I submitted some feedback to documentation regarding the content you cited.

The line in question originated from something I wrote while implementing the %On*Finally set of methods. The "calling method" in this context refers to the method that invokes the %On*Finally() method. In this case, %Save() is the calling method.

%Save may or may not initiate a transaction, depending on a few factors. If %Save does initiate a transaction then that transaction is complete prior to the %OnSaveFinally() call.

%Library.ResultSet remains in the product for backward compatibility reasons but there are better ways to execute class queries. Any class query can be projected as a table valued function (TVF). TVF's can be executed if the class query also declares SQLPROC. A TVF can be included in the FROM item list, it can be joined with other FROM items, it can be ordered, restricted and a subset of available columns made available. Here is a simple example from the Sample.Person class:

select id,name,dob from sample.SP_Sample_By_Name('Ad') order by dob desc

I populated Sample.Person with some generated data and ran the above statement:

USER>set result = $system.SQL.Execute("select id,name,dob from sample.SP_Sample_By_Name('Ad') order by dob desc")

USER>write result.%Next()
1
USER>write result.Name
Adams,Elvira X.

There is a project that will be available soon (don't ask me to define "soon") that will allow the Java programmer to load and compile sources from the local system into an IRIS Server. The IRIS Server does not need to be running on the same system where the files are located.

This example is slightly old as the current implementation of load() returns a list of items loaded and compile() returns a list of items compiled. There are load implementations that accept directories, individual files, any Java streamable, and also JAR files.

SourceLoader sourceLoader = new SourceLoader(connection);
Path path = Paths.get("path/to/samples/cls/Sample");
sourceLoader.load(path, null);
sourceLoader.compile(true);

Yes, of course "inverse" - sorry.

Persistent vs RegisteredObject - not a problem but you are calling a simple class method so we don't need any super class. I used this implementation for the IRIS Class:

Class Utils.CSW1JavaFunctions
{
    ClassMethod IrisReturn(user = "user", pass = "pass") As %Stream.GlobalBinary
    {
         try {
             set cswStream=##class(%Stream.GlobalBinary).%New()
             set cswReturn = {"user":(user), "pass":(pass) }
             do cswReturn.%ToJSON(cswStream)
             return cswStream
         } catch exc {
             write !,"Caught Exception on server: ", exc.AsSQLMessage()
         }
    }
}

And this is a crude hack at the Java code - the anonymous InputStream class could use more work but it does run for this simple example. I'll leave the rest of the InputStream coding to you.

package utils;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.intersystems.jdbc.*;

import java.io.*;
import java.sql.SQLException;


public class Reader {
    public static final String CACHE_CLASS_NAME = "Utils.CSW1JavaFunctions";

    public IRISConnection connection;
    public IRIS iris;

    public Reader(IRISConnection connection) throws SQLException {
        this.connection = connection;
        this.iris = IRIS.createIRIS(connection);
    }
    public static void main(String[] args) throws SQLException {
        IRISDataSource dataSource = new IRISDataSource();
        dataSource.setServerName("localhost");
        dataSource.setPortNumber(51776);
        dataSource.setDatabaseName("USER");
        dataSource.setUser("_SYSTEM");
        dataSource.setPassword("SYS");
        IRISConnection connection = (IRISConnection) dataSource.getConnection();
        Reader reader = new Reader(connection);
        try {
            JsonNode jsonNode = reader.execute("IrisReturn", "java", "jpass");
            System.out.println(jsonNode.toString());
        } catch (Exception exc) {
            exc.printStackTrace();
        }
    }

    public JsonNode execute(String method, Object... args) throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        JsonNode jsonNode = null;
        try {
            IRISObject data  = (IRISObject) iris.classMethodObject(CACHE_CLASS_NAME, method, args[0], args[1]);
            InputStream is = new InputStream() {
                byte[] buffer;
                int pos = 0;
                int len = -1;

                @Override
                public int read() throws IOException {
                    if (pos >= len) {
                        getBuffer();
                    }
                    if (len == -1) {
                      return -1;
                    }
                    return buffer[pos++];
                }

                void getBuffer() {
                    pos = 0;
                    IRISReference readLen = new IRISReference(3200);
                    String string = (String) data.invoke("Read", readLen);
                    if (readLen.getLong() == -1) {
                        buffer = null;
                        len = -1;
                    } else {
                        buffer = string.getBytes();
                        len = buffer.length;
                    }
                }
            };

            jsonNode = (JsonNode) mapper.readTree(is);
            return jsonNode;
        } catch (Exception ex) {
            ex.printStackTrace();
        }
        return null;
    }
}

Running this produces this output:

/usr/lib/jvm/adoptopenjdk-11-hotspot-amd64/bin/java -javaagent:/home/...
{"user":"java","pass":"jpass"}

Process finished with exit code 0