Load Callable classes without reflection

readme.md

@@ -1,8 +1,15 @@
 # lestrange
 
-A playground for dark magic with Java class loaders. This is a work in progress. Currently uses reflection to invoke methods.
+A playground for dark magic with Java class loaders. This is a work in
+progress. There are two implmentations to call methods on dynamically
+loaded classes currently:
+- Using reflection to call a method by name on a class file  passed in
+  an multi-part HTTP POST request
+- Using the interface `Callable` and invoking the `call` method on the
+  object created from the class file passed
 
-This library is an attempt to understand how dynamic class loaders work and how in languages like Clojure, code is evaluated.
+This library is an attempt to understand how dynamic class loaders
+work and how in languages like Clojure, code is evaluated.
 
 ![Bellatrix](/utils/bella.png)
 
@@ -14,19 +21,33 @@ Start the server with:
 mvn clean install exec:java
 ```
 
-Send a class file to be executed:
+Send a class file to be executed via reflection:
 ```bash
 curl -XPOST "localhost:8080/loadclass/?classname=SystemInfo&methodname=info" -F "file=@SystemInfo.class"
 curl -XPOST "localhost:8080/loadclass/?classname=RandomNumber&methodname=sayHello" -F "file=@RandomNumber.class"
 ```
 
+To run the `call` method on a `Callable` class:
+```bash
+curl -XPOST "localhost:8080/callable/?classname=CallableAPI" -F "file=@CallableAPI.class"
+  _              _
+ | |            | |
+ | |     ___ ___| |_ _ __ __ _ _ __   __ _  ___
+ | |    / _ \ __| __| '__/ _` | '_ \ / _` |/ _ \
+ | |____  __\__ \ |_| | | (_| | | | | (_| |  __/
+ |______\___|___/\__|_|  \__,_|_| |_|\__, |\___|
+                                      __/ |
+                                     |___/
+```
+
 # Generating class files
 Ensure that clases are public and the method being accessed is public.
 ```bash
 cd utils
 javac RandomNumber.java
 javac HelloClass.java
 javac SystemInfo.java
+javac CallableAPI.java
 ```
 
 # Notes
@@ -55,6 +76,7 @@ while true;
       curl -XPOST "localhost:8080/loadclass/?classname=SystemInfo&methodname=info" -F "file=@SystemInfo.class";
       curl -XPOST "localhost:8080/loadclass/?classname=HelloClass&methodname=sayHello" -F "file=@HelloClass.class";
       curl -XPOST "localhost:8080/loadclass/?classname=RandomNumber&methodname=sayHello" -F "file=@RandomNumber.class";
+      curl -XPOST "localhost:8080/callable/?classname=CallableAPI" -F "file=@CallableAPI.class";
   done
 ```
 

src/main/java/lestrange/CallableLoader.java

@@ -0,0 +1,47 @@
+package lestrange;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.lang.reflect.Method;
+import java.util.concurrent.Callable;
+
+import javax.servlet.ServletException;
+import javax.servlet.annotation.MultipartConfig;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+import org.eclipse.jetty.http.HttpStatus;
+
+public class CallableLoader extends HttpServlet {
+
+	@Override
+	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+		resp.setStatus(HttpStatus.OK_200);
+		resp.getWriter().println("Use the POST method.");
+	}
+
+	@Override
+	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+		try {
+			String cl = req.getParameter("classname");
+
+			InputStream x = req.getPart("file").getInputStream();
+			SimpleClassLoader hc = new SimpleClassLoader(x);
+
+			@SuppressWarnings("unchecked")
+			Class<Callable<Object>> callable = (Class<Callable<Object>>) hc.loadClass(cl);
+
+			Object result = callable.newInstance().call();
+
+			resp.setStatus(HttpStatus.OK_200);
+			resp.getWriter().println(result == null ? "Result is a null" : result.toString());
+
+		} catch (Exception e) {
+			e.printStackTrace();
+			resp.setStatus(HttpStatus.INTERNAL_SERVER_ERROR_500);
+			resp.getWriter().println("That's too bad... " + e.getMessage());
+		}
+	}
+
+}

src/main/java/lestrange/Main.java

@@ -1,24 +1,29 @@
 package lestrange;
 
 import javax.servlet.MultipartConfigElement;
+import javax.servlet.annotation.MultipartConfig;
+
 import org.eclipse.jetty.server.Server;
 import org.eclipse.jetty.servlet.ServletContextHandler;
 import org.eclipse.jetty.util.thread.QueuedThreadPool;
 
 public class Main {
 	public static void main(String[] args) throws Exception {
 		Server server = new Server(8080);
-		
+
 		QueuedThreadPool tp = (QueuedThreadPool) server.getThreadPool();
 		tp.setLowThreadsThreshold(0);
 		tp.setReservedThreads(-1);
 		tp.setMinThreads(1);
 		tp.setMaxThreads(5);
 
-		ServletContextHandler handler = new ServletContextHandler(server, "/loadclass");
+		ServletContextHandler handler = new ServletContextHandler(server, "/");
+
+		MultipartConfigElement mpc = new MultipartConfigElement("");
+
+		handler.addServlet(ReflectiveLoader.class, "/loadclass/").getRegistration().setMultipartConfig(mpc);
 
-		handler.addServlet(LoaderServlet.class, "/").getRegistration()
-				.setMultipartConfig(new MultipartConfigElement(""));
+		handler.addServlet(CallableLoader.class, "/callable/").getRegistration().setMultipartConfig(mpc);
 
 		server.start();
 		server.join();

src/main/java/lestrange/LoaderServlet.java → src/main/java/lestrange/ReflectiveLoader.java

@@ -11,7 +11,7 @@
 
 import org.eclipse.jetty.http.HttpStatus;
 
-public class LoaderServlet extends HttpServlet {
+public class ReflectiveLoader extends HttpServlet {
 
 	@Override
 	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

utils/CallableAPI.java

@@ -0,0 +1,30 @@
+import java.io.BufferedReader;
+import java.io.DataOutputStream;
+import java.io.InputStreamReader;
+import java.net.HttpURLConnection;
+import java.net.URL;
+import java.util.concurrent.Callable;
+
+public class CallableAPI implements Callable<String> {
+
+	public String call() throws Exception {
+		URL url = new URL("http://artii.herokuapp.com/make?text=Lestrange");
+		HttpURLConnection con = (HttpURLConnection) url.openConnection();
+
+		con.setRequestMethod("GET");
+		con.setConnectTimeout(5000);
+		con.setReadTimeout(5000);
+		con.setDoOutput(true);
+
+		BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
+		String inputLine;
+		StringBuffer content = new StringBuffer();
+		while ((inputLine = in.readLine()) != null) {
+			content.append(inputLine+"\n");
+		}
+
+		in.close();
+		con.disconnect();
+		return content.toString();
+	}
+}