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2.JNI.h解析

96
a_tomcat
2017.04.23 21:50* 字数 265

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;
}
Android JNI
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