The technical principles and application instances of the Apache Log4J Web framework in the Java class library

Apache Log4j is a classic Java class library used to record logs in Java applications.It is one of the most widely used log tools in the Java language, and it provides a powerful log function that allows developers to easily record and manage the logs of applications.In LOG4J, the Web framework is an important component that helps developers to better understand and monitor their web applications.Next, the technical principles of the LOG4J Web framework will be introduced, and an application instance will be provided to illustrate its usage. Technical principle of LOG4J Web framework: 1. Servlet filter: The LOG4J Web framework captures and process the log information of the web application through a Servlet filter.The filter can be called early in the request chain and intercept all log messages from the application. 2. Logging context: The log4j web framework uses a special log context to store and transmit context information related to the current request.It can be shared across threads to ensure that it is associated between the log messages of the same request. 3. MDC (Mapped Diagnostic Context): MDC is an important component of the LOG4J Web framework that allows developers to add custom parameters to the log message.These parameters can be data related to requests, such as request ID, user name, etc.By using MDC, developers can better track and analyze logs. 4. Log file segmentation: The log4j web framework supports dividing the log file according to time or file size.This is very useful for long -run Web applications, which can ensure that the size of the log file will not increase infinitely, making log management easier and efficient. A application example: Below is a simple example, showing how to use the log4j web framework in a Spring Boot application: First, we need to add the following dependencies to the pom.xml file: <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-api</artifactId> <version>2.14.1</version> </dependency> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-core</artifactId> <version>2.14.1</version> </dependency> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-web</artifactId> <version>2.14.1</version> </dependency> </dependencies> Then, add the following configuration in the configuration file (Application.properties or Application.yml) of the Spring Boot application: the following configuration: properties # Set the log location and file name logging.file=logs/myapp.log # Configuration log level logging.level.com.example=DEBUG # Configure log4j web filter log4j2.contextSelector=org.apache.logging.log4j.web.Log4jServletContextSelector log4jContextName=Log4j2 Next, in any class of the application, we can use log4j to record the log.For example: import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; @Controller public class MyController { private static final Logger logger = LogManager.getLogger(MyController.class); @GetMapping("/hello") public String hello() { logger.info("Hello, Log4j Web!"); return "hello"; } } In the above examples, we use @RestController annotations to define a simple controller class as a Spring MVC controller.In the Hello () method, we recorded a log message using log4j. This is just a simple example that demonstrates how to use the LOG4J Web framework in the Spring Boot application.By configured and using log4j log record functions, we can better track and manage log information of the application in order to cause failure and analysis when needed. Summarize: This article introduces the technical principles of the Apache Log4J Web framework and its application instance in the Java library.The LOG4J Web framework provides better web application log records and management functions through the Servlet filter and log context.MDC provides the ability to customize parameters, enabling developers to add context information related to requests.By configured the log file distribution function of log4j, we can better manage the size and number of log files.In practical applications, developers can flexibly use the LOG4J Web framework according to specific needs, and combine other tools and technologies to conduct stronger log analysis and fault investigation.