[英]Java jbytearray access in c (JNI)
I have a set of java classes that I need at my job to be ran in C/C++. 我有一组在我的工作中需要在C / C ++中运行的java类。
And, since I am fairly new to java, I am taking it one step at a time. 而且,由于我对java很新,所以我一步一个脚印。 I've gotten to be able to call java with string, int double etc, but the end results will be getting a byte array back (a pdf document) so I tried sending back a simple two element byte array. 我已经能够用string,int double等调用java了,但是最终结果将得到一个字节数组(pdf文档)所以我试着发回一个简单的两个元素字节数组。
Here is the java: 这是java:
public class ReturnData
{
int returnValue;
String Log;
Byte[] data = new Byte[2];
public ReturnData(int nRetVal, String szLog)
{
this.data[0] = 100;
this.data[1] = 12;
this.returnValue = nRetVal;
this.Log = szLog;
}
}
and here is the c++ code (JNI initialization removed. It works for simple types so ...) 这里是c ++代码(删除了JNI初始化。它适用于简单类型,所以......)
jbyteArray jbyteData = (jbyteArray)jniEnvironment->GetObjectField(jobjRetData,
jniEnvironment->GetFieldID(clsReturn, "data", "Ljava/lang/ByteArray;"));
And now anytime I access the jbyteData element, such as: 现在我随时都可以访问jbyteData元素,例如:
jsize len = jniEnvironment->GetArrayLength(jbyteData);
I get an Exception 我得到一个例外
System.AccessViolationException was unhandled
Message: Attempted to read or write protected memory. This is often an indication that other
memory is corrupt.
Try to change the field Byte[] data = new Byte[2];
尝试更改字段Byte[] data = new Byte[2];
to byte[] data = new byte[2];
to byte[] data = new byte[2];
Then in your JNI method use GetFieldID(clsReturn, "data", "[B"));
然后在你的JNI方法中使用GetFieldID(clsReturn, "data", "[B"));
Edit: To be able to get the internal signature of each type ( [B
for byte[]
in your case) you can declare the field you want to a class (let's call it Test
), compile it and then run javap -s Test
. 编辑:为了能够获得每种类型的内部签名(在你的情况下[B
为byte[]
)你可以声明你想要一个类的字段(让我们称之为Test
),编译它然后运行javap -s Test
。 It produces an output like below: 它产生如下输出:
Compiled from "SimpleMain.java"
public class SimpleMain extends java.lang.Object{
public byte[] data;
Signature: [B // <-- signature shows the internal type
public SimpleMain();
Signature: ()V
public static void main(java.lang.String[]);
Signature: ([Ljava/lang/String;)V
}
For the FieldID, I think you want to use "[B"
instead of "Ljava/lang/ByteArray;"
对于FieldID,我认为你想使用"[B"
而不是"Ljava/lang/ByteArray;"
, which isn't actually a class. ,实际上不是一个班级。
Edit: since you're using the Byte
class, which I missed in my original response, use " [Ljava/lang/Byte;"
编辑:因为您正在使用我在原始响应中遗漏的Byte
类,请使用“ [Ljava/lang/Byte;"
instead 代替
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