java NewString() 和 NewStringUTF() 显示错误无效修改 UTF-8：
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NewString() & NewStringUTF() showing error not valid Modified UTF-8:
提问by Sagar Ekbote
I am trying to pass char*from C++ to java using JNI in android.
I have tried number of ways to pass that data
我正在尝试char*在 android 中使用 JNI 从 C++传递到 java。我已经尝试了多种方法来传递该数据
1) Using NewStringUTF:
1）使用NewStringUTF：
const char* data = getData(); // this method returns a char array.
env->NewStringUTF(data);
Executing above code throws below error
执行上面的代码抛出以下错误
JNI WARNING: input is not valid Modified UTF-8: illegal continuation byte 0x70.
2) Using NewString:
2）使用NewString：
const char* data = getData(); // this method returns a char array.
// passing a byte array to java
jbyteArray trackIDArray = env->NewByteArray(strlen(data));
env->SetByteArrayRegion(trackIDArray, 0, strlen(data), (const jbyte*)trackID);
On java side, I am getting some garbage value. I don't understand how to get this chararray to Java.
在 Java 方面，我得到了一些垃圾值。我不明白如何将这个char数组传递给 Java。
回答by Pavel Zdenek
1) your datais simply not a valid UTF-8 string. Not every char array is automatically a valid UTF-8. You probably have it in some single-byte encoding (like ISO or Windows CP), or it's not a readable string at all.
1) 您data根本不是有效的 UTF-8 字符串。并非每个字符数组都是自动有效的 UTF-8。您可能在某种单字节编码（如 ISO 或 Windows CP）中使用它，或者它根本不是可读的字符串。
2) should be ok, but show the code which fills trackIDfrom data. The fact that you need to hard typecast it to jbyte*is suspicious. This code might be correct, but you can make a mistake on Java side too:
2) 应该没问题，但显示trackID从data. 您需要对其进行硬类型转换这一事实jbyte*令人怀疑。这段代码可能是正确的，但你也可能在 Java 方面犯错误：
If datais not a readable string or is in single-byte encoding which is not "platform's default charset"java.lang.String(byte[]) constructorwon't be able to make a readable string out of it! In that case, you must convert to UTF-8 on C side. You will also release yourself from the dependency on platform specific encoding (which may be wildly different).
如果data不是可读字符串或不是“平台的默认字符集”的单字节编码，则java.lang.String(byte[]) 构造函数将无法从中生成可读字符串！在这种情况下，您必须在 C 端转换为 UTF-8。您还将摆脱对平台特定编码的依赖（这可能会大不相同）。
回答by Joop Eggen
I would suspect datainstead of trackID.
我会怀疑data而不是trackID.
env->SetByteArrayRegion(trackIDArray, 0, strlen(data), (const jbyte*)data);
Then you have the bytes and on the java side may look what encoding it is - by a hex dump or other inspection.
然后你有字节，在 java 端可以看看它是什么编码 - 通过十六进制转储或其他检查。
Later:
之后：
String s = new String(data, "Cp1252"); // Or so.
回答by Sergey Dryganets
NewStringUTF expects you to pass a Modified UTF-8 string. You are likely trying to pass UTF-8.
NewStringUTF 期望您传递修改后的 UTF-8 字符串。您可能正在尝试通过 UTF-8。
There are multiple ways to fix it: Most obvious one is to encode the string to UTF-8 modified in C++ before passing it to Java.
有多种方法可以修复它：最明显的一种方法是将字符串编码为在 C++ 中修改的 UTF-8，然后再将其传递给 Java。
Another way is to pass it to Java as a byte array and use String constructor to convert it from UTF-16.
另一种方法是将其作为字节数组传递给 Java，并使用 String 构造函数将其从 UTF-16 转换。
The second way might be more efficient as in the end Java uses UTF-16 for string representation.
第二种方法可能更有效，因为最终 Java 使用 UTF-16 来表示字符串。
As an alternative approach, you could convert the string to UTF-16 in C++ and pass it to newString JNI function which expects UTF-16.
作为替代方法，您可以在 C++ 中将字符串转换为 UTF-16，并将其传递给需要 UTF-16 的 newString JNI 函数。
回答by Nikolai Ehrhardt
I put very big bytesources (>2kbyte) behind the JNI like this :
我将非常大的字节源（> 2kbyte）放在 JNI 后面，如下所示：
Content of a csv-table:
R"xxx(tbl_Cbla,Column 02,Column 03,Column 04 sdfsdsad,sdfasd,dsfaddf,fdsasdf,fafasa 18,1,10,8,0)xxx"`
csv表的内容：
R"xxx(tbl_Cbla,Column 02,Column 03,Column 04 sdfsdsad,sdfasd,dsfaddf,fdsasdf,fafasa 18,1,10,8,0)xxx"`
std::string data1 =
#include "big_table1.csv"
;
std::string data2 =
#include "big_table2.csv"
;
extern "C" JNIEXPORT jbyteArray JNICALL
Java_com_example_bigData_rawResource(
JNIEnv *env,
jobject /* this */, jint index) {
std::string values;
switch (index) {
case 0: {values = data1;break;}
case 1: {values = data2;break;}
}
int byteCount = values.length();
jbyteArray ret = env->NewByteArray(byteCount);
const jbyte* pNativeMessage = reinterpret_cast<const jbyte*>(values.c_str());
env->SetByteArrayRegion (ret, 0, byteCount, pNativeMessage);
return ret;
}
In Java you can get it back like this, to import the native function is up to you:
在 Java 中，您可以像这样取回它，导入本机函数取决于您：
ByteArrayInputStream bis = null;
try {
bis = new ByteArrayInputStream(rawResource(1);
} catch (Exception e) {
e.printStackTrace();
}
BufferedReader buffer = new BufferedReader(new InputStreamReader(bis, Charset.forName("UTF-8")));
To to handle the buffered reader is also up to you, small exg.:
处理缓冲阅读器也取决于你，小例子：
Strig line = buffer.readLine();
while ((line = buffer.readLine()) != null) {
//play around with 'line'
}
