How to use maven command line to download 2.8 snapshot?

Hello,
     I am complete new to maven,after some googling I got command lines like this:

mvn dependency:get \
    -DrepoUrl=https://oss.sonatype.org/content/repositories/google-snapshots/com/google/ \
    -Dartifact=gwt:gwt:2.8.0-SNAPSHOT

and ran it,got errors like this:

>     -DrepoUrl=https://oss.sonatype.org/content/repositories/google-snapshots/com/google/ \
>     -Dartifact=gwt:gwt:2.8.0-SNAPSHOT
Picked up JAVA_TOOL_OPTIONS: -javaagent:/usr/share/java/jayatanaag.jar
Picked up _JAVA_OPTIONS: -Dawt.useSystemAAFontSettings=on -Dswing.aatext=true -Dswing.defaultlaf=com.sun.java.swing.plaf.gtk.GTKLookAndFeel
[INFO] Scanning for projects...
[INFO]                                                                        
[INFO] ------------------------------------------------------------------------
[INFO] Building Maven Stub Project (No POM) 1
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-dependency-plugin:2.8:get (default-cli) @ standalone-pom ---
[WARNING] repositoryUrl parameter is deprecated. Use remoteRepositories instead
[INFO] Resolving gwt:gwt:jar:2.8.0-SNAPSHOT with transitive dependencies
Downloading: https://oss.sonatype.org/content/repositories/google-snapshots/com/google/gwt/gwt/2.8.0-SNAPSHOT/maven-metadata.xml
Downloaded: https://oss.sonatype.org/content/repositories/google-snapshots/com/google/gwt/gwt/2.8.0-SNAPSHOT/maven-metadata.xml (353 B at 0.2 KB/sec)
Downloading: https://oss.sonatype.org/content/repositories/google-snapshots/com/google/gwt/gwt/2.8.0-SNAPSHOT/gwt-2.8.0-20150709.054321-1.pom
Downloaded: https://oss.sonatype.org/content/repositories/google-snapshots/com/google/gwt/gwt/2.8.0-SNAPSHOT/gwt-2.8.0-20150709.054321-1.pom (3 KB at 4.8 KB/sec)
Downloading: https://oss.sonatype.org/content/repositories/google-snapshots/com/google/com/google/web/bindery/requestfactory/2.8.0-SNAPSHOT/maven-metadata.xml
Downloading: https://oss.sonatype.org/content/repositories/snapshots/com/google/web/bindery/requestfactory/2.8.0-SNAPSHOT/maven-metadata.xml
Downloading: https://oss.sonatype.org/content/repositories/google-snapshots/com/google/com/google/web/bindery/requestfactory/2.8.0-SNAPSHOT/requestfactory-2.8.0-SNAPSHOT.pom
Downloading: https://oss.sonatype.org/content/repositories/snapshots/com/google/web/bindery/requestfactory/2.8.0-SNAPSHOT/requestfactory-2.8.0-SNAPSHOT.pom
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 6.798 s
[INFO] Finished at: 2015-07-10T12:30:19+08:00
[INFO] Final Memory: 15M/271M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-dependency-plugin:2.8:get (default-cli) on project standalone-pom: Couldn't download artifact: Unable to get dependency information for gwt:gwt:jar:2.8.0-SNAPSHOT: Failed to process POM for gwt:gwt:jar:2.8.0-SNAPSHOT: Non-resolvable import POM: Could not find artifact com.google.web.bindery:requestfactory:pom:2.8.0-SNAPSHOT in temp (https://oss.sonatype.org/content/repositories/google-snapshots/com/google/)
[ERROR] gwt:gwt:jar:2.8.0-SNAPSHOT
[ERROR]
[ERROR] from the specified remote repositories:
[ERROR] central (https://repo.maven.apache.org/maven2, releases=true, snapshots=false),
[ERROR] temp (https://oss.sonatype.org/content/repositories/google-snapshots/com/google/, releases=true, snapshots=true)
[ERROR] Path to dependency:
[ERROR] 1) org.apache.maven.plugins:maven-downloader-plugin:jar:1.0
[ERROR] -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

It seems like,requestfactory can't be fetched,so how to fix this problem?

--
You received this message because you are subscribed to the Google Groups "Google Web Toolkit" group.
To unsubscribe from this group and stop receiving emails from it, send an email to google-web-toolkit+unsubscribe@googlegroups.com.
To post to this group, send email to google-web-toolkit@googlegroups.com.
Visit this group at http://groups.google.com/group/google-web-toolkit.
For more options, visit https://groups.google.com/d/optout.