Log4j is an extensible Java logging framework designed to separate logging operations from applications. It allows developers to control the output mode of logging at runtime, thereby enabling dynamic configuration of logging. The key components of Log4j include Logger, Appender, and Layout. The Logger is responsible for logging, the Appender is responsible for configuring the output target of the log, and the Layout is responsible for formatting log messages. The following introduces the key methods commonly used in Log4j and the corresponding Java sample code: 1. Configure Log4j: First, you need to add a dependency for Log4j in the project. You can add the following dependencies in pom.xml: ```xml <dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.17</version> </dependency> ``` Then create a log4j.properties file in the project's resource directory and configure information such as log output method and format. 2. Obtain Logger object: Use the Logger. getLogger() method to obtain the Logger object. The parameter is the class object of the current class, used to specify the class where the log output is located. ```java import org.apache.log4j.Logger; public class MyClass { private static final Logger logger = Logger.getLogger(MyClass.class); } ``` 3. Record log information: Different methods of Logger can be used to record different levels of log information. The commonly used methods include debug(), info(), warn(), error(), and fatal(). The log information that needs to be recorded can be passed as method parameters. ```java logger.debug("This is a debug log message."); logger.info("This is an info log message."); logger.warn("This is a warning log message."); logger.error("This is an error log message."); logger.fatal("This is a fatal log message."); ``` 4. Set log output format: Use the Layout class to set the log output format. Commonly used layouts include PatternLayout, SimpleLayout, and XML Layout. It can be configured in the log4j.properties file. ```properties log4j.appender.console.layout=org.apache.log4j.PatternLayout log4j.appender.console.layout.ConversionPattern=%d %-5p [%c{1}] %m%n ``` 5. Output Log to File: Using FileAppender can output logs to a file. The path to the output file can be configured in the log4j.properties file. ```properties log4j.appender.file=org.apache.log4j.FileAppender log4j.appender.file.File=/path/to/file.log log4j.appender.file.layout=org.apache.log4j.PatternLayout log4j.appender.file.layout.ConversionPattern=%d %-5p [%c{1}] %m%n ``` In summary, using Log4j to record logs requires adding a log4j dependency and configuring the log4j.properties file. Different levels of log information can be recorded through the Logger object, and the output method and format of the logs can be set.

Logback is a Java based logging framework, an improved version of log4j, and a native implementation of SLF4J. It has three core components: Logger, Appender, and Layout. 1. Logger: Logger is the main component of the Logback logging system, used to record log information. The Logger allows you to choose which log level information to record and which Appender to send the log information to for processing. 2. Appender: Appender is used to process the log information sent by the Logger. Logback provides various appenders, including ConsoleAppender (output to console), FileAppender (output to file), RollingFileAppender (support for scrolling of log files), and so on. 3. Layout: Layout is used to format the log information sent by the Logger and provides multiple formatting options by default. Common methods: 1. Use Logger to record log information: ```java import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class MyLogger { private static final Logger LOGGER = LoggerFactory.getLogger(MyLogger.class); public static void main(String[] args) { LOGGER.debug("Debug message"); LOGGER.info("Info message"); LOGGER.warn("Warn message"); LOGGER.error("Error message"); } } ``` 2. Configure Logback.xml: Create a logback.xml file in the src/main/resources directory and define the behavior of the Logger through the configuration file. ```xml <configuration> <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender"> <encoder> <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern> </encoder> </appender> <appender name="FILE" class="ch.qos.logback.core.FileAppender"> <file>myapp.log</file> <encoder> <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern> </encoder> </appender> <logger name="com.example" level="debug"/> <root level="info"> <appender-ref ref="CONSOLE"/> <appender-ref ref="FILE"/> </root> </configuration> ``` Maven Dependency: Add the following dependencies to the pom.xml file: ```xml <dependency> <groupId>ch.qos.logback</groupId> <artifactId>logback-classic</artifactId> <version>1.2.3</version> </dependency> ``` The above is a brief introduction and usage method of Logback, which can be configured and used according to actual needs.

SLF4J (Simple Logging Facade for Java) is a Java logging framework. It provides a simple way to record logs without relying on specific logging implementations. By using SLF4J, we can use a unified API to record logs in our applications and easily switch between underlying log implementations. The key methods of SLF4J include: 1. getLogger (Class<?>clazz): Obtain a Logger instance to record logs for the specified class. Usually, it is recommended to declare the Logger instance as static. 2. Trace (String format, Object... args): Record TRACE level logs and generate specific log messages based on the provided format and parameters. 3. debug (String format, Object... args): Record DEBUG level logs. 4. info (String format, Object... args): Record INFO level logs. 5. warn (String format, Object... args): Record WARN level logs. 6. error (String format, Object... args): Record logs at the ERROR level. The following is the Java sample code for logging using SLF4J: 1. Add Maven dependency: ```xml <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-api</artifactId> <version>1.7.32</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-simple</artifactId> <version>1.7.32</version> <scope>test</scope> </dependency> ``` 2. Prepare an example class: ```java import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class LoggerExample { private static final Logger logger = LoggerFactory.getLogger(LoggerExample.class); public static void main(String[] args) { logger.trace("This is a TRACE message."); logger.debug("This is a DEBUG message."); logger.info("This is an INFO message."); logger.warn("This is a WARN message."); logger.error("This is an ERROR message."); String name = "John"; int age = 30; logger.debug("User {} is {} years old.", name, age); } } ``` In the above example, we use the 'getLogger (Class<?>clazz)' method to obtain a Logger instance, and use different methods to record logs in the 'main' method. Finally, we use parameterized logging to replace specific values with '{}' placeholders. In the above example, we used 'slf4j simple' as the log implementation for SLF4J. You can also choose other logging implementations, such as' log4j 'or' logback '. Based on the selected log implementation, you need to add corresponding dependencies and configurations.

Commons Logging is a Java logging framework that is part of the Apache Commons project. It provides a unified logging API that can adapt to various logging frameworks, such as Log4j, java. util. logging, and so on. By using Commons Logging, it is possible to uniformly record logs in the application without relying on specific log implementations. Below are several commonly used methods in Commons Logging: 1. Logger. getLogger (Class clazz): Obtain a Logger instance with parameters for the class that needs to be logged. 2. Logger. debug (Object message): Output debug level log messages. 3. Logger. info (Object message): Output log messages at the info level. 4. Logger. warn (Object message): Output warning level log messages. 5. Logger. error (Object message): Output error level log messages. 6. Logger. Fatal (Object message): Output Fatal level log messages. 7. Logger. isXXXEnabled(): Determine whether the corresponding level of logging is enabled. The following is a Java sample code for logging using Commons Logging: ```java import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; public class Example { private static final Log LOG = LogFactory.getLog(Example.class); public static void main(String[] args) { LOG.debug("This is a debug message"); LOG.info("This is an info message"); LOG.warn("This is a warn message"); LOG.error("This is an error message"); LOG.fatal("This is a fatal message"); if (LOG.isDebugEnabled()) { LOG.debug("Debug log is enabled"); } } } ``` In the above code, first obtain a Logger instance using the LogFactory. getLog method, with the parameter being the class that needs to be logged. Then use various methods of Logger to output corresponding levels of log messages. Finally, use isDebugEnabled to determine whether to enable debug level log output. If you want to use Commons Logging, you need to add the following maven dependencies to the pom.xml file of the project: ```xml <dependency> <groupId>commons-logging</groupId> <artifactId>commons-logging</artifactId> <version>1.2</version> </dependency> ``` The above is a simple example of using Commons Logging to record logs. You can adjust the log level and output format as needed, and combine them with specific log implementations, such as Log4j.

Log4j2 is a logging framework in Java that can be used to record log information during application runtime. It is part of the Apache Logging Services project and an upgraded version of the Log4j framework, providing better performance and flexibility. Some features of Log4j2 include: 1. High performance: Log4j2 has higher throughput and lower latency compared to Log4j 1. x. 2. Flexible configuration: Support configuration through XML, JSON, and other methods, and can configure different log levels, output targets, log rolling strategies, etc. 3. Multiple output targets: Support output to various targets such as console, file, remote server, etc. 4. Custom Appender: You can extend the log output function by implementing a custom Appender. 5. Asynchronous logging: Support the use of asynchronous logging to improve application performance. The commonly used key classes and methods are as follows: 1. Logger: Logger is the core class of Log4j2, used to record logs. You can obtain the Logger object through the Logger. getLogger (String name) method. When outputting logs, different logging levels (such as ERROR, DEBUG, INFO, etc.) can be used to call different methods of Logger (such as error, debug, info, etc.). ```java import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; public class MyClass { private static final Logger logger = LogManager.getLogger(MyClass.class); public void myMethod() { logger.debug("Debug message"); logger.info("Info message"); logger.error("Error message"); } } ``` 2. LoggerContext: LoggerContext is used to obtain and configure the context information of Log4j2. The current LoggerContext object can be obtained through the LoggerContext. getContext() method. 3. Configuration: Configuration is used to configure the properties and settings of Log4j2. You can build and configure a Configuration object through the ConfigurationBuilder class. 4. Appender: Appender is an interface used to define log output targets. Log4j2 provides multiple built-in Appender implementations, such as ConsoleAppender (output to console), FileAppender (output to file), and so on. 5. Layout: The interface used by Layout to format log messages. Log4j2 also provides multiple built-in Layout implementations, such as PatternLayout (outputting logs according to specified patterns). If Log4j2 is needed, the following Maven dependencies can be added to the pom.xml file: ```xml <dependencies> <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> </dependencies> ``` At the same time, it is necessary to configure the relevant properties and settings of Log4j2 in the application's configuration file (such as log4j2. xml). The above is a brief introduction to Log4j2 and sample code for commonly used methods. For specific usage and configuration methods, please refer to the official documentation of Log4j2.

Java logging is a way to record program runtime information provided by the Java Standard library, which can help developers track and debug applications. Java's built-in logging tools include Java Util Logging (JUL), which is the default logging framework for the Java platform. JUL is a flexible and powerful logging framework mainly composed of the following key classes: 1. Logger: Responsible for creating a log logger. Obtain a Logger instance by calling the 'Logger. getLogger (String name)' method. Logger can be organized hierarchically based on its name, making it convenient to record logs separately for different modules. 2. Handler: Responsible for outputting log information to different targets. JUL supports multiple different handlers, such as ConsoleHandler (console output), FileHandler (file output), and can also customize handlers. 3. Formatter: Responsible for formatting log records into strings displayed on the output target. JUL provides a simple log formatter by default and also supports custom formatters. 4. Level: defines different levels of logs, which are divided into SEVERE, WARNING, INFO, CONFIG, FINE, FINER, and FINEST according to their severity. Below are some commonly used methods and sample Java code to demonstrate how to use JUL to record logs. 1. Configure JUL: The configuration information of JUL is usually placed in a file called 'logging. properties'. The path to the configuration file can be specified through the 'java. util. logging. config. file' system attribute, or the default configuration can be used. The following is a simple configuration file example: ``` #Output Log Format java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter #Set Log Level java.util.logging.ConsoleHandler.level = INFO ``` 2. Create a logger: ```java import java.util.logging.Logger; public class MyLogger { private static final Logger logger = Logger.getLogger(MyLogger.class.getName()); public void logInfo() { logger.info("This is an information log message"); } } ``` 3. Output to console: ```java import java.util.logging.ConsoleHandler; import java.util.logging.Level; import java.util.logging.Logger; public class ConsoleLoggerExample { private static final Logger logger = Logger.getLogger(ConsoleLoggerExample.class.getName()); public static void main(String[] args) { ConsoleHandler consoleHandler = new ConsoleHandler(); ConsoleHandler. setLevel (Level. ALL)// Set the logging level of the handler Logger. addHandler (consoleHandler)// Add Handler to Logger logger.info("This is an information log message"); logger.warning("This is a warning log message"); } } ``` 4. Output to file: ```java import java.io.IOException; import java.util.logging.FileHandler; import java.util.logging.Level; import java.util.logging.Logger; public class FileLoggerExample { private static final Logger logger = Logger.getLogger(FileLoggerExample.class.getName()); public static void main(String[] args) { try { FileHandler fileHandler = new FileHandler("app.log"); FileHandler. setLevel (Level. ALL)// Set the logging level of the handler Logger. addHandler (fileHandler)// Add Handler to Logger logger.info("This is an information log message"); logger.warning("This is a warning log message"); } catch (IOException e) { logger.log(Level.SEVERE, "Failed to create log file", e); } } } ``` The above code example uses JUL to record logs, and the configuration in the example can be customized as needed. For the Handlers and Formatters used in the above example, the corresponding implementations have been provided by default, without the need for additional import dependencies. Tip: JUL is a built-in logging framework in the Java Standard library, so no additional maven dependency is required.

LogFaces is a logging and management tool for Java applications. It provides a visual interface to collect, view, and analyze log messages, and supports multi-threaded and distributed environments. The commonly used key methods are as follows: 1. Record log messages: ``` import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class LogExample { private static final Logger logger = LoggerFactory.getLogger(LogExample.class); public static void main(String[] args) { logger.debug("Debug message"); logger.info("Info message"); logger.warn("Warning message"); logger.error("Error message"); } } ``` Maven Dependency: ```xml <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-api</artifactId> <version>{slf4j-version}</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-log4j12</artifactId> <version>{slf4j-version}</version> </dependency> ``` Where '{slf4j version}' is the SLF4J version number used. 2. Configure LogFaces logger: Add the following configuration to the 'log4j. properties' or' log4j. xml 'file: ``` log4j.appender.logFaces=org.logfaces.log4j.LogFacesAppender log4j.appender.logFaces.append=true log4j.appender.logFaces.layout=org.apache.log4j.PatternLayout log4j.appender.logFaces.layout.ConversionPattern=[%d] [%-5p] [%c{1}] - %m%n ``` 3. Send log messages to the LogFaces server: The address and port of the LogFaces server can be configured in the following ways: Add the following configuration to the 'log4j. properties' or' log4j. xml 'file: ``` log4j.appender.logFaces.host={logfaces-hostname or IP} log4j.appender.logFaces.port={logfaces-port} ``` Where '{logfaces host name or IP}' is the host name or IP address of the LogFaces server, and '{logfaces port}' is the port number of the LogFaces server. The above is an example of integrating with LogFaces using SLF4J and Log4j. Please ensure that the relevant dependencies for SLF4J, Log4j, and LogFaces have been added to the Maven configuration file or Gradle build file of the project.

Sentry is an open source real-time error logging and event monitoring platform that provides a simple and powerful method to capture, record, and aggregate errors and exceptions in applications. By integrating Sentry into Java applications, developers can monitor application errors and exceptions in real-time, as well as collect and analyze event data generated by the application. Sentry's Java client provides a series of methods to record logs and send events to the Sentry server. The following are several commonly used key methods: 1. Initialize Sentry client: When the application starts, the Sentry client needs to be initialized. This can be achieved through the following code: ```java import io.sentry.Sentry; public class MyApp { public static void main(String[] args) { //Initialize Sentry client Sentry.init(options -> { options.setDsn("YOUR_SENTRY_DSN"); }); //Application logic // ... } } ``` Among them, 'YOU'_ SENTRY_ DSN 'is the DSN generated after you create a project on the Sentry platform. 2. Record exception information: The method 'Sentry. captureException()' can be used to record the captured exception information. For example: ```java try { //Some code that may throw exceptions } catch (Exception e) { //Record to Sentry after catching exceptions Sentry.captureException(e); } ``` 3. Record error messages: You can use the method 'Sentry. captureMessage ()' to record custom error messages. For example: ```java Sentry.captureMessage("An error occurred"); ``` 4. Set additional context data: You can use 'Sentry. getContext()' to obtain the Sentry context of the current thread, and use the 'setExtra()' method to add custom key value pair data. For example: ```java Sentry.getContext().setExtra("user_id", 123); Sentry.getContext().setExtra("username", "john_doe"); ``` 5. Add custom label information: You can use the 'Sentry. getContext(). addTag()' method to add custom label information. For example: ```java Sentry.getContext().addTag("environment", "production"); Sentry.getContext().addTag("version", "1.0.0"); ``` The above Java code example uses Sentry's Java client API. To use Sentry in a project, the following dependencies need to be added through Maven: ```xml <dependency> <groupId>io.sentry</groupId> <artifactId>sentry</artifactId> <version>3.0.0</version> </dependency> ``` The above are some basic methods and sample code for using Sentry to record logs. You can use more Sentry provided features in your application to monitor and record error messages and event data according to your own needs.

Graylog is an open source log management system that can help users centrally record, search, and analyze a large amount of log data. It provides a web-based user interface that can monitor data in real-time and support the retrieval and analysis of log data through search, filtering, and alerts. Graylog also supports scalability and high availability, and can be clustered on multiple nodes. In Java, using Graylog to record logs can use Graylog GELF (Graylog Extended Log Format) as the log processor. GELF is a flexible log format that allows users to transfer log data to Graylog servers in a structured manner. The following are common methods and Java code examples for using Graylog to record logs: 1. Import Maven dependencies: ```xml <dependency> <groupId>org.graylog2</groupId> <artifactId>gelfclient</artifactId> <version>1.12.0</version> </dependency> ``` 2. Create a GelfConfiguration object and configure the address and port of the Graylog server: ```java GelfConfiguration config = new GelfConfiguration("graylog-server", 12201) .transport(GelfTransports.UDP); ``` 3. Create a GelfConfiguration object and set other configuration options (optional): ```java config.transport(GelfTransports.UDP) .queueSize(512) .connectTimeout(5000) .reconnectDelay(1000) .tcpNoDelay(true) .sendBufferSize(32768); ``` 4. Create a GelfTransport object and connect to the Graylog server: ```java GelfTransport transport = GelfTransports.create(config); transport.connect(); ``` 5. Record Log: ```java GelfMessageBuilder messageBuilder = new GelfMessageBuilder("This is a log message.") .level(GelfMessageLevel.WARNING) .additionalField("custom_field", "custom_value"); transport.send(messageBuilder.build()); ``` 6. Close connection (optional): ```java transport.close(); ``` By following the above steps, you can use Graylog to record logs. You can adjust the configuration options and log content as needed. It should be noted that flexible use of log levels, custom fields, etc. can help better classify and analyze logs in Graylog. The above is the basic usage of Graylog, and for more advanced features, please refer to the official documentation and API documentation.