JNI——C调用JAVA

提示：扫一扫查出行
【扫一扫了解最新限行尾号】
复制提示

步骤：

1. 创建虚拟机

2. 获得class

3. 实例化对象：获得构造方法（方法名为“<init>”）,构造参数，调用方法

4. 调用方法：又分为获得方法，构造方法，调用方法

操作方法：

1. 编译：javac Hello.java

2. javap -p -s Hello.class：查看Signature

3. gcc -I/usr/lib/jvm/java-1.8.0-openjdk-amd64/include/ -I/usr/lib/jvm/java-1.8.0-openjdk-amd64/include/linux/ -o caller caller.c -L /usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/server -ljvm

4. 执行：LD_LIBRARY_PATH=/usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/server ./caller

举例：

（1）call_static_method

#include <stdio.h>
#include <jni.h> JNIEnv* create_vm(JavaVM** jvm, JNIEnv** env)
{
JavaVMInitArgs args;
JavaVMOption options[];
args.version = JNI_VERSION_1_6;
args.nOptions = ;
options[].optionString = "-Djava.class.path=./";
args.options = options;
args.ignoreUnrecognized = JNI_FALSE;
return JNI_CreateJavaVM(jvm, (void **)env, &args);
} int main(int argc, char **argv)
{
JavaVM* jvm;
JNIEnv* env; jclass cls;
int ret = ; jmethodID mid; /* 1. create java virtual machine */
if(create_vm(&jvm, &env))
{
printf("can not create jvm\n");
return -;
} /* 2. get class */
cls = (*env)->FindClass(env, "Hello");
if(cls == NULL)
{
printf("can not find hello class\n");
ret = -;
goto destory;
} /* 3. create object */ /* 4. call method
* 4.1 get method
* 4.2 create parameter
* 4.3 call method
*/ mid = (*env)->GetStaticMethodID(env, cls, "main", "([Ljava/lang/String;)V");
if(mid == NULL)
{
ret = -;
printf("can not get method\n");
goto destory;
} (*env)->CallStaticVoidMethod(env, cls, mid, NULL); destory:
(*jvm)->DestroyJavaVM(jvm); return ret;
}

（2）call_non_static_method

#include <stdio.h>
#include <jni.h> JNIEnv* create_vm(JavaVM** jvm, JNIEnv** env)
{
JavaVMInitArgs args;
JavaVMOption options[];
args.version = JNI_VERSION_1_6;
args.nOptions = ;
options[].optionString = "-Djava.class.path=./";
args.options = options;
args.ignoreUnrecognized = JNI_FALSE;
return JNI_CreateJavaVM(jvm, (void **)env, &args);
} int main(int argc, char **argv)
{
JavaVM* jvm;
JNIEnv* env; jclass cls;
int ret = ; jmethodID mid;
jmethodID cid; jobject jobj;
jstring jstr; int r; /* 1. create java virtual machine */
if(create_vm(&jvm, &env))
{
printf("can not create jvm\n");
return -;
} /* 2. get class */
cls = (*env)->FindClass(env, "Hello");
if(cls == NULL)
{
printf("can not find hello class\n");
ret = -;
goto destory;
} /* 3. create object
*
*/ cid = (*env)->GetMethodID(env, cls, "<init>", "()V");
if(cid == NULL)
{
printf("can not get construct method\n");
ret = -;
goto destory;
} jobj = (*env)->NewObject(env, cls, cid);
if(jobj == NULL)
{
printf("can not create object\n");
ret = -;
goto destory;
} /* 4. call method
* 4.1 get method
* 4.2 create parameter
* 4.3 call method
*/ mid = (*env)->GetMethodID(env, cls, "sayhello_to", "(Ljava/lang/String;)I");
if(mid == NULL)
{
ret = -;
printf("can not get method\n");
goto destory;
} jstr = (*env)->NewStringUTF(env, "287787472@qq.com"); r = (*env)->CallIntMethod(env, jobj, mid, jstr);
printf("ret = %d\n", r); destory:
(*jvm)->DestroyJavaVM(jvm); return ret;
}