Why does maven download lots of versions of same dependency?

Question

I am running a build on maven 3 and its trying to download many different versions of the same JAR. I didn't specify that JAR as a dependency. Any idea why it is doing that?

Downloading: http://download.java.net/maven/2/org/codehaus/jackson/jackson-core-asl/maven-metadata.xml
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/maven-metadata.xml
Downloading: http://repo1.maven.org/maven2/org/codehaus/jackson/jackson-core-asl/maven-metadata.xml
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/maven-metadata.xml (3 KB at 10.8 KB/sec)
Downloaded: http://repo1.maven.org/maven2/org/codehaus/jackson/jackson-core-asl/maven-metadata.xml (2 KB at 1.8 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.4.0/jackson-core-asl-1.4.0.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.4.0/jackson-core-asl-1.4.0.pom (1016 B at 5.0 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.4.1/jackson-core-asl-1.4.1.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.4.1/jackson-core-asl-1.4.1.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.4.2/jackson-core-asl-1.4.2.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.4.2/jackson-core-asl-1.4.2.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.4.3/jackson-core-asl-1.4.3.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.4.3/jackson-core-asl-1.4.3.pom (1016 B at 5.5 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.4.4/jackson-core-asl-1.4.4.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.4.4/jackson-core-asl-1.4.4.pom (1016 B at 5.0 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.4.5/jackson-core-asl-1.4.5.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.4.5/jackson-core-asl-1.4.5.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.0-SNAPSHOT/maven-metadata.xml
Downloading: http://download.java.net/maven/2/org/codehaus/jackson/jackson-core-asl/1.5.0-SNAPSHOT/maven-metadata.xml
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.0-SNAPSHOT/maven-metadata.xml (372 B at 1.9 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.0-SNAPSHOT/jackson-core-asl-1.5.0-20100311.071608-6.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.0-SNAPSHOT/jackson-core-asl-1.5.0-20100311.071608-6.pom (2 KB at 5.5 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.0/jackson-core-asl-1.5.0.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.0/jackson-core-asl-1.5.0.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.1/jackson-core-asl-1.5.1.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.1/jackson-core-asl-1.5.1.pom (1016 B at 5.5 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.2/jackson-core-asl-1.5.2.pom
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Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.3/jackson-core-asl-1.5.3.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.3/jackson-core-asl-1.5.3.pom (1016 B at 5.3 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.4/jackson-core-asl-1.5.4.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.4/jackson-core-asl-1.5.4.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.5/jackson-core-asl-1.5.5.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.5/jackson-core-asl-1.5.5.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.6/jackson-core-asl-1.5.6.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.6/jackson-core-asl-1.5.6.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.7/jackson-core-asl-1.5.7.pom
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Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.8/jackson-core-asl-1.5.8.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.5.8/jackson-core-asl-1.5.8.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.0-SNAPSHOT/maven-metadata.xml
Downloading: http://download.java.net/maven/2/org/codehaus/jackson/jackson-core-asl/1.6.0-SNAPSHOT/maven-metadata.xml
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.0-SNAPSHOT/maven-metadata.xml (372 B at 1.9 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.0-SNAPSHOT/jackson-core-asl-1.6.0-20100831.034125-5.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.0-SNAPSHOT/jackson-core-asl-1.6.0-20100831.034125-5.pom (2 KB at 5.6 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.0/jackson-core-asl-1.6.0.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.0/jackson-core-asl-1.6.0.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.1/jackson-core-asl-1.6.1.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.1/jackson-core-asl-1.6.1.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.2/jackson-core-asl-1.6.2.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.2/jackson-core-asl-1.6.2.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.3/jackson-core-asl-1.6.3.pom
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Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.4/jackson-core-asl-1.6.4.pom
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Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.5/jackson-core-asl-1.6.5.pom
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Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.6/jackson-core-asl-1.6.6.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.6/jackson-core-asl-1.6.6.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.7/jackson-core-asl-1.6.7.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.6.7/jackson-core-asl-1.6.7.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.0-SNAPSHOT-SNAPSHOT/maven-metadata.xml
Downloading: http://download.java.net/maven/2/org/codehaus/jackson/jackson-core-asl/1.7.0-SNAPSHOT-SNAPSHOT/maven-metadata.xml
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.0-SNAPSHOT-SNAPSHOT/maven-metadata.xml (381 B at 2.0 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.0-SNAPSHOT-SNAPSHOT/jackson-core-asl-1.7.0-SNAPSHOT-20101126.221009-1.pom
Downloading: http://download.java.net/maven/2/org/codehaus/jackson/jackson-core-asl/1.7.0-SNAPSHOT-SNAPSHOT/jackson-core-asl-1.7.0-SNAPSHOT-20101126.221009-1.pom
[WARNING] The POM for org.codehaus.jackson:jackson-core-asl:jar:1.7.0-SNAPSHOT-20101126.221009-1 is missing, no dependency information available
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.0-SNAPSHOT/maven-metadata.xml
Downloading: http://download.java.net/maven/2/org/codehaus/jackson/jackson-core-asl/1.7.0-SNAPSHOT/maven-metadata.xml
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.0-SNAPSHOT/maven-metadata.xml (372 B at 1.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.0-SNAPSHOT/jackson-core-asl-1.7.0-20110105.013252-7.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.0-SNAPSHOT/jackson-core-asl-1.7.0-20110105.013252-7.pom (2 KB at 5.5 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.0/jackson-core-asl-1.7.0.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.0/jackson-core-asl-1.7.0.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.1-SNAPSHOT/maven-metadata.xml
Downloading: http://download.java.net/maven/2/org/codehaus/jackson/jackson-core-asl/1.7.1-SNAPSHOT/maven-metadata.xml
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.1-SNAPSHOT/maven-metadata.xml (372 B at 1.9 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.1-SNAPSHOT/jackson-core-asl-1.7.1-20110111.012521-1.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.1-SNAPSHOT/jackson-core-asl-1.7.1-20110111.012521-1.pom (2 KB at 4.8 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.1/jackson-core-asl-1.7.1.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.1/jackson-core-asl-1.7.1.pom (1016 B at 5.4 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.7.2/jackson-core-asl-1.7.2.pom
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Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.8.0-SNAPSHOT/maven-metadata.xml
Downloading: http://download.java.net/maven/2/org/codehaus/jackson/jackson-core-asl/1.8.0-SNAPSHOT/maven-metadata.xml
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.8.0-SNAPSHOT/maven-metadata.xml (372 B at 1.9 KB/sec)
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Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.8.1-SNAPSHOT/maven-metadata.xml
Downloading: http://download.java.net/maven/2/org/codehaus/jackson/jackson-core-asl/1.8.1-SNAPSHOT/maven-metadata.xml
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Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.8.1-SNAPSHOT/jackson-core-asl-1.8.1-20110515.143306-1.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.8.1-SNAPSHOT/jackson-core-asl-1.8.1-20110515.143306-1.pom (2 KB at 5.5 KB/sec)
Downloading: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.8.1/jackson-core-asl-1.8.1.pom
Downloaded: http://CorporateRepo/org/codehaus/jackson/jackson-core-asl/1.8.1/jackson-core-asl-1.8.1.pom (1016 B at 5.4 KB/sec)

Answer 1

You'll notice it's not actually downloading the jars, just the POMs. My guess would be that the version being specified is not a fixed version, and that maven is digging through the available versions to figure out which one it should use.

Somewhere in the dependency tree this component is being included. You can use mvn dependency:tree to figure out where. Of course, it will still need to download all the POMs even in order to show the tree, but you've already got them now :)