Log4j issue with maven and gwt: org.apache.log4j.X

Question

I have a Maven GWT project. I included Hibernate and HSQLDB as persistence layer. Running the unit tests is fine, but when it try to run the server component, logging does not work and so I am blind to the errors on the server side. The errors I encouter are:

[ERROR] log4j:ERROR A "org.apache.log4j.RollingFileAppender" object is not assig nable to a "org.apache.log4j.Appender" variable. [ERROR] log4j:ERROR The class "org.apache.log4j.Appender" was loaded by [ERROR] log4j:ERROR [sun.misc.Launcher$AppClassLoader@baf1915] whereas object of type [ERROR] log4j:ERROR "org.apache.log4j.RollingFileAppender" was loaded by [WebApp ClassLoader=1312837549@4e404fad]. [ERROR] log4j:ERROR Could not instantiate appender named "file". [ERROR] log4j:ERROR A "org.apache.log4j.ConsoleAppender" object is not assignabl e to a "org.apache.log4j.Appender" variable. [ERROR] log4j:ERROR The class "org.apache.log4j.Appender" was loaded by [ERROR] log4j:ERROR [sun.misc.Launcher$AppClassLoader@baf1915] whereas object of type [ERROR] log4j:ERROR "org.apache.log4j.ConsoleAppender" was loaded by [WebAppClas sLoader=1312837549@4e404fad]. [ERROR] log4j:ERROR Could not instantiate appender named "stdout".

From googling I am pretty sure it is because two instances of the log4j.jar are present. Is there a good way or best practice way to solve this issue? I run the project in development mode from the console. My Pom.xml looks like this:

 <?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>testproject</groupId>
 <artifactId>trustme-mdm-gwtp</artifactId>
 <version>1.0-SNAPSHOT</version>
 <packaging>war</packaging>
 <name>GWTP Basic</name>
 <description>Basic GWTP application</description>


 <properties>
 <!-- client -->
 <gwt.version>2.6.0</gwt.version>
 <gwtp.version>1.2.1</gwtp.version>
 <gin.version>2.1.2</gin.version>


 <!-- server -->
 <guice.version>3.0</guice.version>


 <!-- testing -->
 <junit.version>4.7</junit.version>
 <jukito.version>1.4</jukito.version>


 <!-- maven -->
 <gwt-maven-plugin.version>2.6.0</gwt-maven-plugin.version>
 <maven-surefire-plugin.version>2.6</maven-surefire-plugin.version>
 <maven-compiler-plugin.version>2.3.2</maven-compiler-plugin.version>
 <maven-resources-plugin.version>2.5</maven-resources-plugin.version>
 <maven-processor-plugin.version>2.0.5</maven-processor-plugin.version>
 <maven-build-helper-plugin.version>1.7</maven-build-helper-plugin.version>




 <target.jdk>1.7</target.jdk>
 <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>


 <webappDirectory>${project.build.directory}/${project.build.finalName}</webappDirectory>
 </properties>


 <build>
 <outputDirectory>${webappDirectory}/WEB-INF/classes</outputDirectory>


 <plugins>
 <!-- JUnit Testing - skip *.GwtTest cases -->
 <!-- 'mvn test' - runs the Jukito tests -->
 <plugin>
 <groupId>org.apache.maven.plugins</groupId>
 <artifactId>maven-surefire-plugin</artifactId>
 <version>${maven-surefire-plugin.version}</version>
 <configuration>
 <includes>
 <include>**/*Test.java</include>
 </includes>
 <excludes>
 <exclude>**/*GwtTest.java</exclude>
 </excludes>
 </configuration>
 </plugin>
 <plugin>
 <groupId>org.apache.maven.plugins</groupId>
 <artifactId>maven-compiler-plugin</artifactId>
 <version>2.3.2</version>
 <configuration>
 <source>1.7</source>
 <target>1.7</target>
 </configuration>
 </plugin>


 <!-- GWT -->
 <!-- 'mvn gwt:run' - runs development mode -->
 <!-- 'mvn gwt:debug' - runs debug mode -->
 <!-- 'mvn gwt:compile' - compiles gwt -->
 <!-- 'mvn integration-test' - runs the gwt tests (*GwtTest.java) -->
 <plugin>
 <groupId>org.codehaus.mojo</groupId>
 <artifactId>gwt-maven-plugin</artifactId>
 <version>${gwt.version}</version>
 <configuration>
 <!-- With multiple tests use GwtTestSuite.java for speed -->
 <includes>**/*GwtTest.java</includes>
 <extraJvmArgs>-Xss1024K -Xmx1024M -XX:MaxPermSize=256M</extraJvmArgs>


 <copyWebapp>true</copyWebapp>
 <hostedWebapp>${webappDirectory}</hostedWebapp>


 <runTarget>Project.html</runTarget>
 <modules>
 <module>testproject.Project</module>
 </modules>
 </configuration>
 <executions>
 <execution>
 <goals>
 <goal>compile</goal>
 <goal>test</goal>
 </goals>
 </execution>
 </executions>
 </plugin>
 </plugins>
 </build>


 <dependencies>
 <!-- Google Web Toolkit -->
 <dependency>
 <groupId>com.google.gwt</groupId>
 <artifactId>gwt-user</artifactId>
 <version>${gwt.version}</version>
 </dependency>


 <!-- GWT-Platform -->
 <dependency>
 <groupId>com.gwtplatform</groupId>
 <artifactId>gwtp-all</artifactId>
 <version>${gwtp.version}</version>
 </dependency>


 <!-- DI -->
 <dependency>
 <groupId>com.google.inject</groupId>
 <artifactId>guice</artifactId>
 <version>${guice.version}</version>
 </dependency>
 <dependency>
 <groupId>com.google.inject.extensions</groupId>
 <artifactId>guice-servlet</artifactId>
 <version>${guice.version}</version>
 </dependency>
 <dependency>
 <groupId>com.google.inject.extensions</groupId>
 <artifactId>guice-assistedinject</artifactId>
 <version>${guice.version}</version>
 </dependency>
 <dependency>
 <groupId>com.google.gwt.inject</groupId>
 <artifactId>gin</artifactId>
 <version>${gin.version}</version>
 </dependency>


 <!-- Test -->
 <dependency>
 <groupId>junit</groupId>
 <artifactId>junit</artifactId>
 <version>${junit.version}</version>
 <scope>test</scope>
 </dependency>
 <dependency>
 <groupId>org.jukito</groupId>
 <artifactId>jukito</artifactId>
 <version>${jukito.version}</version>
 <scope>test</scope>
 </dependency>
 <!-- Hibernate -->
 <!-- for JPA, use hibernate-entitymanager instead of hibernate-core -->
 <dependency>
 <groupId>org.hibernate</groupId>
 <artifactId>hibernate-entitymanager</artifactId>
 <version>4.3.5.Final</version>
 </dependency>
 <!-- hSQLDB -->
 <dependency>
 <groupId>org.hsqldb</groupId>
 <artifactId>hsqldb</artifactId>
 <version>2.3.2</version>
 </dependency>
 <!-- add slf4j interfaces to classpath -->
 <dependency>
 <groupId>org.slf4j</groupId>
 <artifactId>slf4j-log4j12</artifactId>
 <version>1.7.7</version>
 </dependency>
 <!--  GWT-Log -->
 <dependency>
 <groupId>com.allen-sauer.gwt.log</groupId>
 <artifactId>gwt-log</artifactId>
 <version>3.3.0</version>
 </dependency>

 </dependencies>
</project>

When I take a look at the \target...\lib folder, these are the jars that are deployed:

antlr-2.7.7.jar aopalliance-1.0.jar commons-collections-3.2.1.jar commons-lang-2.4.jar commons-logging-1.1.1.jar dom4j-1.6.1.jar gin-2.1.2.jar guava-16.0.1.jar guava-gwt-16.0.1.jar guice-3.0.jar guice-assistedinject-3.0.jar guice-servlet-3.0.jar gwt-jackson-0.4.0.jar gwt-log-3.3.0.jar gwtp-all-1.2.1.jar gwtp-clients-common-1.2.1.jar gwtp-crawler-1.2.1.jar gwtp-dispatch-common-client-1.2.1.jar gwtp-dispatch-common-shared-1.2.1.jar gwtp-dispatch-rest-1.2.1.jar gwtp-dispatch-rpc-client-1.2.1.jar gwtp-dispatch-rpc-server-1.2.1.jar gwtp-dispatch-rpc-server-guice-1.2.1.jar gwtp-dispatch-rpc-server-spring-1.2.1.jar gwtp-dispatch-rpc-shared-1.2.1.jar gwtp-mvp-client-1.2.1.jar gwtp-mvp-shared-1.2.1.jar gwtp-processors-1.2.1.jar gwtp-tester-1.2.1.jar gwt-user-2.6.1.jar hibernate-commons-annotations-4.0.4.Final.jar hibernate-core-4.3.5.Final.jar hibernate-entitymanager-4.3.5.Final.jar hibernate-jpa-2.1-api-1.0.0.Final.jar hsqldb-2.3.2.jar jackson-annotations-2.3.0.jar jackson-annotations-2.3.0-sources.jar jandex-1.1.0.Final.jar javassist-3.18.1-GA.jar javax.inject-1.jar jboss-logging-3.1.3.GA.jar jboss-logging-annotations-1.2.0.Beta1.jar jboss-transaction-api_1.2_spec-1.0.0.Final.jar json-20090211.jar jsr305-1.3.9.jar jsr311-api-1.1.1.jar maven-artifact-3.1.1.jar plexus-utils-3.0.15.jar servlet-api-2.5.jar spring-aop-3.2.3.RELEASE.jar spring-beans-3.2.3.RELEASE.jar spring-context-3.2.3.RELEASE.jar spring-core-3.2.3.RELEASE.jar spring-expression-3.2.3.RELEASE.jar spring-web-3.2.3.RELEASE.jar validation-api-1.0.0.GA.jar validation-api-1.0.0.GA-sources.jar velocity-1.7.jar xml-apis-1.0.b2.jar

I changed the pom.xml to this:

<!-- Google Web Toolkit -->
<dependency>
    <groupId>com.google.gwt</groupId>
    <artifactId>gwt-servlet</artifactId>
    <version>${gwt.version}</version>
    <scope>runtime</scope>
</dependency>
<dependency>
    <groupId>com.google.gwt</groupId>
    <artifactId>gwt-user</artifactId>
    <version>${gwt.version}</version>
    <scope>provided</scope>
</dependency>

But still no success...

I inserted a screenshot of the dependency tree. My reputation does not allow to paste images. It is stored here:

Answer 1

You're probably facing the known issue of GWT 2.6.0 that incorrectly loads server-side classes in DevMode: https://code.google.com/p/google-web-toolkit/issues/detail?id=8585

Try using GWT 2.6.1 and see if that fixes the problem.

EDIT: Also, clean-up your dependencies' scopes: you have gwt-user and servlet-api in your WEB-INF/lib, that mustn't be there; you also have a bunch of GWT-specific client-only JARs that shouldn't be there either.

Answer 2

Thanks for the help (especially Thomas). The guide i used for my project stated log4j and slf4j would be necessary as external references in the pom.xml.
I simply removed it and it is working now. This has taught me however, that it really makes life simpler by not combining server and client dependencies.

Answer 3

change log4j dependency scope to provided in maven.check whether there are multiple logger jars.