• JNI高级教程之数据类型转换


    最近做Android开发的人越来越多，Android开发难免会遇到调用本地库，这就需要采用JNI技术，JNI本身并不复杂，但大多数开发者在类型转换上遇到麻烦，今天特地将几种常用类型转换写成一个实例来告诉大家如何转换，尤其是Java的类和C的结构的转换，结构体中嵌套结构体如何处理，这部分网上的资料也比较少。

    1. 编写Java类

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    1. package com.jinhill.util;
    2. public class NativeModule
    3. {
    4.     public native int testArg(int i, boolean b, char c, double d);
    5.     public native byte[] testByte(byte[] b);
    6.     public native String[] testString(String s, String[] sarr);
    7.     public native int setInfo(MyInfo info);
    8.     public native MyInfo getInfo();

    10.     static
    11.     {
    12.         System.loadLibrary("NativeModule");
    13.     }
    14. }

    其中MyInfo类定义如下：

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    1. public class Record
    2. {
    3.     int id;
    4.     String name;
    5.     byte[] data;
    6. }

    8. public class MyInfo
    9. {
    10.     public boolean b;
    11.     public char c;
    12.     public double d;
    13.     public int i;
    14.     public byte[] array;
    15.     public String s;
    16.     public Record rec;
    17. }

    C自定义结构体 

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    1. typedef struct
    2. {
    3.     int id;
    4.     char name[255];
    5.     char data[255];
    6. } Record;

    8. typedef struct
    9. {
    10.     BOOL b;
    11.     char c;
    12.     double d;
    13.     int i;
    14.     char arr[255];
    15.     char sz[255];
    16.     Record rec;
    17. }MyInfo;

    2. 生成jni头文件

    1) 编译javac com/jinhill/util/NativeModule.java

    2) javah –jni com.jinhill.util.NativeModule

    这样com_jinhill_util_NativeModule.h文件就生成好了。

    3. 编写C库

    1) Java与C不同类型参数转换实例

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    1. //不同类型参数处理

    3. JNIEXPORT jintJNICALL Java_com_jinhill_util_NativeModule_testArg
    4. (JNIEnv *env, jobject jo, jint ji, jbooleanjb, jchar jc, jdouble jd)
    5. {
    6.     //获取jint型值
    7.     int i = ji;

    9.     //获取jboolean型值
    10.     BOOL b = jb;

    12.     //获取jdouble型值
    13.     double d = jd;

    15.     //获取jchar型值,Java的char两字节
    16.     char ch[5] = {0};

    18.     int size = 0;

    20.     size = WideCharToMultiByte(CP_ACP,NULL, (LPCWSTR)&jc, -1, ch, 5, NULL, FALSE);

    22.     if(size <= 0)
    23.     {
    24.         return -1;
    25.     }

    27.     Trace("ji=%d,jb=%d,jc=%s,jd=%lf",i, b, ch, d);
    28.     return 0;
    29. }

    2) Java byte与C char数组类型数组转换实例

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    1. //btye数组处理，形参作为输入或输出，返回btye数组

    3. JNIEXPORTjbyteArray JNICALL Java_com_jinhill_util_NativeModule_testByte
    4. (JNIEnv *env, jobject jo, jbyteArray jbArr)
    5. {
    6.     char chTmp[] = "Hello JNI!";
    7.     int nTmpLen = strlen(chTmp);

    9.     //获取jbyteArray
    10.     char *chArr = (char*)env->GetByteArrayElements(jbArr,0);

    12.     //获取jbyteArray长度
    13.     int nArrLen = env->GetArrayLength(jbArr);
    14.     char *szStrBuf =(char*)malloc(nArrLen*2+10);
    15.     memset(szStrBuf, 0, nArrLen*2+10);
    16.     Bytes2String(chArr, nArrLen, szStrBuf,nArrLen*2+10);
    17.     Trace("jbArr=%s", szStrBuf);
    18.     //将jbArr作为输出形参
    19.     memset(chArr, 0, nArrLen);
    20.     memcpy(chArr, chTmp, nTmpLen);

    22.     //返回jbyteArray
    23.     jbyteArray jarrRV =env->NewByteArray(nTmpLen);
    24.     jbyte *jby =env->GetByteArrayElements(jarrRV, 0);
    25.     memcpy(jby, chTmp, strlen(chTmp));
    26.     env->SetByteArrayRegion(jarrRV, 0,nTmpLen, jby);
    27.     return jarrRV;
    28. }
    3) Java String与C char数组类型转换实例

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    1. //String 和String[]处理
    2. JNIEXPORTjobjectArray JNICALL Java_com_jinhill_util_NativeModule_testString
    3. (JNIEnv *env, jobject jo, jstring jstr,jobjectArray joarr)
    4. {
    5.     int i = 0;
    6.     char chTmp[50] = {0};

    8.     //获取jstring值
    9.     const char* pszStr = (char*)env->GetStringUTFChars(jstr, 0);
    10.     Trace("jstr=%s", pszStr);

    12.     //获取jobjectArray值
    13.     int nArrLen =env->GetArrayLength(joarr);
    14.     Trace("joarr len=%d",nArrLen);
    15.     for(i=0; i<nArrLen; i++)
    16.     {
    17.         jstring js =(jstring)env->GetObjectArrayElement(joarr, i);
    18.         const char* psz = (char*)env->GetStringUTFChars(js, 0);
    19.         Trace("joarr[%d]=%s",i, psz);
    20.     }
    21.     
    22.     //将joarr作为输出形参
    23.     jstring jstrTmp = NULL;
    24.     for(i=0; i<nArrLen; i++)
    25.     {
    26.         sprintf(chTmp, "No.%dHello JNI!", i);
    27.         jstrTmp =env->NewStringUTF(chTmp);
    28.         env->SetObjectArrayElement(joarr,i, jstrTmp);
    29.         env->DeleteLocalRef(jstrTmp);
    30.     }

    32.     //返回jobjectArray
    33.     jclass jstrCls =env->FindClass("Ljava/lang/String;");
    34.     jobjectArray jstrArray =env->NewObjectArray(2, jstrCls, NULL);

    36.     for(i=0; i<2; i++)
    37.     {
    38.         sprintf(chTmp, "No. %dReturn JNI!", i);
    39.         jstrTmp =env->NewStringUTF(chTmp);
    40.         env->SetObjectArrayElement(jstrArray,i, jstrTmp);
    41.         env->DeleteLocalRef(jstrTmp);
    42.     }
    43.     return jstrArray;
    44. }

    4) Java 类与C结构体类型转换实例

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    1. JNIEXPORT jint JNICALL Java_com_jinhill_util_NativeModule_setInfo
    2. (JNIEnv *env, jobject jo, jobject jobj)
    3. {
    4.     char chHexTmp[512] = {0};
    5.     //将Java类转换成C结构体
    6.     MyInfo mi;

    8.     //获取Java中的实例类Record
    9.     jclass jcRec = env->FindClass("com/jinhill/util/Record");
    10.     //int id

    12.     jfieldID jfid = env->GetFieldID(jcRec, "id", "I");
    13.     //String name

    15.     jfieldID jfname = env->GetFieldID(jcRec, "name", "Ljava/lang/String;");
    16.     //byte[] data;

    18.     jfieldID jfdata = env->GetFieldID(jcRec, "data", "[B");
    19.     //获取Java中的实例类MyInfo

    21.     jclass jcInfo = env->FindClass("com/jinhill/util/MyInfo");
    22.     //获取类中每一个变量的定义

    24.     //boolean b
    25.     jfieldID jfb = env->GetFieldID(jcInfo, "b", "Z");

    27.     //char c
    28.     jfieldID jfc = env->GetFieldID(jcInfo, "c", "C");

    30.     //double d
    31.     jfieldID jfd = env->GetFieldID(jcInfo, "d", "D");

    33.     //int i
    34.     jfieldID jfi = env->GetFieldID(jcInfo, "i", "I");

    36.     //byte[] array
    37.     jfieldID jfa = env->GetFieldID(jcInfo, "array", "[B");

    39.     //String s
    40.     jfieldID jfs = env->GetFieldID(jcInfo, "s", "Ljava/lang/String;");

    42.     //Record rec;
    43.     jfieldID jfrec = env->GetFieldID(jcInfo, "rec", "Lcom/jinhill/util/Record;");
    44.     //获取实例的变量b的值
    45.     mi.b = env->GetBooleanField(jobj, jfb);
    46.     
    47.     //获取实例的变量c的值
    48.     jchar jc = env->GetCharField(jobj, jfc);
    49.     char ch[5] = {0};
    50.     int size = 0;
    51.     size = WideCharToMultiByte(CP_ACP, NULL, (LPCWSTR)&jc, -1, ch, 5, NULL, FALSE);
    52.     mi.c = ch[0];
    53.     
    54.     //获取实例的变量d的值
    55.     mi.d = env->GetDoubleField(jobj, jfd);
    56.     
    57.     //获取实例的变量i的值
    58.     mi.i = env->GetIntField(jobj, jfi);
    59.     
    60.     //获取实例的变量array的值
    61.     jbyteArray ja = (jbyteArray)env->GetObjectField(jobj, jfa);
    62.     int nArrLen = env->GetArrayLength(ja);
    63.     char *chArr = (char*)env->GetByteArrayElements(ja, 0);
    64.     memcpy(mi.arr, chArr, nArrLen);
    65.     
    66.     //获取实例的变量s的值
    67.     jstring jstr = (jstring)env->GetObjectField(jobj, jfs);
    68.     const char* pszStr = (char*)env->GetStringUTFChars(jstr, 0);
    69.     strcpy(mi.sz, pszStr);

    71.     //获取Record对象
    72.     jobject joRec = env->GetObjectField(jobj, jfrec);
    73.     
    74.     //获取Record对象id值
    75.     mi.rec.id = env->GetIntField(joRec, jfid);
    76.     Trace("mi.rec.id=%d",mi.rec.id);
    77.     
    78.     //获取Record对象name值
    79.     jstring jstrn = (jstring)env->GetObjectField(joRec, jfname);
    80.     pszStr = (char*)env->GetStringUTFChars(jstrn, 0);
    81.     strcpy(mi.rec.name, pszStr);
    82.     
    83.     //获取Record对象data值
    84.     jbyteArray jbd = (jbyteArray)env->GetObjectField(joRec, jfdata);
    85.     nArrLen = env->GetArrayLength(jbd);
    86.     chArr = (char*)env->GetByteArrayElements(jbd, 0);
    87.     memcpy(mi.rec.data, chArr, nArrLen);
    88.     
    89.     //日志输出
    90.     Bytes2String(mi.arr, nArrLen, chHexTmp, sizeof(chHexTmp));
    91.     Trace("mi.arr=%s, mi.b=%d, mi.c=%c, mi.d=%lf, mi.i=%d, mi.sz=%s mi.rec.id=%d, mi.rec.name=%s", chHexTmp, mi.b, mi.c, mi.d, mi.i, mi.sz, mi.rec.id, mi.rec.name);
    92.     return 0;
    93. }

    5) C结构体类型与Java 类转换实例

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    1. JNIEXPORT jobject JNICALL Java_com_jinhill_util_NativeModule_getInfo
    2.   (JNIEnv *env, jobject jo)
    3. {
    4.     wchar_t wStr[255] = {0};
    5.     char chTmp[] = "Hello JNI";
    6.     int nTmpLen = strlen(chTmp);
    7.     //将C结构体转换成Java类

    9.     MyInfo mi;
    10.     memcpy(mi.arr, chTmp, strlen(chTmp));
    11.     mi.b = TRUE;
    12.     mi.c = 'B';
    13.     mi.d = 2000.9;
    14.     mi.i = 8;
    15.     strcpy(mi.sz, "Hello World!");
    16.     mi.rec.id = 2011;
    17.     memcpy(mi.rec.data, "x01x02x03x04x05x06", 6);
    18.     strcpy(mi.rec.name, "My JNI");

    20.     //获取Java中的实例类Record
    21.     jclass jcRec = env->FindClass("com/jinhill/util/Record");

    23.     //int id
    24.     jfieldID jfid = env->GetFieldID(jcRec, "id", "I");

    26.     //String name
    27.     jfieldID jfname = env->GetFieldID(jcRec, "name", "Ljava/lang/String;");

    29.     //byte[] data;
    30.     jfieldID jfdata = env->GetFieldID(jcRec, "data", "[B");


    33.     //获取Java中的实例类
    34.     jclass jcInfo = env->FindClass("com/jinhill/util/MyInfo");

    36.     //获取类中每一个变量的定义
    37.     //boolean b
    38.     jfieldID jfb = env->GetFieldID(jcInfo, "b", "Z");

    40.     //char c
    41.     jfieldID jfc = env->GetFieldID(jcInfo, "c", "C");

    43.     //double d
    44.     jfieldID jfd = env->GetFieldID(jcInfo, "d", "D");

    46.     //int i
    47.     jfieldID jfi = env->GetFieldID(jcInfo, "i", "I");

    49.     //byte[] array
    50.     jfieldID jfa = env->GetFieldID(jcInfo, "array", "[B");

    52.     //String s
    53.     jfieldID jfs = env->GetFieldID(jcInfo, "s", "Ljava/lang/String;");

    55.     //Record rec;
    56.     jfieldID jfrec = env->GetFieldID(jcInfo, "rec", "Lcom/jinhill/util/Record;");

    58.     //创建新的对象
    59.     jobject joRec = env->AllocObject(jcRec);
    60.     env->SetIntField(joRec, jfid, mi.rec.id);
    61.     jstring jstrn = env->NewStringUTF(mi.rec.name);
    62.     env->SetObjectField(joRec, jfname, jstrn);
    63.     jbyteArray jbarr = env->NewByteArray(6);
    64.     jbyte *jb = env->GetByteArrayElements(jbarr, 0);
    65.     memcpy(jb, mi.rec.data, 6);
    66.     env->SetByteArrayRegion(jbarr, 0, 6, jb);
    67.     env->SetObjectField(joRec, jfdata, jbarr);
    68.     //创建新的对象
    69.     jobject joInfo = env->AllocObject(jcInfo);
    70.     //给类成员赋值
    71.     env->SetBooleanField(joInfo, jfb, mi.b);
    72.     // MultiByteToWideChar (CP_ACP, 0, mi.c, -1, wStr, 255);

    74.     // env->SetCharField(joInfo, jfc, (jchar)wStr);
    75.     env->SetCharField(joInfo, jfc, (jchar)mi.c);
    76.     env->SetDoubleField(joInfo, jfd, mi.d);
    77.     env->SetIntField(joInfo, jfi, mi.i);
    78.     jbyteArray jarr = env->NewByteArray(nTmpLen);
    79.     jbyte *jby = env->GetByteArrayElements(jarr, 0);
    80.     memcpy(jby, mi.arr, nTmpLen);
    81.     env->SetByteArrayRegion(jarr, 0, nTmpLen, jby);
    82.     env->SetObjectField(joInfo, jfa, jarr);
    83.     jstring jstrTmp = env->NewStringUTF(chTmp);
    84.     env->SetObjectField(joInfo, jfs, jstrTmp);
    85.     env->SetObjectField(joInfo, jfrec, joRec);
    86.     return joInfo;
    87. }
    4. 编写Java测试代码

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    1. public class TestInfo {

    3.     public static void main(String[] args)
    4.     {
    5.         int i =0;
    6.         String[] sArr = new String[2];
    7.         for(i=0; i<2; i++)
    8.         {
    9.             sArr[i] = "ID=" + i;
    10.         }

    12.         byte[] b = new byte[10];
    13.         for(i=0; i<10; i++)
    14.         {
    15.             b[i] = (byte)i;
    16.         }

    18.         MyInfo mi = new MyInfo();
    19.         mi.array = b;
    20.         mi.b = false;
    21.         mi.c = 'C';
    22.         mi.d = 2011.11;
    23.         mi.i = 1752;
    24.         mi.s = "Hello World!";
    25.         mi.rec = new Record();
    26.         mi.rec.id = 2012;
    27.         mi.rec.name = "Record";
    28.         mi.rec.data = b;
    29.         NativeModule nm = new NativeModule();
    30.         nm.testArg(mi.i, mi.b, mi.c, mi.d);
    31.         byte[] b2 = nm.testByte(mi.array);
    32.         String[] s = nm.testString(mi.s, sArr);
    33.         nm.setInfo(mi);
    34.         MyInfo mi2 = nm.getInfo();
    35.         System.out.println("finish");
    36.     }
    37. }
    5. Java String与 C char数组转换时的中文问题

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    1. //将jstring类型转换成windows类型
    2. char* jstringToWindows( JNIEnv *env, jstring jstr )
    3. {
    4.     int length = (env)->GetStringLength(jstr );
    5.     const jchar* jcstr = (env)->GetStringChars(jstr, 0 );
    6.     char* rtn = (char*)malloc( length*2+1 );
    7.     int size = 0;
    8.     size = WideCharToMultiByte( CP_ACP, 0, (LPCWSTR)jcstr, length,rtn,(length*2+1), NULL, NULL );
    9.     if( size <= 0 )
    10.         return NULL;
    11.     (env)->ReleaseStringChars(jstr, jcstr );
    12.     rtn[size] = 0;
    13.     return rtn;
    14. }

    16. //将windows类型转换成jstring类型
    17. jstring WindowsTojstring( JNIEnv* env, char* str )
    18. {
    19.     jstring rtn = 0;
    20.     int slen = strlen(str);
    21.     unsigned short * buffer = 0;
    22.     if( slen == 0 )
    23.         rtn = (env)->NewStringUTF(str );
    24.     else
    25.     {
    26.         int length = MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, NULL, 0 );
    27.         buffer = (unsigned short *)malloc( length*2 + 1 );
    28.         if( MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, (LPWSTR)buffer, length )>0 )
    29.         rtn = (env)->NewString( (jchar*)buffer, length );
    30.     }
    31.     if( buffer )
    32.         free( buffer );
    33.     return rtn;
    34. }

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  • 原文地址：https://www.cnblogs.com/black/p/5171788.html
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