将字符串转换为JNA的指针 [英] Converting String to Pointer for JNA
问题描述
我正在尝试使用JNA来查询Windows中文件的有效权限。最后，我计划使用 GetEffectiveRightsFromAcl函数，但要这样做，我需要提供一个指向填充的 TRUSTEE结构。 JNA平台（platform.jar）似乎没有定义这个结构，所以我试图自己定义它。以下是我到目前为止：
I'm trying to use JNA to query the effective permissions for a file in Windows. Eventually, I plan on using the GetEffectiveRightsFromAcl function, but to do so, I need to provide a pointer to a populated TRUSTEE structure. The JNA Platform (platform.jar) doesn't appear define this struct, so I'm trying to define it myself instead. Here's what I have so far:
public static class TRUSTEE extends Structure {
public TRUSTEE() {
super();
}
public TRUSTEE(Pointer p) {
super(p);
read();
}
public Pointer pMultipleTrustee;
public int MultipleTrusteeOperation;
public int TrusteeForm;
public int TrusteeType;
public Pointer ptstrName;
}
我正在尝试填充这样的结构：
I'm trying to populate the structure like this:
private TRUSTEE createTrusteeForCurrentUser() {
TRUSTEE result = new TRUSTEE();
result.TrusteeForm = TRUSTEE_FORM.TRUSTEE_IS_NAME;
result.TrusteeType = TRUSTEE_TYPE.TRUSTEE_IS_USER;
String strName = "CURRENT_USER";
// How can I set result.ptstrName using strName?
}
此Google Groups主题建议在<$时使用结构中的 String 字段调用c $ c> char * 。但是，我不认为这在我的情况下是合适的，考虑到 ptstrName 字段可以指向不同类型的东西，具体取决于<$ c $的值C> TrusteeForm 。所以，我想我不知何故需要从 String 转换为指针。我在JNA中找到了 NativeString 类，除了可以工作，除了它是一个包私有类。
This Google Groups thread recommends using String fields in structures when a char * is called for. However, I don't think this is appropriate in my situation, considering the ptstrName field is allowed to point to different types of things, depending on the value of TrusteeForm. So, I think I somehow need to convert from String to Pointer instead. I found the NativeString class in JNA, which would work, except it's a package-private class.
将Java String 转换为本机格式的推荐方法是什么一个指针呢？我甚至使用 TRUSTEE 结构的正确数据类型？我对JNA有些新意，所以如果我遗漏了一些明显的东西，请原谅。
What's the recommended way to convert a Java String to a native format and obtain a Pointer to it? Am I even using the right data type for the TRUSTEE struct? I'm somewhat new to JNA, so please excuse me if I'm missing something obvious.
更新
我找到了解决问题的方法，但是如果有人有更好的解决方案，我仍然希望听到它。
I found a solution to my problem, but if anyone has a better solution I'd still like to hear it.
推荐答案
我通过复制package-private NativeString 类的源代码并在我的项目中创建公共副本来解决了这个问题。由于在构造函数中使用了package-private方法，我不得不进行一次小的更改。
I solved the problem by copying the source code for package-private NativeString class and creating a public copy in my project. I had to make one minor alteration due to the use of a package-private method in the constructor.
更新：正如@fragorl所说注释，下面显示的NativeString的实现到现在已经过时了。
Update: As @fragorl notes in the comments, the implementation of NativeString shown below is by now quite out-of-date.
用法：
private static TRUSTEE createTrusteeForCurrentUser() {
TRUSTEE result = new TRUSTEE();
result.TrusteeForm = TRUSTEE_FORM.TRUSTEE_IS_NAME;
result.TrusteeType = TRUSTEE_TYPE.TRUSTEE_IS_USER;
result.ptstrName = new NativeString("CURRENT_USER",true).getPointer();
result.write();
return result;
}
NativeString.java：
NativeString.java:
/** Provides a temporary allocation of an immutable C string
* (<code>const char*</code> or <code>const wchar_t*</code>) for use when
* converting a Java String into a native memory function argument.
*
* @author Todd Fast, todd.fast@sun.com
* @author twall@users.sf.net
*/
public class NativeString implements CharSequence, Comparable {
private Pointer pointer;
private boolean wide;
/** Create a native string (NUL-terminated array of <code>char</code>).<p>
* If the system property <code>jna.encoding</code> is set, its value will
* be used to encode the native string. If not set or if the encoding
* is unavailable, the default platform encoding will be used.
*/
public NativeString(String string) {
this(string, false);
}
/** Create a native string as a NUL-terminated array of <code>wchar_t</code>
* (if <code>wide</code> is true) or <code>char</code>.<p>
* If the system property <code>jna.encoding</code> is set, its value will
* be used to encode the native <code>char</code>string.
* If not set or if the encoding is unavailable, the default platform
* encoding will be used.
*
* @param string value to write to native memory
* @param wide whether to store the String as <code>wchar_t</code>
*/
public NativeString(String string, boolean wide) {
if (string == null) {
throw new NullPointerException("String must not be null");
}
// Allocate the memory to hold the string. Note, we have to
// make this 1 element longer in order to accommodate the terminating
// NUL (which is generated in Pointer.setString()).
this.wide = wide;
if (wide) {
int len = (string.length() + 1 ) * Native.WCHAR_SIZE;
pointer = new Memory(len);
pointer.setString(0, string, true);
}
else {
byte[] data = Native.toByteArray(string);
pointer = new Memory(data.length + 1);
pointer.write(0, data, 0, data.length);
pointer.setByte(data.length, (byte)0);
}
}
public int hashCode() {
return toString().hashCode();
}
public boolean equals(Object other) {
if (other instanceof CharSequence) {
return compareTo(other) == 0;
}
return false;
}
public String toString() {
String s = wide ? "const wchar_t*" : "const char*";
s += "(" + pointer.getString(0, wide) + ")";
return s;
}
public Pointer getPointer() {
return pointer;
}
public char charAt(int index) {
return toString().charAt(index);
}
public int length() {
return toString().length();
}
public CharSequence subSequence(int start, int end) {
return CharBuffer.wrap(toString()).subSequence(start, end);
}
public int compareTo(Object other) {
if (other == null)
return 1;
return toString().compareTo(other.toString());
}
}
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