Java 正确地从类路径中获取资源

App.class.getClassLoader().getResource("test/App.js");

App.class.getResource("App.js");

App.class.getResource("/test/App.js");

package test;

import java.net.URL;
import java.util.Enumeration;


public class ClassResourceTest {
    Class<ClassResourceTest> cls = ClassResourceTest.class;
    ClassLoader ldr = cls.getClassLoader(); // Thread.currentThread().getContextClassLoader()

    public static void println(Object s) {
        System.out.println(s);
    }

    void showResource(String name) {
        println("## Test resource for: “" + name + "” ##");
        println(String.fORMat("ClassLoader#getResource(\"%s\")=%s", name, ldr.getResource(name)));
        println(String.format("Class#getResource(\"%s\")=%s", name, cls.getResource(name)));
    }
    public final void testForResource() throws Exception {
        showResource("");
        showResource("/");
        showResource(cls.getSimpleName() + ".class");
        String n = cls.getName().replace('.', '/') + ".class";
        showResource(n);
        showResource("/" + n);
        showResource("java/lang/Object.class");
        showResource("/java/lang/Object.class");
    }

    public static void main(String[] args) throws Exception {
        println("java.class.path: " + System.getProperty("java.class.path"));
        println("user.dir: " + System.getProperty("user.dir"));
        println("");
        ClassResourceTest t = new ClassResourceTest();
        t.testForResource();
    }
}

java -classpath test.jar test.ClassResourceTest

import java.net.URL;
import java.util.Enumeration;
public class Test {
    public static void main(String[] args) throws Exception {
        ClassLoader ldr = Test.class.getClassLoader();
        System.out.println("## Test for getResources(‘META-INF/MANIFEST.MF') ##");
        Enumeration<URL> urls = ldr.getResources("META-INF/MANIFEST.MF");
        while(urls.hasMoreElements())
            System.out.println(urls.nextElement());
    }
}

package test;

import java.io.File;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.regex.Matcher;
import java.util.regex.Pattern;


public class AppDirTest {
	Classcls = AppDirTest.class;
	URL codeLocation = getCodeLocation();

	
	public URL getCodeLocation() {
		if (codeLocation != null)
			return codeLocation;
		// Get code location using the CodeSource
		codeLocation = cls.getProtectionDomain().getCodeSource().getLocation();
		if (codeLocation != null)
			return codeLocation;
		// If CodeSource didn't work, use {@link } Class.getResource instead.
		URL r = cls.getResource("");
		synchronized (r) {
			String s = r.toString();
			Pattern jar_re = Pattern.compile("jar:\\s?(.*)!/.*");
			Matcher m = jar_re.matcher(s);
			if (m.find()) { // the code is run from a jar file.
				s = m.group(1);
			} else {
				String p = cls.getPackage().getName().replace('.', '/');
				s = s.substring(0, s.lastIndexOf(p));
			}
			try {
				codeLocation = new URL(s);
			} catch (MalformedURLException e) {
				throw new RuntimeException(e);
			}
		}
		return codeLocation;
	}

	
	public String getAppDir() {
		File f = new File(getCodeLocation().getPath());
		return f.isFile() ? f.getParent() : f.getPath();
	}

	public static void main(String[] args) {
		AppDirTest t = new AppDirTest();
		System.out.println("code location: " + t.getCodeLocation());
		System.out.println("app dir: " + t.getAppDir());
	}

}