如何将java类实例作为参数传递给JNI方法?

问题描述

我想将 java 类对象传递给 JNI 方法，我想在 JNI 方法中调用几个方法，如下所示.

I'd like to pass java class object to JNI method,And I want to call few methods in JNI method like below.

有人有下面这样的例子吗?

Is there anyone who have some example like below?

class JavaClassParameter{
    void javaMethodTobeCalledInJNI(){
        ...java source...
    }
}

class MainJavaClass{
    void somemethod(){
        JavaClassParameter object = new JavaClassParameter();
        JNIMethod(object);
    }

    native void JNIMethod(JavaClassParameter object);
}


// C++ code
void JNIMethod(object){
    object->javaMethodTobeCalledInJNI();
}

推荐答案

你的方法声明:

class MainJavaClass {
    native void JNIMethod(JavaClassParameter object);
}

意味着 javah 应该生成一个转发声明如下:

means javah should generate a forward declaration like the following:

JNIEXPORT void JNICALL Java_MainJavaClass_JNIMethod(JNIEnv* env, jobject mainJavaClass);

在实施过程中，您需要做一些事情:

In the implementation of that, you have a few things to do:

使用FindClass，它接受一个字符串名称:

Use FindClass, which takes a string name:

jclass cls = env->FindClass("JavaClassParameter");

查找 javaMethodTobeCalledInJNI()

使用GetMethodID，获取要检查的类、方法的字符串名称及其签名.由于这是一个没有参数的 void 函数，它的 签名 只是 ()V:

Find javaMethodTobeCalledInJNI()

Use GetMethodID, which takes the class to check, the string name of the method, and its signature. Since this is a void function with no arguments, its signature is just ()V:

jmethodID method = env->GetMethodID(cls, "javaMethodTobeCalledInJNI", "()V");

调用 javaMethodTobeCalledInJNI()

使用 CallVoidMethod，它接受对象实例、方法 ID 和任何参数(在这种情况下没有参数):

Call javaMethodTobeCalledInJNI()

Use CallVoidMethod, which takes the object instance, the method ID, and any arguments (none in this case):

env->CallVoidMethod(mainJavaClass, method);

您应该在每一步之后检查 NULL 结果；如果你从一个 JNI 函数返回一个 NULL 并将它传递给另一个，你通常会导致 JVM 崩溃

---

You should check for NULL results after each step; if you get a NULL back from one JNI function and pass it to another, you'll usually crash the JVM

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