需要gcc编译器
| 字符 | java | c++/c |
|---|---|---|
| V | void | void |
| Z | jboolean | boolean |
| I | jint | int |
| J | jlong | long |
| D | jdouble | double |
| F | jfloat | float |
| B | jbyte | byte |
| C | jchar | char |
| S | jshort | short |
| [I | jintArray[] | int[] |
| [F | jfloatArray[] | float[] |
| [B | jbyteArray | byte[] |
| [C | jcharArray | char[] |
| [S | jshortArray | short[] |
| [D | jdoubleArray | double[] |
| [J | jloneArray | long[] |
| [Z | jbooleanArray | boolean[] |
| Ljava/lang/String | jstring | |
| 其他对象类推 |
(Ljava/lang/String;I)Ljava/lang/String; <===> String helloJNI(String a,int b) (II)V <===> void helloJNI(int a,int b)1.创建Java项目 代码如下
public class JNITest {
public native String helloJNI(String name,int age);
public static void main(String[] args) {
JNITest jniTest = new JNITest();
String z3 = jniTest.helloJNI("z3", 18);
System.out.println(z3);
}
}
关于上述代码解释如下：native表示该函数的实现不是用java实现的，可能是C/C++等语言实现，
2.编写C++实现 2.1 创建JNI.cpp文件// “jni.h” 由先从当前目录去找jni.h
#include "jni.h"
jstring cppJNI(JNIEnv* env, jobject clazz, jstring name, jint age) {
const char* chars = "hello java";
const jstring result = env->NewStringUTF(chars);
const char* nameChar = env->GetStringUTFChars(name, NULL);
return result;
}
JNIEXPORT jint JNI_OnLoad(JavaVM* vm, void* reserved) {
JNIEnv* env;
if (JNI_OK != vm->GetEnv(reinterpret_cast(&env), JNI_VERSION_1_8)) {
printf("JNI_OnLoad cloud not get jni env");
return JNI_ERR;
}
jclass clazz = env->FindClass("com/huf/JNITest");
//通过 JNINativeMethod映射 c++函数与java函数直接的关系，从而不用在C++ 提供的JNI函数时的函数名不需要按照一定规则才能访问
JNINativeMethod methods[] = {
{"helloJNI","(Ljava/lang/String;I)Ljava/lang/String;",(void*)cppJNI},
};
if (env->RegisterNatives(clazz, methods, sizeof(methods) / sizeof((methods)[0])) < 0) {
return JNI_ERR;
}
return JNI_VERSION_1_8;
}
2.2 将jdk环境下的 jni.h与jni_md.h复制到出来
<你的目录>jdk8u322-b06includejni.h
<你的目录>jdk8u322-b06includewin32jni_md.h
2.3 生成动态链接库此步骤需要gcc编译器没有请自行安装
| windows | linux | mac |
|---|---|---|
| dll | so | jnilib |
gcc -shared -o JNITest.dll .JNI.cpp
执行成功会看见JNITest.dll文件
2.4 修改java代码public class JNITest {
static {
System.loadLibrary("JNITest");
}
public native String helloJNI(String name,int age);
public static void main(String[] args) {
JNITest jniTest = new JNITest();
String z3 = jniTest.helloJNI("z3", 18);
System.out.println(z3);
}
}
2.5 执行java main函数测试
不出意外会出现如下错误：
no JNITest in java.library.path
因为它默认会去默认的路径找这个JNITest.dll库，所以我们需要手动指定
-Djava.library.path=E:ideajnisrccomhuf2.6 再次执行
hello java2.7 C++回调java
- c++代码如下
// pch.cpp: 与预编译标头对应的源文件
#include "jni.h"
JNIEnv* m_ENV = NULL;
JavaVM* m_JVM = NULL;
jobject object = NULL;
void callJava(const char* chars, int age) {
bool flag = false;
if (m_JVM->AttachCurrentThread((void**)&m_ENV, NULL) != JNI_OK) {
fprintf(stderr, "AttachCurrentThread errorn");
return;
}
flag = true;
jclass clazz = m_ENV->GetObjectClass(object);
//jclass clazz = m_env->FindClass("com/huf/JNITest");
if (clazz == NULL) {
fprintf(stderr, "GetObjectClass errorn");
if (flag) {
m_JVM->DetachCurrentThread();
}
return;
}
jmethodID method = m_ENV->GetMethodID(clazz, "callBack", "(Ljava/lang/String;I)V");
if (NULL == method) {
if (flag) {
m_JVM->DetachCurrentThread();
}
fprintf(stderr, "GetMethodID errorn");
return;
}
jobject object = m_ENV->AllocObject(clazz);
jstring re = m_ENV->NewStringUTF(chars);
m_ENV->CallVoidMethod(object, method, re, age);
if (flag) {
m_JVM->DetachCurrentThread();
}
}
jstring cppJNI(JNIEnv* env, jobject clazz, jstring name, jint age) {
const char* chars = "hello java";
const jstring result = env->NewStringUTF(chars);
const char* nameChar = env->GetStringUTFChars(name, NULL);
object = clazz;
callJava(nameChar, age);
return result;
}
JNIEXPORT jint JNI_OnLoad(JavaVM* vm, void* reserved) {
JNIEnv* env;
if (JNI_OK != vm->GetEnv(reinterpret_cast(&env), JNI_VERSION_1_8)) {
printf("JNI_OnLoad cloud not get jni env");
return JNI_ERR;
}
m_ENV = env;
m_JVM = vm;
jclass clazz = env->FindClass("com/huf/JNITest");
//通过 JNINativeMethod映射 c++函数与java函数直接的关系，从而不用在C++ 提供的JNI函数时的函数名不需要按照一定规则才能访问
JNINativeMethod methods[] = {
{"helloJNI","(Ljava/lang/String;I)Ljava/lang/String;",(void*)cppJNI},
};
if (env->RegisterNatives(clazz, methods, sizeof(methods) / sizeof((methods)[0])) < 0) {
return JNI_ERR;
}
return JNI_VERSION_1_8;
}
- java代码如下：
public class JNITest {
static {
System.loadLibrary("JNITest");
}
public native String helloJNI(String name,int age);
public void callBack(String name, int age) {
System.out.println("c++ ======> java");
System.out.printf("name : %s n age : %d n", name, age);
}
public static void main(String[] args) {
JNITest jniTest = new JNITest();
String z3 = jniTest.helloJNI("z3", 18);
System.out.println(z3);
}
}
最后
可以将无用文件删除只留下如图
