How to Create Java class/es files dynamically?

Question

I need a way to run a java method for ex. createModule("Login") and as an output to have:

1. New folder named mod_login
2. Inside on mod_login java classes files created from a template

If the template is

class Name extends Blah implement Blah {

    private createdInt;

    private int getCreatedInt() {
        return createdInt;
    }

}

In return I want to get a dynamically created class:

 class Login extends Blah implement Blah {

    private loginInt;

    private int getLoginInt() {
        return loginInt;
    }
}

Tried to look into groovy to do it, but could not find anything usefull.

P.S. it shouldn't happen on runtime, it's a more like a helper to instantiate these modules with just 1 button, instead of typing them

Answer 1

Working example which will help you.

import java.io.File;
import java.io.FileWriter;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.Arrays;

import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.StandardLocation;
import javax.tools.ToolProvider;

public class HelloWorld {

public static void main(String[] args) throws Exception {

    // create an empty source file
    File sourceFile = File.createTempFile("Hello", ".java");
    sourceFile.deleteOnExit();

    // generate the source code, using the source filename as the class name
    String classname = sourceFile.getName().split("\\.")[0];
    String sourceCode = "public class " + classname + "{ public void hello() { System.out.print(\"Hello world\");}}";

    // write the source code into the source file
    FileWriter writer = new FileWriter(sourceFile);
    writer.write(sourceCode);
    writer.close();

    // compile the source file
    JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
    StandardJavaFileManager fileManager = compiler.getStandardFileManager(null, null, null);
    File parentDirectory = sourceFile.getParentFile();
    fileManager.setLocation(StandardLocation.CLASS_OUTPUT, Arrays.asList(parentDirectory));
    Iterable<? extends JavaFileObject> compilationUnits = fileManager.getJavaFileObjectsFromFiles(Arrays.asList(sourceFile));
    compiler.getTask(null, fileManager, null, null, null, compilationUnits).call();
    fileManager.close();

    // load the compiled class
    URLClassLoader classLoader = URLClassLoader.newInstance(new URL[] { parentDirectory.toURI().toURL() });
    Class<?> helloClass = classLoader.loadClass(classname);

    // call a method on the loaded class
    Method helloMethod = helloClass.getDeclaredMethod("hello");
    helloMethod.invoke(helloClass.newInstance());
 }
}