如何确定一个类来自哪个JAR文件?

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我现在不是在IDE前面,只是看看API规范。

CodeSource src = MyClass.class.getProtectionDomain().getCodeSource();
if (src != null) {
    URL jar = src.getLocation();
}

我想确定一个类来自哪个JAR文件。这就是做这件事的方法吗?

提问于
用户回答回答于

是的。它适用于所有类,但由引导类加载器加载的类除外。另一种确定方法是:

Class klass = String.class;
URL location = klass.getResource('/' + klass.getName().replace('.', '/') + ".class");

getProtectionDomain().getCodeSource().getLocation()方法返回类文件本身的位置。例如:

jar:file:/jdk/jre/lib/rt.jar!/java/lang/String.class
file:/projects/classes/pkg/MyClass$1.class

klass.getResource()方法返回JAR文件或CLASSPATH的位置。

file:/Users/home/java/libs/ejb3-persistence-1.0.2.GA.jar
file:/projects/classes
用户回答回答于
/**
 * If the provided class has been loaded from a jar file that is on the local file system, will find the absolute path to that jar file.
 * 
 * @param context The jar file that contained the class file that represents this class will be found. Specify {@code null} to let {@code LiveInjector}
 *                find its own jar.
 * @throws IllegalStateException If the specified class was loaded from a directory or in some other way (such as via HTTP, from a database, or some
 *                               other custom classloading device).
 */
public static String findPathJar(Class<?> context) throws IllegalStateException {
    if (context == null) context = LiveInjector.class;
    String rawName = context.getName();
    String classFileName;
    /* rawName is something like package.name.ContainingClass$ClassName. We need to turn this into ContainingClass$ClassName.class. */ {
        int idx = rawName.lastIndexOf('.');
        classFileName = (idx == -1 ? rawName : rawName.substring(idx+1)) + ".class";
    }

    String uri = context.getResource(classFileName).toString();
    if (uri.startsWith("file:")) throw new IllegalStateException("This class has been loaded from a directory and not from a jar file.");
    if (!uri.startsWith("jar:file:")) {
        int idx = uri.indexOf(':');
        String protocol = idx == -1 ? "(unknown)" : uri.substring(0, idx);
        throw new IllegalStateException("This class has been loaded remotely via the " + protocol +
                " protocol. Only loading from a jar on the local file system is supported.");
    }

    int idx = uri.indexOf('!');
    //As far as I know, the if statement below can't ever trigger, so it's more of a sanity check thing.
    if (idx == -1) throw new IllegalStateException("You appear to have loaded this class from a local jar file, but I can't make sense of the URL!");

    try {
        String fileName = URLDecoder.decode(uri.substring("jar:file:".length(), idx), Charset.defaultCharset().name());
        return new File(fileName).getAbsolutePath();
    } catch (UnsupportedEncodingException e) {
        throw new InternalError("default charset doesn't exist. Your VM is borked.");
    }
}

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