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https://issues.apache.org/jira/browse/APEXCORE-304?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15121393#comment-15121393
 ] 

ASF GitHub Bot commented on APEXCORE-304:
-----------------------------------------

Github user chinmaykolhatkar commented on a diff in the pull request:

    https://github.com/apache/incubator-apex-core/pull/208#discussion_r51119455
  
    --- Diff: engine/src/main/java/com/datatorrent/stram/StramLocalCluster.java 
---
    @@ -318,6 +333,21 @@ public StramLocalCluster(LogicalPlan dag) throws 
IOException, ClassNotFoundExcep
         }
       }
     
    +  private void addExtraJarsToClasspath(Set<String> jars)
    +      throws InvocationTargetException, IllegalAccessException, 
MalformedURLException, NoSuchMethodException
    +  {
    +    List<URL> jarUrls = new LinkedList<>();
    +    for (String jarPath : jars) {
    +      File file = new File(jarPath);
    +      URL url = file.toURI().toURL();
    +      jarUrls.add(url);
    +    }
    +
    +    ClassLoader prevCl = Thread.currentThread().getContextClassLoader();
    +    ClassLoader urlCl = URLClassLoader.newInstance(jarUrls.toArray(new 
URL[jarUrls.size()]), prevCl);
    +    Thread.currentThread().setContextClassLoader(urlCl);
    --- End diff --
    
    Thomas can answer this question better. But here is additional information 
as per my understanding:
    The place where Constructor of StramLocalCluster is called is a common 
point where both code paths joins.
    
    But there is a slight difference in how the operators are loaded by these 2 
paths.
    
    In LocalMode.runApp, the operator classes are already part of the System 
class loader. This is because when ApplicationTest is launched the operators 
are already in classpath provided by maven.
    
    StreamAppLauncher.runLocal is invoked by an application launched from dtcli 
(a java process). dtcli do not have operators present in its system classpath.
    
    Hence, in StramAppLauncher.runLocal (dtcli -local), there is a context 
class loader created which has information about operator classes. This context 
classloader is later used to load the operator classes.



> Ability to add jars to classpath in populateDAG
> -----------------------------------------------
>
>                 Key: APEXCORE-304
>                 URL: https://issues.apache.org/jira/browse/APEXCORE-304
>             Project: Apache Apex Core
>          Issue Type: Improvement
>            Reporter: Chinmay Kolhatkar
>            Assignee: Chinmay Kolhatkar
>
> This will have following functionality:
> 1) In populateDAG one would be allowed to add given local jar path to 
> classpath of the application.
> 2) Optionally delete the given jar file after copying to HDFS is done.



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