Java — How to dynamically compile and load external java classes | Code Factory

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package com.example.java.programming;import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import javax.tools.Diagnostic;
import javax.tools.DiagnosticCollector;
import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
public class InlineCompiler { public static void main(String[] args) {
StringBuilder sb = new StringBuilder(64);
sb.append("package com.example.java.programming;\n");
sb.append("public class HelloWorld implements com.example.java.programming.InlineCompiler.DoStuff {\n");
sb.append(" public void doStuff() {\n");
sb.append(" System.out.println(\"Hello world\");\n");
sb.append(" }\n");
sb.append("}\n");
File helloWorldJava = new File("src/main/java/com/example/java/programming/HelloWorld.java");
if (helloWorldJava.getParentFile().exists() || helloWorldJava.getParentFile().mkdirs()) {
try {
Writer writer = null;
try {
writer = new FileWriter(helloWorldJava);
writer.write(sb.toString());
writer.flush();
} finally {
try {
writer.close();
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* Start - Compilation Requirements
**/
DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
StandardJavaFileManager fileManager = compiler.getStandardFileManager(diagnostics, null, null);
// This sets up the class path that the compiler will use.
// I've added the .jar file that contains the DoStuff interface within in it...
List<String> optionList = new ArrayList<String>();
optionList.add("-classpath");
optionList.add(System.getProperty("java.class.path") + File.pathSeparator + "dist/InlineCompiler.jar");

Iterable<? extends JavaFileObject> compilationUnit = fileManager.getJavaFileObjectsFromFiles(Arrays.asList(helloWorldJava));
JavaCompiler.CompilationTask task = compiler.getTask(null, fileManager, diagnostics, optionList, null, compilationUnit);
/**
* End - Compilation Requirements
**/

/*
* If you don't want to Execute/Run class file then return task.call()
* task.call() Returns : true if and only all the files compiled without errors;false otherwise
*/
if (task.call()) {
/**
* Start - Load and execute
**/
System.out.println("Yeah");
// Create a new custom class loader, pointing to the directory that contains the
// compiled classes, this should point to the top of the package structure!
URLClassLoader classLoader = new URLClassLoader(new URL[] { new File("./").toURI().toURL() });
// Load the class from the classloader by name....
Class<?> loadedClass = classLoader.loadClass("com.example.java.programming.HelloWorld");
// Create a new instance...
Object obj = loadedClass.newInstance();
// Santity check
if (obj instanceof DoStuff) {
// Cast to the DoStuff interface
DoStuff stuffToDo = (DoStuff) obj;
// Run it
stuffToDo.doStuff();
}
/**
* End - Load and execute
**/
} else {
for (Diagnostic<? extends JavaFileObject> diagnostic : diagnostics.getDiagnostics()) {
System.out.format("Error on line %d in %s%n", diagnostic.getLineNumber(), diagnostic.getSource().toUri());
}
}
fileManager.close();
} catch (IOException | ClassNotFoundException | InstantiationException | IllegalAccessException exp) {
exp.printStackTrace();
}
}
}
public static interface DoStuff {
public void doStuff();
}
}

Output :

Yeah
Hello world