Android的JNI开发涉及的char和string之间的互相转换
来源:互联网 发布:软件系统响应时间 编辑:程序博客网 时间:2024/06/15 20:29
转至http://blog.csdn.net/wang_shuai_ww/article/details/52329221
参考了文章:http://blog.csdn.NET/ztp800201/article/details/7388189,http://blog.csdn.Net/liaowenfeng/article/details/8668085
总结如下:
在jni中使用env是有两种情况的,C语言和c++语言。
C语言互相转换版本:
-
- jstring CStr2Jstring( JNIEnv* env,const char* str )
- {
- jsize len = strlen(str);
-
- jclass strClass = (*env)->FindClass(env, "java/lang/String");
-
- jstring encoding = (*env)->NewStringUTF(env, "GB2312");
-
- jmethodID ctorID = (*env)->GetMethodID(env, strClass, "<init>", "([BLjava/lang/String;)V");
-
- jbyteArray bytes = (*env)->NewByteArray(env, len);
-
- (*env)->SetByteArrayRegion(env, bytes, 0, len, (jbyte*)str);
-
- return (jstring)(*env)->NewObject(env, strClass, ctorID, bytes, encoding);
- }
-
-
- char * Jstring2CStr( JNIEnv * env, jstring jstr )
- {
- char * rtn = NULL;
- jclass clsstring = (*env)->FindClass(env, "java/lang/String");
- jstring strencode = (*env)->NewStringUTF(env, "GB2312");
- jmethodID mid = (*env)->GetMethodID(env, clsstring, "getBytes", "(Ljava/lang/String;)[B");
- jbyteArray barr= (jbyteArray)(*env)->CallObjectMethod(env, jstr,mid,strencode);
- jsize alen = (*env)->GetArrayLength(env, barr);
- jbyte * ba = (*env)->GetByteArrayElements(env, barr,JNI_FALSE);
- if(alen > 0)
- {
- rtn = (char*)malloc(alen+1);
- memcpy(rtn,ba,alen);
- rtn[alen]=0;
- }
- (*env)->ReleaseByteArrayElements(env, barr,ba,0);
-
- return rtn;
- }
C++版本如下:
-
- jstring CStr2Jstring( 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((jsize)strlen(pat));
-
- (env)->SetByteArrayRegion(bytes, 0, (jsize)strlen(pat), (jbyte*)pat);
-
- jstring encoding = (env)->NewStringUTF("GB2312");
-
- return (jstring)(env)->NewObject(strClass, ctorID, bytes, encoding);
-
- }
- char * Jstring2CStr( JNIEnv * env, jstring jstr )
- {
- char * rtn = NULL;
- jclass clsstring = env->FindClass("java/lang/String");
- jstring strencode = env->NewStringUTF("GB2312");
- 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;
- }
注意上面两种情况env的不同使用方法,具体的解释可参考jni..h头文件中的说明:另外注意下面这句话的不同,主要指“”里的字符串,两个版本不同,我用的是C语言,刚开始是用网上下面的一个版本,运行总是崩掉,最后换成上面一个版本才OK。C++的版本有人如果遇到注意一下即可。C语言版本:
- jclass strClass = (*env)->FindClass(env, "java/lang/String");
C++版本:
- jclass strClass = (env)->FindClass("Ljava/lang/String;");
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