JNI——C呼び出しJAVA

手順:
1.仮想マシンの作成
2.classを取得
3.オブジェクトのインスタンス化:構築メソッド(メソッド名")、構築パラメータ、呼び出しメソッドを取得
4.呼び出し方法:獲得方法、構築方法、呼び出し方法に分けられる
 
操作方法:
1.コンパイル:javac Hello.java
2. javap -p -s Hello.class:Signatureの表示
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.実行:LD_LIBRARY_PATH=/usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/server ./caller
 
 
例:
(1)call_static_method

 1 #include 
 2 #include 
 3 
 4  
 5 JNIEnv* create_vm(JavaVM** jvm, JNIEnv** env) 
 6 {    
 7         JavaVMInitArgs args;  
 8         JavaVMOption options[1];  
 9         args.version = JNI_VERSION_1_6;  
10         args.nOptions = 1;  
11         options[0].optionString = "-Djava.class.path=./";  
12         args.options = options;  
13         args.ignoreUnrecognized = JNI_FALSE;  
14         return JNI_CreateJavaVM(jvm, (void **)env, &args);   
15 }  
16 
17 int main(int argc, char **argv)
18 {
19     JavaVM* jvm;
20     JNIEnv* env;
21 
22     jclass cls;
23     int ret = 0;
24 
25     jmethodID mid;
26         
27     /* 1. create java virtual machine */
28     if(create_vm(&jvm, &env))
29     {
30         printf("can not create jvm
");
31         return -1;
32     }
33 
34     /* 2. get class */
35     cls = (*env)->FindClass(env, "Hello");
36     if(cls == NULL)
37     {
38         printf("can not find hello class
");
39         ret = -1;
40         goto destory;
41     }
42 
43     /* 3. create object */
44 
45     /* 4. call method 
46      *  4.1 get method
47      *  4.2 create parameter
48      *  4.3 call method
49      */
50 
51     mid = (*env)->GetStaticMethodID(env, cls, "main", "([Ljava/lang/String;)V");
52     if(mid == NULL)
53     {
54         ret = -1;
55         printf("can not get method
");
56         goto destory;
57     }
58 
59     (*env)->CallStaticVoidMethod(env, cls, mid, NULL);
60 
61 destory:
62     (*jvm)->DestroyJavaVM(jvm);
63     
64     return ret;
65 }

 
(2)call_non_static_method

 1 #include 
 2 #include 
 3 
 4  
 5 JNIEnv* create_vm(JavaVM** jvm, JNIEnv** env) 
 6 {    
 7         JavaVMInitArgs args;  
 8         JavaVMOption options[1];  
 9         args.version = JNI_VERSION_1_6;  
10         args.nOptions = 1;  
11         options[0].optionString = "-Djava.class.path=./";  
12         args.options = options;  
13         args.ignoreUnrecognized = JNI_FALSE;  
14         return JNI_CreateJavaVM(jvm, (void **)env, &args);   
15 }  
16 
17 int main(int argc, char **argv)
18 {
19     JavaVM* jvm;
20     JNIEnv* env;
21 
22     jclass cls;
23     int ret = 0;
24 
25     jmethodID mid;
26     jmethodID cid;
27 
28     jobject jobj;
29     jstring jstr;
30 
31     int r;
32         
33     /* 1. create java virtual machine */
34     if(create_vm(&jvm, &env))
35     {
36         printf("can not create jvm
");
37         return -1;
38     }
39 
40     /* 2. get class */
41     cls = (*env)->FindClass(env, "Hello");
42     if(cls == NULL)
43     {
44         printf("can not find hello class
");
45         ret = -1;
46         goto destory;
47     }
48 
49     /* 3. create object 
50      *  
51      */
52 
53     cid = (*env)->GetMethodID(env, cls, "", "()V");
54     if(cid == NULL)
55     {
56         printf("can not get construct method
");
57         ret = -1;
58         goto destory;
59     }
60 
61     jobj = (*env)->NewObject(env, cls, cid);
62     if(jobj == NULL)
63     {
64         printf("can not create object
");
65         ret = -1;
66         goto destory;
67     }
68     
69     /* 4. call method 
70      *  4.1 get method
71      *  4.2 create parameter
72      *  4.3 call method
73      */
74 
75     mid = (*env)->GetMethodID(env, cls, "sayhello_to", "(Ljava/lang/String;)I");
76     if(mid == NULL)
77     {
78         ret = -1;
79         printf("can not get method
");
80         goto destory;
81     }
82 
83     jstr = (*env)->NewStringUTF(env, "[email protected]");
84     
85     r = (*env)->CallIntMethod(env, jobj, mid, jstr);
86     printf("ret = %d
", r);
87     
88 destory:
89     (*jvm)->DestroyJavaVM(jvm);
90     
91     return ret;
92 }