JNI调用机制(二)

public class JNITest2 {
	public String name;

	public static String sayHello(String name) {
		return "Hello, " + name + "!";
	}

	public String sayHello() {
		return "Hello, " + name + "!";
	}
}

#include <jni.h>
#include <string.h>
#include <stdio.h>

//环境变量PATH在windows和linux的分隔符定义
#ifdef _WIN32
#define PATH_SEPARATOR ';'
#else 
#define PATH_SEPARATOR ':'
#endif


int main (void) {

	JavaVMOption options[1]; //相当于命令行里传入的参数
	JNIEnv *env;  //JNI环境
	JavaVM *jvm;  //我们需要创建的虚拟机实例
	JavaVMInitArgs vm_args;  //虚拟机创建的初始化参数，这个参数里面会包含JavaVMOption

	long status;
	jclass cls;
	jmethodID mid;
	jfieldID fid;
	jobject obj;

	options[0].optionString = "-Djava.class.path=.";  //传入路径，作为JVM寻找class的用户自定义路径，我们的JNITest2.clsss就在当前路径（当然也可以在别的路径）
	memset(&vm_args, 0, sizeof(vm_args));
	vm_args.version = JNI_VERSION_1_4; //Java版本，这个宏在jni.h中有定义
	vm_args.nOptions = 1;  //传入的Options有多长，我们这只有一个，所以是1
	vm_args.options = options;  // 把JavaVMOption传给JavaVMInitArgs中

	status = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args); //启动虚拟机，通过status返回值，可知道虚拟机启动情况

	if (status != JNI_ERR) {
		cls = (*env)->FindClass(env, "JNITest2"); //获取class对象
		if (cls != 0) {
			//Java中类名格式是java.lang.String，但是ClassName格式不同，是java/lang/String
			//获取静态方法 
			mid = (*env)->GetStaticMethodID(env, cls, "sayHello", "(Ljava/lang/String;)Ljava/lang/String;");
			if (mid != 0) {
				const char* name = "World";
				jstring arg = (*env)->NewStringUTF(env, name);
				jstring result = (jstring)(*env)->CallStaticObjectMethod(env, cls, mid, arg);
				const char* str = (*env)->GetStringUTFChars(env, result, 0);
				printf("Result of sayHello: %s\n", str);
				(*env)->ReleaseStringUTFChars(env, result, 0);
			}
			//调用指定的构造函数，构造函数的名字叫<init>
			mid = (*env)->GetMethodID(env, cls, "<init>", "()V");  //调用非静态方法
			obj = (*env)->NewObject(env, cls, mid);
			if (obj == 0) {
				printf("Create object failed!\n");
			}
			//属性也有静态和非静态之分，有static为静态，无为非静态
			fid = (*env)->GetFieldID(env, cls, "name", "Ljava/lang/String;");
			if (fid != 0) {
				const char* name = "stackvoid";
				jstring arg = (*env)->NewStringUTF(env, name);
				(*env)->SetObjectField(env, obj, fid, arg);//修改属性
			}
			//调用成员方法
			mid = (*env)->GetMethodID(env, cls, "sayHello", "()Ljava/lang/String;");
			if (mid != 0) {
				jstring result = (jstring)(*env)->CallObjectMethod(env, obj, mid);
				const char* str = (*env)->GetStringUTFChars(env, result, 0);
				printf("Result of sayHello: %s\n", str);
				(*env)->ReleaseStringUTFChars(env, result, 0);
			}
		}
		(*jvm)->DestoryJavaVM(jvm);
		return 0;
	}
	else {
		printf("JVM Created failed!\n");
		return -1;
	}

}