JNI高级教程之数据类型转换

作者：陈波 2011/10/30（转载请注明出处,From:http://blog.csdn.net/jinhill/article/details/6918821）

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

package com.jinhill.util;

public class NativeModule {

    public native int testArg(int i, boolean b, char c, double d);

    public native byte[] testByte(byte[] b);

    public native String[] testString(String s, String[] sarr);

    public native int setInfo(MyInfo info);

    public native MyInfo getInfo();

    static {

       System.loadLibrary("NativeModule");

    }

}

其中MyInfo类定义如下：

public class Record {

    int id;

    String name;

    byte[] data;

}

public class MyInfo {

    public boolean b;

    public char c;

    public double d;

    public int i;

    public byte[] array;

    public String s;

    public Record rec;

}

C自定义结构体

typedef struct{

    int id;

    char name[255];

    char data[255];

}Record;

typedef struct{

    BOOL b;

    char c;

    double d;

    int i;

    char arr[255];

    char sz[255];

    Record rec;

}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

//不同类型参数处理

JNIEXPORT jintJNICALL Java_com_jinhill_util_NativeModule_testArg

  (JNIEnv *env, jobject jo, jint ji, jbooleanjb,  jchar jc, jdouble jd)

{

         //获取jint型值

         int i = ji;

         //获取jboolean型值

         BOOL b = jb;

         //获取jdouble型值

         double d = jd;

         //获取jchar型值,Java的char两字节

         char ch[5] = {0};

         int size = 0;

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

         if(size <= 0)

         {

                   return -1;

        }

         Trace("ji=%d,jb=%d,jc=%s,jd=%lf",i, b, ch, d);

         return 0;

}

2)        Java byte与C char数组类型数组转换实例

//btye数组处理，形参作为输入或输出，返回btye数组

JNIEXPORTjbyteArray JNICALL Java_com_jinhill_util_NativeModule_testByte

  (JNIEnv *env, jobject jo, jbyteArray jbArr)

{

         char chTmp[] = "Hello JNI!";

         int nTmpLen = strlen(chTmp);

         //获取jbyteArray

         char *chArr = (char*)env->GetByteArrayElements(jbArr,0);

         //获取jbyteArray长度

         int nArrLen = env->GetArrayLength(jbArr);

         char *szStrBuf =(char*)malloc(nArrLen*2+10);

         memset(szStrBuf, 0, nArrLen*2+10);

         Bytes2String(chArr, nArrLen, szStrBuf,nArrLen*2+10);

         Trace("jbArr=%s", szStrBuf);

         //将jbArr作为输出形参

         memset(chArr, 0, nArrLen);

         memcpy(chArr, chTmp, nTmpLen);

         //返回jbyteArray

         jbyteArray jarrRV =env->NewByteArray(nTmpLen); 

    jbyte *jby =env->GetByteArrayElements(jarrRV, 0);

         memcpy(jby, chTmp, strlen(chTmp));

    env->SetByteArrayRegion(jarrRV, 0,nTmpLen, jby); 

         return jarrRV;

}

3)        Java String与C char数组类型转换实例

//String 和String[]处理

JNIEXPORTjobjectArray JNICALL Java_com_jinhill_util_NativeModule_testString

  (JNIEnv *env, jobject jo, jstring jstr,jobjectArray joarr)

{

         int i = 0;

         char chTmp[50] = {0};

         //获取jstring值

         const char* pszStr = (char*)env->GetStringUTFChars(jstr, 0);

         Trace("jstr=%s", pszStr);

         //获取jobjectArray值

         int nArrLen =env->GetArrayLength(joarr);

         Trace("joarr len=%d",nArrLen);

         for(i=0; i<nArrLen; i++)

         {

                   jstring js =(jstring)env->GetObjectArrayElement(joarr, i);

                   const char* psz = (char*)env->GetStringUTFChars(js, 0);

                   Trace("joarr[%d]=%s",i, psz);

         }

         //将joarr作为输出形参

         jstring jstrTmp = NULL;

         for(i=0; i<nArrLen; i++)

         {

                   sprintf(chTmp, "No.%dHello JNI!", i);

                   jstrTmp =env->NewStringUTF(chTmp);

                   env->SetObjectArrayElement(joarr,i, jstrTmp);

                   env->DeleteLocalRef(jstrTmp);

         }

         //返回jobjectArray

         jclass jstrCls =env->FindClass("Ljava/lang/String;");

         jobjectArray jstrArray =env->NewObjectArray(2, jstrCls, NULL);

         for(i=0; i<2; i++)

         {

                   sprintf(chTmp, "No. %dReturn JNI!", i);

                   jstrTmp =env->NewStringUTF(chTmp);

                   env->SetObjectArrayElement(jstrArray,i, jstrTmp);

                   env->DeleteLocalRef(jstrTmp);

         }

         return jstrArray;

}

4)        Java 类与C结构体类型转换实例

JNIEXPORT jint JNICALL Java_com_jinhill_util_NativeModule_setInfo

  (JNIEnv *env, jobject jo, jobject jobj)

{

    char chHexTmp[512] = {0};

    //将Java类转换成C结构体

    MyInfo mi;

    //获取Java中的实例类Record

    jclass jcRec = env->FindClass("com/jinhill/util/Record");

    //int id

    jfieldID jfid = env->GetFieldID(jcRec, "id", "I");

    //String name

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

    //byte[] data;

    jfieldID jfdata = env->GetFieldID(jcRec, "data", "[B");

    //获取Java中的实例类MyInfo

    jclass jcInfo = env->FindClass("com/jinhill/util/MyInfo");

    //获取类中每一个变量的定义

    //boolean b

    jfieldID jfb = env->GetFieldID(jcInfo, "b", "Z");

    //char c

    jfieldID jfc = env->GetFieldID(jcInfo, "c", "C");

    //double d

    jfieldID jfd = env->GetFieldID(jcInfo, "d", "D");

    //int i

    jfieldID jfi = env->GetFieldID(jcInfo, "i", "I");

    //byte[] array

    jfieldID jfa = env->GetFieldID(jcInfo, "array", "[B");

    //String s

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

    //Record rec;

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

    //获取实例的变量b的值

    mi.b = env->GetBooleanField(jobj, jfb);

    //获取实例的变量c的值

    jchar jc = env->GetCharField(jobj, jfc);

    char ch[5] = {0};

    int size = 0;

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

    mi.c = ch[0];

    //获取实例的变量d的值

    mi.d = env->GetDoubleField(jobj, jfd);

    //获取实例的变量i的值

    mi.i = env->GetIntField(jobj, jfi);

    //获取实例的变量array的值

    jbyteArray ja = (jbyteArray)env->GetObjectField(jobj, jfa);

    int  nArrLen = env->GetArrayLength(ja);

    char *chArr = (char*)env->GetByteArrayElements(ja, 0);

    memcpy(mi.arr, chArr, nArrLen);

    //获取实例的变量s的值

    jstring jstr = (jstring)env->GetObjectField(jobj, jfs);

    const char* pszStr = (char*)env->GetStringUTFChars(jstr, 0);

    strcpy(mi.sz, pszStr);

    //获取Record对象

    jobject joRec = env->GetObjectField(jobj, jfrec);

    //获取Record对象id值

    mi.rec.id = env->GetIntField(joRec, jfid);

    Trace("mi.rec.id=%d",mi.rec.id);

    //获取Record对象name值

    jstring jstrn = (jstring)env->GetObjectField(joRec, jfname);

    pszStr = (char*)env->GetStringUTFChars(jstrn, 0);

    strcpy(mi.rec.name, pszStr);

    //获取Record对象data值

    jbyteArray jbd = (jbyteArray)env->GetObjectField(joRec, jfdata);

    nArrLen = env->GetArrayLength(jbd);

    chArr = (char*)env->GetByteArrayElements(jbd, 0);

    memcpy(mi.rec.data, chArr, nArrLen);

    //日志输出

    Bytes2String(mi.arr, nArrLen, chHexTmp, sizeof(chHexTmp)); 

   Trace("mi.arr=%s, mi.b=%d, mi.c=%c, mi.d=%lf, mi.i=%d, \n mi.sz=%s\n 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);

     return 0;

}

5)        C结构体类型与Java 类转换实例

JNIEXPORT jobject JNICALL Java_com_jinhill_util_NativeModule_getInfo

  (JNIEnv *env, jobject jo)

{

    wchar_t wStr[255] = {0};

    char chTmp[] = "Hello JNI";

    int nTmpLen = strlen(chTmp);

    //将C结构体转换成Java类

    MyInfo mi;

    memcpy(mi.arr, chTmp, strlen(chTmp));

    mi.b = TRUE;

    mi.c = 'B';

    mi.d = 2000.9;

    mi.i = 8;

    strcpy(mi.sz, "Hello World!");

    mi.rec.id = 2011;

    memcpy(mi.rec.data, "\x01\x02\x03\x04\x05\x06", 6);

    strcpy(mi.rec.name, "My JNI");

    //获取Java中的实例类Record

    jclass jcRec = env->FindClass("com/jinhill/util/Record");

    //int id

    jfieldID jfid = env->GetFieldID(jcRec, "id", "I");

    //String name

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

    //byte[] data;

    jfieldID jfdata = env->GetFieldID(jcRec, "data", "[B");

    //获取Java中的实例类

    jclass jcInfo = env->FindClass("com/jinhill/util/MyInfo");

    //获取类中每一个变量的定义

    //boolean b

    jfieldID jfb = env->GetFieldID(jcInfo, "b", "Z");

    //char c

    jfieldID jfc = env->GetFieldID(jcInfo, "c", "C");

    //double d

    jfieldID jfd = env->GetFieldID(jcInfo, "d", "D");

    //int i

    jfieldID jfi = env->GetFieldID(jcInfo, "i", "I");

    //byte[] array

    jfieldID jfa = env->GetFieldID(jcInfo, "array", "[B");

    //String s

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

    //Record rec;

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

    //创建新的对象

    jobject joRec = env->AllocObject(jcRec);

    env->SetIntField(joRec, jfid, mi.rec.id);

    jstring jstrn = env->NewStringUTF(mi.rec.name);

    env->SetObjectField(joRec, jfname, jstrn);

    jbyteArray jbarr = env->NewByteArray(6); 

    jbyte *jb = env->GetByteArrayElements(jbarr, 0);

    memcpy(jb, mi.rec.data, 6);

    env->SetByteArrayRegion(jbarr, 0, 6, jb);

    env->SetObjectField(joRec, jfdata, jbarr);

    //创建新的对象

    jobject joInfo = env->AllocObject(jcInfo);

    //给类成员赋值

    env->SetBooleanField(joInfo, jfb, mi.b);

//  MultiByteToWideChar (CP_ACP, 0, mi.c, -1, wStr, 255);

//  env->SetCharField(joInfo, jfc, (jchar)wStr);

    env->SetCharField(joInfo, jfc, (jchar)mi.c);

   

    env->SetDoubleField(joInfo, jfd, mi.d);

    env->SetIntField(joInfo, jfi, mi.i);

    jbyteArray jarr = env->NewByteArray(nTmpLen); 

    jbyte *jby = env->GetByteArrayElements(jarr, 0);

    memcpy(jby, mi.arr, nTmpLen);

    env->SetByteArrayRegion(jarr, 0, nTmpLen, jby);

    env->SetObjectField(joInfo, jfa, jarr);

    jstring jstrTmp = env->NewStringUTF(chTmp);

    env->SetObjectField(joInfo, jfs, jstrTmp);

    env->SetObjectField(joInfo, jfrec, joRec);

    return joInfo;

}

4.        编写Java测试代码

public class TestInfo {

    /**

     * @param args

     */

    public static void main(String[] args) {

       int i  =0;

       String[] sArr = new String[2];

       for(i=0; i<2; i++)

       {

           sArr[i] = "ID=" + i;

       }

       byte[] b = new byte[10];

       for(i=0; i<10; i++)

       {

           b[i] = (byte)i;

       }

       MyInfo mi = new MyInfo();

       mi.array = b;

       mi.b = false;

       mi.c = 'C';

       mi.d = 2011.11;

       mi.i = 1752;

       mi.s = "Hello World!";

      

       mi.rec = new Record();

       mi.rec.id = 2012;

       mi.rec.name = "Record";

       mi.rec.data = b;

       NativeModule nm = new NativeModule();

       nm.testArg(mi.i, mi.b, mi.c, mi.d);

       byte[] b2 = nm.testByte(mi.array);

       String[] s = nm.testString(mi.s, sArr);

       nm.setInfo(mi);

       MyInfo mi2 = nm.getInfo();

       System.out.println("finish");

    }

}

5.   Java String与 C char数组转换时的中文问题

//将jstring类型转换成windows类型
char* jstringToWindows( JNIEnv *env, jstring jstr )
{
int length = (env)->GetStringLength(jstr );
const jchar* jcstr = (env)->GetStringChars(jstr, 0 );
char* rtn = (char*)malloc( length*2+1 );
int size = 0;
size = WideCharToMultiByte( CP_ACP, 0, (LPCWSTR)jcstr, length,rtn,(length*2+1), NULL, NULL );
if( size <= 0 )
return NULL;
(env)->ReleaseStringChars(jstr, jcstr );
rtn[size] = 0;
return rtn;
}

//将windows类型转换成jstring类型
jstring WindowsTojstring( JNIEnv* env, char* str )
{
jstring rtn = 0;
int slen = strlen(str);
unsigned short * buffer = 0;
if( slen == 0 )
rtn = (env)->NewStringUTF(str );
else
{
int length = MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, NULL, 0 );
buffer = (unsigned short *)malloc( length*2 + 1 );
if( MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, (LPWSTR)buffer, length )>0 )
rtn = (env)->NewString( (jchar*)buffer, length );
}
if( buffer )
free( buffer );
return rtn;
}