标签：machine library ptr null get def style export usr
1、什么是JNI：
在C中实现这个方法，在方法内部输出“Hello World"，然后再回到Java中进行调用。分为以下步骤:
建立一个类:JNIDemo
public class JNIDemo {
static { /* 1. load */
System.loadLibrary("native"); /* libnative.so */
}
public native static void hello();
public native static int hello(String str, int []a);
public static void main(String[] args) {
System.out.println("JNIDemo");
/* 1. load */
System.loadLibrary("native"); /* libnative.so */
/* 2. map hello java<-->c c_hello */
/* 3. call */
hello();
}
}
编译java
$ javac JNIDemo.java
gen jiu java wenjian cahn sheng tou wenjian xie C wenjian
$ javah -jni JNIDemo
Output JNIDemo.h
/* DO NOT EDIT THIS FILE - it is machine generated */ #include <jni.h> /* Header for class JNIDemo */ #ifndef _Included_JNIDemo #define _Included_JNIDemo #ifdef __cplusplus extern "C" { #endif /* * Class: JNIDemo * Method: hello * Signature: ()V */ JNIEXPORT void JNICALL Java_JNIDemo_hello__ (JNIEnv *, jclass); /* * Class: JNIDemo * Method: hello * Signature: (Ljava/lang/String;[I)I */ JNIEXPORT jint JNICALL Java_JNIDemo_hello__Ljava_lang_String_2_3I (JNIEnv *, jclass, jstring, jintArray); #ifdef __cplusplus } #endif #endif
new native.c
#include <jni.h> /* /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/ */
#include <stdio.h>
#if 0
typedef struct {
char *name; /* Java里调用的函数名 */
char *signature; /* JNI字段描述符, 用来表示Java里调用的函数的参数和返回值类型 */
void *fnPtr; /* C语言实现的本地函数 */
} JNINativeMethod;
#endif
void c_hello(JNIEnv *env, jobject cls)
{
printf("Hello, world!\n");
}
static const JNINativeMethod methods[] = {
{"hello", "()V", (void *)c_hello},
};
/* System.loadLibrary */
JNIEXPORT jint JNICALL
JNI_OnLoad(JavaVM *jvm, void *reserved)
{
JNIEnv *env;
jclass cls;
if ((*jvm)->GetEnv(jvm, (void **)&env, JNI_VERSION_1_4)) {
return JNI_ERR; /* JNI version not supported */
}
cls = (*env)->FindClass(env, "JNIDemo");
if (cls == NULL) {
return JNI_ERR;
}
/* 2. map hello java<-->c c_hello */
if((*env)->RegisterNatives(env, cls, methods, 1) < 0)
return JNI_ERR;
return JNI_VERSION_1_4;
}
指定头文件路径 -I /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/ 编译产生库
$ gcc -I /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/ -fPIC -shared -o libnative.so native.c
运行
$ java JNIDemo
结果
JNIDemo
Hello, world!
标签：machine library ptr null get def style export usr
原文地址：http://www.cnblogs.com/CZM-/p/7635484.html
