Slf4j and log4j2 process logs

About log4j

Log4j + Slf4j Is the most common use combination , But we know that Log4j It has stopped updating at present .Apache A new Log4j2 Instead of Log4j,Log4j2 It's right Log4j The upgrade , Its predecessor Log4j There has been a significant improvement in comparison , And provided many Logback Available improvements , At the same time Logback Some inherent problems in the architecture . therefore ,Log4j2 + Slf4j Should be the general trend of the future .

About slf4j

1. LF4J Unlike other logging libraries , It is quite different from other logging libraries .SLF4J(Simple logging Facade for Java) Not a real logging implementation , It's an abstraction layer （ abstraction layer）, It allows you to use any logging library in the background . If written for internal and external use API Or generic class libraries , Then you really don't want clients that use your library to have to use the logging library of your choice .
2. If a project is already in use log4j, And you load a library of classes , For example Apache Active MQ—— It depends on another logging library logback, Then you need to load it in as well . But if Apache Active MQ Used SLF4J, You can continue to use your logging library without the pain of loading and maintaining a new logging framework .
3. in general ,SLF4J Make your code independent of any particular log API, This is for API Great ideas from developers . The idea of abstract logging libraries is not new, though , and Apache commons logging It's already in use , but SLF4J Is rapidly becoming Java World logging standards .

Use case

introduce slf4j and log4j2 The core of the package

<!-- slf4j Core packages -->
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.25</version>
</dependency>
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>jcl-over-slf4j</artifactId>
    <version>1.7.25</version>
    <scope>runtime</scope>
</dependency>

<!--log4j2 Core packages -->
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>2.8.2</version>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-api</artifactId>
    <version>2.8.2</version>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-slf4j-impl</artifactId>
    <version>2.8.2</version>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-web</artifactId>
    <version>2.8.2</version>
    <scope>runtime</scope>
</dependency>

<!--log4j2  Asynchronous rely on -->
<dependency>
    <groupId>com.lmax</groupId>
    <artifactId>disruptor</artifactId>
    <version>3.3.6</version>
</dependency>

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log4j2.xml

<?xml version="1.0" encoding="UTF-8"?>
<configuration status="off" monitorInterval="120">
    <properties>
        <property name="LOG_HOME">/mytest_log</property>
    </properties>
    <appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
        </Console>

        <!--RollingFile  Global synchronization  RandomAccessFile  For asynchronous -->
        <RollingRandomAccessFile name="rootAppeder"
                                 fileName="${LOG_HOME}/rattanapi.log"
                                 filePattern="${LOG_HOME}/$${date:yyyy-MM}/rattanapi-root-%d{yyyy-MM-dd}-%i.log">
            <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %ex%msg%n"/>
            <Policies>
                <TimeBasedTriggeringPolicy interval="1"/>
                <SizeBasedTriggeringPolicy size="100 MB"/>
            </Policies>
            <DefaultRolloverStrategy max="30"/>
        </RollingRandomAccessFile>

        <!-- Error log output -->
        <RollingRandomAccessFile name="errorAppeder"
                                 fileName="${LOG_HOME}/rattanapi-error.log"
                                 filePattern="${LOG_HOME}/$${date:yyyy-MM}/rattanapi-error-%d{yyyy-MM-dd}-%i.log">
            <Filters>
                <ThresholdFilter level="ERROR" onMatch="ACCEPT" onMismatch="DENY"/>
            </Filters>
            <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %ex%msg%n"/>
            <Policies>
                <TimeBasedTriggeringPolicy interval="1"/>
                <SizeBasedTriggeringPolicy size="100 MB"/>
            </Policies>
            <DefaultRolloverStrategy max="30"/>
        </RollingRandomAccessFile>

    </appenders>

    <loggers>
        <asyncRoot level="info">
            <!-- Depending on whether the configuration file is open or not  console Output  -->
            <appender-ref ref="Console"/>
            <appender-ref ref="rootAppeder"/>
            <appender-ref ref="errorAppeder"/>
        </asyncRoot>
    </loggers>
</configuration>

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web.xml Set in log4j2 Listeners and filters （servlet3.0 And above versions do not require this step ） Development Servlet3.0 The program needs some environmental support .

<!-- about log4j2,Servlet2.5 Previous versions required -->
   <listener>
      <listener-class>org.apache.logging.log4j.web.Log4jServletContextListener</listener-class>
   </listener>
   <filter>
      <filter-name>log4jServletFilter</filter-name>
      <filter-class>org.apache.logging.log4j.web.Log4jServletFilter</filter-class>
   </filter>
<filter-mapping>
      <filter-name>log4jServletFilter</filter-name>
      <url-pattern>/*</url-pattern>
      <dispatcher>REQUEST</dispatcher>
      <dispatcher>FORWARD</dispatcher>
      <dispatcher>INCLUDE</dispatcher>
      <dispatcher>ERROR</dispatcher>
 </filter-mapping>

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Be careful ：log4j2 No longer supported properties The file , Only support xml,json or yaml, Does not specify the location of the default in src/main/resources The lookup .

If you need to customize the location , It needs to be up there web.xml Add the following code in

<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:applicationContext.xml</param-value>
</context-param>
<context-param>
    <param-name>log4jConfiguration</param-name>
    <param-value>classpath:log4j2.xml</param-value>
</context-param>

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import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Main {
    private static final Logger logger = LoggerFactory.getLogger(Main.class);
    public static void main(String[] args) {
    String world = "world";
    logger.info("hellp world:{}",world);
    logger.error("exception e");
    }
}

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