从Java传递的数据类型，以使用JNI C（反之亦然） [英] Passing data types from Java to C (or vice versa) using JNI

问题描述

使用JNI可以，我们通过自定义数据类型从Java到C（或相反）？我看到原始数据类型的映射在C类型却不太清楚，如果我们能够在我们自己的数据类型发送（例如跨发送或返回一个Employee对象什么的！）。

Using JNI can we pass custom data types from Java to C (or vice versa)? I see a mapping of primitive datatypes to types in C however not too sure if we can send across our own data types (e.g. Send across or return an Employee object or something!).

推荐答案

如果你要使用大量的对象做这个，像痛饮将是最好的。你可以使用jobject类型绕过自定义对象。语法是不是很好，也许有写这个更好的方法。

If you're going to be doing this with a lot of objects, something like Swig would be best. You could use jobject type to pass around custom objects. The syntax isn't nice, perhaps there is a better way to write this.

例如Employee对象：

Example Employee object:

public class Employee {
    private int age;

    public Employee(int age) {
        this.age = age;
    }

    public int getAge() {
        return age;
    }
}

调用此code一些客户端：

Call this code from some client:

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);
}

您可以有JNI功能，像这样从Java传递一个Employee对象为C，作为jobject方法参数：

You could have JNI functions like this for passing an employee object from Java to C, as a jobject method argument:

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;
}

传递雇员对象返回从C到Java作为jobject，您可以使用：

Passing an employee object back from C to Java as a jobject, you could use:

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;
}

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