Determine Which Jar File a Class Is From

Determine which JAR file a class is from

Yes. It works for all classes except classes loaded by bootstrap classloader. The other way to determine is:

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

As notnoop pointed out klass.getResource() method returns the location of the class file itself. For example:

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

The getProtectionDomain().getCodeSource().getLocation() method returns the location of the jar file or CLASSPATH

file:/Users/home/java/libs/ejb3-persistence-1.0.2.GA.jar
file:/projects/classes

Java: How do I know which jar file to use given a class name?

You also have this eclipse plugin: jarclassfinder

The user enters the name of the class not found (or the name of the class that the Java project needs to access). The plug-in will search the selected directory (and subdirectories) for JAR files containing that class.

All results are displayed in a table in a custom view. The user can then browse this table and select the JAR file to add to his Java project's build path. The user then right-clicks on the entry in the table and, from the context menu, selects the build path to which to add it.

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Update 2013, as I mention in "searching through .jar files eclipse", it is no longer maintained, and the alternatives are sparse.

As sunleo comments below:

with Eclipse, Ctfl+Shift+T remains the easiest alternative to look for a type

(with the jar name displayed in the status bar).

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user862268 comments below:

For mac, it is cmd+shift+T in Eclipse to find the class and associated jar.

Find a class somewhere inside dozens of JAR files?

Eclipse can do it, just create a (temporary) project and put your libraries on the projects classpath. Then you can easily find the classes.

Another tool, that comes to my mind, is Java Decompiler. It can open a lot of jars at once and helps to find classes as well.

Determining which jar did the .class come from in Eclipse IDE

Activate "Link with editor" in the Package Explorer (the double arrow) and press F3. Eclipse expands the class in a library. (Make sure, that the editor, that shows Persistence.class has the focus).

For the next step, assuming you use m2eclipse, open the pom editor and look at the Dependency Hierarchy Tab. That gives a first hint where the dependency comes from. It may be transitive.

How to get names of classes inside a jar file?

Unfortunately, Java doesn't provide an easy way to list classes in the "native" JRE. That leaves you with a couple of options: (a) for any given JAR file, you can list the entries inside that JAR file, find the .class files, and then determine which Java class each .class file represents; or (b) you can use a library that does this for you.

Option (a): Scanning JAR files manually

In this option, we'll fill classNames with the list of all Java classes contained inside a jar file at /path/to/jar/file.jar.

List<String> classNames = new ArrayList<String>();
ZipInputStream zip = new ZipInputStream(new FileInputStream("/path/to/jar/file.jar"));
for (ZipEntry entry = zip.getNextEntry(); entry != null; entry = zip.getNextEntry()) {
    if (!entry.isDirectory() && entry.getName().endsWith(".class")) {
        // This ZipEntry represents a class. Now, what class does it represent?
        String className = entry.getName().replace('/', '.'); // including ".class"
        classNames.add(className.substring(0, className.length() - ".class".length()));
    }
}

Option (b): Using specialized reflections libraries

Guava

Guava has had ClassPath since at least 14.0, which I have used and liked. One nice thing about ClassPath is that it doesn't load the classes it finds, which is important when you're scanning for a large number of classes.

ClassPath cp=ClassPath.from(Thread.currentThread().getContextClassLoader());
for(ClassPath.ClassInfo info : cp.getTopLevelClassesRecurusive("my.package.name")) {
    // Do stuff with classes here...
}

Reflections

I haven't personally used the Reflections library, but it seems well-liked. Some great examples are provided on the website like this quick way to load all the classes in a package provided by any JAR file, which may also be useful for your application.

Reflections reflections = new Reflections("my.project.prefix");

Set<Class<? extends SomeType>> subTypes = reflections.getSubTypesOf(SomeType.class);

Set<Class<?>> annotated = reflections.getTypesAnnotatedWith(SomeAnnotation.class);

How to find Jar to which an Java class belongs

You could start by searching for the class on JarFinder.

http://www.findjar.com/

Not perfect as sometimes a class is in more than one JAR. But this may help narrow down the search.

If the link stops working, there are other similar services that can be found using you favourite search engine.

Java - How to find out which Jar file an import comes from?

You can use CodeSource#getLocation() for this. The CodeSource is available by ProtectionDomain#getCodeSource(). The ProtectionDomain in turn is available by Class#getProtectionDomain().

URL location = ObjectMakerFactory.class.getProtectionDomain().getCodeSource().getLocation();
System.out.println(location.getPath());
// ...

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