Custom JAX-RS ParamConverter doesn't work for collection and array types

[sithmein]

I was trying to create a custom javax.ws.rs.ext.ParamConverter<List<String>>. The idea is to convert query parameters such as "ids=i1,i2,i3" into a list of strings i1, i2, i3 in the resource class. The convert is instantiated correctly and used but the call actually fails with

java.lang.ClassCastException: Cannot cast java.util.Arrays$ArrayList to java.lang.String

I did a bit of debugging and it seems there is some special treatment for collections and arrays in org.apache.cxf.jaxrs.utils.InjectionUtils which partially ignores the custom ParamConverter. It's called but the returned value as assume to be the type inside the collection.
Attached is a small example project to reproduce the issue:

• mvn package
• java -jar com.knime.enterprise.cloud.service.repository.app/target/cloud.service.repository.app-0.0.2-SNAPSHOT.jar
• curl http://localhost:9080/repository/foo?ids=1,2,3

The relevant code is in com.knime.enterprise.cloud.service.repository.impl/src/main/java/com/knime/enterprise/cloud/service/repository/impl/v4
This occurs in Open Liberty 18.0.0.3.

jar-zip.zip

[bpaskin-ibm]

This has nothing to do with the findings of the IBM team, but I believe you need a ? instead of a / after foo to read in the query parameters, which 1,2,3 will be read in as a String first. I do run into the same issue with your sample code.

[WhiteCat22]

Looks like some of the logic we are doing in InjectionUtils.injectIntoCollectionOrArray() to get the realType could use some work.

paramType=interface java.util.List and genericType=java.util.List<java.lang.String> until that point.

[WhiteCat22]

I tested with CXF 3.2.8 and the issue does not occur, so this must be the result of some change we've made to CXF.

Uploading the war file (with source) I used to reproduce with vanilla CXF (change .zip to .war)
CXFParamConverter.zip

[andymc12]

This issue should be resolved in the next Liberty release. Thanks.