Allow using custom library builds

README.md

@@ -1,15 +1,13 @@
-Battery
-=======
+# Battery
 
 Java 8+ JNI wrapper to the [starship battery](https://crates.io/crates/starship-battery) crate.
 
-Usage
------
+## Usage
 
 The library can be installed from the `releases` repository on [maven.lostluma.net](https://maven.lostluma.net/#/releases/net/lostluma/battery) in two variants:
 
 - `default`: Downloads, validates, and caches the dynamic library on demand. Saves bandwidth and disk space.
-- `bundled`: Contains the dynamic library for all platforms. Recommended for situations in which first startup may be offline.
+- `bundled`: Contains the dynamic library for all platforms. Recommended if first application startup may be offline.
 
 The dynamic library is comes prebuilt for the following platforms:
 
@@ -19,7 +17,9 @@ The dynamic library is comes prebuilt for the following platforms:
 | MacOS   | yes     | yes   |         |
 | Windows | yes     | yes   |         |
 
-Misc
-----
+Running on other platforms is also possible, however some manual setup is required:  
+First build the project with Cargo, then set the `battery.natives.path` system property to the file path.
+
+## Misc
 
 This is my first time using both Rust and JNI :)

src/main/java/net/lostluma/battery/impl/Constants.java

@@ -11,6 +11,7 @@ public final class Constants {
     public static final String NATIVES_VERSION = "1.2.0";
 
     public static final Path DEFAULT_CACHE_DIR = getDefaultCacheDir();
+    public static final String NATIVES_PATH_PROPERTY = "battery.natives.path";
 
     private static String getUserHome() {
         return System.getProperty("user.home");

src/main/java/net/lostluma/battery/impl/util/NativeUtil.java

@@ -9,6 +9,7 @@
 import java.net.URL;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.Paths;
 import java.nio.file.StandardCopyOption;
 import java.util.Properties;
 
@@ -44,6 +45,23 @@ public static void setAllowDownloads(boolean value) {
     }
 
     private static void load0() throws IOException, LibraryLoadError{
+        Path path;
+        String custom = System.getProperty(Constants.NATIVES_PATH_PROPERTY);
+
+        if (custom == null) {
+            path = getPath();
+        } else {
+            path = Paths.get(custom);
+        }
+
+        try {
+            System.load(path.toAbsolutePath().toString());
+        } catch (UnsatisfiedLinkError e) {
+            throw new LibraryLoadError(e);
+        }
+    }
+
+    private static Path getPath() throws IOException, LibraryLoadError {
         Properties properties = new Properties();
 
         try (InputStream stream = NativeUtil.class.getResourceAsStream(METADATA)) {
@@ -84,11 +102,7 @@ private static void load0() throws IOException, LibraryLoadError{
             }
         }
 
-        try {
-            System.load(path.toAbsolutePath().toString());
-        } catch (UnsatisfiedLinkError e) {
-            throw new LibraryLoadError(e);
-        }
+        return path;
     }
 
     private static String getArch() {