JNI 数据类型转换

本人刚学习JNI，费了好大劲走了好多弯路才做了个例子，现帖出来，让和我一样的初学者参考，希望能有所帮助

下面是 Test.c

#include <jni.h> #include "com_test_Test.h" #include <stdio.h> #include <stdlib.h> #include <strings.h> //获取字符串 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); } //获取，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; } //获取，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; } //获取，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; } //获取，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; } //获取，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; } //获取，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; }

-----------------------------------------------------------------

下面是Test.java

package com.test; public class Test { private native void sayHello(String str); private native int add(int a, int b); private native float getFloat(float f); private native double getDouble(double d); private native boolean getBoolean(boolean b); private native String getString(String str); private native String[] getStringArray(String[] sa); 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((float) 20.123)); 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" }; Object[] obj = test.getStringArray(ss); System.out.print("string[]--> "); for (Object object : obj) { System.out.print(object + " "); } } }