingFilter

基于4.1.7.RELEASE

Filter处理request log的基类，提供了在filterChain.doFilter调用前后的回调函数，其实现类有CommonsRequestLoggingFilter，Log4jNestedDiagnosticContextFilter，ServletContextRequestLoggingFilter。

其核心代码为doFilterInternal方法：

@Override
protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
      throws ServletException, IOException {

   boolean isFirstRequest = !isAsyncDispatch(request);
   HttpServletRequest requestToUse = request;

   if (isIncludePayload() && isFirstRequest && !(request instanceof ContentCachingRequestWrapper)) {
      requestToUse = new ContentCachingRequestWrapper(request);
   }

   boolean shouldLog = shouldLog(requestToUse);
   if (shouldLog && isFirstRequest) {
      beforeRequest(requestToUse, getBeforeMessage(requestToUse));
   }
   try {
      filterChain.doFilter(requestToUse, response);
   }
   finally {
      if (shouldLog && !isAsyncStarted(requestToUse)) {
         afterRequest(requestToUse, getAfterMessage(requestToUse));
      }
   }
}

在调用filterChain.doFilter方法前后分别调用beforeRequest和afterRequest，而这两个方法具体实现由子类决定，根据功能不同来决定记录日志的方法，

在beforeRequest中和afterRequest中分别调用了  getBeforeMessage，getAfterMessage，这两个方法代码如下

private String getBeforeMessage(HttpServletRequest request) {
   return createMessage(request, this.beforeMessagePrefix, this.beforeMessageSuffix);
}

private String getAfterMessage(HttpServletRequest request) {
   return createMessage(request, this.afterMessagePrefix, this.afterMessageSuffix);
}

最终都会进入到createMessage中去，只是前缀后缀不同，

before的Msg格式是： Before request [  Msg  ]

after的Msg格式是 ： After request [  Msg  ]

这里的Msg具体内容则由createMessage决定

protected String createMessage(HttpServletRequest request, String prefix, String suffix) {
   StringBuilder msg = new StringBuilder();
   msg.append(prefix);
   msg.append("uri=").append(request.getRequestURI());
   if (isIncludeQueryString()) {
      msg.append('?').append(request.getQueryString());
   }
   if (isIncludeClientInfo()) {
      String client = request.getRemoteAddr();
      if (StringUtils.hasLength(client)) {
         msg.append(";client=").append(client);
      }
      HttpSession session = request.getSession(false);
      if (session != null) {
         msg.append(";session=").append(session.getId());
      }
      String user = request.getRemoteUser();
      if (user != null) {
         msg.append(";user=").append(user);
      }
   }
   if (isIncludePayload() && request instanceof ContentCachingRequestWrapper) {
      ContentCachingRequestWrapper wrapper = (ContentCachingRequestWrapper) request;
      byte[] buf = wrapper.getContentAsByteArray();
      if (buf.length > 0) {
         int length = Math.min(buf.length, getMaxPayloadLength());
         String payload;
         try {
            payload = new String(buf, 0, length, wrapper.getCharacterEncoding());
         }
         catch (UnsupportedEncodingException e) {
            payload = "[unknown]";
         }
         msg.append(";payload=").append(payload);
      }

   }
   msg.append(suffix);
   return msg.toString();
}

根据具体的参数设置的不同，其表现出不同的形式，msg的最基本格式为

Before/After request [  uri=xxx  ]

设置includeQueryString=true:

Before/After request [  uri=xxx?a=xx&b=xxx  ]

设置includeClientInfo=true:

Before/After request [  uri=xxx?a=xxx&b=xxx;client=xxx;session=sessionId;user=xxx  ]

设置includePayload=true:

先判断request的content的长度，如果超过设置maxPayload的长度，则按照maxPayload进行截取，如果出现异常，则payload=[unknown]

Before/After request [  uri=xxx?a=xxx&b=xxx;client=xxx;session=sessionId;user=xxx;payload=xxx/[unknown]  ]

下面来看其子类对应的不同的实现

CommonsRequestLoggingFilter：
@Override
protected boolean shouldLog(HttpServletRequest request) {
   return logger.isDebugEnabled();
}

@Override
protected void beforeRequest(HttpServletRequest request, String message) {
   logger.debug(message);
}

@Override
protected void afterRequest(HttpServletRequest request, String message) {
   logger.debug(message);
}

其主要是调用初始化时候设置的GenericFilterBean中的logger进行记录。

Log4jNestedDiagnosticContextFilter：

其采用了Log4j来进行日志记录。自定义变量

protected final Logger log4jLogger = Logger.getLogger(getClass());

ServletContextRequestLoggingFilter：

使用ServletContext来记录日志