对多个类使用log4j2

Question

这里的答案:https://stackoverflow.com/questions/7624895/how-to-use-log4j-with-multiple-classes#=是我找到的最好的答案。这已经是过去几年的想法了，现在有些事情已经不同了。

我的目标是在所有将消息打印到日志（控制台和文件）的java类中共享一个记录器。

我使用的是log4j2:http://logging.apache.org/log4j/2.x/manual/configuration.html

import org.apache.logging.log4j.Logger;

public class App {
    private static final Logger LOGGER = Logger.getLogger("GLOBAL");
    public static void main(){
        ...calling other classes
  }
}

import org.apache.logging.log4j.Logger;
public class secondClass {
    private final Logger LOGGER = Logger.getLogger("GLOBAL");
    public void writeLog(){
      LOGGER.log(Level.INFO, "A simple string");
  }
}

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn">
    <Properties>
        <Property name="basePath">/var/log</Property>
    </Properties>

    <Appenders>
        <RollingFile name="fileLogger" fileName="${basePath}/myApp.log" filePattern="${basePath}/myApp-%d{yyyy-MM-dd}.log">
            <PatternLayout pattern="[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n" />
            <Policies>
                <TimeBasedTriggeringPolicy interval="1" modulate="true" />
            </Policies>
        </RollingFile>

       <Console name="console" target="SYSTEM_OUT">
            <PatternLayout pattern="[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n" />
        </Console>
    </Appenders>
    <Loggers>
        <Logger name="java.util.logging.Logger" level="ALL" additivity="true">
            <appender-ref ref="fileLogger" level="ALL" />
        </Logger>
        <Root level="ALL" additivity="false">
            <appender-ref ref="console" />
        </Root>
    </Loggers>
</Configuration>

我（或多或少）知道我应该使用LogManager，事实是我应该将其称为：

private static final Logger logger = LogManager.getLogger(MyApp.class);

或者，在main（）中，可能如下所示：

private static Logger LOGGER = null;

@BeforeClass
public static void setLogger() {
    System.setProperty("log4j.configurationFile","log4j.xml");
    LOGGER = LogManager.getLogger();
}

因为，我相信，使用LogManager我可以将日志指向xml文件以获得其设置。但是当我构建并运行它时，CLI rage在第一个日志时退出，报告:异常出现在myapp.modules.database. (database.java:67) 的线程“main”java.lang.NullPointerException中

..和许多其他搜索结果都超过了6年。

pom.xml：

<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-api</artifactId>
    <version>2.10.0</version>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>2.10.0</version>
</dependency>

Answer 1

您在几个层面上是错误的：您将JDK的记录器与log4j2的记录器混合在一起，您没有记录到几个追加器，等等。

以下是您应该做的：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.example</groupId>
    <artifactId>log4j2test</artifactId>
    <version>0.1</version>
    <packaging>jar</packaging>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <version>2.10.0</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.10.0</version>
        </dependency>
    </dependencies>
</project>

这基本上是你唯一没有错误的地方。

package so47656300;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class App {

  private static final Logger logger = LogManager.getLogger(App.class);

  public static void main(String[] args) {
    logger.info("App.main - starting");
    new SecondClass();
    logger.info("App.main - ending");
  }
}

package so47656300;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class SecondClass {

  private static final Logger logger = LogManager.getLogger(SecondClass.class);

  public SecondClass() {
    logger.info("SecondClass - starting");
    logger.info("SecondClass - ending");
  }
}

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
    <Properties>
        <Property name="basePath">/var/log</Property>
    </Properties>
    <Appenders>
        <RollingFile name="fileLogger" fileName="${basePath}/myApp.log" filePattern="${basePath}/myApp-%d{yyyy-MM-dd}.log">
            <PatternLayout pattern="[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n" />
            <Policies>
                <TimeBasedTriggeringPolicy interval="1" modulate="true" />
            </Policies>
        </RollingFile>

        <Console name="console" target="SYSTEM_OUT">
            <PatternLayout pattern="[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n" />
        </Console>
    </Appenders>
    <Loggers>
        <Root level="INFO">
            <AppenderRef ref="console"/>
            <AppenderRef ref="fileLogger"/>
        </Root>
    </Loggers>
</Configuration>

null

[INFO ] 2017-12-05 16:52:32.218 [main] App - App.main - starting
[INFO ] 2017-12-05 16:52:32.221 [main] SecondClass - SecondClass - starting
[INFO ] 2017-12-05 16:52:32.222 [main] SecondClass - SecondClass - ending
[INFO ] 2017-12-05 16:52:32.222 [main] App - App.main - ending

[INFO ] 2017-12-05 16:52:32.218 [main] App - App.main - starting
[INFO ] 2017-12-05 16:52:32.221 [main] SecondClass - SecondClass - starting
[INFO ] 2017-12-05 16:52:32.222 [main] SecondClass - SecondClass - ending
[INFO ] 2017-12-05 16:52:32.222 [main] App - App.main - ending