How to call main() method of a class using reflection in java

Question

When calling the main method of a Java class from another main method using reflection,

Class thisClass = loader.loadClass(packClassName);
Method thisMethod          


        

Answer 1

For your stated requirements (dynamically invoke the main method of a random class, with reflection you have alot of unnecessary code.

• You do not need to invoke a constructor for the class
• You do not need to introspect the classes fields
• Since you are invoking a static method, you do not even need a real object to invoke the method on

You can adapt the following code to meet your needs:

try {
    final Class<?> clazz = Class.forName("blue.RandomClass");
    final Method method = clazz.getMethod("main", String[].class);

    final Object[] args = new Object[1];
    args[0] = new String[] { "1", "2"};
    method.invoke(null, args);
} catch (final Exception e) {
    e.printStackTrace();
}

Answer 2

Perceptions answer looks correct; if you need load from a Jar not in the class path you can use a URL class loader

     try {
        URL[] urls;
        URLClassLoader urlLoader;

        urls = ...;

        urlLoader = new URLClassLoader(urls);

        @SuppressWarnings("rawtypes")
        Class runClass = urlLoader.loadClass(classToRun);

        Object[] arguments = new Object[]{args};
        Method mainMethod = runClass.getMethod("main", String[].class);
        mainMethod.invoke(null, arguments);
      } catch (Exception e) {
        e.printStackTrace();
      }