java:加载jar包中的动态库

た入场券 2022-03-17 11:01 421阅读 0赞

java中`System.load(String)方法`可以加载一个动态库，有时为了便于管理和发行，我们会把动态库打包jar包一起发行。这时如何加载jar包中的动态库呢?  
原理也很简单，就是先把动态库解压到系统临时文件夹，再调用`System.load(String)`方法加载动态库，github上这个项目[native-utils][]上提供了完整实现代码，我做了一些简化，实现如下：

package net.gdface.cassdk;
    
    import java.io.*;
    import java.nio.file.Files;
    import java.nio.file.StandardCopyOption;
    
    /**
     * A simple library class which helps with loading dynamic libraries stored in the
     * JAR archive. These libraries usually contain implementation of some methods in
     * native code (using JNI - Java Native Interface).
     * 
     * @see <a href="http://adamheinrich.com/blog/2012/how-to-load-native-jni-library-from-jar">http://adamheinrich.com/blog/2012/how-to-load-native-jni-library-from-jar</a>
     * @see <a href="https://github.com/adamheinrich/native-utils">https://github.com/adamheinrich/native-utils</a>
     *
     */
    public class NativeUtils {
        
     
        /**
         * The minimum length a prefix for a file has to have according to {@link File#createTempFile(String, String)}}.
         */
        private static final int MIN_PREFIX_LENGTH = 3;
        public static final String NATIVE_FOLDER_PATH_PREFIX = "nativeutils";
    
        /**
         * Temporary directory which will contain the DLLs.
         */
        private static File temporaryDir;
    
        /**
         * Private constructor - this class will never be instanced
         */
        private NativeUtils() {
        
        }
    
        /**
         * 从jar包中加载动态库
         * 先将jar包中的动态库复制到系统临时文件夹，然后加载动态库，并且在JVM退出时自动删除。
         * The file from JAR is copied into system temporary directory and then loaded. The temporary file is deleted after
         * exiting.
         * Method uses String as filename because the pathname is "abstract", not system-dependent.
         * 
         * @param path 要加载动态库的路径，必须以'/'开始,比如 /lib/mylib.so，必须以'/'开始
         * @param loadClass 用于提供{@link ClassLoader}加载动态库的类，如果为null,则使用NativeUtils.class
         * @throws IOException 动态库读写错误
         * @throws FileNotFoundException 没有在jar包中找到指定的文件
         */
        public static synchronized void loadLibraryFromJar(String path, Class<?> loadClass) throws IOException {
        
     
            if (null == path || !path.startsWith("/")) {
        
                throw new IllegalArgumentException("The path has to be absolute (start with '/').");
            }
     
            // Obtain filename from path
            String[] parts = path.split("/");
            String filename = (parts.length > 1) ? parts[parts.length - 1] : null;
     
            // Check if the filename is okay
            if (filename == null || filename.length() < MIN_PREFIX_LENGTH) {
        
                throw new IllegalArgumentException("The filename has to be at least 3 characters long.");
            }
     
            // 创建临时文件夹
            if (temporaryDir == null) {
        
                temporaryDir = createTempDirectory(NATIVE_FOLDER_PATH_PREFIX);
                temporaryDir.deleteOnExit();
            }
    		// 临时文件夹下的动态库名
            File temp = new File(temporaryDir, filename);
            Class<?> clazz = loadClass == null ? NativeUtils.class	: loadClass;
            // 从jar包中复制文件到系统临时文件夹
            try (InputStream is = clazz.getResourceAsStream(path)) {
        
                Files.copy(is, temp.toPath(), StandardCopyOption.REPLACE_EXISTING);
            } catch (IOException e) {
        
                temp.delete();
                throw e;
            } catch (NullPointerException e) {
        
                temp.delete();
                throw new FileNotFoundException("File " + path + " was not found inside JAR.");
            }
    		// 加载临时文件夹中的动态库
            try {
        
                System.load(temp.getAbsolutePath());
            } finally {
        
            	// 设置在JVM结束时删除临时文件
            	temp.deleteOnExit();
            }
        }
    	/**
    	 * 在系统临时文件夹下创建临时文件夹
    	 */
        private static File createTempDirectory(String prefix) throws IOException {
        
            String tempDir = System.getProperty("java.io.tmpdir");
            File generatedDir = new File(tempDir, prefix + System.nanoTime());
            
            if (!generatedDir.mkdir())
                throw new IOException("Failed to create temp directory " + generatedDir.getName());
            
            return generatedDir;
        }
    }

# 持续改进代码gitee仓库位置 #

[https://gitee.com/l0km/common-java/blob/master/common-base/src/main/java/net/gdface/utils/NativeUtils.java][https_gitee.com_l0km_common-java_blob_master_common-base_src_main_java_net_gdface_utils_NativeUtils.java]

[native-utils]: https://github.com/adamheinrich/native-utils
[https_gitee.com_l0km_common-java_blob_master_common-base_src_main_java_net_gdface_utils_NativeUtils.java]: https://gitee.com/l0km/common-java/blob/master/common-base/src/main/java/net/gdface/utils/NativeUtils.java