基于NDK下的编码转换，当然是直接调用C/C++下的实现效率更高，下面介绍2种方案（不建议通过JNI调用JAVA的实现，尽管这样也能实现编码的转换）。
1. 采用Android系统自带的libicuuc.so库
2. 采用第三方编码转换库libiconv，源码链接：http://ftp.gnu.org/pub/gnu/libiconv/
libiconv的使用有3个函数:
a) iconv_t iconv_open (const char* tocode, const char* fromcode);
b) size_t iconv (iconv_t cd, const char* * inbuf , size_t * inbytesleft, char* * outbuf , size_t * outbytesleft);
inbytesleft：inbuf的字符串长度；
outbytesleft：输入为outbuf所指向的缓冲区长度，输出为剩余没用到的缓冲区长度；因此转换后的字符串长度为(outbuflen - outbytesleft)；
inbuf, outbuf：返回时指针都后移了，需要注意。
c) int iconv_close (iconv_t cd);
这里采用Android系统自带的库进行编码转换，当然也可采用第三方支持。以下贴出代码段
（gbk和Unicode的互转因为没有用到，所以未贴出，但我想你应该要会了吧）：
#include "libcnv.h"
/* use dl API include file */
#include <dlfcn.h>
/* typedef a function pointer to pointer ucnv_convert method */
/*
see the source code define
int32_t ucnv_convert(const char *toConverterName, const char *fromConverterName,
char *target, int32_t targetSize,
const char *source, int32_t sourceSize,
int32_t * err)
*/
typedef int32_t (*TUCNVCONVERT)(const char *lpcOutEcd, const char *lpcInEcd,
char* lpOutBuf, int32_t nOutBufLen,
const char* lpcInStr, int32_t nInStrLen,
int32_t *pnErrCode);
/* pointer libicuuc.so dl lib */
static void* g_lpdlIcuuc = 0;
/* ucnv_convert method pointer */
static TUCNVCONVERT g_lpfnUcnvConvert = 0;
//在libicuuc.so中找到函数ucnv_convert
int dl_icuuc_init()
{
g_lpfnUcnvConvert = 0;
g_lpdlIcuuc = dlopen("/system/lib/libicuuc.so", RTLD_LAZY);
if (g_lpdlIcuuc != 0)
{
int i, j;
char szDLFnName[32]={0};
i = 3;
j = 8;
//android2.1, ucnv_convert_3_8
//android2.2, ucnv_convert_4_2
//android2.3, ucnv_convert_44
//android4.0, ucnv_convert_46
g_lpfnUcnvConvert = (TUCNVCONVERT)dlsym(g_lpdlIcuuc, "ucnv_convert_3_8");
while (0 == g_lpfnUcnvConvert)
{
memset(szDLFnName, 0, 32*sizeof(char));
sprintf(szDLFnName, "ucnv_convert_%d%d", i, j);
g_lpfnUcnvConvert = (TUCNVCONVERT)dlsym(g_lpdlIcuuc, szDLFnName);
if (g_lpfnUcnvConvert != 0){
return 1;
}
sprintf(szDLFnName, "ucnv_convert_%d_%d", i, j);
g_lpfnUcnvConvert = (TUCNVCONVERT)dlsym(g_lpdlIcuuc, szDLFnName);
if (g_lpfnUcnvConvert != 0){
return 1;
}
j++;
if (j > 9){
j = 1;
i++;
if (i > 5){
break;
}
}
}
}
return 0;
}
int dl_icuuc_uninit()
{
if (g_lpdlIcuuc != 0)
{
dlclose(g_lpdlIcuuc);
g_lpdlIcuuc = 0;
}
return 1;
}
//utf-8,gb2312,ucs4
//utf-8: 一个英文字母或者是数字占用一个字节，汉字占3个字节
//gb2312: 一个英文字母或者是数字占用一个字节，汉字占2个字节
int32_t dl_icuuc_gbk2utf8(char *outbuf, int32_t buflen, const char *instring, int32_t inlen)
{
int32_t iret;
iret = 0;
if (outbuf != 0 && instring != 0)
{
if (g_lpfnUcnvConvert != 0)
{
int32_t err_code = 0;
iret = g_lpfnUcnvConvert("utf-8", "gb2312"
,outbuf, buflen
,instring, inlen
,&err_code);
}
}
return iret;
}
int32_t dl_icuuc_utf82gbk(char *outbuf, int32_t buflen, const char *instring, int32_t inlen)
{
int32_t iret;
iret = 0;
if (outbuf != 0 && instring != 0)
{
if (g_lpfnUcnvConvert != 0)
{
int32_t err_code = 0;
iret = g_lpfnUcnvConvert("gb2312", "utf-8"
,outbuf, buflen
,instring, inlen
,&err_code);
}
}
return iret;
}
int32_t dl_icuuc_unicode2utf8(char *outbuf, int32_t buflen, const unsigned short *instring, int32_t inlen)
{
int32_t iret;
iret = 0;
if (outbuf != 0 && instring != 0)
{
if (g_lpfnUcnvConvert != 0)
{
int32_t err_code = 0;
iret = g_lpfnUcnvConvert("utf-8", "ucs4"
,outbuf, buflen
,(const char *)instring, inlen*sizeof(unsigned short)/sizeof(char)
,&err_code);
}
}
return iret;
}
int32_t dl_icuuc_utf82unicode(unsigned short *outbuf, int32_t buflen, const char *instring, int32_t inlen)
{
int32_t iret;
iret = 0;
if (outbuf != 0 && instring != 0)
{
if (g_lpfnUcnvConvert != 0)
{
int32_t err_code = 0;
iret = g_lpfnUcnvConvert("ucs4", "utf-8"
,(char *)outbuf, buflen*sizeof(unsigned short)/sizeof(char)
,instring, inlen
,&err_code);
}
}
return iret;
}