NullPointerException and DataBoundConstructor

[Jens Keller]

Hi, 

I wrote an SCM plugin some time ago and from time to time it is throwing a NullPointerException at the following location:

 @Override
 public boolean checkout(AbstractBuild<?, ?> build, Launcher launcher, FilePath workspace, BuildListener listener, File changelogFile) throws IOException, InterruptedException {
    return innerScm.checkout(new FilePath(changelogFile), getRevisionStateFileFileForBuild(build), workspace);
 }

I'm using "innerScm" to have an internal API that is easier to unit-test for me, and in the "outer" scm there is basically only this adapter code.

What is null is the "innerScm".

I also see Null pointer exceptions thrown at this location sometimes:

        @Override

       public ChangeLogParser createChangeLogParser() {

               return new ChangeLogParser() {

                       @SuppressWarnings("rawtypes")

                       @Override

                       public ChangeLogSet<? extends Entry> parse(AbstractBuild build, File changelogFile) throws IOException {

                               return new HanaChangeLogSet(build, innerScm.parseChangeLog(changelogFile));

                       }

               };

       }

I don't understand how this can happen, because I only have the following constructor:

private final transient DatabaseInnerSCM innerScm;

@DataBoundConstructor
public DatabaseSCM(String connection, String objectFilter, boolean shouldDownloadContent, RepositoryBrowser<HanaChangeLogSet.Entry> browser) {
 this.connection = connection;
 this.objectFilter = objectFilter;
 this.shouldDownloadContent = shouldDownloadContent;
 this.browser = browser;

 Repository repository = new SQLRepository(new SQLConnectionProviderImpl());

 ObjectFilter[] filters = new ObjectFilterParser().parseMultiple(this.objectFilter);

 this.innerScm = new DatabaseInnerSCM(repository, filters, shouldDownloadContent);

}

So from the code I don't see how this could become null when going through the constructor.

Does the Jenkins framework have any other way to assign the field than using the data-bound constructor?

Best regards

Jens

[Robert Sandell]

XStream deserialization is not using the constructor, and since the innerScm field is transient the field won't be on disk.

You should recreate it in a readResolve method.

/B

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Robert Sandell

Software Engineer

CloudBees Inc.

[Jens Keller]

Hi Robert,

I see...this makes sense, thanks a lot!!

Currently I have a hard time reproducing the issue, can you tell me under which circumstances the data-bound constructor is invoked, and when the "readResolved" / XStream deserialization is being used?

Ideally I will also write a regression test for this, therefore it would be good to know.

Best regards

Jens

[Slide]

DataBoundConstructor is called when the confguration screen is POSTed. XStream deserialization is done when the item is being loaded from disk.

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[Jens Keller]

Thanks a lot to all.

I've created a regression test like this - just create a new job based on another job's config XML, which failed when executing it.

After implementing the readResolve method the test passed.

The following page I found also very helpful, though my issue here is not a backward compatibility/migration topic

https://wiki.jenkins-ci.org/display/JENKINS/Hint+on+retaining+backward+compatibility

Best regards

Jens

@Test
public void givenJobCreatedFromXml_shouldWork() throws Exception {
    createInMemoDB("MYDB");
    FreeStyleProject project1 = createProjectWithScmForNamedConnection("project1", "MYDB");
    InputStream xmlConfig = new FileInputStream(project1.getConfigFile().getFile());
    FreeStyleProject project2 = (FreeStyleProject) j.hudson.createProjectFromXML("project2", xmlConfig);
    triggerBuildAndAssert(project2, Result.SUCCESS);

}