Android NDK开发三:java和C\C++交互
转自:http://www.cnblogs.com/shangdahao/archive/2013/05/02/3053971.html
1、定义native方法并加载动态链接库:
2、实现native方法:
若要定义静态方法:
头文件可以用javah工具生成:
进入命令行,切换到项目的bin目录下的classes下面,执行 javah -classpath . -jni 包.类名。
或者:cd 到src目录中,执行 javah 包.类名
3、数据
原始数据类型:
![](//img-blog.csdn.net/20130703160532359?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvZHVhbnlpcGVuZw==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast)
引用数据类型:
![](//img-blog.csdn.net/20130703160544781?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvZHVhbnlpcGVuZw==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast)
4、字符窜的操作:
1)新建字符串:
2)把java string转换成c string
5、数组的操作:
1)新建java数组:
2)获取数组的值:
获取数组指针:
6、C\C++获取java成员变量
1)获取Field ID
2)获取Static Field
7、C\C++调用java函数
1)获取Method ID:
成员函数:
静态函数:
2)调用:
变量和函数的描述符:
![](//img-blog.csdn.net/20130703161325015?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvZHVhbnlpcGVuZw==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast)
javap工具可以提取从编译过的class files 中提取这些描述符:
8、处理异常:
从c\c++抛异常:
9、本地和全局变量:
1)本地变量在函数结束时自动释放内存:
2)新建全局变量:
3)释放全局变量:
4)弱全局引用:
弱全局引用可以被内存自动回收:
10、线程:
native线程不能和java直接通信,必须先绑定到javaVM
1、定义native方法并加载动态链接库:
public class HelloJni extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); TextView tv = new TextView(this); tv.setText( stringFromJNI() ); setContentView(tv); } public native String stringFromJNI(); public native String unimplementedStringFromJNI(); static { System.loadLibrary("hello-jni"); } }
2、实现native方法:
#include <string.h> #include <jni.h> jstring Java_com_example_hellojni_HelloJni_stringFromJNI( JNIEnv* env, jobject thiz ) { return (*env)->NewStringUTF(env, "Hello from JNI !"); //in c return env->NewStringUTF("Hello from JNI !"); //in c++ }
若要定义静态方法:
JNIEXPORT jstring JNICALL Java_com_example_hellojni_HelloJni_stringFromJNI (JNIEnv * env, jclass clazz);
头文件可以用javah工具生成:
进入命令行,切换到项目的bin目录下的classes下面,执行 javah -classpath . -jni 包.类名。
或者:cd 到src目录中,执行 javah 包.类名
3、数据
原始数据类型:
引用数据类型:
4、字符窜的操作:
1)新建字符串:
jstring javaString; javaString = (*env)->NewStringUTF(env, "Hello World!");
2)把java string转换成c string
const jbyte* str; jboolean isCopy; str = (*env)->GetStringUTFChars(env, javaString, &isCopy); if (0 != str) { printf("Java string: %s", str); if (JNI_TRUE == isCopy) { printf("C string is a copy of the Java string."); } else { printf("C string points to actual string."); } (*env)->ReleaseStringUTFChars(env, javaString, str);
5、数组的操作:
1)新建java数组:
jintArray javaArray; javaArray = (*env)->NewIntArray(env, 10); if (0 != javaArray) { /* You can now use the array. */ }
2)获取数组的值:
jint nativeArray[10]; //将java array 复制到 c array (*env)->GetIntArrayRegion(env, javaArray, 0, 10, nativeArray); //将 c array 还原城 java array (*env)->SetIntArrayRegion(env, javaArray, 0, 10, nativeArray);
获取数组指针:
jint* nativeDirectArray; jboolean isCopy; nativeDirectArray = (*env)->GetIntArrayElements(env, javaArray, &isCopy); //... (*env)->ReleaseIntArrayElements(env, javaArray, nativeDirectArray, 0);
6、C\C++获取java成员变量
public class JavaClass { /** Instance field */ private String instanceField = "Instance Field"; /** Static field */ private static String staticField = "Static Field"; ... }
1)获取Field ID
jclass clazz; clazz = (*env)->GetObjectClass(env, instance); jfieldID instanceFieldId; instanceFieldId = (*env)->GetFieldID(env, clazz, "instanceField", "Ljava/lang/String;"); jfieldID staticFieldId; staticFieldId = (*env)->GetStaticFieldID(env, clazz, "staticField", "Ljava/lang/String;");
2)获取Static Field
jstring staticField; staticField = (*env)->GetStaticObjectField(env, clazz, staticFieldId);
7、C\C++调用java函数
public class JavaClass { /** * Instance method. */ private String instanceMethod() { return "Instance Method"; } /** * Static method. */ private static String staticMethod() { return "Static Method"; } ... }
1)获取Method ID:
成员函数:
jmethodID instanceMethodId; instanceMethodId = (*env)->GetMethodID(env, clazz, "instanceMethod", "()Ljava/lang/String;");
静态函数:
jmethodID staticMethodId; staticMethodId = (*env)->GetStaticMethodID(env, clazz, "staticMethod", "()Ljava/lang/String;");
2)调用:
jstring instanceMethodResult; instanceMethodResult = (*env)->CallStringMethod(env, instance, instanceMethodId);
变量和函数的描述符:
javap工具可以提取从编译过的class files 中提取这些描述符:
javap –classpath bin/classes –p –s com.example.hellojni.HelloJni
8、处理异常:
public class JavaClass { /** * Throwing method. */ private void throwingMethod() throws NullPointerException { throw new NullPointerException("Null pointer"); } /** * Access methods native method. */ private native void accessMethods(); }
jthrowable ex; ... (*env)->CallVoidMethod(env, instance, throwingMethodId); ex = (*env)->ExceptionOccurred(env); if (0 != ex) { (*env)->ExceptionClear(env); /* Exception handler. */ }
从c\c++抛异常:
jclass clazz; ... clazz = (*env)->FindClass(env, "java/lang/NullPointerException"); if (0 ! = clazz) { (*env)->ThrowNew(env, clazz, "Exception message."); }
9、本地和全局变量:
1)本地变量在函数结束时自动释放内存:
jclass clazz; clazz = (*env)->FindClass(env, "java/lang/String");
2)新建全局变量:
jclass localClazz; jclass globalClazz; ... localClazz = (*env)->FindClass(env, "java/lang/String"); globalClazz = (*env)->NewGlobalRef(env, localClazz); ... (*env)->DeleteLocalRef(env, localClazz);
3)释放全局变量:
(*env)->DeleteGlobalRef(env, globalClazz);
4)弱全局引用:
弱全局引用可以被内存自动回收:
jclass weakGlobalClazz; weakGlobalClazz = (*env)->NewWeakGlobalRef(env, localClazz); if (JNI_FALSE == (*env)->IsSameObject(env, weakGlobalClazz, NULL)) { /* Object is still live and can be used. */ } else { /* Object is garbage collected and cannot be used. */ } (*env)->DeleteWeakGlobalRef(env, weakGlobalClazz);
10、线程:
synchronized(obj) { /* Synchronized thread-safe code block. */ }
if (JNI_OK == (*env)->MonitorEnter(env, obj)) { /* Error handling. */ } /* Synchronized thread-safe code block. */ if (JNI_OK == (*env)->MonitorExit(env, obj)) { /* Error handling. */ }
native线程不能和java直接通信,必须先绑定到javaVM
JavaVM* cachedJvm; ... JNIEnv* env; ... /* Attach the current thread to virtual machine. */ (*cachedJvm)->AttachCurrentThread(cachedJvm, &env, NULL); /* Thread can communicate with the Java application using the JNIEnv interface. */ /* Detach the current thread from virtual machine. */ (*cachedJvm)->DetachCurrentThread(cachedJvm);