JNI 數據類型轉換

#include <jni.h>
#include "com_test_Test.h"
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>

//獲取字符串
JNIEXPORT void JNICALL Java_com_test_Test_sayHello(JNIEnv * env, jobject obj,
  jstring s) {

 char * str = (char *) (*env)->GetStringUTFChars(env, s, 0);
 printf("\n c-string: hello - %s", str);

}

//獲取，返回 string
JNIEXPORT jstring JNICALL Java_com_test_Test_getString(JNIEnv * env,
  jobject obj, jstring s) {
 char * st = (char *) (*env)->GetStringUTFChars(env, s, 0);
 printf("\n c-string:  %s", st);

 char * str = "hello wang wu!";
 jstring rtn;
 rtn = (*env)->NewStringUTF(env, str);
 return rtn;
}

//獲取，返回 string []
JNIEXPORT jobjectArray JNICALL Java_com_test_Test_getStringArray(JNIEnv * env,
  jobject obj, jobjectArray arr) {
 int len = (*env)->GetArrayLength(env, arr);
 printf("\n c-stringArray :");
 int i = 0;
 for (i = 0; i < len; i++) {
  jobject obj = (*env)->GetObjectArrayElement(env, arr, i);
  jstring str = (jstring) obj;
  const char * szStr = (*env)->GetStringUTFChars(env, str, 0);
  printf(" %d-%s ", i, szStr);
  (*env)->ReleaseStringChars(env, str, szStr);
 }

 //-----返回----
 jstring str;
 jobjectArray args = 0;
 jsize size = 5;
 char* sa[] = { "Hello,", "world!", "zhang", "san", "yuang" };
 int j = 0;
 jclass objClass = (*env)->FindClass(env, "java/lang/String");
 args = (*env)->NewObjectArray(env, size, objClass, 0);
 for (j = 0; j < size; j++) {
  str = (*env)->NewStringUTF(env, sa[j]);
  (*env)->SetObjectArrayElement(env, args, j, str);
 }
 return args;
}

//獲取，返回byte[]
JNIEXPORT jbyteArray JNICALL Java_com_test_Test_getByteArray(JNIEnv * env, jobject obj,
                                              jbyteArray array)
{
    //將java傳進來的數組的內容，拷貝到新建的數組中，返回給java
    jbyte* array_p = (*env)->GetByteArrayElements(env, array, NULL);
    int length = (*env)->GetArrayLength(env, array);
    jbyteArray javaArray = (*env)->NewByteArray(env, length);
    jbyte* javaArray_p = (*env)->GetByteArrayElements(env, javaArray, NULL);
    memcpy(javaArray_p, array_p, length * sizeof(jbyte));
    (*env)->ReleaseByteArrayElements(env, array, array_p, JNI_ABORT);
    (*env)->ReleaseByteArrayElements(env, javaArray, javaArray_p, 0);
    return javaArray;
}

//獲取，返回int
JNIEXPORT jint JNICALL Java_com_test_Test_add(JNIEnv * env, jobject obj,
  jint a, jint b) {
 int i = a;
 int j = b;
 printf("\n c-int: %d - %d", i, j);
 char str[256];
 sprintf(str, "%d", i + j);
 return (jint) i + j;
}

//獲取，返回float
JNIEXPORT jfloat JNICALL Java_com_test_Test_getFloat(JNIEnv * env, jobject obj,
  jfloat f) {
 float fl = f;
 printf("\n c-float: %3f", fl);

 fl = 200.555;
 return (jfloat) fl;
}

//獲取，返回 double
JNIEXPORT jdouble JNICALL Java_com_test_Test_getDouble(JNIEnv * env,
  jobject obj, jdouble dou) {
 double d = dou;
 printf("\n c-double: %3f", d);

 d = 800.88;
 return (jdouble) d;
}

//獲取，返回boolean
JNIEXPORT jboolean JNICALL Java_com_test_Test_getBoolean(JNIEnv * env,
  jobject obj, jboolean bool) {

 unsigned char b = bool;
 printf("\n c-boolean: %lu  ", b);
 if (b) {
  printf("true");
 } else {
  printf("false");
 }

 b = 1;
 return (jboolean) b;
}

下面是Test.java

package com.test;

public class Test {
    private static native void sayHello(String str);

    private static native String getString(String str);

    private static native String[] getStringArray(String[] sa);

    private static native byte[] getByteArray(byte[] a);

    private static native int add(int a, int b);

    private static native float getFloat(float f);

    private static native double getDouble(double d);

    private static native boolean getBoolean(boolean b);

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

 public static void main(String[] args) {
  Test test = new Test();
  test.sayHello("zhang san");
  System.out.println("int     --> " + test.add(10, 20));
  System.out.println("float   --> " + test.getFloat(20.123f));
  System.out.println("double  --> " + test.getDouble(100.369));
  System.out.println("boolean --> " + test.getBoolean(true));
  System.out.println("string  --> " + test.getString("wang Wu"));

  String[] ss = { "hello", "-", "zhang", "san" };
  String[] str = test.getStringArray(ss);
  System.out.print("string[]-->  ");
  for (String string : str) {
   System.out.print(string + " ");
  }

 }

}