我发现JNI的问题是c调用Java代码。环境WIN10 JDK1.8目前,我需要C 代码来调用Java代码。起初,我写了一个demothat成功了。代码显示如下:
public class Sample2 {
public String name;
public static String sayHello(String name) {
return "Hello, " + name + "!";
}
public String sayHello() {
return "Hello, " + name + "!";
}
}
一些C 代码如下:
int main(){
printf("hello world");
JavaVMOption options[3];
JNIEnv* env;
JavaVM* jvm;
JavaVMInitArgs vm_args;
long status;
jclass cls;
jmethodID mid;
jfieldID fid;
jobject obj;
char opt1[] = "-Djava.compiler=NONE";
char opt2[] = "-Djava.class.path=.";
char opt3[] = "-verbose:NONE";
options[0].optionString = opt1; options[0].extraInfo = NULL;
options[1].optionString = opt2; options[1].extraInfo = NULL;
options[2].optionString = opt3; options[2].extraInfo = NULL;
memset(&vm_args, 0, sizeof(vm_args));
vm_args.version = JNI_VERSION_1_8;
vm_args.nOptions = 1;
vm_args.options = options;
vm_args.ignoreUnrecognized = 0;
// 启动虚拟机
status = JNI_CreateJavaVM(&jvm, (void**)& env, &vm_args);
if (status != JNI_ERR){
// 先获得class对象
cls = env->FindClass("Sample2");
}
}
我使用Eclipse将Java代码编译到.class文件中,将.class文件复制到我的C 项目中,以上演示C 调用Java java函数成功了,FindClass函数返回正常。
。因为我必须在我自己的java中介绍第三方jar package org.eclipse.client.mqttv3-1.2.0.jar。我想引用JAR软件包功能,然后将.class文件复制到C 项目时在Eclipse中成功运行。C 代码中的Jni_createjavm成功返回,但是FindClass总是返回null,我不知道为什么。我没有更改其他零件代码。一些Java代码:
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;
import org.eclipse.paho.client.mqttv3.*;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
public class Sample2 {
public String name;
static MqttAsyncClient mqttClient = null;
static String username = "xxx";
static String password = "xxx";
static String broker = "xxx";
public static void main(String[] args) throws InterruptedException {
System.out.print("hello");
}
public static void start() {
String clientId = "mqttserver" + String.valueOf(System.currentTimeMillis());
try {
mqttClient = new MqttAsyncClient(broker, clientId, new MemoryPersistence());
} catch (Exception me) {
me.printStackTrace();
}
}
添加开始功能时 mqttClient = new MqttAsyncClient(broker, clientId, new MemoryPersistence());
在代码后,会出现问题
在此处查看
char opt1[] = "-Djava.compiler=NONE";
char opt2[] = "-Djava.class.path=.";
char opt3[] = "-verbose:NONE";
options[0].optionString = opt1; options[0].extraInfo = NULL;
options[1].optionString = opt2; options[1].extraInfo = NULL;
options[2].optionString = opt3; options[2].extraInfo = NULL;
memset(&vm_args, 0, sizeof(vm_args));
vm_args.version = JNI_VERSION_1_8;
vm_args.nOptions = 1;
您正在传递三个选项(已定义三个选项的选项数组(,但是,您说了类似的话
vm_args.nOptions = 1;
这意味着您仅通过一个选项。这意味着您的选择
char opt2[] = "-Djava.class.path=.";
char opt3[] = "-verbose:NONE";
甚至没有阅读。您必须将代码更改为
vm_args.nOptions = 3;
另外,请确保戴上java.class.path
所有JAR
s,文件夹,您的代码要求的类别为。