Incorrect results in mvn dependency:analyze

Question

I've been searching for a tool, which is able to show you unused dependecies. I soon stumbled over the maven command mvn dependency:analyze. The problem with this is, that it often detects "unused" dependencies which let the build fail if missing.

Here is an example from an optimized Project:

$ mvn dependency:analyze

[INFO] Building LogfileTool 0.1
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] >>> maven-dependency-plugin:2.8:analyze (default-cli) > test-compile @ LogfileTool >>>
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ LogfileTool ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 1 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ LogfileTool ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 7 source files to C:\Projects\LogfileToolMa\LogfileTool\target\classes
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ LogfileTool ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory C:\Projects\LogfileToolMa\LogfileTool\src\test\resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ LogfileTool ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] <<< maven-dependency-plugin:2.8:analyze (default-cli) < test-compile @ LogfileTool <<<
[INFO]
[INFO] --- maven-dependency-plugin:2.8:analyze (default-cli) @ LogfileTool ---
[WARNING] Unused declared dependencies found:
[WARNING]    log4j:apache-log4j-extras:jar:1.2.17:compile
[WARNING]    org.projectlombok:lombok:jar:1.16.18:provided
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS

Dependencies in Pom.xml

<dependencies>

<!-- Logger -->
<dependency>
  <groupId>log4j</groupId>
  <artifactId>log4j</artifactId>
  <version>1.2.17</version>
</dependency>
<dependency>
  <groupId>log4j</groupId>
  <artifactId>apache-log4j-extras</artifactId>
  <version>1.2.17</version>
</dependency>


<!-- Generating Getter, Setter etc. -->
<dependency>
  <groupId>org.projectlombok</groupId>
  <artifactId>lombok</artifactId>
  <version>1.16.18</version>
  <scope>provided</scope>
</dependency>

<dependency>
  <groupId>commons-io</groupId>
  <artifactId>commons-io</artifactId>
  <version>2.4</version>
  <type>jar</type>
</dependency>

</dependencies>

The used Packages of Lombok are:

lombok.AccessLevel
lombok.Data
lombok.Getter
lombok.Setter

By Removing lombok from my POM i get the following Error by Buildig the Project

-------------------------------------------------------------
COMPILATION ERROR : 
-------------------------------------------------------------
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[7,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[8,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[9,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[10,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[26,2] cannot find symbol
  symbol: class Data
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[13,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[14,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[15,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[16,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[26,2] cannot find symbol
  symbol: class Data
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[34,4] cannot find symbol
  symbol:   class Getter
  location: class  ch.glue.logfiletool.logfiletool.config_handler.LogfileSearchConfig
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[35,4] cannot find symbol
  symbol:   class Setter
  location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileSearchConfig
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[35,4] cannot find symbol
  symbol:   class Getter
  location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileParseConfig
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[36,4] cannot find symbol
  symbol:   class Setter
  location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileParseConfig
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[62,7] cannot find symbol
  symbol:   method setXmlToRead(java.lang.String)
  location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileSearchConfig
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[63,7] cannot find symbol
  symbol:   method setPathToLogfiles(java.lang.String)
  location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileSearchConfig
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[63,7] cannot find symbol
  symbol:   method setPathForStorage(java.lang.String)
  location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileParseConfig
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[64,7] cannot find symbol
  symbol:   method setPathToLogfile(java.lang.String)
  location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileParseConfig
ch/glue/logfiletool/logfiletool/log_handler/LogfileReader.java:[93,50] cannot find symbol
  symbol:   method getPathToLogfiles()
  location: variable logfileSearchConfig of type ch.glue.logfiletool.logfiletool.config_handler.LogfileSearchConfig
ch/glue/logfiletool/logfiletool/log_handler/LogfileReader.java:[95,100] cannot find symbol
  symbol:   method getXmlToRead()
  location: variable logfileSearchConfig of type ch.glue.logfiletool.logfiletool.config_handler.LogfileSearchConfig
ch/glue/logfiletool/logfiletool/Main.java:[61,51] cannot find symbol
  symbol:   method getPathToLogfile()
  location: variable logfileToolConfig of type ch.glue.logfiletool.logfiletool.config_handler.LogfileParseConfig
ch/glue/logfiletool/logfiletool/Main.java:[71,52] cannot find symbol
  symbol:   method getPathForStorage()
  location: variable logfileToolConfig of type ch.glue.logfiletool.logfiletool.config_handler.LogfileParseConfig
22 errors 
-------------------------------------------------------------
------------------------------------------------------------------------
BUILD FAILURE
------------------------------------------------------------------------
Total time: 1.747 s
Finished at: 2017-09-27T10:04:20+02:00
Final Memory: 14M/210M
------------------------------------------------------------------------
Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project LogfileTool: Compilation failure: Compilation failure:
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[7,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[8,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[9,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[10,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[26,2] cannot find symbol
symbol: class Data
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[13,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[14,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[15,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[16,14] package lombok does not exist
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[26,2] cannot find symbol
symbol: class Data
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[34,4] cannot find symbol
symbol:   class Getter
location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileSearchConfig
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[35,4] cannot find symbol
symbol:   class Setter
location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileSearchConfig
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[35,4] cannot find symbol
symbol:   class Getter
location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileParseConfig
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[36,4] cannot find symbol
symbol:   class Setter
location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileParseConfig
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[62,7] cannot find symbol
symbol:   method setXmlToRead(java.lang.String)
location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileSearchConfig
ch/glue/logfiletool/logfiletool/config_handler/LogfileSearchConfig.java:[63,7] cannot find symbol
symbol:   method setPathToLogfiles(java.lang.String)
location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileSearchConfig
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[63,7] cannot find symbol
symbol:   method setPathForStorage(java.lang.String)
location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileParseConfig
ch/glue/logfiletool/logfiletool/config_handler/LogfileParseConfig.java:[64,7] cannot find symbol
symbol:   method setPathToLogfile(java.lang.String)
location: class ch.glue.logfiletool.logfiletool.config_handler.LogfileParseConfig
ch/glue/logfiletool/logfiletool/log_handler/LogfileReader.java:[93,50] cannot find symbol
symbol:   method getPathToLogfiles()
location: variable logfileSearchConfig of type ch.glue.logfiletool.logfiletool.config_handler.LogfileSearchConfig
ch/glue/logfiletool/logfiletool/log_handler/LogfileReader.java:[95,100] cannot find symbol
symbol:   method getXmlToRead()
location: variable logfileSearchConfig of type ch.glue.logfiletool.logfiletool.config_handler.LogfileSearchConfig
ch/glue/logfiletool/logfiletool/Main.java:[61,51] cannot find symbol
symbol:   method getPathToLogfile()
location: variable logfileToolConfig of type ch.glue.logfiletool.logfiletool.config_handler.LogfileParseConfig
ch/glue/logfiletool/logfiletool/Main.java:[71,52] cannot find symbol
symbol:   method getPathForStorage()
location: variable logfileToolConfig of type ch.glue.logfiletool.logfiletool.config_handler.LogfileParseConfig
-> [Help 1]

To see the full stack trace of the errors, re-run Maven with the -e switch.
Re-run Maven using the -X switch to enable full debug logging.

For more information about the errors and possible solutions, please read the following articles:
[Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException

And without log4j-extras i get following Error by running the Project

log4j:ERROR Could not instantiate class [org.apache.log4j.rolling.RollingFileAppender].
java.lang.ClassNotFoundException: org.apache.log4j.rolling.RollingFileAppender 

Both log4j and lombok are used in my Project. Do you have an Idea how to fix this or where this is comming from?

thank you in advance

Answer 1

I have also been running into the issue where project Lombok has been marked by dependency:analyze as an Unused declared dependency. Project Lombok does most of its magic compile time, and as such most annotations are removed after compilation. This is why Maven's dependency analyzer does not recognize it. And why it also fails to detect dependencies that are loaded using SPI.

We have worked around this by explicitly telling the Dependency analyzer plugin to ignore Project Lombok. This can be done with the <usedDependency> configuration option, or the more fine-grained <ignoreUnusedDeclaredDependency> as such:

<pluginManagement>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-dependency-plugin</artifactId>
            <version>3.0.2</version>
            <configuration>
                <ignoredUnusedDeclaredDependencies>
                    <ignoredUnusedDeclaredDependency>org.projectlombok:lombok</ignoredUnusedDeclaredDependency>
                </ignoredUnusedDeclaredDependencies>
            </configuration>
        </plugin>
    </plugins>
</pluginManagement>

PS regarding scopes: Lombok is a compile time dependency, but need not be on the classpath at runtime (or end up in your lib folder). The provided dependency states that the jar should be present for compilation, but at run-time it is expected to be provided by the runtime environment (e.g. the container you run it in). Since Lombok is not needed at runtime, there will be no problems when your runtime does not provide Lombok, contrary to what you'd expect from the Maven dependency declaration.