Can Matlab access a Java function that starts with an underscore

When I issue Matlab commands which end up using the Jackson FasterXML Java library, MATLAB returns a Java exception:

java.lang.NoSuchMethodError: com.fasterxml.jackson.dataformat.yaml.YAMLFactory._createContentReference(Ljava/lang/Object;)Lcom/fasterxml/jackson/core/io/ContentReference;

The Java function (writen by a different team) that I am calling from MATLAB goes through the following stages

final var mapper = new ObjectMapper(new YAMLFactory());

mapper.registerModule(new JavaTimeModule());

final URI url;

final var configFile = new File(filename);

url = configFile.toURI();

final JsonNode original = mapper.readTree(url.toURL());

so this last line calls function in com.fasterxml.jackson.databind.ObjectMapper

public JsonNode readTree(URL source) throws IOException

{

_assertNotNull("source", source);

return _readTreeAndClose(_jsonFactory.createParser(source));

}

calling function in com.fasterxml.jackson.dataformat.yaml.YAMLFactory

(in public class YAMLFactory extends JsonFactory as the mapper was passed a YAMLFactory)

@Override

public YAMLParser createParser(URL url) throws IOException

{

IOContext ctxt = _createContext(_createContentReference(url), true);

return _createParser(_decorate(_optimizedStreamFromURL(url), ctxt), ctxt);

}

_createContentReference is in the JsonFactory class and is not overriden in YAMLFactory

protected ContentReference _createContentReference(Object contentAccessor) {

// 21-Mar-2021, tatu: For now assume "canHandleBinaryNatively()" is reliable

// indicator of textual vs binary format:

return ContentReference.construct(!canHandleBinaryNatively(), contentAccessor);

}

To prove that MATLAB could have created the ContentReference if I had been able to get to the function

>> createContRef = javaMethod('construct', 'com.fasterxml.jackson.core.io.ContentReference', true, URL)

createContRef = com.fasterxml.jackson.core.io.ContentReference@fce56075

Unfortunately, I rarely deal with Java so not sure if my issue is:-

a) MATLAB cant cope with the underscore in the function name

b) The issue is that the _createContentReference function is in a parent class

c) something else

I have all the relevant jar files in javaclasspath as below

C:\Users\....\jackson-annotations-2.13.1.jar

C:\Users\....\jackson-core-2.13.1.jar

C:\Users\....\jackson-databind-2.13.1.jar

C:\Users\....\jackson-dataformat-yaml-2.13.1.jar

C:\Users\....\jackson-datatype-jsr310-2.13.1.jar

Appreciate any help.

[Richard Floyd]

Testing further has ruled out option a) as the problem

a) MATLAB cant cope with the underscore in the function name

If the same function is moved from the parent to the child it can be called successfully.

So, seems to be problem b)

[Richard Floyd]

Okay, so I think I now understand my own issue as I've found that Matlab 2019b already loads PART of the Jackson libraries (i'm assuming an older version than the one I need to use) as part of the java static path

C:\Program Files\MATLAB\R2019b\java\jarext\jackson\jackson-core.jar

But, i'm forced to use the new jackson dataformat classes from my .jar

C:\Users\....\jackson-dataformat-yaml-2.13.1.jar

These are loaded after the above static path so Matlab is trying to find the _createContentReference function in the old jackson-core.jar which doesn't appear to have the function being called.

So, I need to work out how to load the new Jackson jar's at the top of the static path or somehow remove the old Jackson static entries added by Matlab. Hopefully that won't affect Matlab internally calling the Jackson libraries.

Answer 1

[Richard Floyd]

Thankfully https://undocumentedmatlab.com/articles/static-java-classpath-hacks had the answer with the <before> entry in my javaclasspath.txt file

Obviously care needs to be taken with this as we are overriding the MATLAB versions

<before>
# Java classpath entries (The following come first on MATLAB static path)
# (Override internal ones -> see C:\Program Files\MATLAB\R2019b\java\jarext\jackson)
C:\Users\....\jackson-annotations-2.13.1.jar
C:\Users\....\jackson-core-2.13.1.jam
C:\Users\....\jackson-databind-2.13.1.jar
C:\Users\....\jackson-dataformat-yaml-2.13.1.jar
C:\Users\....\jackson-datatype-jsr310-2.13.1.jar