c如何调用java

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[1];        args.version = JNI_VERSION_1_6;        args.nOptions = 1;        options[0].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 = 0;   jmethodID mid;        /* 1. create java virtual machine */  if(create_vm(&jvm, &env))  {      printf("can not create jvm\n");      return -1;  }   /* 2. get class */  cls = (*env)->FindClass(env, "Hello");  if(cls == NULL)  {      printf("can not find hello class\n");      ret = -1;      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 = -1;      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[1];    args.version = JNI_VERSION_1_6;    args.nOptions = 1;    options[0].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 = 0;  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 -1; }  /* 2. get class */ cls = (*env)->FindClass(env, "Hello"); if(cls == NULL) {  printf("can not find hello class\n");  ret = -1;  goto destory; }  /* 3. create object  *   */  cid = (*env)->GetMethodID(env, cls, "<init>", "()V"); if(cid == NULL) {  printf("can not get construct method\n");  ret = -1;  goto destory; }  jobj = (*env)->NewObject(env, cls, cid); if(jobj == NULL) {  printf("can not create object\n");  ret = -1;  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 = -1;  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; }

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