Java与C++语言在JNI下的交互

java环境下调用VC++编写的动态链接库文件

一，开发平台：

MyEclipse 6.0，VC++6.0

二，JNI基础知识：

JNI(java native interface)，JAVA本地接口调用，目的是为了JAVA可以调用本地程序。

三，交互过程：

1，建立java类。例如，建立一个RSA加密解密的类：

package zkxx.ctais2.client.common;public class RsaEncrypt {/** * @param args */public native String GetKeys();public native String Encrypt(String source,String PublicKey);public native String Decrypt(String cipher,String PrivateKey);static {System.loadLibrary("RSAEncrypt");}public static void main(String[] args) {}} 

2，生成C++语言的头文件：

1）注意：利用javah工具生成头文件需要注意，类的包结构，和class文件存储的路径。

例如：本地class文件存储路径：E:/lclai/lclai/src/

包结构应为：E:/lclai/lclai/src/com/org/lclai

RsaEncrypt.java应该存放在包路径下。

2）CMD命令提示符下进入E:/lclai/lclai/src/com/org/lclai路径

输入命令：javac RsaEncrypt.java

回车。

把生成的class文件拷贝到路径E:/lclai/lclai/src/

CMD命令提示符下进入E:/lclai/lclai/src/

输入命令：javah -classpath E:/lclai/lclai/src -jni com.org.lclai.RsaEncrypt

回车。

在路径E:/lclai/lclai/src/便会生成以包结构和类名结合的头文件。

3，编写cpp文件

cpp文件头需要包含刚刚生成的.h文件，此外还需要包含jni.h.

// RSAEncrypt.cpp : Defines the initialization routines for the DLL.//#include "stdafx.h"#include "RSAEncrypt.h"#include "CryptoPP32.h"#include "zkxx_ctais2_client_common_RsaEncrypt.h"#include "jni.h"#ifdef _DEBUG#define new DEBUG_NEW#undef THIS_FILEstatic char THIS_FILE[] = __FILE__;#endif////Note!////If this DLL is dynamically linked against the MFC//DLLs, any functions exported from this DLL which//call into MFC must have the AFX_MANAGE_STATE macro//added at the very beginning of the function.////For example:////extern "C" BOOL PASCAL EXPORT ExportedFunction()//{//AFX_MANAGE_STATE(AfxGetStaticModuleState());//// normal function body here//}////It is very important that this macro appear in each//function, prior to any calls into MFC. This means that//it must appear as the first statement within the //function, even before any object variable declarations//as their constructors may generate calls into the MFC//DLL.////Please see MFC Technical Notes 33 and 58 for additional//details.///////////////////////////////////////////////////////////////////////////////// CRSAEncryptAppextern "C" __declspec(dllexport) char* RSAGenKeys(){char*result="";CRSAEncryptApp rsa;result=rsa.GenKeys();return result;}extern "C" __declspec(dllexport) char* RSAEncrypt(char *publickey, char *source){char*result="";CRSAEncryptApp rsa;result=rsa.Encrypt(publickey,source);return result;}extern "C" __declspec(dllexport) char* RSADecrypt(char *privatekey, char *cipher){char*result="";CRSAEncryptApp rsa;result=rsa.Decrypt(privatekey,cipher);return result;}BEGIN_MESSAGE_MAP(CRSAEncryptApp, CWinApp)//{{AFX_MSG_MAP(CRSAEncryptApp)// NOTE - the ClassWizard will add and remove mapping macros here.// DO NOT EDIT what you see in these blocks of generated code!//}}AFX_MSG_MAPEND_MESSAGE_MAP()/////////////////////////////////////////////////////////////////////////////// CRSAEncryptApp constructionCRSAEncryptApp::CRSAEncryptApp(){// TODO: add construction code here,// Place all significant initialization in InitInstance}/////////////////////////////////////////////////////////////////////////////// The one and only CRSAEncryptApp objectCRSAEncryptApp theApp;char* CRSAEncryptApp::GenKeys(){// 生成公钥和私钥字符串char* charPriv;char* charPub;CString temp1,temp2;char* result="err";CString publickey,privatekey;bool IsOk=CryptoPP32::RSAES_PKCS_GenKeyStrings(&charPriv, &charPub);if(IsOk){publickey=charPub;privatekey=charPriv;temp1=publickey+"##"+privatekey;result=temp1.GetBuffer(temp1.GetLength());}return result;}char* CRSAEncryptApp::Encrypt(char *publickey, char *source){//讲明文加密，返回密文char*cipher="";char* result="err";bool IsOk=CryptoPP32::RSAES_PKCS_EncryptString(publickey,source,&cipher);if(IsOk){//AfxMessageBox(cipher);result=cipher;}return result;}char* CRSAEncryptApp::Decrypt(char *privatekey, char *cipher){//解密密文，返回明文char*plain="";char*result="err";bool IsOk=CryptoPP32::RSAES_PKCS_DecryptString(privatekey,cipher,&plain);if(IsOk){//AfxMessageBox(plain);result=plain;}return result;}//--------------------------------------------------------------------------//static char* jstringTostring(JNIEnv* env, jstring jstr){ char* rtn = NULL; jclass clsstring = env->FindClass("java/lang/String"); jstring strencode = env->NewStringUTF("utf-8"); jmethodID mid = env->GetMethodID(clsstring, "getBytes", "(Ljava/lang/String;)[B"); jbyteArray barr= (jbyteArray)env->CallObjectMethod(jstr, mid, strencode); jsize alen = env->GetArrayLength(barr); jbyte* ba = env->GetByteArrayElements(barr, JNI_FALSE); if (alen > 0) { rtn = (char*)malloc(alen + 1); memcpy(rtn, ba, alen); rtn[alen] = 0; } env->ReleaseByteArrayElements(barr, ba, 0); return rtn;}static jstring stoJstring(JNIEnv* env, const char* pat){ jclass strClass = env->FindClass("Ljava/lang/String;"); jmethodID ctorID = env->GetMethodID( strClass, "<init>", "([BLjava/lang/String;)V"); jbyteArray bytes = env->NewByteArray(strlen(pat)); env->SetByteArrayRegion(bytes, 0, strlen(pat), (jbyte*)pat); jstring encoding = env->NewStringUTF("utf-8"); return (jstring)env->NewObject(strClass, ctorID, bytes, encoding);}JNIEXPORT jstring JNICALL Java_com_org_lclai_RsaEncrypt_GetKeys (JNIEnv *env, jobject jo){jstring result;CRSAEncryptApp rsa;//CString res;char*res="";res=rsa.GenKeys();result=env->NewStringUTF(res);return result;}JNIEXPORT jstring JNICALL Java_com_org_lclai_RsaEncrypt_Encrypt (JNIEnv *env, jobject jo, jstring publickey, jstring source){jstring result;CRSAEncryptApp rsa;char* pubkey="";char* sour="";pubkey=jstringTostring(env,publickey);sour=jstringTostring(env,source);char*cipher=rsa.Encrypt(pubkey,sour);result=stoJstring(env,cipher);return result;}JNIEXPORT jstring JNICALL Java_com_org_lclai_RsaEncrypt_Decrypt (JNIEnv *env, jobject jo, jstring privatekey , jstring cipher){jstring result;CRSAEncryptApp rsa;char* privkey="";char* ciphertext="";privkey=jstringTostring(env,privatekey);ciphertext=jstringTostring(env,cipher);char*plain=rsa.Decrypt(privkey,ciphertext);result=stoJstring(env,plain);return result;}