using slf4j with plugins --> CL problems?!

[tuxedo0801]

Hey there,

My plugins use slf4j ... Of course, the main application also use slf4j.

The main application uses the "slf4j-jdk14" logger.

If my plugins not just contain slf4j-api, but also sld4f-jdk14, I get an kind of warning:

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/......../.m2/repository/org/slf4j/slf4j-jdk14/1.7.12/slf4j-jdk14-1.7.12.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/......../logicplugin/target/lib/slf4j-jdk14-1.7.12.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.slf4j.impl.JDK14LoggerFactory]

Makes sense...(but applications works...) --> Having the jdk14-lib two times is confusing. So, If I exclude the slf4j-jdk14 from my plugin (but keep in main application), I get this (and applications does not work):

2015-10-03 11:47:20.700 SEVERE [main] ro.fortsoft.pf4j.DefaultPluginFactory.create: null
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:408)
    at ro.fortsoft.pf4j.DefaultPluginFactory.create(DefaultPluginFactory.java:61)
    at ro.fortsoft.pf4j.PluginWrapper.getPlugin(PluginWrapper.java:63)
    at ro.fortsoft.pf4j.DefaultPluginManager.startPlugins(DefaultPluginManager.java:226)
    at de.root1.kad.KadMain.<init>(KadMain.java:45)
    at de.root1.kad.KadMain.main(KadMain.java:60)
Caused by: java.lang.LinkageError: loader constraint violation: when resolving method "org.slf4j.impl.StaticLoggerBinder.getLoggerFactory()Lorg/slf4j/ILoggerFactory;" the class loader (instance of ro/fortsoft/pf4j/PluginClassLoader) of the current class, org/slf4j/LoggerFactory, and the class loader (instance of sun/misc/Launcher$AppClassLoader) for the method's defining class, org/slf4j/impl/StaticLoggerBinder, have different Class objects for the type org/slf4j/ILoggerFactory used in the signature
    at org.slf4j.LoggerFactory.getILoggerFactory(LoggerFactory.java:335)
    at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:283)
    at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:304)
    at de.root1.kad.logicplugin.LogicPlugin.<init>(LogicPlugin.java:56)
    ... 9 more

Exception in thread "main" java.lang.NullPointerException
    at ro.fortsoft.pf4j.DefaultPluginManager.startPlugins(DefaultPluginManager.java:226)
    at de.root1.kad.KadMain.<init>(KadMain.java:45)
    at de.root1.kad.KadMain.main(KadMain.java:60)

Anyone else facing this issue?

I've not yet digged into the root-cause, but it seems that this is a classloader issue with pf4j plugin classloader?!

any ideas before I investige time to find the cause?

br,
Alex

[tuxedo0801]

Issue solved:

        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.12</version>
            <scope>provided</scope>
        </dependency>

The trick is the "provided" scope. I also had to exclude the lib from being copied to target/lib for development mode:

            <!-- Put dependencies to target/lib/ folder, so that we can depend on during development runtime -->
            <plugin>
                <artifactId>maven-dependency-plugin</artifactId>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <id>copy libs</id>
                        <goals>
                            <goal>copy-dependencies</goal>
                        </goals>
                        <configuration>
                            <outputDirectory>${project.build.directory}/lib</outputDirectory>
                            <excludeScope>provided</excludeScope>
                       </configuration>
                    </execution>
                </executions>
            </plugin>

The maven-dependency-plugin part is again special and for my case only. But maybe it helps others too.