韦东山视频第3课第2节_JNI_C调用JAVA_P【学习笔记】
C调JAVA方法主要步骤如下:
一、C代码调用java的静态方法
Hello.java
1 public class Hello{ 2 public static void main(String args[]){ 3 System.out.println("Hello World!"); 4 } 5 6 public static void sayhello_to(String name){ 7 8 } 9 10 public static void sayhello_to(){ 11 12 } 13 14 }
caller.c
1 #include <stdio.h> 2 #include <jni.h> 3 4 5 jint 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 18 int main(int argc, char **argv) 19 { 20 JavaVM* jvm; 21 JNIEnv* env; 22 23 jclass cls; 24 int ret = 0; 25 26 jmethodID mid; 27 28 if (create_vm(&jvm, &env)) { 29 printf("can not create jvm\n"); 30 return -1; 31 } 32 33 cls = (*env)->FindClass(env, "Hello"); 34 if (cls == NULL) { 35 printf("can not find hello class\n"); 36 ret = -1; 37 goto destroy; 38 } 39 40 mid = (*env)->GetStaticMethodID(env, cls, "main","([Ljava/lang/String;)V"); 41 if (mid == NULL) { 42 ret = -1; 43 printf("can not get method\n"); 44 goto destroy; 45 } 46 47 (*env)->CallStaticVoidMethod(env, cls, mid, NULL); 48 49 destroy: 50 51 (*jvm)->DestroyJavaVM(jvm); 52 return ret; 53 }
编译运行命令:
1 javac Hello.java 2 3 javap -p -s Hello.class 4 5 gcc -I/usr/lib/jvm/java-1.7.0-openjdk-amd64/include/ -o caller caller.c -L /usr/lib/jvm/java-7-openjdk-amd64/jre/lib/amd64/server -ljvm 6 7 LD_LIBRARY_PATH=/usr/lib/jvm/java-7-openjdk-amd64/jre/lib/amd64/server ./caller
二、C调java非静态方法
Hello.java
1 public class Hello{ 2 public static void main(String args[]){ 3 System.out.println("Hello World!"); 4 } 5 6 public int sayhello_to(String name){ 7 System.out.println("java Hello World! " + name); 8 return 123; 9 } 10 11 public static void sayhello_to(){ 12 13 } 14 15 }
caller.c
1 #include <stdio.h> 2 #include <jni.h> 3 4 5 jint 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 18 int main(int argc, char **argv) 19 { 20 JavaVM* jvm; 21 JNIEnv* env; 22 23 jclass cls; 24 int ret = 0; 25 26 jmethodID mid; 27 jmethodID cid; 28 29 jobject jobj; 30 jstring jstr; 31 32 int r; 33 34 if (create_vm(&jvm, &env)) { 35 printf("can not create jvm\n"); 36 return -1; 37 } 38 39 cls = (*env)->FindClass(env, "Hello"); 40 if (cls == NULL) { 41 printf("can not find hello class\n"); 42 ret = -1; 43 goto destroy; 44 } 45 46 cid = (*env)->GetMethodID(env, cls, "<init>", "()V"); 47 if (cid == NULL) { 48 ret = -1; 49 printf("can not get constructor method"); 50 goto destroy; 51 } 52 53 jobj = (*env)->NewObject(env, cls, cid); 54 if (jobj == NULL) { 55 ret = -1; 56 printf("can not create object"); 57 goto destroy; 58 } 59 60 mid = (*env)->GetMethodID(env, cls, "sayhello_to","(Ljava/lang/String;)I"); 61 if (mid == NULL) { 62 ret = -1; 63 printf("can not get method\n"); 64 goto destroy; 65 } 66 67 jstr = (*env)->NewStringUTF(env, "weidongshan@qq.com"); 68 69 r = (*env)->CallIntMethod(env, jobj, mid, jstr); 70 printf("jni ret = %d\n", r); 71 72 destroy: 73 74 (*jvm)->DestroyJavaVM(jvm); 75 return ret; 76 }
运行结果:
二、C调java非静态方法，并设置属性
Hello.java
1 public class Hello{ 2 private String name; 3 private int age; 4 5 public static void main(String args[]){ 6 System.out.println("Hello World!"); 7 } 8 9 public int sayhello_to(String name){ 10 System.out.println("java Hello , " + name + " I'm " + this.name + "," + age+"years old"); 11 return 123; 12 } 13 14 public static void sayhello_to(){ 15 16 } 17 18 }
caller.c
1 #include <stdio.h> 2 #include <jni.h> 3 4 5 jint 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 18 int main(int argc, char **argv) 19 { 20 JavaVM* jvm; 21 JNIEnv* env; 22 23 jclass cls; 24 int ret = 0; 25 26 jmethodID mid; 27 jmethodID cid; 28 29 jobject jobj; 30 jstring jstr; 31 32 jfieldID nameID; 33 jfieldID ageID; 34 35 int r; 36 37 if (create_vm(&jvm, &env)) { 38 printf("can not create jvm\n"); 39 return -1; 40 } 41 42 cls = (*env)->FindClass(env, "Hello"); 43 if (cls == NULL) { 44 printf("can not find hello class\n"); 45 ret = -1; 46 goto destroy; 47 } 48 49 cid = (*env)->GetMethodID(env, cls, "<init>", "()V"); 50 if (cid == NULL) { 51 ret = -1; 52 printf("can not get constructor method"); 53 goto destroy; 54 } 55 56 jobj = (*env)->NewObject(env, cls, cid); 57 if (jobj == NULL) { 58 ret = -1; 59 printf("can not create object"); 60 goto destroy; 61 } 62 63 nameID = (*env)->GetFieldID(env, cls, "name", "Ljava/lang/String;"); 64 if (nameID == NULL) { 65 ret = -1; 66 printf("can not get field name"); 67 goto destroy; 68 } 69 jstr = (*env)->NewStringUTF(env, "Bill"); 70 (*env)->SetObjectField(env, jobj, nameID, jstr); 71 72 ageID = (*env)->GetFieldID(env, cls, "age", "I"); 73 if (ageID == NULL) { 74 ret = -1; 75 printf("can not get field age"); 76 goto destroy; 77 } 78 (*env)->SetIntField(env, jobj, ageID, 10); 79 80 mid = (*env)->GetMethodID(env, cls, "sayhello_to","(Ljava/lang/String;)I"); 81 if (mid == NULL) { 82 ret = -1; 83 printf("can not get method\n"); 84 goto destroy; 85 } 86 87 jstr = (*env)->NewStringUTF(env, "weidongshan@qq.com"); 88 89 r = (*env)->CallIntMethod(env, jobj, mid, jstr); 90 printf("ret = %d\n", r); 91 92 destroy: 93 94 (*jvm)->DestroyJavaVM(jvm); 95 return ret; 96 }
运行结果:
相关代码可以在这里下载:
https://github.com/zzb2760715357/100ask/tree/master/java
觉得不错，就给我点小支持吧，蟹蟹
