With the shaded jar from dropwizard I got: Class path contains multiple SLF4J bindings

Question

I probably made something stupid here. There is something (smallish) wrong with my dropwizard setup. Running the shaded jar works fine, but when executing integration tests I get this warning:

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/graphhopper/web/target/graphhopper-web-0.11-SNAPSHOT.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/home/user/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.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 [ch.qos.logback.classic.util.ContextSelectorStaticBinder]
INFO  [2018-04-08 18:44:27,653] org.eclipse.jetty.util.log: Logging initialized @1090ms to org.eclipse.jetty.util.log.Slf4jLog

Where graphhopper-web-0.11-SNAPSHOT.jar is the shaded jar with dropwizard (with logback).

This usually means that more than one slf4j binding is on the classpath but I could reject this theory and only slf4j-api is there, plus the logback dependency for dropwizard. I also have analyzed the dependency graph with Netbeans and

mvn dependency:tree -Dverbose -Dincludes=org.slf4j

(see output here) but couldn't find something problematic.

Can it be that the shaded jar (with logback) is somehow put into the classpath with the other jars (including logback) for mvn clean install? How could I avoid this?

Reproduce it via:

git clone https://github.com/graphhopper/graphhopper
cd web
mvn clean install

See this issue.

Answer 1

imported your code into my intellij community edition, added exclusion as follows to all the dependency in pom.xml of web module. It resolve issues given issue. You may have do changes in respective module.

example:

<dependency>
  <groupId>io.dropwizard</groupId>
  <artifactId>dropwizard-core</artifactId>
  <version>1.2.2</version>
  <exclusions>
    <exclusion>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-api</artifactId>
    </exclusion>
  </exclusions>
</dependency>

Answer 2

The issue is the jar logback-classic-1.2.3.jar has a actual file /org/slf4j/impl/StaticLoggerBinder.class, so jar exclusion won't work.

You need to change the configuration of the maven-shade-plugin

<configuration>
    <createDependencyReducedPom>true</createDependencyReducedPom>
    <filters>
        <filter>
          <artifact>ch.qos.logback:logback-classic</artifact>
          <excludes>
            <exclude>org/slf4j/impl/**</exclude>
          </excludes>
        </filter>
        <filter>
            <artifact>*:*</artifact>
            <excludes>
                <exclude>META-INF/*.SF</exclude>
                <exclude>META-INF/*.DSA</exclude>
                <exclude>META-INF/*.RSA</exclude>
            </excludes>
        </filter>
    </filters>
</configuration>

Once you do that all is good and the warning is gone

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------< com.graphhopper:graphhopper-web >-------------------
[INFO] Building GraphHopper Web 0.11-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ graphhopper-web ---
[INFO] Deleting /Users/tarun.lalwani/Desktop/tarunlalwani.com/tarunlalwani/workshop/ub16/so/graphhopper/web/target
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ graphhopper-web ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 118 resources
[INFO]
[INFO] --- maven-compiler-plugin:3.5.1:compile (default-compile) @ graphhopper-web ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 19 source files to /Users/tarun.lalwani/Desktop/tarunlalwani.com/tarunlalwani/workshop/ub16/so/graphhopper/web/target/classes
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ graphhopper-web ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 1 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.5.1:testCompile (default-testCompile) @ graphhopper-web ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 9 source files to /Users/tarun.lalwani/Desktop/tarunlalwani.com/tarunlalwani/workshop/ub16/so/graphhopper/web/target/test-classes
[INFO]
[INFO] --- maven-surefire-plugin:2.19.1:test (default-test) @ graphhopper-web ---

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running com.graphhopper.http.WebHelperTest
Tests run: 5, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.151 sec - in com.graphhopper.http.WebHelperTest
Running com.graphhopper.http.IPFilterTest
20:29:46.762 [main] DEBUG com.graphhopper.http.IPFilter - whitelist:[4.5.67.1, 1.2.3.4]
20:29:46.765 [main] DEBUG com.graphhopper.http.IPFilter - blacklist:[8.9.7.3]
20:29:46.765 [main] DEBUG com.graphhopper.http.IPFilter - blacklist:[4.5.67.1, 1.2.3.4]
20:29:46.766 [main] DEBUG com.graphhopper.http.IPFilter - whitelist:[4.5.67.1, 1.2.3.4]
20:29:46.766 [main] DEBUG com.graphhopper.http.IPFilter - whitelist:[1.2.3*, 4.5.67.1, 7.8.*.3]
Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.003 sec - in com.graphhopper.http.IPFilterTest

Results :

Tests run: 8, Failures: 0, Errors: 0, Skipped: 0

Edit-1: 26-Apr-2018

Updates from https://github.com/graphhopper/graphhopper/issues/1328

I believe the issue is that you run the Dropwizard app integration tests as integration test during the verify phase of the build. This phase gets invoked after the package phase where you create a shaded jar and replace the original jar with it.

[INFO] Replacing original artifact with shaded artifact.
[INFO] Replacing /home/travis/build/graphhopper/graphhopper/web/target/graphhopper-web-0.11-SNAPSHOT.jar with /home/travis/build/graphhopper/graphhopper/web/target/graphhopper-web-0.11-SNAPSHOT-shaded.jar

As a result you have two jars in the classpath with two slf4j bindings (graphhopper-web-0.11-SNAPSHOT and logback-classic-1.2.3.jar). There's no need to create a shaded jar for running an integration test against a Dropwizard application, it can be run as a unit test. So, if you configure graphhopper-web to run its integration tests during the test phase, there will be no warning:

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-failsafe-plugin</artifactId>
            <version>2.19.1</version>
            <executions>
                <execution>
                    <goals>
                        <goal>integration-test</goal>
                        <goal>verify</goal>
                    </goals>
                </execution>
            </executions>
            <configuration>
                <excludes>
                    <exclude>com.graphhopper.http.**</exclude>
                </excludes>
            </configuration>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-surefire-plugin</artifactId>
            <version>2.19.1</version>
            <configuration>
                <argLine>-Xmx100m -Xms100m</argLine>
                <includes>
                    <include>com.graphhopper.http.**</include>
                </includes>
            </configuration>
        </plugin>

Another option is to rename them from *IT to *Test, so they are not automatically matched as integration tests.