什么是JNI？
JNI 是java本地开发接口.
JNI 是一个协议,这个协议用来沟通java代码和外部的本地代码(c/c++).
通过这个协议,java代码就可以调用外部的c/c++代码,
外部的c/c++代码也可以调用java代码.
Android系统源码中随处可见JNI的使用.
图片1.png
前面说了JNI是一个协议，这份协议就定义在jni.h头文件中，所以首先要把这份协议读懂知道这份协议中有什么接口可以使用。
路径：/android-ndk-r10e/platforms/android-21/arch-arm/usr/include/jni.h
jni.h的组成
JNI.h (1).png
- JNI基本数据类型定义
/*
* Primitive types that match up with Java equivalents.
*/
#ifdef HAVE_INTTYPES_H
# include <inttypes.h> /* C99 */
typedef uint8_t jboolean; /* unsigned 8 bits */
typedef int8_t jbyte; /* signed 8 bits */
typedef uint16_t jchar; /* unsigned 16 bits */
typedef int16_t jshort; /* signed 16 bits */
typedef int32_t jint; /* signed 32 bits */
typedef int64_t jlong; /* signed 64 bits */
typedef float jfloat; /* 32-bit IEEE 754 */
typedef double jdouble; /* 64-bit IEEE 754 */
#else
typedef unsigned char jboolean; /* unsigned 8 bits */
typedef signed char jbyte; /* signed 8 bits */
typedef unsigned short jchar; /* unsigned 16 bits */
typedef short jshort; /* signed 16 bits */
typedef int jint; /* signed 32 bits */
typedef long long jlong; /* signed 64 bits */
typedef float jfloat; /* 32-bit IEEE 754 */
typedef double jdouble; /* 64-bit IEEE 754 */
#endif
/* "cardinal indices and sizes" */
typedef jint jsize;
- JNI数据类型的定义
#ifdef __cplusplus
/*
* Reference types, in C++
*/
class _jobject {};
class _jclass : public _jobject {};
class _jstring : public _jobject {};
class _jarray : public _jobject {};
class _jobjectArray : public _jarray {};
class _jbooleanArray : public _jarray {};
class _jbyteArray : public _jarray {};
class _jcharArray : public _jarray {};
class _jshortArray : public _jarray {};
class _jintArray : public _jarray {};
class _jlongArray : public _jarray {};
class _jfloatArray : public _jarray {};
class _jdoubleArray : public _jarray {};
class _jthrowable : public _jobject {};
typedef _jobject* jobject;
typedef _jclass* jclass;
typedef _jstring* jstring;
typedef _jarray* jarray;
typedef _jobjectArray* jobjectArray;
typedef _jbooleanArray* jbooleanArray;
typedef _jbyteArray* jbyteArray;
typedef _jcharArray* jcharArray;
typedef _jshortArray* jshortArray;
typedef _jintArray* jintArray;
typedef _jlongArray* jlongArray;
typedef _jfloatArray* jfloatArray;
typedef _jdoubleArray* jdoubleArray;
typedef _jthrowable* jthrowable;
typedef _jobject* jweak;
#else /* not __cplusplus */
/*
* Reference types, in C.
*/
typedef void* jobject;
typedef jobject jclass;
typedef jobject jstring;
typedef jobject jarray;
typedef jarray jobjectArray;
typedef jarray jbooleanArray;
typedef jarray jbyteArray;
typedef jarray jcharArray;
typedef jarray jshortArray;
typedef jarray jintArray;
typedef jarray jlongArray;
typedef jarray jfloatArray;
typedef jarray jdoubleArray;
typedef jobject jthrowable;
typedef jobject jweak;
#endif /* not __cplusplus */
- JNI字段与函数ID的定义
struct _jfieldID; /* opaque structure */
typedef struct _jfieldID* jfieldID; /* field IDs */
struct _jmethodID; /* opaque structure */
typedef struct _jmethodID* jmethodID; /* method IDs */
- JNI函数返回值联合体定义
typedef union jvalue {
jboolean z;
jbyte b;
jchar c;
jshort s;
jint i;
jlong j;
jfloat f;
jdouble d;
jobject l;
} jvalue;
- JNI引用类型的定义
typedef enum jobjectRefType {
JNIInvalidRefType = 0,
JNILocalRefType = 1,
JNIGlobalRefType = 2,
JNIWeakGlobalRefType = 3
} jobjectRefType;
- JNI本地函数描述定义
typedef struct {
const char* name;
const char* signature;
void* fnPtr;
} JNINativeMethod;
- java虚拟机接口
/*
* JNI invocation interface.
*/
struct JNIInvokeInterface {
void* reserved0;
void* reserved1;
void* reserved2;
jint (*DestroyJavaVM)(JavaVM*);
jint (*AttachCurrentThread)(JavaVM*, JNIEnv**, void*);
jint (*DetachCurrentThread)(JavaVM*);
jint (*GetEnv)(JavaVM*, void**, jint);
jint (*AttachCurrentThreadAsDaemon)(JavaVM*, JNIEnv**, void*);
};
/*
* C++ version.
*/
struct _JavaVM {
const struct JNIInvokeInterface* functions;
#if defined(__cplusplus)
jint DestroyJavaVM()
{ return functions->DestroyJavaVM(this); }
jint AttachCurrentThread(JNIEnv** p_env, void* thr_args)
{ return functions->AttachCurrentThread(this, p_env, thr_args); }
jint DetachCurrentThread()
{ return functions->DetachCurrentThread(this); }
jint GetEnv(void** env, jint version)
{ return functions->GetEnv(this, env, version); }
jint AttachCurrentThreadAsDaemon(JNIEnv** p_env, void* thr_args)
{ return functions->AttachCurrentThreadAsDaemon(this, p_env, thr_args); }
#endif /*__cplusplus*/
};
- 异常常量与其他常量定义
/*
* Manifest constants.
*/
#define JNI_FALSE 0
#define JNI_TRUE 1
#define JNI_VERSION_1_1 0x00010001
#define JNI_VERSION_1_2 0x00010002
#define JNI_VERSION_1_4 0x00010004
#define JNI_VERSION_1_6 0x00010006
#define JNI_OK (0) /* no error */
#define JNI_ERR (-1) /* generic error */
#define JNI_EDETACHED (-2) /* thread detached from the VM */
#define JNI_EVERSION (-3) /* JNI version error */
#define JNI_COMMIT 1 /* copy content, do not free buffer */
#define JNI_ABORT 2 /* free buffer w/o copying back */
#endif /* JNI_H_ */
- JNI本地接口，与java交互的函数定义（转载，出处未知）
/*
* Table of interface function pointers.
*/
struct JNINativeInterface {
void* reserved0;
void* reserved1;
void* reserved2;
void* reserved3;
//获取JNI版本号
jint (*GetVersion)(JNIEnv *);
//通过制定ClassLoader对象加载类
jclass (*DefineClass)(JNIEnv*, const char*, jobject, const jbyte*,
jsize);
//获取指定的Class类对象
jclass (*FindClass)(JNIEnv*, const char*);
//通过指定的java.lang.reflect.Method对象获取方法ID
jmethodID (*FromReflectedMethod)(JNIEnv*, jobject);
//通过指定的java.lang.reflect.Field对象获取字段ID
jfieldID (*FromReflectedField)(JNIEnv*, jobject);
/* spec doesn't show jboolean parameter */
//通过指定的方法ID获取java.lang.reflect.Method对象
jobject (*ToReflectedMethod)(JNIEnv*, jclass, jmethodID, jboolean);
//获取指定类的父类
jclass (*GetSuperclass)(JNIEnv*, jclass);
//判断指定类是否继承自某类或实现了某个接口
jboolean (*IsAssignableFrom)(JNIEnv*, jclass, jclass);
/* spec doesn't show jboolean parameter */
//通过指定的字段ID获取java.lang.reflect.Field对象
jobject (*ToReflectedField)(JNIEnv*, jclass, jfieldID, jboolean);
//抛出指定的Throwable对象
jint (*Throw)(JNIEnv*, jthrowable);
//抛出指定的Throwable对象，并制定消息
jint (*ThrowNew)(JNIEnv *, jclass, const char *);
//获取未被清空或捕获的异常
jthrowable (*ExceptionOccurred)(JNIEnv*);
//同printStackTrace()
void (*ExceptionDescribe)(JNIEnv*);
//清除已被抛出的异常
void (*ExceptionClear)(JNIEnv*);
//抛出致命错误
void (*FatalError)(JNIEnv*, const char*);
//Push/PopLocalFrame函数提供了本地引用管理的简便方法，在该函数对之间的代码段，所有创建的显式本地引用无需手动调用DeleteLocalReference函数释放，PopLocalFrame函数会自动释放这些本地引用
jint (*PushLocalFrame)(JNIEnv*, jint);
jobject (*PopLocalFrame)(JNIEnv*, jobject);
//创建全局引用，必须被显式清除
jobject (*NewGlobalRef)(JNIEnv*, jobject);
//清除全局引用
void (*DeleteGlobalRef)(JNIEnv*, jobject);
//清除本地引用，通常本地引用在原生代码返回时会自动清除，但是对于大数据，比如在循环中频繁创建Java对象，而该对象的只在一次循环中有效，这种情况下有必要显式调用DeleteLocalRef以通知VM尽快释放该对象。
void (*DeleteLocalRef)(JNIEnv*, jobject);
//判断是否为同一对象，可通过该方法判断弱引用是否已被释放(NULL)
jboolean (*IsSameObject)(JNIEnv*, jobject, jobject);
//创建本地引用
jobject (*NewLocalRef)(JNIEnv*, jobject);
//确保当前线程可以创建指定数量的本地引用
jint (*EnsureLocalCapacity)(JNIEnv*, jint);
//创建一个新的对象，只分配内存，不调用任何构造方法（应该是为了方便通过CallNonvirtual<Type>Method方法调用父类的构造函数初始化对象）
jobject (*AllocObject)(JNIEnv*, jclass);
//通过指定的构造函数创建对象，变长参数形式
jobject (*NewObject)(JNIEnv*, jclass, jmethodID, ...);
//同上，va_list形式
jobject (*NewObjectV)(JNIEnv*, jclass, jmethodID, va_list);
//同上，数组形式
jobject (*NewObjectA)(JNIEnv*, jclass, jmethodID, jvalue*);
//获取对象的Class类对象
jclass (*GetObjectClass)(JNIEnv*, jobject);
//同instanceOf
jboolean (*IsInstanceOf)(JNIEnv*, jobject, jclass);
//获取实例（非静态）方法的ID
jmethodID (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);
//调用实例方法，object表示返回值类型
jobject (*CallObjectMethod)(JNIEnv*, jobject, jmethodID, ...);
jobject (*CallObjectMethodV)(JNIEnv*, jobject, jmethodID, va_list);
jobject (*CallObjectMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
jboolean (*CallBooleanMethod)(JNIEnv*, jobject, jmethodID, ...);
jboolean (*CallBooleanMethodV)(JNIEnv*, jobject, jmethodID, va_list);
jboolean (*CallBooleanMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
jbyte (*CallByteMethod)(JNIEnv*, jobject, jmethodID, ...);
jbyte (*CallByteMethodV)(JNIEnv*, jobject, jmethodID, va_list);
jbyte (*CallByteMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
jchar (*CallCharMethod)(JNIEnv*, jobject, jmethodID, ...);
jchar (*CallCharMethodV)(JNIEnv*, jobject, jmethodID, va_list);
jchar (*CallCharMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
jshort (*CallShortMethod)(JNIEnv*, jobject, jmethodID, ...);
jshort (*CallShortMethodV)(JNIEnv*, jobject, jmethodID, va_list);
jshort (*CallShortMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
jint (*CallIntMethod)(JNIEnv*, jobject, jmethodID, ...);
jint (*CallIntMethodV)(JNIEnv*, jobject, jmethodID, va_list);
jint (*CallIntMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
jlong (*CallLongMethod)(JNIEnv*, jobject, jmethodID, ...);
jlong (*CallLongMethodV)(JNIEnv*, jobject, jmethodID, va_list);
jlong (*CallLongMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
jfloat (*CallFloatMethod)(JNIEnv*, jobject, jmethodID, ...) __NDK_FPABI__;
jfloat (*CallFloatMethodV)(JNIEnv*, jobject, jmethodID, va_list) __NDK_FPABI__;
jfloat (*CallFloatMethodA)(JNIEnv*, jobject, jmethodID, jvalue*) __NDK_FPABI__;
jdouble (*CallDoubleMethod)(JNIEnv*, jobject, jmethodID, ...) __NDK_FPABI__;
jdouble (*CallDoubleMethodV)(JNIEnv*, jobject, jmethodID, va_list) __NDK_FPABI__;
jdouble (*CallDoubleMethodA)(JNIEnv*, jobject, jmethodID, jvalue*) __NDK_FPABI__;
void (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);
void (*CallVoidMethodV)(JNIEnv*, jobject, jmethodID, va_list);
void (*CallVoidMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
//调用非虚实例方法，通过class对象指定调用哪个类的非虚函数（应该是某对象不调用自己的构造类的方法实现，而是调用父类的方法实现，这个方法节省了子类对象向父类对象的强制转换）
jobject (*CallNonvirtualObjectMethod)(JNIEnv*, jobject, jclass,
jmethodID, ...);
jobject (*CallNonvirtualObjectMethodV)(JNIEnv*, jobject, jclass,
jmethodID, va_list);
jobject (*CallNonvirtualObjectMethodA)(JNIEnv*, jobject, jclass,
jmethodID, jvalue*);
jboolean (*CallNonvirtualBooleanMethod)(JNIEnv*, jobject, jclass,
jmethodID, ...);
jboolean (*CallNonvirtualBooleanMethodV)(JNIEnv*, jobject, jclass,
jmethodID, va_list);
jboolean (*CallNonvirtualBooleanMethodA)(JNIEnv*, jobject, jclass,
jmethodID, jvalue*);
jbyte (*CallNonvirtualByteMethod)(JNIEnv*, jobject, jclass,
jmethodID, ...);
jbyte (*CallNonvirtualByteMethodV)(JNIEnv*, jobject, jclass,
jmethodID, va_list);
jbyte (*CallNonvirtualByteMethodA)(JNIEnv*, jobject, jclass,
jmethodID, jvalue*);
jchar (*CallNonvirtualCharMethod)(JNIEnv*, jobject, jclass,
jmethodID, ...);
jchar (*CallNonvirtualCharMethodV)(JNIEnv*, jobject, jclass,
jmethodID, va_list);
jchar (*CallNonvirtualCharMethodA)(JNIEnv*, jobject, jclass,
jmethodID, jvalue*);
jshort (*CallNonvirtualShortMethod)(JNIEnv*, jobject, jclass,
jmethodID, ...);
jshort (*CallNonvirtualShortMethodV)(JNIEnv*, jobject, jclass,
jmethodID, va_list);
jshort (*CallNonvirtualShortMethodA)(JNIEnv*, jobject, jclass,
jmethodID, jvalue*);
jint (*CallNonvirtualIntMethod)(JNIEnv*, jobject, jclass,
jmethodID, ...);
jint (*CallNonvirtualIntMethodV)(JNIEnv*, jobject, jclass,
jmethodID, va_list);
jint (*CallNonvirtualIntMethodA)(JNIEnv*, jobject, jclass,
jmethodID, jvalue*);
jlong (*CallNonvirtualLongMethod)(JNIEnv*, jobject, jclass,
jmethodID, ...);
jlong (*CallNonvirtualLongMethodV)(JNIEnv*, jobject, jclass,
jmethodID, va_list);
jlong (*CallNonvirtualLongMethodA)(JNIEnv*, jobject, jclass,
jmethodID, jvalue*);
jfloat (*CallNonvirtualFloatMethod)(JNIEnv*, jobject, jclass,
jmethodID, ...) __NDK_FPABI__;
jfloat (*CallNonvirtualFloatMethodV)(JNIEnv*, jobject, jclass,
jmethodID, va_list) __NDK_FPABI__;
jfloat (*CallNonvirtualFloatMethodA)(JNIEnv*, jobject, jclass,
jmethodID, jvalue*) __NDK_FPABI__;
jdouble (*CallNonvirtualDoubleMethod)(JNIEnv*, jobject, jclass,
jmethodID, ...) __NDK_FPABI__;
jdouble (*CallNonvirtualDoubleMethodV)(JNIEnv*, jobject, jclass,
jmethodID, va_list) __NDK_FPABI__;
jdouble (*CallNonvirtualDoubleMethodA)(JNIEnv*, jobject, jclass,
jmethodID, jvalue*) __NDK_FPABI__;
void (*CallNonvirtualVoidMethod)(JNIEnv*, jobject, jclass,
jmethodID, ...);
void (*CallNonvirtualVoidMethodV)(JNIEnv*, jobject, jclass,
jmethodID, va_list);
void (*CallNonvirtualVoidMethodA)(JNIEnv*, jobject, jclass,
jmethodID, jvalue*);
//获取成员字段ID
jfieldID (*GetFieldID)(JNIEnv*, jclass, const char*, const char*);
//获取字段值
jobject (*GetObjectField)(JNIEnv*, jobject, jfieldID);
jboolean (*GetBooleanField)(JNIEnv*, jobject, jfieldID);
jbyte (*GetByteField)(JNIEnv*, jobject, jfieldID);
jchar (*GetCharField)(JNIEnv*, jobject, jfieldID);
jshort (*GetShortField)(JNIEnv*, jobject, jfieldID);
jint (*GetIntField)(JNIEnv*, jobject, jfieldID);
jlong (*GetLongField)(JNIEnv*, jobject, jfieldID);
jfloat (*GetFloatField)(JNIEnv*, jobject, jfieldID) __NDK_FPABI__;
jdouble (*GetDoubleField)(JNIEnv*, jobject, jfieldID) __NDK_FPABI__;
//设置字段值
void (*SetObjectField)(JNIEnv*, jobject, jfieldID, jobject);
void (*SetBooleanField)(JNIEnv*, jobject, jfieldID, jboolean);
void (*SetByteField)(JNIEnv*, jobject, jfieldID, jbyte);
void (*SetCharField)(JNIEnv*, jobject, jfieldID, jchar);
void (*SetShortField)(JNIEnv*, jobject, jfieldID, jshort);
void (*SetIntField)(JNIEnv*, jobject, jfieldID, jint);
void (*SetLongField)(JNIEnv*, jobject, jfieldID, jlong);
void (*SetFloatField)(JNIEnv*, jobject, jfieldID, jfloat) __NDK_FPABI__;
void (*SetDoubleField)(JNIEnv*, jobject, jfieldID, jdouble) __NDK_FPABI__;
//获取静态方法ID
jmethodID (*GetStaticMethodID)(JNIEnv*, jclass, const char*, const char*);
//调用静态方法
jobject (*CallStaticObjectMethod)(JNIEnv*, jclass, jmethodID, ...);
jobject (*CallStaticObjectMethodV)(JNIEnv*, jclass, jmethodID, va_list);
jobject (*CallStaticObjectMethodA)(JNIEnv*, jclass, jmethodID, jvalue*);
jboolean (*CallStaticBooleanMethod)(JNIEnv*, jclass, jmethodID, ...);
jboolean (*CallStaticBooleanMethodV)(JNIEnv*, jclass, jmethodID,
va_list);
jboolean (*CallStaticBooleanMethodA)(JNIEnv*, jclass, jmethodID,
jvalue*);
jbyte (*CallStaticByteMethod)(JNIEnv*, jclass, jmethodID, ...);
jbyte (*CallStaticByteMethodV)(JNIEnv*, jclass, jmethodID, va_list);
jbyte (*CallStaticByteMethodA)(JNIEnv*, jclass, jmethodID, jvalue*);
jchar (*CallStaticCharMethod)(JNIEnv*, jclass, jmethodID, ...);
jchar (*CallStaticCharMethodV)(JNIEnv*, jclass, jmethodID, va_list);
jchar (*CallStaticCharMethodA)(JNIEnv*, jclass, jmethodID, jvalue*);
jshort (*CallStaticShortMethod)(JNIEnv*, jclass, jmethodID, ...);
jshort (*CallStaticShortMethodV)(JNIEnv*, jclass, jmethodID, va_list);
jshort (*CallStaticShortMethodA)(JNIEnv*, jclass, jmethodID, jvalue*);
jint (*CallStaticIntMethod)(JNIEnv*, jclass, jmethodID, ...);
jint (*CallStaticIntMethodV)(JNIEnv*, jclass, jmethodID, va_list);
jint (*CallStaticIntMethodA)(JNIEnv*, jclass, jmethodID, jvalue*);
jlong (*CallStaticLongMethod)(JNIEnv*, jclass, jmethodID, ...);
jlong (*CallStaticLongMethodV)(JNIEnv*, jclass, jmethodID, va_list);
jlong (*CallStaticLongMethodA)(JNIEnv*, jclass, jmethodID, jvalue*);
jfloat (*CallStaticFloatMethod)(JNIEnv*, jclass, jmethodID, ...) __NDK_FPABI__;
jfloat (*CallStaticFloatMethodV)(JNIEnv*, jclass, jmethodID, va_list) __NDK_FPABI__;
jfloat (*CallStaticFloatMethodA)(JNIEnv*, jclass, jmethodID, jvalue*) __NDK_FPABI__;
jdouble (*CallStaticDoubleMethod)(JNIEnv*, jclass, jmethodID, ...) __NDK_FPABI__;
jdouble (*CallStaticDoubleMethodV)(JNIEnv*, jclass, jmethodID, va_list) __NDK_FPABI__;
jdouble (*CallStaticDoubleMethodA)(JNIEnv*, jclass, jmethodID, jvalue*) __NDK_FPABI__;
void (*CallStaticVoidMethod)(JNIEnv*, jclass, jmethodID, ...);
void (*CallStaticVoidMethodV)(JNIEnv*, jclass, jmethodID, va_list);
void (*CallStaticVoidMethodA)(JNIEnv*, jclass, jmethodID, jvalue*);
//获取静态字段ID
jfieldID (*GetStaticFieldID)(JNIEnv*, jclass, const char*,
const char*);
//获取字段值
jobject (*GetStaticObjectField)(JNIEnv*, jclass, jfieldID);
jboolean (*GetStaticBooleanField)(JNIEnv*, jclass, jfieldID);
jbyte (*GetStaticByteField)(JNIEnv*, jclass, jfieldID);
jchar (*GetStaticCharField)(JNIEnv*, jclass, jfieldID);
jshort (*GetStaticShortField)(JNIEnv*, jclass, jfieldID);
jint (*GetStaticIntField)(JNIEnv*, jclass, jfieldID);
jlong (*GetStaticLongField)(JNIEnv*, jclass, jfieldID);
jfloat (*GetStaticFloatField)(JNIEnv*, jclass, jfieldID) __NDK_FPABI__;
jdouble (*GetStaticDoubleField)(JNIEnv*, jclass, jfieldID) __NDK_FPABI__;
//设置字段值
void (*SetStaticObjectField)(JNIEnv*, jclass, jfieldID, jobject);
void (*SetStaticBooleanField)(JNIEnv*, jclass, jfieldID, jboolean);
void (*SetStaticByteField)(JNIEnv*, jclass, jfieldID, jbyte);
void (*SetStaticCharField)(JNIEnv*, jclass, jfieldID, jchar);
void (*SetStaticShortField)(JNIEnv*, jclass, jfieldID, jshort);
void (*SetStaticIntField)(JNIEnv*, jclass, jfieldID, jint);
void (*SetStaticLongField)(JNIEnv*, jclass, jfieldID, jlong);
void (*SetStaticFloatField)(JNIEnv*, jclass, jfieldID, jfloat) __NDK_FPABI__;
void (*SetStaticDoubleField)(JNIEnv*, jclass, jfieldID, jdouble) __NDK_FPABI__;
//通过指定Unicode格式字符数组构造Java String
jstring (*NewString)(JNIEnv*, const jchar*, jsize);
//获取Unicode字符的长度
jsize (*GetStringLength)(JNIEnv*, jstring);
//获取字符数组
const jchar* (*GetStringChars)(JNIEnv*, jstring, jboolean*);
//通知VM可以释放String和由GetStringChars获取的字符数组
void (*ReleaseStringChars)(JNIEnv*, jstring, const jchar*);
//通过指定UTF-8格式字符数组构造Java String
jstring (*NewStringUTF)(JNIEnv*, const char*);
jsize (*GetStringUTFLength)(JNIEnv*, jstring);
/* JNI spec says this returns const jbyte*, but that's inconsistent */
const char* (*GetStringUTFChars)(JNIEnv*, jstring, jboolean*);
void (*ReleaseStringUTFChars)(JNIEnv*, jstring, const char*);
//获取数组长度
jsize (*GetArrayLength)(JNIEnv*, jarray);
//通过指定的Class类对象和初始元素初始化一个Java对象数组
jobjectArray (*NewObjectArray)(JNIEnv*, jsize, jclass, jobject);
//获取指定索引的对象元素
jobject (*GetObjectArrayElement)(JNIEnv*, jobjectArray, jsize);
//设置指定索引的对象元素
void (*SetObjectArrayElement)(JNIEnv*, jobjectArray, jsize, jobject);
//构造基本类型的Java数组
jbooleanArray (*NewBooleanArray)(JNIEnv*, jsize);
jbyteArray (*NewByteArray)(JNIEnv*, jsize);
jcharArray (*NewCharArray)(JNIEnv*, jsize);
jshortArray (*NewShortArray)(JNIEnv*, jsize);
jintArray (*NewIntArray)(JNIEnv*, jsize);
jlongArray (*NewLongArray)(JNIEnv*, jsize);
jfloatArray (*NewFloatArray)(JNIEnv*, jsize);
jdoubleArray (*NewDoubleArray)(JNIEnv*, jsize);
//获取基本类型元素的C数组
jboolean* (*GetBooleanArrayElements)(JNIEnv*, jbooleanArray, jboolean*);
jbyte* (*GetByteArrayElements)(JNIEnv*, jbyteArray, jboolean*);
jchar* (*GetCharArrayElements)(JNIEnv*, jcharArray, jboolean*);
jshort* (*GetShortArrayElements)(JNIEnv*, jshortArray, jboolean*);
jint* (*GetIntArrayElements)(JNIEnv*, jintArray, jboolean*);
jlong* (*GetLongArrayElements)(JNIEnv*, jlongArray, jboolean*);
jfloat* (*GetFloatArrayElements)(JNIEnv*, jfloatArray, jboolean*);
jdouble* (*GetDoubleArrayElements)(JNIEnv*, jdoubleArray, jboolean*);
//通知VM可以释放Java数组和由前述方法族获取的C数组
void (*ReleaseBooleanArrayElements)(JNIEnv*, jbooleanArray,
jboolean*, jint);
void (*ReleaseByteArrayElements)(JNIEnv*, jbyteArray,
jbyte*, jint);
void (*ReleaseCharArrayElements)(JNIEnv*, jcharArray,
jchar*, jint);
void (*ReleaseShortArrayElements)(JNIEnv*, jshortArray,
jshort*, jint);
void (*ReleaseIntArrayElements)(JNIEnv*, jintArray,
jint*, jint);
void (*ReleaseLongArrayElements)(JNIEnv*, jlongArray,
jlong*, jint);
void (*ReleaseFloatArrayElements)(JNIEnv*, jfloatArray,
jfloat*, jint);
void (*ReleaseDoubleArrayElements)(JNIEnv*, jdoubleArray,
jdouble*, jint);
//获取子数组
void (*GetBooleanArrayRegion)(JNIEnv*, jbooleanArray,
jsize, jsize, jboolean*);
void (*GetByteArrayRegion)(JNIEnv*, jbyteArray,
jsize, jsize, jbyte*);
void (*GetCharArrayRegion)(JNIEnv*, jcharArray,
jsize, jsize, jchar*);
void (*GetShortArrayRegion)(JNIEnv*, jshortArray,
jsize, jsize, jshort*);
void (*GetIntArrayRegion)(JNIEnv*, jintArray,
jsize, jsize, jint*);
void (*GetLongArrayRegion)(JNIEnv*, jlongArray,
jsize, jsize, jlong*);
void (*GetFloatArrayRegion)(JNIEnv*, jfloatArray,
jsize, jsize, jfloat*);
void (*GetDoubleArrayRegion)(JNIEnv*, jdoubleArray,
jsize, jsize, jdouble*);
/* spec shows these without const; some jni.h do, some don't */
//设置子数组
void (*SetBooleanArrayRegion)(JNIEnv*, jbooleanArray,
jsize, jsize, const jboolean*);
void (*SetByteArrayRegion)(JNIEnv*, jbyteArray,
jsize, jsize, const jbyte*);
void (*SetCharArrayRegion)(JNIEnv*, jcharArray,
jsize, jsize, const jchar*);
void (*SetShortArrayRegion)(JNIEnv*, jshortArray,
jsize, jsize, const jshort*);
void (*SetIntArrayRegion)(JNIEnv*, jintArray,
jsize, jsize, const jint*);
void (*SetLongArrayRegion)(JNIEnv*, jlongArray,
jsize, jsize, const jlong*);
void (*SetFloatArrayRegion)(JNIEnv*, jfloatArray,
jsize, jsize, const jfloat*);
void (*SetDoubleArrayRegion)(JNIEnv*, jdoubleArray,
jsize, jsize, const jdouble*);
//映射原生代码
jint (*RegisterNatives)(JNIEnv*, jclass, const JNINativeMethod*,
jint);
jint (*UnregisterNatives)(JNIEnv*, jclass);
jint (*MonitorEnter)(JNIEnv*, jobject);
jint (*MonitorExit)(JNIEnv*, jobject);
//获取当前线程关联的VM
jint (*GetJavaVM)(JNIEnv*, JavaVM**);
//获取子串
void (*GetStringRegion)(JNIEnv*, jstring, jsize, jsize, jchar*);
void (*GetStringUTFRegion)(JNIEnv*, jstring, jsize, jsize, char*);
void* (*GetPrimitiveArrayCritical)(JNIEnv*, jarray, jboolean*);
void (*ReleasePrimitiveArrayCritical)(JNIEnv*, jarray, void*, jint);
// Get/ReleaseStringCritical必须成对出现，语义和Get/ReleaseStringChars一样，但代码段中不能阻塞当前线程，也不能调用任何其他的JNI函数
const jchar* (*GetStringCritical)(JNIEnv*, jstring, jboolean*);
void (*ReleaseStringCritical)(JNIEnv*, jstring, const jchar*);
jweak (*NewWeakGlobalRef)(JNIEnv*, jobject);
void (*DeleteWeakGlobalRef)(JNIEnv*, jweak);
//判断是否有挂起的异常
jboolean (*ExceptionCheck)(JNIEnv*);
jobject (*NewDirectByteBuffer)(JNIEnv*, void*, jlong);
void* (*GetDirectBufferAddress)(JNIEnv*, jobject);
jlong (*GetDirectBufferCapacity)(JNIEnv*, jobject);
/* added in JNI 1.6 */
jobjectRefType (*GetObjectRefType)(JNIEnv*, jobject);
};
常用工具类
//将const char类型转换成jstring类型
jstring CStr2Jstring( JNIEnv* env, const char* pat )
{
// 定义java String类 strClass
jclass strClass = (env)->FindClass("Ljava/lang/String;");
// 获取java String类方法String(byte[],String)的构造器,用于将本地byte[]数组转换为一个新String
jmethodID ctorID = (env)->GetMethodID(strClass, "<init>", "([BLjava/lang/String;)V");
// 建立byte数组
jbyteArray bytes = (env)->NewByteArray((jsize)strlen(pat));
// 将char* 转换为byte数组
(env)->SetByteArrayRegion(bytes, 0, (jsize)strlen(pat), (jbyte*)pat);
//设置String, 保存语言类型,用于byte数组转换至String时的参数
jstring encoding = (env)->NewStringUTF("GB2312");
//将byte数组转换为java String,并输出
return (jstring)(env)->NewObject(strClass, ctorID, bytes, encoding);
}
char * Jstring2CStr( JNIEnv * env, jstring jstr )
{
char * rtn = NULL;
jclass clsstring = env->FindClass("java/lang/String");
jstring strencode = env->NewStringUTF("GB2312");
jmethodID mid = env->GetMethodID(clsstring, "getBytes", "(Ljava/lang/String;)[B");
jbyteArray barr= (jbyteArray)env->CallObjectMethod(jstr,mid,strencode);
jsize alen = env->GetArrayLength(barr);
jbyte * ba = env->GetByteArrayElements(barr,JNI_FALSE);
if(alen > 0)
{
rtn = (char*)malloc(alen+1); //new char[alen+1];
memcpy(rtn,ba,alen);
rtn[alen]=0;
}
env->ReleaseByteArrayElements(barr,ba,0);
return rtn;
}
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