JNA loading DLL and its application in jar

Demand related

• demand
  Use JNI Mode load DLL, And encapsulated as SDK For others .
• Method
  • Native JNI The way
  • call JNA frame

1. Native JNI The method is suitable for customized dll, That is, having dll In the case of source code , Strong operability ; However, if there are too many methods and structures involved , You need to write many type conversions by yourself
2. JNA It can be used in all kinds of scenes , It saves effort in type conversion , It's necessary for lazy people

This time, the target is a header file windows32 position dll file , So choose to use JNA.

Be careful , the reason being that win32 platform , So it's used throughout 32 Bit JDK, Used here jdk_1.8.152_x86.

DLL relevant

Of course, in order to step on the pit, if conditions permit, it is still self created dll To try . So I choose to sacrifice Universe first IDE, Kill a chicken with an ox knife — Generate a simple dll file .
The header file :

#pragma once

#define DLL_API _declspec(dllexport) 

extern "C" {
    
	DLL_API int getVersion(void);
	DLL_API int add(int a, int b);
}

Source code ：

#include "pch.h"
#include "soft.h"

int getVersion(void) {
    
	return 2;
}

int add(int a, int b) {
    
	return a + b;
}

Next, naturally, is generation DLL. Here are some configurations to pay attention to ：

1. Use Release/win32 To generate solutions
2. choice “ Use... In a static library MFC”

It can be configured as shown in the figure ：

If not configured like this , There will be Can’t find dependent libraries problem , It means the current dll Rely on others dll, But I can't find it in the current environment . Specific dependencies can be used dependencywalker Conduct detection query , A situation similar to the following figure shows the lack of dependency ：

The configuration. , You can pick up a fresh one dll file .

good , Now let's simulate a situation — The source code is missing . This becomes the requirement mentioned at the beginning .

JNA relevant

JNA It's a mature framework , Of course, it's organized . All heroes can be in github Get the latest version on , The portal is here ：
jna
The latest version is 5.5.0. Here is also a direct report of its jar Of maven Address ：
jna-5.5.0
jna-platform-5.5.0
Two bags , The former is equivalent to the kernel package , The latter is similar to the plug-in package . Generally, you can download the former .

then …

You'll find this jar The bag is really big .

Now it's 1.4M size , And we generated in the previous step Dll File size ：

Kill chicken with ox knife X 2.

This can't be tolerated , You have to cut it .

By opening the jar Package we can see ：

This is a compatible package for various environments , All we need here is win32 Bit , We have to find a way Get the source code and delete it , Regenerate another jna Of jar Wrap it up .
However, in maven The provision of the jna-5.5.0-sources.jar These platform related things are not in the source package , So you can only close it manually . Fortunately, the platform related compatibility packages here are not class file , It is Various types so file 、dll file 、jnilib file etc. . So you can close it directly .

Specific operation ：

1. hold jna-5.5.0-sources.jar Copy all the code in the source package
2. hold jna-5.5.0.jar Copy the required environment compatibility package under the directory
3. Generate jar package

stay IDEA It's probably like this in the middle of the story ：

All we need here is win32-x86 Environmental support for , So only the compatible packages of this environment are copied , You can see , Just add jnidispatch.dll File can .
Then configure artifacts, Fast generation jar package ：

So I found a size 288KB Only supported win32-x86 Of jna package ：

Although it's still a little big , But let's get together first .

Use JNA load DLL

First test it in the external project . First, the previously generated SimpleDll.dll Files in Project root Next , Then just write an inheritance Libary The interface of , load dll And the statement dll The method in ：

import com.sun.jna.Library;
import com.sun.jna.Native;

public interface ISimpleDll extends Library {
    
	ISimpleDll INSTANCE = Native.loadLibrary("SimpleDll", ISimpleDll.class);

	int getVersion();

	int add(int a, int b);
}

Finally, you can call ：

public class Main {
    

    public static void main(String[] args) {
    
        System.out.println(ISimpleDll.INSTANCE.getVersion());
        System.out.println(ISimpleDll.INSTANCE.add(1,2));
    }
}

Output ：

2
3

Its directory structure is as follows ：

So far JNA Bao He DLL All files are normal .

stay jar Use in JNA load DLL

stay jar The package uses JNA load dll, The biggest problem is actually routing problem , That is to say How to make jna stay jar The package can still find the corresponding dll file .

take SimpleDll Files in Libary Module Root directory , And hit jar package ：

Then prompt when using ：

Exception in thread "main" java.lang.UnsatisfiedLinkError: Unable to load library 'SimpleDll':
 The specified module was not found .

 The specified module was not found .

 The specified module was not found .

Can't obtain InputStream for win32-x86/SimpleDll.dll
	at com.sun.jna.NativeLibrary.loadLibrary(NativeLibrary.java:302)
	at com.sun.jna.NativeLibrary.getInstance(NativeLibrary.java:455)
	at com.sun.jna.Library$Handler.<init>(Library.java:192)
	at com.sun.jna.Native.loadLibrary(Native.java:646)
	at com.sun.jna.Native.loadLibrary(Native.java:630)
	at SomeSDK.<init>(SomeSDK.java:16)
	at SomeSDK.<init>(SomeSDK.java:3)
	at SomeSDK$Holder.<clinit>(SomeSDK.java:6)
	at SomeSDK.getInstance(SomeSDK.java:10)
	at Main.main(Main.java:4)

Seems to want win32-x86 Go down to the directory and find this dll file , That's easy —

Change it artifacts Configuration of , Just add a directory manually ：

Sure enough .
New version of the JNA It seems that some changes have been made in the search on the path .

Last , all JAVA Upload the code to github Yes .
JnaDemo

Last, last , Again , Used throughout this commissioning win32 Of dll, as well as 32 Bit JDK.