Current IdealGraphVisualizer build files (http://hg.openjdk.java.net/jdk/hs, eeac8b750f4a tip)
cause 'ant build/run'' to fail in '.../src/IdealGraphVisualizer' because 'bootstrap.url' points to a HTTP server that is not up anymore and returns a 503, generating the following output:

~/hg/jdk10/hs/src/utils/IdealGraphVisualizer$ ant build
Buildfile: /home/gromero/hg/jdk10/hs/src/utils/IdealGraphVisualizer/build.xml

download:
     [echo] Downloading clusters ide|platform
      [get] Getting: http://deadlock.netbeans.org/hudson/job/nbms-and-javadoc/lastSuccessfulBuild/artifact/nbbuild/netbeans/harness/tasks.jar
      [get] To: /tmp/tasks.jar
      [get] Error opening connection java.io.IOException: Server returned HTTP response code: 503 for URL: http://deadlock.netbeans.org/hudson/job/nbms-and-javadoc/lastSuccessfulBuild/artifact/nbbu
/netbeans/harness/tasks.jar
      [get] Error opening connection java.io.IOException: Server returned HTTP response code: 503 for URL:
http://deadlock.netbeans.org/hudson/job/nbms-and-javadoc/lastSuccessfulBuild/artifact/nbbuild/netbeans/harness/tasks.jar
      [get] Error opening connection java.io.IOException: Server returned HTTP response code: 503 for URL:
http://deadlock.netbeans.org/hudson/job/nbms-and-javadoc/lastSuccessfulBuild/artifact/nbbuild/netbeans/harness/tasks.jar
      [get] Can't get http://deadlock.netbeans.org/hudson/job/nbms-and-javadoc/lastSuccessfulBuild/artifact/nbbuild/netbeans/harness/tasks.jar to /tmp/tasks.jar

BUILD FAILED
/home/gromero/hg/jdk10/hs/src/utils/IdealGraphVisualizer/build.xml:7: The following error occurred while executing this line:
/home/gromero/hg/jdk10/hs/src/utils/IdealGraphVisualizer/nbproject/build-impl.xml:41: The following error occurred while executing this line:
/home/gromero/hg/jdk10/hs/src/utils/IdealGraphVisualizer/nbproject/platform.xml:27: Can't get
http://deadlock.netbeans.org/hudson/job/nbms-and-javadoc/lastSuccessfulBuild/artifact/nbbuild/netbeans/harness/tasks.jar to /tmp/tasks.jar

Total time: 0 seconds

Accordingly to [1] the HTTP server currently set in 'bootstrap.url' went out of service.

[1] https://netbeans.org/bugzilla/show_bug.cgi?id=238447