Create new ClassLoader to reload Class

Question

I want to create a new ClassLoader everytime my method is called.

So I can reload a class without exiting my program.

A way how I can update a class loaded by ClassLoader would also be a solution.

How can I achieve that?

I load a JavaCompiler sourcecode compiled class with loadClass("string"), then I run this class with JUnitCore. After that I edit the source code in the *.java, compile it with the JavaCompiler and want to reload it again. — Arian, Mar 22 '12 at 09:32

score 11 · Accepted Answer · answered Mar 26 '12 at 09:37

I found a good explained answer here:

http://www.exampledepot.com/egs/java.lang/reloadclass.html

The important thing is to have two binary folders, in my case: one for the testcases and one for the program source.

Quote:

URL[] urls = null;
try {
    // Convert the file object to a URL
    File dir = new File(System.getProperty("user.dir")
        +File.separator+"dir"+File.separator);
    URL url = dir.toURL();        // file:/c:/almanac1.4/examples/
    urls = new URL[]{url};
} catch (MalformedURLException e) {
}

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

    // Load in the class
    Class cls = cl.loadClass("MyReloadableClassImpl");

Just to add - this solution works only if your reloaded class doesn't have any method deletion/new class reference. The problem with this approach is that if someone fogets to add dependent classes first, this might create NoClassDefFoundError. The best thing is to reload all classes without fully stoppping the application. — ha9u63a7, Jan 10 '18 at 10:18

score 6 · Answer 2 · answered Oct 26 '12 at 08:28

6

saw this ? ClassLoader Load / Reload Example

I think this blog can satisfy your requirement.

answered Oct 26 '12 at 08:28

liam xu

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Create new ClassLoader to reload Class

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