分类： C/C++
2008-08-05 14:00:22
Java中文乱码问题在很多情况下都可能发生：不同应用间，不同平台间等等，但以上问题已有大量优秀的文章讨论过，这里不作深入探讨，详见参考2、3、4、5。下面简要总结一下：
public class Encoding {
public static void main(String[] args) {
System.out.println(System.getProperty("file.encoding"));
}
}
javac在不指定encoding参数时，如果区域设定不正确，则可能造成编/解码错误，这个问题在编译一个从别的环境传过来的文件时可能发生；
下面重点讨论JNI中在C 程序与Java程序间进行数据传递时需要注意的问题。
在JNI中jstring采用的是UCS-2编码，与Java中String的编码方式一致。但是在C 中，字符串是用char（8位）或者wchar_t（16位，Unicode编码与jchar一致，但并非所有开发平台上都是Unicode编码，详见参考6），下面的程序证明了这一点（编译环境：VC6）：
#includeJNI提供了几个方法来实现jstring与char/wchar_t之间的转换。using namespace std; int main() { locale loc( "Chinese-simplified" ); //locale loc( "chs" ); //locale loc( "ZHI" ); //locale loc( ".936" ); wcout.imbue( loc ); wcout << L"中文" << endl; //若没有L，会出问题 wchar_t wch[] = {0x4E2D, 0x6587, 0x0}; //"中文"二字的Unicode编码 wcout << wch << endl; return 0; }
jsize GetStringLength(jstring str) const jchar *GetStringChars(jstring str, jboolean *isCopy) void ReleaseStringChars(jstring str, const jchar *chars)此外，为了便于以UTF-8方式进行传输、存储，JNI还提供了几个操作UTF格式的方法：
jsize GetStringUTFLength(jstring str) const char* GetStringUTFChars(jstring str, jboolean *isCopy) void ReleaseStringUTFChars(jstring str, const char* chars)GetStringChars返回的是Unicode格式的编码串，而GetStringUTFChars返回的是UTF-8格式的编码串。 要创建一个jstring，可以用如下方式：
jstring NewJString( JNIEnv * env, LPCTSTR str )
{
if (!env || !str)
return 0;
int slen = strlen(str);
jchar * buffer = new jchar[slen];
int len = MultiByteToWideChar(CP_ACP, 0, str, strlen(str), buffer, slen);
if (len > 0 && len < slen)
buffer[len] = 0;
jstring js = env->NewString(buffer, len);
delete [] buffer;
return js;
}
而要将一个jstring对象转为一个char字符串数组，可以：
int JStringToChar( JNIEnv * env, jstring str, LPTSTR desc, int desc_len )
{
int len = 0;
if (desc == NULL || str == NULL)
return -1;
// Check buffer size
if (env->GetStringLength(str) * 2 1 > desc_len)
{
return -2;
}
memset(desc, 0, desc_len);
const wchar_t * w_buffer = env->GetStringChars(str, 0);
len = WideCharToMultiByte(CP_ACP, 0, w_buffer, wcslen(w_buffer) 1, desc, desc_len, NULL, NULL);
env->ReleaseStringChars(str, w_buffer);
if (len > 0 && len < desc_len)
desc[len] = 0;
return strlen(desc);
}
当然，按照上面的分析，你也可以直接将GetStringChars的返回结果作为wchar_t串来进行操作。或者，如果你愿意，你也可以将GetStringUTFChars的结果通过MultiByteToWideChar转换为UCS2编码串，再通过WideCharToMultiByte转换为多字节串。
const char* pstr = env->GetStringUTFChars(str, false); int nLen = MultiByteToWideChar( CP_UTF8, 0, pstr, -1, NULL, NULL );//得到UTF-8编码的字符串长度 LPWSTR lpwsz = new WCHAR[nLen]; MultiByteToWideChar( CP_UTF8, 0, pstr, -1, lpwsz, nLen );//转换的结果是UCS2格式的编码串 int nLen1 = WideCharToMultiByte( CP_ACP, 0, lpwsz, nLen, NULL, NULL, NULL, NULL ); LPSTR lpsz = new CHAR[nLen1]; WideCharToMultiByte( CP_ACP, 0, lpwsz, nLen, lpsz, nLen1, NULL, NULL );//将UCS2格式的编码串转换为多字节 cout << "Out:" << lpsz << endl; delete [] lpwsz; delete [] lpsz;当然，我相信很少有人想要或者需要这么做。 这里需要注意一点，GetStringChars的返回值是jchar，而GetStringUTFChars的返回值是const char*。 除了上面的办法外，当需要经常在jstring和char*之间进行转换时我们还有一个选择，那就是下面的这个类。这个类本来是一个叫Roger S. Reynolds的老外提供的，想法非常棒，但用起来却不太灵光，因为作者将考虑的重心放在UTF格式串上，但在实际操作中，我们往往使用的却是ACP（ANSI code page）串。下面是原作者的程序：
class UTFString {
private:
UTFString (); // Default ctor - disallowed
public:
// Create a new instance from the specified jstring
UTFString(JNIEnv* env, const jstring& str) :
mEnv (env),
mJstr (str),
mUtfChars ((char* )mEnv->GetStringUTFChars (mJstr, 0)),
mString (mUtfChars) { }
// Create a new instance from the specified string
UTFString(JNIEnv* env, const string& str) :
mEnv (env),
mString (str),
mJstr (env->NewStringUTF (str.c_str ())),
mUtfChars ((char* )mEnv->GetStringUTFChars (mJstr, 0)) { }
// Create a new instance as a copy of the specified UTFString
UTFString(const UTFString& rhs) :
mEnv (rhs.mEnv),
mJstr (mEnv->NewStringUTF (rhs.mUtfChars)),
mUtfChars ((char* )mEnv->GetStringUTFChars (mJstr, 0)),
mString (mUtfChars) { }
// Delete the instance and release allocated storage
~UTFString() { mEnv->ReleaseStringUTFChars (mJstr, mUtfChars); }
// assign a new value to this instance from the given string
UTFString & operator =(const string& rhs) {
mEnv->ReleaseStringUTFChars (mJstr, mUtfChars);
mJstr = mEnv->NewStringUTF (rhs.c_str ());
mUtfChars = (char* )mEnv->GetStringUTFChars (mJstr, 0);
mString = mUtfChars;
return *this;
}
// assign a new value to this instance from the given char*
UTFString & operator =(const char* ptr) {
mEnv->ReleaseStringUTFChars (mJstr, mUtfChars);
mJstr = mEnv->NewStringUTF (ptr);
mUtfChars = (char* )mEnv->GetStringUTFChars (mJstr, 0);
mString = mUtfChars;
return *this;
}
// Supply operator methods for converting the UTFString to a string
// or char*, making it easy to pass UTFString arguments to functions
// that require string or char* parameters.
string & GetString() { return mString; }
operator string() { return mString; }
operator const char* () { return mString.c_str (); }
operator jstring() { return mJstr; }
private:
JNIEnv* mEnv; // The enviroment pointer for this native method.
jstring mJstr; // A copy of the jstring object that this UTFString represents
char* mUtfChars; // Pointer to the data returned by GetStringUTFChars
string mString; // string buffer for holding the "value" of this instance
};
我将它改了改：
class JNIString {
private:
JNIString (); // Default ctor - disallowed
public:
// Create a new instance from the specified jstring
JNIString(JNIEnv* env, const jstring& str) :
mEnv (env) {
const jchar* w_buffer = env->GetStringChars (str, 0);
mJstr = env->NewString (w_buffer,
wcslen (w_buffer)); // Deep Copy, in usual case we only need
// Shallow Copy as we just need this class to
// provide some convenience for handling jstring
mChars = new char[wcslen (w_buffer) * 2 1];
WideCharToMultiByte (CP_ACP, 0, w_buffer, wcslen (w_buffer) 1, mChars, wcslen (w_buffer) * 2 1,
NULL, NULL);
env->ReleaseStringChars (str, w_buffer);
mString = mChars;
}
// Create a new instance from the specified string
JNIString(JNIEnv* env, const string& str) :
mEnv (env) {
int slen = str.length ();
jchar* buffer = new jchar[slen];
int len = MultiByteToWideChar (CP_ACP, 0, str.c_str (), str.length (), buffer, slen);
if (len > 0 && len < slen)
buffer[len] = 0;
mJstr = env->NewString (buffer, len);
delete [] buffer;
mChars = new char[str.length () 1];
strcpy (mChars, str.c_str ());
mString.empty ();
mString = str.c_str ();
}
// Create a new instance as a copy of the specified JNIString
JNIString(const JNIString& rhs) :
mEnv (rhs.mEnv) {
const jchar* wstr = mEnv->GetStringChars (rhs.mJstr, 0);
mJstr = mEnv->NewString (wstr, wcslen (wstr));
mEnv->ReleaseStringChars (rhs.mJstr, wstr);
mChars = new char[strlen (rhs.mChars) 1];
strcpy (mChars, rhs.mChars);
mString = rhs.mString.c_str ();
}
// Delete the instance and release allocated storage
~JNIString() { delete [] mChars; }
// assign a new value to this instance from the given string
JNIString & operator =(const string& rhs) {
delete [] mChars;
int slen = rhs.length ();
jchar* buffer = new jchar[slen];
int len = MultiByteToWideChar (CP_ACP, 0, rhs.c_str (), rhs.length (), buffer, slen);
if (len > 0 && len < slen)
buffer[len] = 0;
mJstr = mEnv->NewString (buffer, len);
delete [] buffer;
mChars = new char[rhs.length () 1];
strcpy (mChars, rhs.c_str ());
mString = rhs.c_str ();
return *this;
}
// Supply operator methods for converting the JNIString to a string
// or char*, making it easy to pass JNIString arguments to functions
// that require string or char* parameters.
string & GetString() { return mString; }
operator string() { return mString; }
operator const char* () { return mString.c_str (); }
operator jstring() { return mJstr; }
private:
JNIEnv* mEnv; // The enviroment pointer for this native method.
jstring mJstr; // A copy of the jstring object that this JNIString represents
char* mChars; // Pointer to a ANSI code page char array
string mString; // string buffer for holding the "value" of this instance (ANSI code page)
};
后者除了将面向UTF编码改成了面向ANSI编码外，还去掉了operator =(const char* ptr)的定义，因为 operator
=(const string& rhs)可以在需要的时候替代前者而无需任何额外编码。（因为按照C 规范，const
reference可以自动转换，详见本人另一文章“关于 const
reference 的几点说明”）