使用JNI我们可以将自定义数据类型从Java传递到C(反之亦然)吗?我看到原始数据类型到C中的类型的映射,但是不太确定我们是否可以发送我们自己的数据类型(例如发送或返回一个Employee对象或其他东西!)。
答案 0 :(得分:69)
如果你要用很多物品做这件事,像Swig这样的东西最好。您可以使用jobject类型来传递自定义对象。语法不好,或许有更好的方法来编写它。
示例员工对象:
public class Employee {
private int age;
public Employee(int age) {
this.age = age;
}
public int getAge() {
return age;
}
}
从某个客户端调用此代码:
public class Client {
public Client() {
Employee emp = new Employee(32);
System.out.println("Pass employee to C and get age back: "+getAgeC(emp));
Employee emp2 = createWithAge(23);
System.out.println("Get employee object from C: "+emp2.getAge());
}
public native int getAgeC(Employee emp);
public native Employee createWithAge(int age);
}
你可以使用这样的JNI函数将employee对象从Java传递给C,作为jobject方法参数:
JNIEXPORT jint JNICALL Java_Client_getAgeC(JNIEnv *env, jobject callingObject, jobject employeeObject) {
jclass employeeClass = (*env)->GetObjectClass(env, employeeObject);
jmethodID midGetAge = (*env)->GetMethodID(env, employeeClass, "getAge", "()I");
int age = (*env)->CallIntMethod(env, employeeObject, midGetAge);
return age;
}
将员工对象从C作为作业传递回Java,您可以使用:
JNIEXPORT jobject JNICALL Java_Client_createWithAge(JNIEnv *env, jobject callingObject, jint age) {
jclass employeeClass = (*env)->FindClass(env,"LEmployee;");
jmethodID midConstructor = (*env)->GetMethodID(env, employeeClass, "<init>", "(I)V");
jobject employeeObject = (*env)->NewObject(env, employeeClass, midConstructor, age);
return employeeObject;
}