CODEWITHSUNDEEP
javaclassreflectionruntimepackage
Wicia
Wicia

Reputation: 565

How to get a package name of .class file?

I have an unusual problem which is concerned to dynamic loading java .class file at run-time. All I want to do is to load a .class file and basing on it create a Class object.

Input: an absolute path of .class file.

Basing on it i want to load class by ClassLoader, so I need a path of root directory where file is located and full class name e.g com.test.MyClass. Basing on mentioned absolute path I can only get a class name but I can't get a package name which is "hiden" in this file.

Here is code of my "loading class method": 

    public static void loadClass(String directory){

        // Get file root directory
        String rootDirectory = new File(directory).getParent();

        // Get rid of file extension
        String className = getFileNameWithoutExtension(directory);

        URL[] urls = null;
        ClassLoader cl = null;

        try {
            // Convert File to a URL and save them
            urls = new URL[]{new File(rootDirectory).toURI().toURL()};

            // Create a new class loader with the directory
            cl = new URLClassLoader(urls);

            // Load in the class
            dynamicClass = cl.loadClass(className);
        } 
        catch (MalformedURLException e) 
        {

    } 
    catch (ClassNotFoundException e) 
    {

    }
    catch (NoClassDefFoundError e)
    {
        // Basing on error message get the class package name
        String classPackage = getClassPackage(e.getMessage());

        try {             

           // Load the class once more!
           dynamicClass = cl.loadClass(classPackage);
        } 
        catch (ClassNotFoundException ex) 
        {

        }
    }
}

Second method is used to get package name from exception message:

private static String getClassPackage(String errorMsg){

    // Start and end index of cutting
    int startIndex = errorMsg.lastIndexOf(" ") + 1;
    int endIndex = errorMsg.length() - 1;

    // Let's save a substring
    String classPackage = errorMsg.substring(startIndex, endIndex);

    // Replace char '/' to '.'
    classPackage = classPackage.replace('/', '.');

    return classPackage;
}

Code of method getFileNameWithoutExtension:

private static String getFileNameWithoutExtension(String path){
    int start = path.lastIndexOf(File.separator) + 1;
    int end = path.lastIndexOf(DOT);
    end = start < end ? end : path.length();
    String name = path.substring(start, end);

    return name;
}

Where the static final variable is:

private static final String DOT = ".";

And here is my question: is it possible to get package name from .class file without using this kind of trick?

Upvotes: 1

Views: 17628

Answers (3)

William Reed
William Reed

Reputation: 1844

You can use the Foo.class.getPackage().getName() method to determine this. 

    public Package getPackage()

Returns:

the package of the class, or null if no package information is available from the archive or codebase.

Using getName() :

    public String getName()

Returns:

The fully-qualified name of this package as defined in section 6.5.3 of The Java™ Language Specification, for example, java.lang

Upvotes: 8

Akhilesh Dhar Dubey
Akhilesh Dhar Dubey

Reputation: 2148

You can do like this-

String packName = new Object(){}.getClass().getPackage().getName();        
System.out.println(packName);

Upvotes: 0

ADTC
ADTC

Reputation: 10121

Since you already have the required data in className, just use it again. You don't need the getClassPackage method.

    catch (NoClassDefFoundError e)
    {
        // Basing on error message get the class package name
        //But we already have the class name in className variable!
        //String classPackage = getClassPackage(e.getMessage());

        try {             

           // Load the class once more!
           dynamicClass = cl.loadClass(className);
        } 
        catch (ClassNotFoundException ex) 
        {

        }
    }

And if you want to get the package name only (not sure why), you can just get it from the class name:

String packageName = className.substring(0, className.lastIndexOf('.'));
dynamicClass = cl.loadClass(packageName);

Upvotes: 0

Related Questions