The function and technology implementation principles of the Apache Log4J Web framework in the Java class library

Apache log4j is one of the most commonly used log record tools in Java.It provides developers with a flexible and configurable method to record the operating information of the application in order to easily debug and investigate.In Web development, using log4j can record HTTP requests and response information, as well as abnormalities and error stack tracking produced during the operation of the application, thereby helping developers better understand the behavior and operating conditions of the application. The LOG4J Web framework provides the LOG4J expansion API, making developers more convenient and easy to integrate using LOG4J in Web applications.The log4j web framework provides functions through two key components: log4jfilter and log4jservlet. First, let's take a look at the log4jfilter.LOG4JFILTER is a servlet filter that can be used to intercept HTTP requests and responses and record related information.Developers can configure LOG4JFILTER in the deployment descriptor (such as web.xml files) of the web application.In the configuration, you can specify the level, format, goal, etc. of the log output.For example, the following is a basic LOG4JFILTER configuration example: <filter> <filter-name>log4jFilter</filter-name> <filter-class>org.apache.log4j.filter.Log4jFilter</filter-class> <init-param> <param-name>excludedResponseHeaders</param-name> <param-value>Content-Type,Content-Length</param-value> </init-param> </filter> <filter-mapping> <filter-name>log4jFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> In the above example, we define a filter called "LOG4JFILTER" and apply it to all URL mode.In the filter configuration, we also set up some initialization parameters, such as `ExcludedResponseheaders`, which is used to specify the response header that does not need to be recorded. Next, let's take a look at the log4jservlet.LOG4JSERVLET is a Servlet component that can pass the abnormalities and error information in the web application to the log4j system for recording.Developers can configure the LOG4JSERVLET to the global error page of the web application in order to capture and handle the abnormalities of all application levels.The following is a simple LOG4JSERVLET configuration example: <error-page> <exception-type>java.lang.Throwable</exception-type> <location>/log4jServlet</location> </error-page> <servlet> <servlet-name>log4jServlet</servlet-name> <display-name>Log4j Error Servlet</display-name> <servlet-class>org.apache.log4j.servlet.Log4jServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>log4jServlet</servlet-name> <url-pattern>/log4jServlet</url-pattern> </servlet-mapping> In the above example, we define an error page that capture the abnormalities of all Throwable type and redirect the request to the "/log4jservlet" URL path.We also define a Servlet called "Log4JSERVLET", which will use the Log4jServlet class to process the error request. With the support of these two components, the log4j web framework can provide the following functions in the Java class library: 1. Intercept HTTP request and response, record related information: log4jfilter allows developers to intercept HTTP requests and responses, and record custom information, such as request URL, request parameters, response status code, and so on.By configured log output levels and formats, the detailed degree of logging can be controlled flexibly. 2. Record application abnormalities and error messages: Log4JSERVLET, as a global error processor, can capture all abnormalities and error messages of the application and pass them to the log4j system record.This is very helpful for problem investigation and error tracking. To sum up, the functions of the Apache Log4J Web framework in the Java library mainly include HTTP requests and response records, as well as the capture and records of application abnormalities and error information.Developers can implement these functions by configure LOG4JFILTER and LOG4JSERVLET, and flexibly control the formats and levels of log output to meet the needs of the application.