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

InetAddress loopback = InetAddress.getLoopbackAddress();

InetSocketAddress addr = new InetSocketAddress (loopback, 0);

var server1 = HttpServer.create(addr,100);

var proxy = HttpServer.create(addr,100);

proxy.createContext("/test",new ProxyHandler(new ProxyHandler.HostPort(server1.getAddress().getHostName(),server1.getAddress().getPort(),"http")));

server1.createContext("/test", (HttpExchange exchange) -> {

exchange.sendResponseHeaders(200,0);

if(exchange.getRequestMethod().equals("POST")) {

exchange.getRequestBody().transferTo(exchange.getResponseBody());

exchange.getResponseBody().close();

} else {

try (var os = exchange.getResponseBody()) {

os.write("hello".getBytes());

}

}

});

proxy.start();

server1.start();

try {

var client = HttpClient.newHttpClient();

var uri = URIBuilder.newBuilder().scheme("http").host(server1.getAddress().getHostName()).port(server1.getAddress().getPort()).path("/test").build();

var response = client.send(HttpRequest.newBuilder(uri).build(),HttpResponse.BodyHandlers.ofString());

if(!response.body().equals("hello")) throw new IllegalStateException("incorrect body "+response.body());

uri = URIBuilder.newBuilder().scheme("http").host(proxy.getAddress().getHostName()).port(proxy.getAddress().getPort()).path("/test").build();

response = client.send(HttpRequest.newBuilder(uri).build(),HttpResponse.BodyHandlers.ofString());

if(!response.body().equals("hello")) throw new IllegalStateException("incorrect body "+response.body());

response = client.send(HttpRequest.newBuilder(uri).POST(HttpRequest.BodyPublishers.ofString("senditback")).build(),HttpResponse.BodyHandlers.ofString());

if(!response.body().equals("senditback")) throw new IllegalStateException("incorrect body "+response.body());

} finally {

server1.stop(0);

proxy.stop(0);

}

}

}