[ClassUtil.java] to get the location of a class. #JavaGuide

ClassUtil.java

import java.net.MalformedURLException;
import java.net.URL;

import lombok.extern.slf4j.Slf4j;

/**
 * 参考: https://github.com/scijava/scijava-common/blob/scijava-common-2.62.1/src/main/java/org/scijava/util/ClassUtils.java#L296-L355
 * @author Yang Guanrong
 * @date 2020/04/10 12:30
 */
@Slf4j
public class ClassUtil {

    /**
     * 获取类所在的jar的classes路径
     *
     * <p>
     * 如果类是在文件系统（如 /path/to/package/TheClass.class）则返回基本目录（如 file:/path/to）， 如果类是在JAR文件中（如
     * /path/to/the-jar.jar!/the/package/TheClass），则返回jar中路径（如 jar:file:/path/to/the-jar.jar!/BOOT-INF/classes!/），
     * 如果发生错误，则返回null
     * </p>
     */
    public static URL getLocation(Class<?> clazz) {
        if (clazz == null) {
            // could not load the class
            return null;
        }
        try {
            URL codeSourceLocation = clazz.getProtectionDomain().getCodeSource().getLocation();
            if (codeSourceLocation != null) {
                return codeSourceLocation;
            }
        } catch (Exception e) {
            // SecurityException: Cannot access protection domain.
            // NullPointerException: Protection domain or code source is null.
        }
        final URL classResource = clazz.getResource(clazz.getSimpleName() + ".class");
        if (classResource == null) {
            // cannot find class resource
            return null;
        }
        String url = classResource.toString();
        // java.io.File -> java/io/File.class
        String suffix = clazz.getCanonicalName().replace('.', '/') + ".class";
        if (!url.endsWith(suffix)) {
            if (isDebugEnable()) {
                log.debug("Weired URL: {} should end with {}", url, suffix);
            }
            // weired URL
            return null;
        }

        String classesUrl = url.substring(0, url.length() - suffix.length());
        try {
            return new URL(classesUrl);
        } catch (MalformedURLException e) {
            if (isDebugEnable()) {
                log.debug(e.getMessage(), e);
            }
            return null;
        }
    }

    public static URL getFileLocation(Class<?> clazz) {
	    URL url = getLocation(clazz);
	    if(url == null) {
			return url;
	    }
	    String path = url.toString();
	    if(path.startsWith("jar:")) {
		    // 移除 "jar:" prefix 和 "!/" 后缀
			path = path.substring(4, path.length() - 2);
	    }
	    try {
		    return new URL(path);
	    } catch (MalformedURLException e) {
		    if (isDebugEnable()) {
			    log.debug(e.getMessage(), e);
		    }
		    return null;
	    }
    }

    private static boolean isDebugEnable() {
        return log.isDebugEnabled();
    }
}