如何在jni(java到c++)以及(c++到java)中传递和返回属性数组

Question

如何传递和返回jni(java到c++(以及(c++到java(中的属性数组

import java.util.*; 

public class Test { 
public native static Properties[] getStudentDetails();   
public static void main(String[] args) {
System.loadLibrary("Sample");
int a= 10;
Properties[] records = getStudentDetails();      
for(Properties record:records){
System.out.print("ntype:"+record.getProperty("type"));
System.out.print("ttime:"+record.getProperty("time"));
System.out.print("tsource:"+record.getProperty("source"));
System.out.print("teid:"+record.getProperty("eid"));
System.out.println("");
}
}   
}

它给我错误

Answer 1

假设您可以访问某个std::vector<SearchRecord*> searchRecordResult：

extern "C"
JNIEXPORT jobjectArray JNICALL Java_Test_getStudentDetails(JNIEnv *env, jclass cls) {
// Get Properties class, its constructor and the put method
jclass cls_Properties = env->FindClass("java/util/Properties");
jmethodID mid_Properties_ctor = env->GetMethodID(cls_Properties, "<init>", "()V");
jmethodID mid_Properties_put = env->GetMethodID(cls_Properties, "put", "(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;");
// Construct the key Strings up front
jstring key_type = env->NewStringUTF("type");
jstring key_time = env->NewStringUTF("time");
jstring key_source = env->NewStringUTF("source");
jstring key_eid = env->NewStringUTF("eid");
jobjectArray ret = env->NewObjectArray(searchRecordResult.size(), cls_Properties, 0);
for (int i = 0; i < searchRecordResult.size(); i++) {
auto result = searchRecordResult[i];
// Allocate and fill a Properties object, making sure to clean up the value Strings.
env->PushLocalFrame(5);
jobject prop = env->NewObject(cls_Properties, mid_Properties_ctor);
env->CallObjectMethod(prop, mid_Properties_put, key_type, env->NewStringUTF(result->type));
env->CallObjectMethod(prop, mid_Properties_put, key_time, env->NewStringUTF(result->time));
env->CallObjectMethod(prop, mid_Properties_put, key_source, env->NewStringUTF(result->source));
env->CallObjectMethod(prop, mid_Properties_put, key_eid, env->NewStringUTF(result->eid));
prop = env->PopLocalFrame(prop);
env->SetObjectArrayElement(ret, i, prop);
}
return ret;
}

核心循环只是构造Properties对象，用put填充它们的属性，并将它们分配到ret阵列上的右侧插槽。