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