JNI如何访问Java对象（整数）
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JNI how to access Java Object (Integer)
提问by user271290
I have a JNI method to access java method which returns an Integer object. I do not want to return the primitive int type because this code will be modified to handle Generic objects. The following is what I have. I am not able to get the value of the Integer that I pass. The output at C++ side is something like
我有一个 JNI 方法来访问返回一个 Integer 对象的 java 方法。我不想返回原始 int 类型，因为将修改此代码以处理 Generic 对象。以下是我所拥有的。我无法获得我传递的 Integer 的值。C++ 端的输出类似于
value = 0x4016f3d0
How can I get the actual value of Integer object that I pass at C++ end?
如何获得我在 C++ 端传递的 Integer 对象的实际值？
Please help.
请帮忙。
Thanks,
谢谢，
-H
-H
GenericPeer.cpp
通用对等文件
JNIEXPORT void JNICALL Java_GenericPeer_print (JNIEnv *jenv, jclass jcls, jobject data){
jclass peerCls = jenv->GetObjectClass(data);
jmethodID mGetValue = jenv->GetMethodID(peerCls, "getValue","()Ljava/lang/Integer;");
if(mGetValue == NULL){
return (-1);
}
jobject value = jenv->CallObjectMethod(data, mGetValue);
cout<<"value = "<<value<<endl;
}
GenericPeer.java
通用Peer.java
public class GenericPeer {
public static native void print(Data d);
static {
System.load("/home/usr/workspace/GenericJni/src/libGenericJni.so");
}
}
Data.java
数据.java
public class Data {
private Integer value;
pubilc Data(Integer v){
this.value = v;
}
public Integer getValue() { return value; }
public void setValue(Integer value) {
this.value = value;
}
}
Test.java (Main class)
Test.java（主类）
public class Test {
public static void main(String[] args){
Integer i = new Integer(1);
Data d = new Data(i);
GenericPeer.print(d);
}
}
采纳答案by jarnbjo
You have to invoke the intValuemethod on the Integer instance to get its primitive value. Use FindClassinstead of GetObjectClass(as in your code) to get a reference to the class java.lang.Integer and then GetMethodIDand CallObjectMethodto actually invoke the intValuemethod.
您必须调用intValueInteger 实例上的方法以获取其原始值。使用FindClass替代GetObjectClass（如在你的代码），以获得对类java.lang.Integer中的引用，然后GetMethodID与CallObjectMethod实际调用的intValue方法。
回答by user271290
Thanks Jarnbjo,
谢谢Jarnbjo，
It works now! This is what I have:
它现在有效！这就是我所拥有的：
JNIEXPORT jint JNICALL Java_GenericPeer_print (JNIEnv *jenv, jclass jcls, jobject data){
jclass peerCls = jenv->GetObjectClass(data);
jmethodID mGetValue = jenv->GetMethodID(peerCls, "getValue","()Ljava/lang/Integer;");
if (mGetValue == NULL){
return(-1);
}
jobject value = jenv->CallObjectMethod(data, mGetValue);
if(value == NULL){
cout<<"jobject value = NULL"<<endl;
return(-1);
}
//getValue()
jclass cls = jenv->FindClass("java/lang/Integer");
if(cls == NULL){
outFile<<"cannot find FindClass(java/lang/Integer)"<<endl;
}
jmethodID getVal = jenv->GetMethodID(cls, "intValue", "()I");
if(getVal == NULL){
outFile<<"Couldnot find Int getValue()"<<endl;
}
int i = jenv->CallIntMethod(value, getVal);
}
