在 Java 中在运行时为本机库添加新路径
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Adding new paths for native libraries at runtime in Java
提问by Sergio
Is it possible to add a new path for native libraries at runtime ?.
(Instead of starting Java with the property java.library.path), so a call to System.loadLibrary(nativeLibraryName)will include that path when trying to find nativeLibraryName.
Is that possible or these paths are frozen once the JVM has started ?
是否可以在运行时为本机库添加新路径？。（而不是使用属性 java.library.path 启动 Java），因此System.loadLibrary(nativeLibraryName)在尝试 find 时调用将包含该路径nativeLibraryName。一旦 JVM 启动，这是可能的还是这些路径被冻结？
回答by ben75
[This solution don't work with Java 10+]
[此解决方案不适用于 Java 10+]
It seems impossible without little hacking (i.e. accessing private fields of the ClassLoader class)
如果没有一点点黑客攻击，这似乎是不可能的（即访问 ClassLoader 类的私有字段）
This blogprovide 2 ways of doing it.
这个博客提供了两种方法。
For the record, here is the short version.
为了记录，这里是简短的版本。
Option 1:fully replace java.library.path with the new value)
选项 1：用新值完全替换 java.library.path）
public static void setLibraryPath(String path) throws Exception {
System.setProperty("java.library.path", path);
//set sys_paths to null so that java.library.path will be reevalueted next time it is needed
final Field sysPathsField = ClassLoader.class.getDeclaredField("sys_paths");
sysPathsField.setAccessible(true);
sysPathsField.set(null, null);
}
Option 2:add a new path to the current java.library.path
选项 2：向当前 java.library.path 添加新路径
/**
* Adds the specified path to the java library path
*
* @param pathToAdd the path to add
* @throws Exception
*/
public static void addLibraryPath(String pathToAdd) throws Exception{
final Field usrPathsField = ClassLoader.class.getDeclaredField("usr_paths");
usrPathsField.setAccessible(true);
//get array of paths
final String[] paths = (String[])usrPathsField.get(null);
//check if the path to add is already present
for(String path : paths) {
if(path.equals(pathToAdd)) {
return;
}
}
//add the new path
final String[] newPaths = Arrays.copyOf(paths, paths.length + 1);
newPaths[newPaths.length-1] = pathToAdd;
usrPathsField.set(null, newPaths);
}
回答by Matthew Gerring
I used this in Java 12/13 which should work for any JVM with MethodHandles:
我在 Java 12/13 中使用了它，它应该适用于任何带有 MethodHandles 的 JVM：
Lookup cl = MethodHandles.privateLookupIn(ClassLoader.class, MethodHandles.lookup());
VarHandle sys_paths = cl.findStaticVarHandle(ClassLoader.class, "sys_paths", String[].class);
sys_paths.set(null);
It has the benefit of being a Java API.
它具有作为 Java API 的好处。
It is replaces the:
它取代了：
final Field sysPathsField = ClassLoader.class.getDeclaredField("sys_paths");
sysPathsField.setAccessible(true);
sysPathsField.set(null, null);
