Simple jUnit Rule to create a HttpServer

_HowToUseTest.java

import static org.junit.Assert.assertEquals;

import org.junit.Rule;
import org.junit.Test;
import base.junitrules.HttpServerRule;
import base.junitrules.SuccessHandler;

public class _HowToUseTest {
	
	@Rule
	public HttpServerRule httpServer = new HttpServerRule();
	
	@Test
	public void shouldRespondASimpleHttpGet() {
	  
		String uri = "/triadworks/instructors/2020/description";
		httpServer.registerHandler(uri, new SuccessHandler("@rponte is cute body!"));
	  
		HttpClient httpClient = new HttpClient();
		String response = httpClient.doGet(completeUri(uri));
	  
		assertEquals("body content", "@rponte is cute body!", body);
	}
	
	public String completeUri(String uriPath) {
		return httpServer.getUriFor(uriPath);
	}
}

DownloadFileHttpHandler.java

package base.junitrules;

import java.io.File;
import java.io.IOException;

import org.apache.commons.io.FileUtils;

import java.net.HttpURLConnection;

import com.sun.net.httpserver.HttpExchange;
import com.sun.net.httpserver.HttpHandler;

public class DownloadFileHttpHandler implements HttpHandler {
	
	private final File file;
	private final String contentType = "application/zip";

	public DownloadFileHttpHandler(File fileToDownload) {
		this.file = fileToDownload;
	}

	@Override
	public void handle(HttpExchange exchange) throws IOException {
		exchange.getResponseHeaders().add("Content-Type", contentType);
		exchange.sendResponseHeaders(HttpURLConnection.HTTP_OK, file.length());
		FileUtils.copyFile(this.file, exchange.getResponseBody());
		exchange.close();
	}

}

HttpServerRule.java

package base.junitrules;

import java.net.InetSocketAddress;
import org.junit.rules.ExternalResource;
import com.sun.net.httpserver.HttpHandler;
import com.sun.net.httpserver.HttpServer;

/**
 * Simulates a HTTP Server
 */
public class HttpServerRule extends ExternalResource {
	
	private static final int PORT = 6991;
	
	private HttpServer server;

	@Override
	protected void before() throws Throwable {
		server = HttpServer.create(new InetSocketAddress(PORT), 0); // localhost:6991
		server.setExecutor(null); // creates a default executor
        	server.start();
	}
	
	@Override
	protected void after() {
		if (server != null) {
			server.stop(0); // doesn't wait all current exchange handlers complete
		}
	}
	
	public String getUriFor(String path) {
		if (!path.startsWith("/")) {
			path = "/" + path;
		}
		String host = "http://localhost:" + PORT;
		return host + path;
	}
	
	public void registerHandler(String uriToHandle, HttpHandler httpHandler) {
		server.createContext(uriToHandle, httpHandler);
	}
}

InternalServerErrorHandler.java

package base.http.handler;

import java.io.IOException;

import org.apache.commons.io.IOUtils;

import java.net.HttpURLConnection;

import com.sun.net.httpserver.HttpExchange;
import com.sun.net.httpserver.HttpHandler;

public class InternalServerErrorHandler implements HttpHandler {

	private String responseBody = "";
	private String contentType = "text/plain";
	
	public InternalServerErrorHandler() {}
	
	public InternalServerErrorHandler(String responseBody) {
		this.responseBody = responseBody;
	}

	@Override
	public void handle(HttpExchange exchange) throws IOException {
		exchange.getResponseHeaders().add("Content-Type", contentType);
		exchange.sendResponseHeaders(HttpURLConnection.HTTP_INTERNAL_ERROR, responseBody.length());
		IOUtils.write(responseBody, exchange.getResponseBody());
		exchange.close();
	}

}

SuccessHandler.java

package base.http.handler;

import java.io.IOException;

import org.apache.commons.io.IOUtils;

import java.net.HttpURLConnection;

import com.sun.net.httpserver.HttpExchange;
import com.sun.net.httpserver.HttpHandler;

public class SuccessHandler implements HttpHandler {

	private String responseBody = "";
	private String contentType = "text/plain";
	
	public SuccessHandler() {}
	
	public SuccessHandler(String responseBody) {
		this.responseBody = responseBody;
	}

	@Override
	public void handle(HttpExchange exchange) throws IOException {
		exchange.getResponseHeaders().add("Content-Type", contentType);
		exchange.sendResponseHeaders(HttpURLConnection.HTTP_OK, responseBody.length());
		IOUtils.write(responseBody, exchange.getResponseBody());
		exchange.close();
	}

}

Nice!

This is awesome!! thank you!
I have converted it to a junit5 extension here: https://gist.github.com/ahmed-musallam/f6238afb3895a23d03b5a09899392108