一般,指定JVM的native library路径,只需要用下面的参数就好了
-Djava.library.path=PATH_TO_NATIVE_LIBRARY
Tomcat指定native library路径时,还是不要使用这边参数的好。
建议直接修改PATH环境变量,将dll或so放到环境变量PATH的路径下就好了。
TOMCAT默认将PATH赋值给-Djava.library.path参数的。
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一般,指定JVM的native library路径,只需要用下面的参数就好了
-Djava.library.path=PATH_TO_NATIVE_LIBRARY
Tomcat指定native library路径时,还是不要使用这边参数的好。
建议直接修改PATH环境变量,将dll或so放到环境变量PATH的路径下就好了。
TOMCAT默认将PATH赋值给-Djava.library.path参数的。
最近又用jni写了一个编码工具,从中抽出了最简单的代码,如下:
1、Compress4j.java
package com.neohope.test.compress.jni; /** * * @author Hansen */ public class Compress4j { private native int encodeR(String inFilePath,String outFilePaht); private native int decodeR(String inFilePath,String outFilePaht); static{ try{ System.loadLibrary("compress4j"); }catch(UnsatisfiedLinkError e){ //nothing to do System.out.println("Error: Couldn't load compress4j"); System.out.println(e.getMessage()); e.printStackTrace(); } } public String encode(String inFilePath,String outFilePath) { encodeR(inFilePath, outFilePath); return "xxxxx"; } public String decode(String inFilePath,String outFilePath) { decodeR(inFilePath, outFilePath); return "xxxxx"; } }
2、找到生成的classes文件夹,运行命令行:
javah -classpath . -jni com.neohope.test.compress.jni.Compress4j
3、生成的.h文件如下
/* DO NOT EDIT THIS FILE - it is machine generated */ #include <jni.h> /* Header for class com_neohoe_test_compress_jni_Compress4j */ #ifndef _Included_com_neohoe_test_compress_jni_Compress4j #define _Included_com_neohoe_test_compress_jni_Compress4j #ifdef __cplusplus extern "C" { #endif /* * Class: com_neohoe_test_compress_jni_Compress4j * Method: encodeR * Signature: (Ljava/lang/String;Ljava/lang/String;)I */ JNIEXPORT jint JNICALL Java_com_neohoe_test_compress_jni_Compress4j_encodeR (JNIEnv *, jobject, jstring, jstring); /* * Class: com_neohoe_test_compress_jni_Compress4j * Method: decodeR * Signature: (Ljava/lang/String;Ljava/lang/String;)I */ JNIEXPORT jint JNICALL Java_com_neohoe_test_compress_jni_Compress4j_decodeR (JNIEnv *, jobject, jstring, jstring); #ifdef __cplusplus } #endif #endif
3、编写成的.cc文件如下
#include "com_neohoe_test_compress_jni_Compress4j.h" JNIEXPORT jint JNICALL Java_com_neohoe_test_compress_jni_Compress4j_encodeR (JNIEnv *env, jobject, jstring inpathjs, jstring outpathjs) { //first convert jstring to const char* const char* inpath = env->GetStringUTFChars( inpathjs, false); const char* outpath = env->GetStringUTFChars( outpathjs, false); //... return 0; } JNIEXPORT jint JNICALL Java_com_neohoe_test_compress_jni_Compress4j_decodeR (JNIEnv *env, jobject, jstring inpathjs, jstring outpathjs) { //first convert jstring to const char* const char* inpath = env->GetStringUTFChars( inpathjs, false); const char* outpath = env->GetStringUTFChars( outpathjs, false); //... return 0; }
4、在VS工程中,新增头文件目录
%JAVA_HOME%/include
%JAVA_HOME%/include/win32
5、编译为dll即可使用啦
6、关于mt和md的问题
编译为MT和MTd的话,用JNI是没有任何问题的
编译为MD的话,需要安装VC2010sp1可再发行包
编译为MDd的话,就比较麻烦了,手动复制依赖的dll后,我用c++调用dll可以成功,但用jni就一直提示:缺少依赖的dll
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