JNI Resources，jniresources

JNI Resources，jniresources

- http://docs.oracle.com/javase/1.5.0/docs/guide/jni/spec/jniTOC.html

- http://docs.oracle.com/javase/1.3/docs/guide/jni/spec/jniTOC.doc.html

- http://java.sun.com/docs/books/jni/jniexamples.tar.gz

- http://java.sun.com/docs/books/jni/download/jni.pdf

- http://www.cs.technion.ac.il/~gabr/papers/cuj_jni.pdf

- Java Native Interface: Programmer's Guide and Specification

- C call Java string

//Prints a string, waits for user input, and then returns the line
that the user has typed in.

class Prompt {

  // native method that prints a prompt and reads a line
  private native String getLine(String prompt);
  public static void main(String args[]) {
    Prompt p = new Prompt();
    String input = p.getLine("Type a line: ");
    System.out.println("User typed: " + input);
  }
  
  static {
    System.loadLibrary("Prompt");
  }
}

JNIEXPORT jstring JNICALL
Java_Prompt_getLine(JNIEnv *env, jobject obj, jstring prompt)
{
  char buf[128];
  const jbyte *str;
  str = (*env)->GetStringUTFChars(env, prompt, NULL);
  if (str == NULL) {
    return NULL; /* OutOfMemoryError already thrown */
  }  
  printf("%s", str);
  (*env)->ReleaseStringUTFChars(env, prompt, str);
  /* We assume here that the user does not type more than * 127 characters */
  scanf("%s", buf);
  return (*env)->NewStringUTF(env, buf);
}

JNIEXPORT jstring JNICALL 
Java_Prompt_getLine(JNIEnv *env, jobject obj, jstring prompt)
{
    /* assume the prompt string and user input has less than 128
       characters */
    char outbuf[128], inbuf[128];
    int len = (*env)->GetStringLength(env, prompt);
    (*env)->GetStringUTFRegion(env, prompt, 0, len, outbuf);
    printf("%s", outbuf);
    scanf("%s", inbuf);
    return (*env)->NewStringUTF(env, inbuf);
}

- C called Java array

class IntArray {
    private native int sumArray(int[] arr);
    public static void main(String[] args) {
        IntArray p = new IntArray();
        int arr[] = new int[10];
        for (int i = 0; i < 10; i++) {
            arr[i] = i;
        }
        int sum = p.sumArray(arr);
        System.out.println("sum = " + sum);
    }

    static {
        System.loadLibrary("IntArray");
    }
}

JNIEXPORT jint JNICALL 
Java_IntArray_sumArray(JNIEnv *env, jobject obj, jintArray arr)
{
    jint buf[10];
    jint i, sum = 0;
    (*env)->GetIntArrayRegion(env, arr, 0, 10, buf);
    for (i = 0; i < 10; i++) {  // GetArrayLength to get length of the arry.
        sum += buf[i];
    }
    return sum;
}

JNIEXPORT jint JNICALL 
Java_IntArray_sumArray(JNIEnv *env, jobject obj, jintArray arr)
{
    jint *carr;
    jint i, sum = 0;
    carr = (*env)->GetIntArrayElements(env, arr, NULL);
    if (carr == NULL) {
        return 0; /* exception occurred */
    }

    for (i=0; i<10; i++) {
        sum += carr[i];
    }

    (*env)->ReleaseIntArrayElements(env, arr, carr, 0);
    return sum;
}

- C called Java 2D array

class ObjectArrayTest {
    private static native int[][] initInt2DArray(int size);
    public static void main(String[] args) {
        int[][] i2arr = initInt2DArray(3);
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                 System.out.print(" " + i2arr[i][j]);
            }
            System.out.println();
        }
    }
    static {
        System.loadLibrary("ObjectArrayTest");
    }
}

JNIEXPORT jobjectArray JNICALL
Java_ObjectArrayTest_initInt2DArray(JNIEnv *env, jclass cls, jint size)
{
    jobjectArray result;
    int i;
    jclass intArrCls = (*env)->FindClass(env, "[I");
    if (intArrCls == NULL) {
        return NULL; /* exception thrown */
    }
    result = (*env)->NewObjectArray(env, size, intArrCls, NULL);
    if (result == NULL) {
        return NULL; /* out of memory error thrown */
    }
    for (i = 0; i < size; i++) {
        jint tmp[256];  /* make sure it is large enough! */
        int j;
        jintArray iarr = (*env)->NewIntArray(env, size);
        if (iarr == NULL) {
            return NULL; /* out of memory error thrown */
        }
        for (j = 0; j < size; j++) {
            tmp[j] = i + j;
        }
        (*env)->SetIntArrayRegion(env, iarr, 0, size, tmp);
        (*env)->SetObjectArrayElement(env, result, i, iarr);
        (*env)->DeleteLocalRef(env, iarr);
    }
    return result;
}

- C called JAVA InstanceField

class InstanceFieldAccess {
    private String s;

    private native void accessField();
    public static void main(String args[]) {
        InstanceFieldAccess c = new InstanceFieldAccess();
        c.s = "abc";
        c.accessField();
        System.out.println("In Java:");
        System.out.println("  c.s = \"" + c.s + "\"");
    }
    static {
        System.loadLibrary("InstanceFieldAccess");
    }
}

JNIEXPORT void JNICALL 
Java_InstanceFieldAccess_accessField(JNIEnv *env, jobject obj)
{
    jfieldID fid;   /* store the field ID */
    jstring jstr;
    const char *str;

    /* Get a reference to objÆs class */
    jclass cls = (*env)->GetObjectClass(env, obj);

    printf("In C:\n");

    /* Look for the instance field s in cls */
    fid = (*env)->GetFieldID(env, cls, "s",
                             "Ljava/lang/String;");
    if (fid == NULL) {
        return; /* failed to find the field */
    }

    /* Read the instance field s */
    jstr = (*env)->GetObjectField(env, obj, fid);
    str = (*env)->GetStringUTFChars(env, jstr, 0);
    if (str == NULL) {
        return; /* out of memory */
    }
    printf("  c.s = \"%s\"\n", str);
    (*env)->ReleaseStringUTFChars(env, jstr, str);

    /* Create a new string and overwrite the instance field */
    jstr = (*env)->NewStringUTF(env, "123");
    (*env)->SetObjectField(env, obj, fid, jstr);
}

- C called JAVA instance methods

class InstanceMethodCall {
    private native void nativeMethod();
    private void callback() {
        System.out.println("In Java");
    }
    public static void main(String args[]) {
        InstanceMethodCall c = new InstanceMethodCall();
        c.nativeMethod();
    }
    static {
        System.loadLibrary("InstanceMethodCall");
    }
}

JNIEXPORT void JNICALL 
Java_InstanceMethodCall_nativeMethod(JNIEnv *env, jobject obj)
{
    jclass cls = (*env)->GetObjectClass(env, obj);
    jmethodID mid = 
        (*env)->GetMethodID(env, cls, "callback", "()V");
    if (mid == NULL) {
        return; /*  method not found */
    }
    printf("In C\n");
    (*env)->CallVoidMethod(env, obj, mid);
}