Log4J 2 Interoperability

Log4J is split into log4j-api and log4j-core jars:

<dependency>
  <groupId>org.apache.logging.log4j</groupId>
  <artifactId>log4j-api</artifactId>
  <version>${log4j2.version}</version>
</dependency>
<dependency>
  <groupId>org.apache.logging.log4j</groupId>
  <artifactId>log4j-core</artifactId>
  <version>${log4j2.version}</version>
</dependency>

To configure GeoTools to use Log4J API:

GeoTools.setLoggerFactory("org.geotools.util.logging.Log4J2LoggerFactory");

Reference:

Log4j Guidance

Communication from different Logging frameworks have to Log4J 2 API:

To bridge slf4j to Log4J:

  • Include the following jar:

    <dependency>
  <groupId>org.apache.logging.log4j</groupId>
  <artifactId>log4j-slf4j18-impl</artifactId>
  <version>${log4j2.version}</version>
</dependency>

  • This routes slf4j api calls to log4j-core.

To bridge java util logging to Log4J:

  • Include the following jar:

    <dependency>
  <groupId>org.apache.logging.log4j</groupId>
  <artifactId>log4j-jul</artifactId>
  <version>${log4j2.version}</version>
</dependency>

  • This bridge provides the following mapping:

    • java.util.logging.Filter: yes

    • java.util.logging.Handler: no

    Levels:

    Java Level

    Log4j Level

    OFF

    OFF

    FATAL

    FATAL

    SEVERE

    ERROR

    WARNING

    WARN

    INFO

    INFO

    CONFIG

    CONFIG

    FINE

    DEBUG

    FINER

    TRACE

    FINEST

    FINEST

    ALL

    ALL

  • There are several ways to enable java.util.logging bridge to Log4J:

    • System property:

      -Djava.util.logging.manager=org.apache.logging.log4j.jul.LogManager

    • System property during application init:

      System.setProperty("java.util.logging.manager","org.apache.logging.log4j.jul.LogManager");

    • Setup configure application logging.properties with the following:

      handlers = org.apache.logging.log4j.jul.Log4jBridgeHandler
org.apache.logging.log4j.jul.Log4jBridgeHandler.propagateLevels = true

    • Explicitly call Log4jBridgeHandler.install() during application init:

    Log4jBridgeHandler.install();

  • To bridge Log4J 1.x to Log4J (replacing the need for Reload4J):

    <dependency>
  <groupId>org.apache.logging.log4j</groupId>
  <artifactId>log4j-1.2-api</artifactId>
  <version>${log4j2.version}</version>
</dependency>

    Reference: https://logging.apache.org/log4j/2.x/manual/migration.html

Log4j Integration

The following example is taken from our integration testing, this test only has Log4j 2 API in play so GeoTools.init()` is able to unambiguously determine ``Log4JLoggerFactory can be used.

  1. Setup pom.xml with dependencies on geotools and Log4J:

    <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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.geotools.tutorial</groupId>
  <artifactId>log4j</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>
  <name>GeoTools Log4j Integration Example</name>
  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.deploy.skip>true</maven.deploy.skip>
    <geotools.version>31-SNAPSHOT</geotools.version>
    <log4j2.version>2.17.2</log4j2.version>
  </properties>
  <dependencies>
    <dependency>
      <groupId>org.geotools</groupId>
      <artifactId>gt-metadata</artifactId>
      <version>${geotools.version}</version>
    </dependency>
    <dependency>
      <groupId>org.geotools.ogc</groupId>
      <artifactId>net.opengis.ows</artifactId>
      <version>${geotools.version}</version>
    </dependency>
    <dependency>
      <groupId>org.apache.logging.log4j</groupId>
      <artifactId>log4j-api</artifactId>
      <version>${log4j2.version}</version>
    </dependency>
    <dependency>
      <groupId>org.apache.logging.log4j</groupId>
      <artifactId>log4j-core</artifactId>
      <version>${log4j2.version}</version>
    </dependency>
    <!-- java util logging logging to log4j 2 -->
    <dependency>
      <groupId>org.apache.logging.log4j</groupId>
      <artifactId>log4j-jul</artifactId>
      <version>${log4j2.version}</version>
    </dependency>
    <!-- commons logging bridge to log4j 2 -->
    <!--
    <dependency>
      <groupId>org.apache.logging.log4j</groupId>
      <artifactId>log4j-jcl</artifactId>
      <version>${log4j2.version}</version>
    </dependency>
    -->
    <!-- slf4j bridge to log4j 2 -->
    <!--<dependency>
      <groupId>org.apache.logging.log4j</groupId>
      <artifactId>log4j-slf4j-impl</artifactId>
      <version>${log4j2.version}</version>
    </dependency>
    -->
  </dependencies>
  <repositories>
    <repository>
      <id>osgeo</id>
      <name>OSGeo Release Repository</name>
      <url>https://repo.osgeo.org/repository/release/</url>
      <snapshots><enabled>false</enabled></snapshots>
      <releases><enabled>true</enabled></releases>
    </repository>
    <repository>
      <id>osgeo-snapshot</id>
      <name>OSGeo Snapshot Repository</name>
      <url>https://repo.osgeo.org/repository/snapshot/</url>
      <snapshots><enabled>true</enabled></snapshots>
      <releases><enabled>false</enabled></releases>
    </repository>
  </repositories>

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-jar-plugin</artifactId>
        <version>3.3.0</version>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.11.0</version>
        <configuration>
          <source>11</source>
          <target>11</target>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-resources-plugin</artifactId>
        <version>3.1.0</version>
      </plugin>
      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>exec-maven-plugin</artifactId>
        <version>3.1.0</version>
        <configuration>
          <executable>java</executable>
          <arguments>
            <argument>-classpath</argument>
            <!-- uses dependencies and build directory -->
            <classpath/>
            <argument>-Djava.awt.headless=true</argument>
            <argument>org.geotools.tutorial.logging.Log4JIntegration</argument>
          </arguments>
        </configuration>
        <executions>
          <execution>
            <id>jul</id>
            <phase>integration-test</phase>
            <goals>
              <goal>exec</goal>
            </goals>
            <configuration>
              <executable>java</executable>
              <arguments>
                <argument>-classpath</argument>
                <!-- uses dependencies and build directory -->
                <classpath/>
                <argument>-Djava.util.logging.manager=org.apache.logging.log4j.jul.LogManager</argument>
                <argument>-Dlog4j2.configurationFile=log4j2-production.xml</argument>
                <argument>-Djava.awt.headless=true</argument>
                <argument>org.geotools.tutorial.logging.Log4JIntegration</argument>
              </arguments>
            </configuration>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>
</project>

  2. Configure log4j wtih log4j2.xml added to src/main/resources:

    <?xml version="1.0" encoding="UTF-8"?>
<!-- Concise Syntax -->
<Configuration status="info" dest="out">
    <CustomLevels>
      <CustomLevel name="CONFIG" intLevel="450" />
      <CustomLevel name="FINEST" intLevel="700" />
    </CustomLevels>>
    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%date{HH:mm:ss.SSS} %-6level [%logger{2}] - %msg%n"/>
        </Console>
    </Appenders>
    <Loggers>
        <Logger name="org.geotools.tutorial.logging" level="all" additivity="false">
            <AppenderRef ref="Console"/>
        </Logger>
        <Logger name="org.geotools" level="debug" additivity="false">
            <AppenderRef ref="Console"/>
        </Logger>
        <Root level="error">
            <AppenderRef ref="Console"/>
        </Root>
    </Loggers>
</Configuration>

    Of interest above is defining the CONFIG and FINEST custom levels.

  3. During startup logback will search for log4j2.xml on the CLASSPATH.

    To search for a different file on the classpath use -Dlog4j2.configurationFile=log4j2-production.xml.

  4. Application Log4JIntegration.java startup example for src/min/java.

    Example is taking care to call GeoTools.init() prior to logger use:

    /*
 *    GeoTools - The Open Source Java GIS Toolkit
 *    http://geotools.org
 *
 *    (C) 2016, Open Source Geospatial Foundation (OSGeo)
 *
 *    This file is hereby placed into the Public Domain. This means anyone is
 *    free to do whatever they wish with this file. Use it well and enjoy!
 */
package org.geotools.tutorial.logging;

import java.util.logging.Logger;

import org.geotools.util.factory.GeoTools;
import org.geotools.util.logging.Log4J2LoggerFactory;
import org.geotools.util.logging.Logging;
/** Example illustrating use of Log4J 2 API and startup environment. */
public class Log4JIntegration {
    static {
        GeoTools.init();
    }

    static final Logger LOGGER = Logging.getLogger(Log4JIntegration.class);

    public static void main(String args[]) {
        LOGGER.info("Welcome to Log4j Integration Example");
        if (!LOGGER.getClass().getName().equals("org.geotools.util.logging.Log4J2Logger")) {
            LOGGER.severe("Log4J2Logger expected, but was:" + LOGGER.getClass().getName());
        }

        // Log4J2 properties
        LOGGER.info("Welcome to Log4j Integration Example");
        checkProperty("log4j2.configurationFile");
        LOGGER.config("Configuration " + Logging.ALL.lookupConfiguration());

        LOGGER.finest("Everything is finest...");
        LOGGER.finer("Everything is finer...");
        LOGGER.fine("Everything is fine...");
        LOGGER.config("Everything is configured...");
        LOGGER.log(Logging.OPERATION, "Everything is operating...");
        LOGGER.info("Everything is okay.");
        LOGGER.warning("Everything is alarming!");
        LOGGER.severe("Everything is terrible!");
        LOGGER.log(Logging.FATAL, "Everything has died!");
    }

    private static void checkProperty(String property) {
        if (System.getProperties().containsKey(property)) {
            LOGGER.config(property + "=" + System.getProperty(property));
        }
    }
}

  5. An exec:exec target is provided to make this easier to test:

    mvn exec:exec

    Is the equivalent of:

    java -Djava.awt.headless=true \\
     org.geotools.tutorial.logging.Log4JIntegration

  6. An exec:exec@jul target is provided to try out a more realistic production setting.

    mvn exec:exec@jul

    Is the equivalent of:

    java -Djava.util.logging.manager=org.apache.logging.log4j.jul.LogManager \\
     -Dlog4j2.configurationFile=log4j2-production.xml \\
     -Djava.awt.headless=true \\
     org.geotools.tutorial.logging.Log4JIntegration

    This makes use of the log4j2-production.xml configuration, and sets up log4j jul bridge.

    <?xml version="1.0" encoding="UTF-8"?>
<!-- Concise Syntax -->
<Configuration status="info" dest="out">
    <CustomLevels>
      <CustomLevel name="CONFIG" intLevel="450" />
      <CustomLevel name="FINEST" intLevel="700" />
    </CustomLevels>>
    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%date{HH:mm:ss.SSS} %-6level [%logger{2}] - %msg%n"/>
        </Console>
    </Appenders>
    <Loggers>
        <Logger name="org.geotools" level="config" additivity="false">
            <AppenderRef ref="Console"/>
        </Logger>
        <Root level="error">
            <AppenderRef ref="Console"/>
        </Root>
    </Loggers>
</Configuration>

    This logging configuration reduces the levels recorded.