1.Java代码CallApi.java
class CallApi{ private native String showMessageBox(String msg); private native double getRandomDouble(); static{ try{ System.loadLibrary("CallApi"); System.out.println("Loaded CallApi"); }catch(UnsatisfiedLinkError e){ //nothing to do System.out.println("Couldn't load CallApi"); System.out.println(e.getMessage()); } } public static void main(String args[]){ CallApi api = new CallApi(); double randomNumber = api.getRandomDouble(); String retval = api.showMessageBox("Hello from Java!\n"+ "The native random number: "+randomNumber); System.out.println("The native string: "+retval); } }
2.生成dll的CallApi.h文件
javah -classpath . -jni CallApi
/* DO NOT EDIT THIS FILE - it is machine generated */ #include <jni.h> /* Header for class CallApi */ #ifndef _Included_CallApi #define _Included_CallApi #ifdef __cplusplus extern "C" { #endif /* * Class: CallApi * Method: showMessageBox * Signature: (Ljava/lang/String;)Ljava/lang/String; */ JNIEXPORT jstring JNICALL Java_CallApi_showMessageBox (JNIEnv *, jobject, jstring); /* * Class: CallApi * Method: getRandomDouble * Signature: ()D */ JNIEXPORT jdouble JNICALL Java_CallApi_getRandomDouble (JNIEnv *, jobject); #ifdef __cplusplus } #endif #endif
3.手写dll的CallApi.c文件
#include"CallApi.h" #include <windows.h> #include <time.h> //#pragma comment(lib,"user32.lib") JNIEXPORT jstring JNICALL Java_CallApi_showMessageBox (JNIEnv *env, jobject thisObject, jstring js) { //first convert jstring to const char for use in MessageBox const jbyte* argvv = (*env)->GetStringUTFChars(env, js, NULL); char* argv =(char *) argvv; //Call MessageBoxA MessageBox(NULL, argv, "Called from Java!", MB_ICONEXCLAMATION | MB_OK); return js; } JNIEXPORT jdouble JNICALL Java_CallApi_getRandomDouble (JNIEnv *env, jobject thisObject) { double num1; srand((unsigned)(time(0))); num1 = ((double)rand()/(double)RAND_MAX); return num1; }
4.编译
注意1:要引用jdk下的include目录下文件,因此要增加引用文件路径
注意2:用MT而不是MD
5.运行
java -Djava.library.path=. CallApi