JNI动态库开发和调试
JNI
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Hello World
使用vscode cmake生成 library 项目 -
写一个HelloWorld.java
public class HelloWorld {static {System.loadLibrary("hello"); // 加载本地库}public static void main(String[] args){final var helloWorld = new HelloWorld();helloWorld.sayHello(); // 调用本地方法System.out.println(helloWorld.getString()); // 调用本地方法并打印结果}// 声明本地方法public native void sayHello();public native String getString(); } -
执行
javac -h . HelloWorld.java生成HelloWorld.h,简单改造一下为HelloWorld.hpp/* DO NOT EDIT THIS FILE - it is machine generated */ /* Header for class HelloWorld */#ifndef _Included_HelloWorld #define _Included_HelloWorld#include <jni.h> #include <iostream>/** Class: HelloWorld* Method: sayHello* Signature: ()V*/ extern "C" JNIEXPORT void JNICALL Java_HelloWorld_sayHello(JNIEnv*, jobject);/** Class: HelloWorld* Method: getString* Signature: ()Ljava/lang/String;*/ extern "C" JNIEXPORT jstring JNICALL Java_HelloWorld_getString(JNIEnv*, jobject);#endif // _Included_HelloWorld -
实现头文件
HelloWorld.cpp#include "HelloWorld.hpp"extern "C" JNIEXPORT void JNICALL Java_HelloWorld_sayHello(JNIEnv* env, jobject obj) {(void)env;(void)obj;std::cout << "Hello, World from JNI!" << std::endl; }extern "C" JNIEXPORT jstring JNICALL Java_HelloWorld_getString(JNIEnv* env, jobject obj) {(void)obj;return env->NewStringUTF("Hello from JNI!"); } -
cmake配置
cmake_minimum_required(VERSION 3.22.1) project(hello VERSION 0.1.0 LANGUAGES C CXX)# ✅ 设置 C++ 标准 set(CMAKE_CXX_STANDARD 26) set(CMAKE_CXX_STANDARD_REQUIRED ON) # 强制使用指定标准 set(CMAKE_CXX_EXTENSIONS OFF) # 禁用编译器扩展（使用纯标准）# 查找源文件 file(GLOB_RECURSE SOURCES CONFIGURE_DEPENDS"src/*.cpp""src/*.c" ) message("SOURCES: ${SOURCES}") message("CMAKE_PROJECT_NAME: ${CMAKE_PROJECT_NAME}")# 设置头文件目录 # 设置头文件包含目录 message(CMAKE_PROJECT_NAME: ${CMAKE_PROJECT_NAME}) message(PROJECT_NAME: ${PROJECT_NAME}) message(CMAKE_CURRENT_SOURCE_DIR: ${CMAKE_CURRENT_SOURCE_DIR})add_library(${CMAKE_PROJECT_NAME} SHARED main.cpp ${SOURCES})if(WIN32) # 让 JNI 在 Windows/MinGW 下生成 hello.dll，避免默认的 libhello.dll set_target_properties(${CMAKE_PROJECT_NAME} PROPERTIESPREFIX ""OUTPUT_NAME ${CMAKE_PROJECT_NAME} ) endif()# 设置头文件包含路径 target_include_directories(${CMAKE_PROJECT_NAME}PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include/jniPUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include/bsdiffPUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include/brotliPUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include/HelloWorld )if(MSVC)target_compile_options(${CMAKE_PROJECT_NAME} PRIVATE /W4 /WX) else()message("no MSVC")target_compile_options(${CMAKE_PROJECT_NAME} PRIVATE -Wall-Werror # 警告转错误-Wextra # 发现更多潜在的逻辑和风格问题-pedantic # 追求极致的标准兼容性-D NDEBUG # 定义 NDEBUG 以禁用 assert() 的评估) endif()include(CTest) enable_testing()set(CPACK_PROJECT_NAME ${PROJECT_NAME}) set(CPACK_PROJECT_VERSION ${PROJECT_VERSION}) include(CPack) -
build生成动态库
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执行命令
java "--enable-native-access=ALL-UNNAMED" "-Djava.library.path=.\build" HelloWorld.java -
调试
.vscode/launch.json{// Use IntelliSense to learn about possible attributes.// Hover to view descriptions of existing attributes.// For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387"version": "0.2.0","configurations": [{"name": "(gdb) Attach","type": "cppdbg","request": "attach","program": "D:/SoftWare/jdk25/bin/java.exe","processId": "${command:pickProcess}","MIMode": "gdb","miDebuggerPath": "D:/SoftWare/msys64/ucrt64/bin/gdb.exe","setupCommands": [{"description": "Enable pretty-printing for gdb","text": "-enable-pretty-printing","ignoreFailures": true},{"description": "Set Disassembly Flavor to Intel","text": "-gdb-set disassembly-flavor intel","ignoreFailures": true}]}] } -
修改HelloWorld.java
public class HelloWorld {static {System.loadLibrary("hello"); // 加载本地库}public static void main(String[] args) throws Exception{System.out.println("PID: " + ProcessHandle.current().pid()); // 打出 PID 方便选进程System.in.read(); // 暂停，等你附加 GDB 后按回车继续final var helloWorld = new HelloWorld();helloWorld.sayHello(); // 调用本地方法System.out.println(helloWorld.getString()); // 调用本地方法并打印结果}// 声明本地方法public native void sayHello();public native String getString(); } -
调试
java "--enable-native-access=ALL-UNNAMED" "-Djava.library.path=.\build" HelloWorld.java # vscode 运行 debug (gdb) Attach # 去C++打点然后回车简单项目的话可以使用下面的命令。
g++ -shared -fPIC -I"$JAVA_HOME/include" -I"$JAVA_HOME/include/linux" \BrotliNative.c -o libbrotli_jni.so
FFM API
全称: Foreign Function & Memory API.
ffm可以直接调用c/c++函数不需要再使用jni包一层了。
新建vscode library项目
main.cpp
#include <iostream>extern "C" __declspec(dllexport) // windows 独有，其他不需要 __declspec(dllexport)
void sayHello(){std::cout << "Hello, from hello_ffm!\n";
}extern "C" __declspec(dllexport)
const char* getString(){return "Hello, from getString!";
}
HelloWorld.java
import java.lang.foreign.*;
import java.lang.invoke.*;
import java.util.Optional;public class HelloWorld {static {System.loadLibrary("hello_ffm");}@SuppressWarnings("UnnecessaryModifier")public static void main(@SuppressWarnings("unused") final String[] args) throws Throwable {final Linker linker = Linker.nativeLinker();final SymbolLookup lookup = SymbolLookup.loaderLookup();// 调用 void sayHello()final MethodHandle sayHello = linker.downcallHandle(lookup.find("sayHello").orElseThrow(),FunctionDescriptor.ofVoid());sayHello.invoke();// 调用 const char* getString() → 返回指针final MethodHandle getString = linker.downcallHandle(lookup.find("getString").orElseThrow(),FunctionDescriptor.of(ValueLayout.ADDRESS));// invoke 和 invokeExact（调用点类型静态类型）区别 Optional.ofNullable(getString.invoke()).filter(MemorySegment.class::isInstance).map(MemorySegment.class::cast).ifPresent((MemorySegment result) -> {// 从指针读取字符串final String str = result.reinterpret(Long.MAX_VALUE).getString(0);System.out.println("str: " + str);});// final MemorySegment result = (MemorySegment) getString.invokeExact();// // 从指针读取字符串// final String str = result.reinterpret(Long.MAX_VALUE).getString(0);// System.out.println("str: " + str);}
}// java "--enable-native-access=ALL-UNNAMED" "-Djava.library.path=.\build" HelloWorld.java
调试
HelloWorld.java
import java.lang.foreign.*;
import java.lang.invoke.*;
import java.util.Optional;public class HelloWorld {static {System.loadLibrary("hello_ffm");}@SuppressWarnings("UnnecessaryModifier")public static void main(@SuppressWarnings("unused") final String[] args) throws Throwable {System.out.println("PID: " + ProcessHandle.current().pid()); // 打出 PID 方便选进程System.in.read(); // 暂停，等你附加 GDB 后按回车继续final Linker linker = Linker.nativeLinker();final SymbolLookup lookup = SymbolLookup.loaderLookup();// 调用 void sayHello()final MethodHandle sayHello = linker.downcallHandle(lookup.find("sayHello").orElseThrow(),FunctionDescriptor.ofVoid());sayHello.invoke();// 调用 const char* getString() → 返回C/C++ 常量区字符串 指针final MethodHandle getString = linker.downcallHandle(lookup.find("getString").orElseThrow(),FunctionDescriptor.of(ValueLayout.ADDRESS));Optional.ofNullable(getString.invoke()).filter(MemorySegment.class::isInstance).map(MemorySegment.class::cast).ifPresent((MemorySegment result) -> {// 从指针读取字符串final String str = result.reinterpret(Long.MAX_VALUE).getString(0);System.out.println("str: " + str);});// final MemorySegment result = (MemorySegment) getString.invokeExact();// // 从指针读取字符串// final String str = result.reinterpret(Long.MAX_VALUE).getString(0);// System.out.println("str: " + str);}
}// java "--enable-native-access=ALL-UNNAMED" "-Djava.library.path=.\build" HelloWorld.java
.vscode/launch.json
{// Use IntelliSense to learn about possible attributes.// Hover to view descriptions of existing attributes.// For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387"version": "0.2.0","configurations": [{"name": "(gdb) Attach","type": "cppdbg","request": "attach","program": "D:/SoftWare/jdk25/bin/java.exe","processId": "${command:pickProcess}","MIMode": "gdb","miDebuggerPath": "D:/SoftWare/msys64/ucrt64/bin/gdb.exe","setupCommands": [{"description": "Enable pretty-printing for gdb","text": "-enable-pretty-printing","ignoreFailures": true},{"description": "Set Disassembly Flavor to Intel","text": "-gdb-set disassembly-flavor intel","ignoreFailures": true}]}]
}
Kotlin 也可以使用
internal suspend fun main(args: Array<String>): Unit = coroutineScope {val linker: Linker? = Linker.nativeLinker()val stdlib: SymbolLookup? = linker?.defaultLookup()val methodAddress: MemorySegment? = stdlib?.find("strlen")?.orElseThrow()val strlenFuncDesc: FunctionDescriptor = FunctionDescriptor.of(ValueLayout.JAVA_INT, ValueLayout.ADDRESS)val methodHande: MethodHandle? = linker?.downcallHandle(methodAddress, strlenFuncDesc)// 堆外，只能由创建者线程访问，手动管理Arena.ofConfined().use { arena: Arena ->val cString: MemorySegment = arena.allocateFrom("Hello World!")val length: Long? = methodHande?.invoke(cString) as? Longlogger.info { "length: $length" }}delay(100)
}
FFM 调用 bsdiff
package io.githubimport io.github.oshai.kotlinlogging.KLogger
import io.github.oshai.kotlinlogging.KotlinLogging
import java.lang.foreign.Arena
import java.lang.foreign.FunctionDescriptor
import java.lang.foreign.Linker
import java.lang.foreign.SymbolLookup
import java.lang.foreign.ValueLayout
import java.lang.invoke.MethodHandle
import java.nio.file.Pathprivate val logger: KLogger = KotlinLogging.logger {}internal object CxxUtils {private val CREATE_PATCH: MethodHandleprivate val APPLY_PATCH: MethodHandleinit {// 1. 先用传统的系统方法加载，它会识别 -Djava.library.pathSystem.loadLibrary("bsdiff")// 2. 使用 loaderLookup，它能找到上面加载的库里的函数val symbolLookup: SymbolLookup = SymbolLookup.loaderLookup()// // 对应Java返回值类型 // 参数列表类型 val desc: FunctionDescriptor = FunctionDescriptor.of(ValueLayout.JAVA_INT, ValueLayout.ADDRESS, ValueLayout.ADDRESS, ValueLayout.ADDRESS)val linker: Linker = Linker.nativeLinker()CREATE_PATCH = linker.downcallHandle(symbolLookup.find("bsdiff_create_patch")?.orElseThrow(), desc)APPLY_PATCH = linker.downcallHandle(symbolLookup.find("bsdiff_apply_patch")?.orElseThrow(), desc)}internal fun bsDiffCreatePatch(oldPath: String, newPath: String, patchPath: String){Arena.ofConfined().use { arena: Arena ->val result: Int = CREATE_PATCH.invoke(arena.allocateFrom(oldPath),arena.allocateFrom(newPath),arena.allocateFrom(patchPath),) as Intlogger.info { "bsDiffCreatePatch result: $result" }if (result != 0){throw RuntimeException("bsdiff_create_patch error")}}}internal fun bsDiffApplyPatch(oldPath: String, newPath: String, patchPath: String){Arena.ofConfined().use { arena: Arena ->val result: Int = APPLY_PATCH.invoke(arena.allocateFrom(oldPath),arena.allocateFrom(newPath),arena.allocateFrom(patchPath),) as Intlogger.info { "bsDiffApplyPatch result: $result" }if (result != 0){throw RuntimeException("bsdiff_create_patch error")}}}
}
使用官方工具
jextract --output src/main/java \-t io.github.bsdiff \ # 包名-l bsdiff \ # library name HelloWorld.h
C++ 代码请参考 myfaverate-bsdiff