how to access a method of C++ library (DLL) in java

Question

I have one c++ dll file. And I know the methods used in it. I need to call these methods from my java code. I don't have access to modify the DLL file. Please provide me a solution to do this.

Answer 1

I created JavaCPP exactly for that purpose. I'll copy/paste some sample code and explanations from the page:

The most common use case involves accessing some legacy library written for C++, for example, inside a file named LegacyLibrary.h containing this C++ class:

#include <string>

namespace LegacyLibrary {
    class LegacyClass {
        public:
            const std::string& get_property() { return property; }
            void set_property(const std::string& property) { this->property = property; }
            std::string property;
    };
}

To get the job done with JavaCPP, we can easily define a Java class such as this one--although one could use the Parser to produce it from the header file as demonstrated below:

import com.googlecode.javacpp.*;
import com.googlecode.javacpp.annotation.*;

@Platform(include="LegacyLibrary.h")
@Namespace("LegacyLibrary")
public class LegacyLibrary {
    public static class LegacyClass extends Pointer {
        static { Loader.load(); }
        public LegacyClass() { allocate(); }
        private native void allocate();

        // to call the getter and setter functions 
        public native @StdString String get_property(); public native void set_property(String property);

        // to access the member variable directly
        public native @StdString String property();     public native void property(String property);
    }

    public static void main(String[] args) {
        // Pointer objects allocated in Java get deallocated once they become unreachable,
        // but C++ destructors can still be called in a timely fashion with Pointer.deallocate()
        LegacyClass l = new LegacyClass();
        l.set_property("Hello World!");
        System.out.println(l.property());
    }
}

Alternately, we can produce a Java interface by parsing the header file with a config class such as this one:

@Properties(target="LegacyLibrary", value=@Platform(include="LegacyLibrary.h"))
public class LegacyLibraryConfig implements Parser.InfoMapper {
    public void map(Parser.InfoMap infoMap) {
    }
}

And the following build commands:

$ javac -cp  javacpp.jar LegacyLibraryConfig.java
$ java  -jar javacpp.jar LegacyLibraryConfig
$ javac -cp  javacpp.jar LegacyLibrary.java
$ java  -jar javacpp.jar LegacyLibrary

For more complex examples including Maven/IDE integration, check out the JavaCPP Presets!