How to call java in c-Javagetting Started-php.cn

Steps:

1. Create a virtual machine;

2. Get class;

3. Instantiate the object: obtain the construction method (the method name is " "), construction parameters, and call the method.

4. Calling method: It is divided into obtaining method, constructing method and calling method.

Operation method:

1. Compile: javac Hello.java

2. javap -p -s Hello.class: View 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. Execute: LD_LIBRARY_PATH=/usr/lib/ jvm/java-8-openjdk-amd64/jre/lib/amd64/server ./caller

Example:

(1)call_static_method

#include  #include  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; }

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(2)call_non_static_method

#include  #include  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, "", "()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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