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How to create and use class instances in C# from JAR files?

I'm aware of all the other questions about this topic, but I haven't found a good solution for my problem. Currently I am trying to use Java code in my C# project. I've already tried to convert the JAR files into .DLL files with IKVM, but this didn't work for me because the JAR files are to complicated to translate into C# because not every component, which were used in Java, can be found in C#. The normal call of the JAR file doesn't work for me either because I need to work with the class instances of the declared classes in the Java code.
Back to my question: Does anybody know how I could use Java code in my project? I've heard that it may be possible to implement Java code like it would be native, is that true? Note that I've to work with the class instances of the classes declared in the Java code.
I highly appreciate any kind of help, sheers!
Edit:
My work around would be that I include batch files, which are calling the JAR files. I will include these batch files into my C# Project and work with the batch files. This may be a even better approach for me because every input and output of the JAR files are done via XML files.

This kind of mixup are not generally a good approach. I think the .Net Framework is very mature and you can find everything you want to do your work.
I would suggest you the following approach :
You can wrap your Java library in a REST API and call it in your C# code. Your REST API can be hosted on an external server or use an embedded server or even a spring boot project.
You can read this post for more details.

How to read drl file by using drools API? Is there any function in drools that can parse drl file into some value or other formats?

I am trying to visualize some drl file not using drools workbench(or business central). I've found the function to create drl file by passing value. However, I can't find the way to do opposite thing.
I expect to parse the existed drl file into some value or other format that can be easily used in my Vue project. At the moment I am looking for it in Drools souce code but can't find it.
I don't want to use drools workbench because it's not convenient enough to use. But if there are some functions or libraries in its souce code, please let me know. It's also very helpful.
I am using drools 7.0.0.final now.
Thanks for reading my question, if you have any idea, please help me.

I'm not sure about what you're trying to achieve, but let me give you some hints.
The org.drools.compiler.compiler.DrlParser in the drools-compiler module will parse the DRL and generate the PackageDescr, pretty much an AST of the rule file. Take a look at org.drools.compiler.compiler.DrlParserTest for an example.
The org.drools.compiler.builder.impl.KnowledgeBuilderImpl will create the *Impl* classes which are used by the runtime of Drools.
Alternatively you can take a look at the drools-model-compiler module, in which theres a compiler org.drools.modelcompiler.builder.ModelBuilderImpl that compiles *Descrs into a Java DSL we created recently, the executable model. see org.drools.modelcompiler.CompilerTest and org.drools.modelcompiler.PatternDSLTest
Let me know if it helps.
Good luck

Java library to assist in XSD creation?

Is anyone aware of a library that makes the process of creating XSDs in Java a little easier than using something like a DocumentBuilder? Something like a helper or utility class. I came across the org.eclipse.xsd maven jar but I'm having ClassNotFoundException issues when working with it in Eclipse and I'm not entirely sure it's meant to be used as a standalone kind of thing. This is a bit difficult to Google for as well since there are lot of search results around automatic generation/translation from Java to XSD and vice versa.
Essentially what I need to do is to programmatically create an XSD from a certain source of data -- not Java classes.

Apache XMLSchema is a lightweight Java object model that can be used to manipulate and generate XML schema representations. You can use it to read XML Schema (xsd) files into memory and analyze or modify them, or to create entirely new schemas from scratch.
The fact that with this API one can create an XSD from scratch, it sounds as a starting point to achieve the ask; as to the fitness, it depends on what that "certain source of data" is.

How to create WSDL file given SOAP WSDL operations

I haven't had any experience with web service related development. So, any ideas will be greatly appreciated.
Suppose, I have a file listing draft specification of WSDL operations. Following is one example. How would I go about creating the WSDL file. Is notepad sufficient or do I need to have WSDL editor?
getHostSystemInfo
Returns detailed information about host systems specified via given IDs.
input HostSystemIdCollection(Collection of Strings)
Output HostSystemInfoCollection
HostSystemInfo
Id: mandatory
Properties: Following properties should be provided for host systems
HostSystemName
HostSystemProperty1
HostSystemProperty2
HostSystemProperty3
....
....

If the question is just "how do I create the WSDL" then you could indeed use Notepad and just write it, it's only XML after all. However, writing syntactically correct XML by hand is pretty dull, and error prone. So I would recommend using WSDL aware tooling for example an Eclipse editor
An alternative is to write some Java which expresses the interface, and from it generate the WSDL. There are many ways of doing this, including starting with an EJB and annotating it accordingly. A few googles should help you find what you need.
My experience is that simple POC situations tend to work well starting at the Java. Larger scale projects benfit from considered designs starting at the WSDL.

coding WSDL by hand is a big pain! i used a XML editor for creation of and then generated the stubs with JAXWS. It is important to understand and differences of the WSDL styles, which is not trivial (have a look at WSDL styles). a good help is to import the WSDL schema to your IDE (eclipse, idea) and then work with autocompletion.
just for interest, why are you using WSDL + SOAP. if you have a choice and you use anyway HTTP, have a look at REST. It can make implementation of web-api a LOT easier, both on server side and for api-clients.

If you haven't done any web services before, I would strongly recommend a WSDL Editor. The Netbeans has a plugin that should help.
The other way of doing it, which may be easier is by using the Java annotations defined in JSR 181.

Of course you could use the worst text editor in the world (!) but I'd seriously consider using any decent XML editor or IDE (Eclipse's WSDL support is pretty decent). This will save you a lot of pain and suffer.
Or, if this is an option, you could just annotate a Java class with JAX-WS annotations and have your WSDL dynamically generated from the Java code. Personally, I prefer the WSDL-first approach, the Java-first approach is just a suggestion to get you started.

You could use Axis2 to create that for you.

Executing Constantly Changing Logic

I writing a dynamic HTML parsers functionality.
I will want to modify existing parsers and also would want to add more parsers (I expect parsers will be modified as sites a remodified and new parsers will be needed for new sites).
I started writing a generic functionality which use a XML with conditions and rules for each site but as this works fine for now, I'm pretty sure it will need constant modifications...
The parsers will parse and write the data to a DB.
My application runs on JBOSS 4.
Any known best practice for that?
Thanks,
Rod
Thanks for your answer. Maybe I was unclear. I realized that imm. from the rate my question got. What I am writing feature that manage parsers execution. Each parser will parse a different text document structure. Documents structure might change from time to time and more new structured document will be added to be parsed. I dont want to recompile build deploy my application for each arser change.
I want to manage the execution of each parser as theymight be executed in parralel or according to execution rules.
Does Using Java ScriptingEngine might be a good option?

There are lots of ways to have some code that can be modified without redeploying. Using groovy scripts to do the parsing is one. Is is a rather simple matter to check to see if the script has been modified and automatically reload it.

The design sounds convoluted to me, but IFF you prove to yourself there's not a much simpler way to accomplish the same task, you may want a rules engine like Drools...