在JAR中整合Kotlin Native可执行文件与JVM回退机制的实践指南

// native_module/src/nativeMain/kotlin/com/example/NativeLib.kt
package com.example

import kotlinx.cinterop.ExportForCppRuntime

class NativeLib {
    @ExportForCppRuntime("calculateSum")
    fun calculateSum(a: Int, b: Int): Int {
        return a + b
    }
}

// native_module/build.gradle.kts
plugins {
    kotlin("multiplatform")
}

kotlin {
    // 针对不同平台编译
    linuxX64()
    macosX64()
    mingwX64() // Windows
    // ... 其他目标

    sourceSets {
        val nativeMain by getting {
            // Your native code here
        }
    }
}

// src/main/java/com/example/MyApplication.java
package com.example;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.nio.file.StandardCopyOption;

public class MyApplication {

    // 声明native方法
    public native int calculateSum(int a, int b);

    // 静态代码块用于加载本地库
    static {
        boolean nativeLoaded = false;
        String osName = System.getProperty("os.name").toLowerCase();
        String osArch = System.getProperty("os.arch").toLowerCase();
        String libraryName = "native_module"; // Kotlin Native模块名

        String resourcePath = null;
        String tempFileName = null;

        if (osName.contains("win")) {
            resourcePath = "lib/" + osArch + "/" + libraryName + ".dll";
            tempFileName = libraryName + ".dll";
        } else if (osName.contains("mac")) {
            resourcePath = "lib/" + osArch + "/" + libraryName + ".dylib";
            tempFileName = libraryName + ".dylib";
        } else if (osName.contains("linux")) {
            resourcePath = "lib/" + osArch + "/" + libraryName + ".so";
            tempFileName = libraryName + ".so";
        }

        if (resourcePath != null) {
            try (InputStream in = MyApplication.class.getClassLoader().getResourceAsStream(resourcePath)) {
                if (in != null) {
                    File tempFile = File.createTempFile(libraryName + "-", "." + getFileExtension(tempFileName));
                    tempFile.deleteOnExit(); // 确保JVM退出时删除临时文件
                    Files.copy(in, tempFile.toPath(), StandardCopyOption.REPLACE_EXISTING);
                    System.load(tempFile.getAbsolutePath());
                    nativeLoaded = true;
                    System.out.println("Native library loaded successfully: " + tempFile.getAbsolutePath());
                }
            } catch (IOException | UnsatisfiedLinkError e) {
                System.err.println("Failed to load native library from " + resourcePath + ": " + e.getMessage());
                // Fallback to JVM implementation will happen if nativeLoaded remains false
            }
        }

        if (!nativeLoaded) {
            System.out.println("Native library not loaded. Falling back to JVM implementation.");
            // 在这里可以设置一个标志，或者直接实例化一个使用JVM实现的类
            // 例如：isNativeAvailable = false;
        }
    }

    private static String getFileExtension(String fileName) {
        int dotIndex = fileName.lastIndexOf('.');
        return (dotIndex == -1) ? "" : fileName.substring(dotIndex + 1);
    }

    // JVM回退实现
    public int calculateSumJVM(int a, int b) {
        System.out.println("Using JVM fallback for calculateSum.");
        return a + b;
    }

    public static void main(String[] args) {
        MyApplication app = new MyApplication();
        int result;
        try {
            // 尝试调用Native方法
            result = app.calculateSum(10, 20);
            System.out.println("Result from Native: " + result);
        } catch (UnsatisfiedLinkError e) {
            // 如果native方法调用失败，说明本地库未加载或方法未找到，回退到JVM实现
            result = app.calculateSumJVM(10, 20);
            System.out.println("Result from JVM Fallback: " + result);
        }
    }
}

// 主应用/build.gradle
// ...
sourceSets {
    main {
        resources {
            // 假设你的Kotlin Native项目生成的本地库在 build/libs 目录下
            // 你需要根据实际情况调整路径，可能需要将它们复制到一个统一的资源目录
            // 这里只是一个概念性的示例，实际操作可能需要一个copy任务
            srcDirs 'path/to/kotlin/native/binaries' // 包含所有平台编译产物的目录
            include 'lib/**' // 包含lib目录下的所有本地库文件
        }
    }
}

jar {
    // 确保资源文件被打包
    from sourceSets.main.resources
}
// ...