Simple HTTP server in Java using only Java SE API

Is there a way to create a very basic HTTP server (supporting only GET/POST) in Java using just the Java SE API, without writing code to manually parse HTTP requests and manually format HTTP responses? The Java SE API nicely encapsulates the HTTP client functionality in HttpURLConnection, but is there an analog for HTTP server functionality?

Just to be clear, the problem I have with a lot of ServerSocket examples I've seen online is that they do their own request parsing/response formatting and error handling, which is tedious, error-prone, and not likely to be comprehensive, and I'm trying to avoid it for those reasons.

Since Java SE 6, there's a builtin HTTP server in Sun Oracle JRE. The Java 9 module name is jdk.httpserver. The com.sun.net.httpserver package summary outlines the involved classes and contains examples.

Here's a kickoff example copypasted from their docs. You can just copy'n'paste'n'run it on Java 6+.
_{(to all people trying to edit it nonetheless, because it's an ugly piece of code, please don't, this is a copy paste, not mine, moreover you should never edit quotations unless they have changed in the original source)}

> package com.stackoverflow.q3732109; >
> import java.io.IOException; > import java.io.OutputStream; > import java.net.InetSocketAddress; >
> import com.sun.net.httpserver.HttpExchange; > import com.sun.net.httpserver.HttpHandler; > import com.sun.net.httpserver.HttpServer; >
> public class Test { >
> public static void main(String[] args) throws Exception { > HttpServer server = HttpServer.create(new InetSocketAddress(8000), 0); > server.createContext("/test", new MyHandler()); > server.setExecutor(null); // creates a default executor > server.start(); > } >
> static class MyHandler implements HttpHandler { > @Override > public void handle(HttpExchange t) throws IOException { > String response = "This is the response"; > t.sendResponseHeaders(200, response.length()); > OutputStream os = t.getResponseBody(); > os.write(response.getBytes()); > os.close(); > } > } > > }

Noted should be that the response.length() part in their example is bad, it should have been response.getBytes().length. Even then, the getBytes() method must explicitly specify the charset which you then specify in the response header. Alas, albeit misguiding to starters, it's after all just a basic kickoff example.

Execute it and go to http://localhost:8000/test and you'll see the following response:

> This is the response

---

As to using com.sun.* classes, do note that this is, in contrary to what some developers think, absolutely not forbidden by the well known FAQ Why Developers Should Not Write Programs That Call 'sun' Packages. That FAQ concerns the sun.* package (such as sun.misc.BASE64Encoder) for internal usage by the Oracle JRE (which would thus kill your application when you run it on a different JRE), not the com.sun.* package. Sun/Oracle also just develop software on top of the Java SE API themselves like as every other company such as Apache and so on. Moreover, this specific HttpServer must be present in every JDK so there is absolutely no means of "portability" issue like as would happen with sun.* package. Using com.sun.* classes is only discouraged (but not forbidden) when it concerns an implementation of a certain Java API, such as GlassFish (Java EE impl), Mojarra (JSF impl), Jersey (JAX-RS impl), etc.

Check out NanoHttpd

> NanoHTTPD is a light-weight HTTP server designed for embedding in other applications, released under a Modified BSD licence.

It is being developed at Github and uses Apache Maven for builds & unit testing"

The com.sun.net.httpserver solution is not portable across JREs. Its better to use the official webservices API in javax.xml.ws to bootstrap a minimal HTTP server...

import java.io._
import javax.xml.ws._
import javax.xml.ws.http._
import javax.xml.transform._
import javax.xml.transform.stream._

@WebServiceProvider
@ServiceMode(value=Service.Mode.PAYLOAD) 
class P extends Provider[Source] {
  def invoke(source: Source) = new StreamSource( new StringReader("<p>Hello There!</p>"));
}

val address = "http://127.0.0.1:8080/"
Endpoint.create(HTTPBinding.HTTP_BINDING, new P()).publish(address)

println("Service running at "+address)
println("Type [CTRL]+[C] to quit!")

Thread.sleep(Long.MaxValue)

EDIT: this actually works! The above code looks like Groovy or something. Here is a translation to Java which I tested:

import java.io.*;
import javax.xml.ws.*;
import javax.xml.ws.http.*;
import javax.xml.transform.*;
import javax.xml.transform.stream.*;

@WebServiceProvider
@ServiceMode(value = Service.Mode.PAYLOAD)
public class Server implements Provider<Source> {

	public Source invoke(Source request) {
		return  new StreamSource(new StringReader("<p>Hello There!</p>"));
	}

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

		String address = "http://127.0.0.1:8080/";
		Endpoint.create(HTTPBinding.HTTP_BINDING, new Server()).publish(address);

		System.out.println("Service running at " + address);
		System.out.println("Type [CTRL]+[C] to quit!");

		Thread.sleep(Long.MAX_VALUE);
	}
}

I like this question because this is an area where there's continuous innovation and there's always a need to have a light server especially when talking about embedded servers in small(er) devices. I think answers fall into two broad groups.

1. Thin-server: server-up static content with minimal processing, context or session processing.
2. Small-server: ostensibly a has many httpD-like server qualities with as small a footprint as you can get away with.

While I might consider HTTP libraries like: Jetty, Apache Http Components, Netty and others to be more like a raw HTTP processing facilities. The labelling is very subjective, and depends on the kinds of thing you've been call-on to deliver for small-sites. I make this distinction in the spirit of the question, particularly the remark about...

• "...without writing code to manually parse HTTP requests and manually format HTTP responses..."

These raw tools let you do that (as described in other answers). They don't really lend themselves to a ready-set-go style of making a light, embedded or mini-server. A mini-server is something that can give you similar functionality to a full-function web server (like say, Tomcat) without bells and whistles, low volume, good performance 99% of the time. A thin-server seems closer to the original phrasing just a bit more than raw perhaps with a limited subset functionality, enough to make you look good 90% of the time. My idea of raw would be makes me look good 75% - 89% of the time without extra design and coding. I think if/when you reach the level of WAR files, we've left the "small" for bonsi servers that looks like everything a big server does smaller.

Thin-server options

• Grizzly
• UniRest (multiple-languages)
• NanoHTTPD (just one file)

Mini-server options:

• Spark Java ... Good things are possible with lots of helper constructs like Filters, Templates, etc.
• MadVoc ... aims to be bonsai and could well be such ;-)

Among the other things to consider, I'd include authentication, validation, internationalisation, using something like FreeMaker or other template tool to render page output. Otherwise managing HTML editing and parameterisation is likely to make working with HTTP look like noughts-n-crosses. Naturally it all depends on how flexible you need to be. If it's a menu-driven FAX machine it can be very simple. The more interactions, the 'thicker' your framework needs to be. Good question, good luck!

Have a look at the "Jetty" web server Jetty. Superb piece of Open Source software that would seem to meet all your requirments.

If you insist on rolling your own then have a look at the "httpMessage" class.

Once upon a time I was looking for something similar - a lightweight yet fully functional HTTP server that I could easily embed and customize. I found two types of potential solutions:

• Full servers that are not all that lightweight or simple (for an extreme definition of lightweight.)
• Truly lightweight servers that aren't quite HTTP servers, but glorified ServerSocket examples that are not even remotely RFC-compliant and don't support commonly needed basic functionality.

So... I set out to write JLHTTP - The Java Lightweight HTTP Server.

You can embed it in any project as a single (if rather long) source file, or as a ~50K jar (~35K stripped) with no dependencies. It strives to be RFC-compliant and includes extensive documentation and many useful features while keeping bloat to a minimum.

Features include: virtual hosts, file serving from disk, mime type mappings via standard mime.types file, directory index generation, welcome files, support for all HTTP methods, conditional ETags and If-* header support, chunked transfer encoding, gzip/deflate compression, basic HTTPS (as provided by the JVM), partial content (download continuation), multipart/form-data handling for file uploads, multiple context handlers via API or annotations, parameter parsing (query string or x-www-form-urlencoded body), etc.

I hope others find it useful :-)

Spark is the simplest, here is a quick start guide: http://sparkjava.com/

It's possible to create an httpserver that provides basic support for J2EE servlets with just the JDK and the servlet api in a just a few lines of code.

I've found this very useful for unit testing servlets, as it starts much faster than other lightweight containers (we use jetty for production).

Most very lightweight httpservers do not provide support for servlets, but we need them, so I thought I'd share.

The below example provides basic servlet support, or throws and UnsupportedOperationException for stuff not yet implemented. It uses the com.sun.net.httpserver.HttpServer for basic http support.

import java.io.*;
import java.lang.reflect.*;
import java.net.InetSocketAddress;
import java.util.*;

import javax.servlet.*;
import javax.servlet.http.*;

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

@SuppressWarnings("deprecation")
public class VerySimpleServletHttpServer {
    HttpServer server;
    private String contextPath;
    private HttpHandler httpHandler;

    public VerySimpleServletHttpServer(String contextPath, HttpServlet servlet) {
        this.contextPath = contextPath;
        httpHandler = new HttpHandlerWithServletSupport(servlet);
    }

    public void start(int port) throws IOException {
        InetSocketAddress inetSocketAddress = new InetSocketAddress(port);
        server = HttpServer.create(inetSocketAddress, 0);
        server.createContext(contextPath, httpHandler);
        server.setExecutor(null);
        server.start();
    }

    public void stop(int secondsDelay) {
        server.stop(secondsDelay);
    }

    public int getServerPort() {
        return server.getAddress().getPort();
    }

}

final class HttpHandlerWithServletSupport implements HttpHandler {

    private HttpServlet servlet;

    private final class RequestWrapper extends HttpServletRequestWrapper {
        private final HttpExchange ex;
        private final Map<String, String[]> postData;
        private final ServletInputStream is;
        private final Map<String, Object> attributes = new HashMap<>();

        private RequestWrapper(HttpServletRequest request, HttpExchange ex, Map<String, String[]> postData, ServletInputStream is) {
            super(request);
            this.ex = ex;
            this.postData = postData;
            this.is = is;
        }

        @Override
        public String getHeader(String name) {
            return ex.getRequestHeaders().getFirst(name);
        }

        @Override
        public Enumeration<String> getHeaders(String name) {
            return new Vector<String>(ex.getRequestHeaders().get(name)).elements();
        }

        @Override
        public Enumeration<String> getHeaderNames() {
            return new Vector<String>(ex.getRequestHeaders().keySet()).elements();
        }

        @Override
        public Object getAttribute(String name) {
            return attributes.get(name);
        }

        @Override
        public void setAttribute(String name, Object o) {
            this.attributes.put(name, o);
        }

        @Override
        public Enumeration<String> getAttributeNames() {
            return new Vector<String>(attributes.keySet()).elements();
        }

        @Override
        public String getMethod() {
            return ex.getRequestMethod();
        }

        @Override
        public ServletInputStream getInputStream() throws IOException {
            return is;
        }

        @Override
        public BufferedReader getReader() throws IOException {
            return new BufferedReader(new InputStreamReader(getInputStream()));
        }

        @Override
        public String getPathInfo() {
            return ex.getRequestURI().getPath();
        }

        @Override
        public String getParameter(String name) {
            String[] arr = postData.get(name);
            return arr != null ? (arr.length > 1 ? Arrays.toString(arr) : arr[0]) : null;
        }

        @Override
        public Map<String, String[]> getParameterMap() {
            return postData;
        }

        @Override
        public Enumeration<String> getParameterNames() {
            return new Vector<String>(postData.keySet()).elements();
        }
    }

    private final class ResponseWrapper extends HttpServletResponseWrapper {
        final ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        final ServletOutputStream servletOutputStream = new ServletOutputStream() {

            @Override
            public void write(int b) throws IOException {
                outputStream.write(b);
            }
        };

        private final HttpExchange ex;
        private final PrintWriter printWriter;
        private int status = HttpServletResponse.SC_OK;

        private ResponseWrapper(HttpServletResponse response, HttpExchange ex) {
            super(response);
            this.ex = ex;
            printWriter = new PrintWriter(servletOutputStream);
        }

        @Override
        public void setContentType(String type) {
            ex.getResponseHeaders().add("Content-Type", type);
        }

        @Override
        public void setHeader(String name, String value) {
            ex.getResponseHeaders().add(name, value);
        }

        @Override
        public javax.servlet.ServletOutputStream getOutputStream() throws IOException {
            return servletOutputStream;
        }

        @Override
        public void setContentLength(int len) {
            ex.getResponseHeaders().add("Content-Length", len + "");
        }

        @Override
        public void setStatus(int status) {
            this.status = status;
        }

        @Override
        public void sendError(int sc, String msg) throws IOException {
            this.status = sc;
            if (msg != null) {
                printWriter.write(msg);
            }
        }

        @Override
        public void sendError(int sc) throws IOException {
            sendError(sc, null);
        }

        @Override
        public PrintWriter getWriter() throws IOException {
            return printWriter;
        }

        public void complete() throws IOException {
            try {
                printWriter.flush();
                ex.sendResponseHeaders(status, outputStream.size());
                if (outputStream.size() > 0) {
                    ex.getResponseBody().write(outputStream.toByteArray());
                }
                ex.getResponseBody().flush();
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                ex.close();
            }
        }
    }

    public HttpHandlerWithServletSupport(HttpServlet servlet) {
        this.servlet = servlet;
    }

    @SuppressWarnings("deprecation")
    @Override
    public void handle(final HttpExchange ex) throws IOException {
        byte[] inBytes = getBytes(ex.getRequestBody());
        ex.getRequestBody().close();
        final ByteArrayInputStream newInput = new ByteArrayInputStream(inBytes);
        final ServletInputStream is = new ServletInputStream() {

            @Override
            public int read() throws IOException {
                return newInput.read();
            }
        };

        Map<String, String[]> parsePostData = new HashMap<>();

        try {
            parsePostData.putAll(HttpUtils.parseQueryString(ex.getRequestURI().getQuery()));

            // check if any postdata to parse
            parsePostData.putAll(HttpUtils.parsePostData(inBytes.length, is));
        } catch (IllegalArgumentException e) {
            // no postData - just reset inputstream
            newInput.reset();
        }
        final Map<String, String[]> postData = parsePostData;

        RequestWrapper req = new RequestWrapper(createUnimplementAdapter(HttpServletRequest.class), ex, postData, is);

        ResponseWrapper resp = new ResponseWrapper(createUnimplementAdapter(HttpServletResponse.class), ex);

        try {
            servlet.service(req, resp);
            resp.complete();
        } catch (ServletException e) {
            throw new IOException(e);
        }
    }

    private static byte[] getBytes(InputStream in) throws IOException {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        while (true) {
            int r = in.read(buffer);
            if (r == -1)
                break;
            out.write(buffer, 0, r);
        }
        return out.toByteArray();
    }

    @SuppressWarnings("unchecked")
    private static <T> T createUnimplementAdapter(Class<T> httpServletApi) {
        class UnimplementedHandler implements InvocationHandler {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                throw new UnsupportedOperationException("Not implemented: " + method + ", args=" + Arrays.toString(args));
            }
        }

        return (T) Proxy.newProxyInstance(UnimplementedHandler.class.getClassLoader(),
                new Class<?>[] { httpServletApi },
                new UnimplementedHandler());
    }
}

All the above answers details about Single main threaded Request Handler.

setting:

 server.setExecutor(java.util.concurrent.Executors.newCachedThreadPool());

Allows multiple request serving via multiple threads using executor service.

So the end code will be something like below:

import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import com.sun.net.httpserver.HttpExchange;
import com.sun.net.httpserver.HttpHandler;
import com.sun.net.httpserver.HttpServer;
public class App {
    public static void main(String[] args) throws Exception {
        HttpServer server = HttpServer.create(new InetSocketAddress(8000), 0);
        server.createContext("/test", new MyHandler());
        //Thread control is given to executor service.
        server.setExecutor(java.util.concurrent.Executors.newCachedThreadPool());
        server.start();
    }
    static class MyHandler implements HttpHandler {
        @Override
        public void handle(HttpExchange t) throws IOException {
            String response = "This is the response";
            long threadId = Thread.currentThread().getId();
            System.out.println("I am thread " + threadId );
            response = response + "Thread Id = "+threadId;
            t.sendResponseHeaders(200, response.length());
            OutputStream os = t.getResponseBody();
            os.write(response.getBytes());
            os.close();
        }
    }
}

You may also have a look at some NIO application framework such as:

1. Netty: http://jboss.org/netty
2. Apache Mina: http://mina.apache.org/ or its subproject AsyncWeb: http://mina.apache.org/asyncweb/

I can strongly recommend looking into Simple, especially if you don't need Servlet capabilities but simply access to the request/reponse objects. If you need REST you can put Jersey on top of it, if you need to output HTML or similar there's Freemarker. I really love what you can do with this combination, and there is relatively little API to learn.

This code is better than ours, you only need to add 2 libs: javax.servelet.jar and org.mortbay.jetty.jar.

Class Jetty:

package jetty;

import java.util.logging.Level;
import java.util.logging.Logger;
import org.mortbay.http.SocketListener;
import org.mortbay.jetty.Server;
import org.mortbay.jetty.servlet.ServletHttpContext;

public class Jetty {

    public static void main(String[] args) {
        try {
            Server server = new Server();
            SocketListener listener = new SocketListener();      
            
            System.out.println("Max Thread :" + listener.getMaxThreads() + " Min Thread :" + listener.getMinThreads());
            
            listener.setHost("localhost");
            listener.setPort(8070);
            listener.setMinThreads(5);
            listener.setMaxThreads(250);
            server.addListener(listener);            

            ServletHttpContext context = (ServletHttpContext) server.getContext("/");
            context.addServlet("/MO", "jetty.HelloWorldServlet");
            
            server.start();
            server.join();
           
        /*//We will create our server running at http://localhost:8070
        Server server = new Server();
        server.addListener(":8070");

        //We will deploy our servlet to the server at the path '/'
        //it will be available at http://localhost:8070
        ServletHttpContext context = (ServletHttpContext) server.getContext("/");
        context.addServlet("/MO", "jetty.HelloWorldServlet");

        server.start();
        */
            
        } catch (Exception ex) {
            Logger.getLogger(Jetty.class.getName()).log(Level.SEVERE, null, ex);
        }
        
    }
} 

Servlet class:

package jetty;

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HelloWorldServlet extends HttpServlet
{
    @Override
    protected void doGet(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws ServletException, IOException
    {
        String appid = httpServletRequest.getParameter("appid");
        String conta = httpServletRequest.getParameter("conta");
        
        System.out.println("Appid : "+appid);
        System.out.println("Conta : "+conta);
        
        httpServletResponse.setContentType("text/plain");
        PrintWriter out = httpServletResponse.getWriter();
        out.println("Hello World!");
        out.close();
    }
}

checkout Simple. its a pretty simple embeddable server with built in support for quite a variety of operations. I particularly love its threading model..

Amazing!

Check out takes. Look at https://github.com/yegor256/takes for quick info

Try this https://github.com/devashish234073/Java-Socket-Http-Server/blob/master/README.md

This API has creates an HTTP server using sockets.

1. It gets a request from the browser as text
2. Parses it to retrieve URL info, method, attributes, etc.
3. Creates dynamic response using the URL mapping defined
4. Sends the response to the browser.

For example the here's how the constructor in the Response.java class converts a raw response into an http response:

public Response(String resp){
    Date date = new Date();
    String start = "HTTP/1.1 200 OK\r\n";
    String header = "Date: "+date.toString()+"\r\n";
    header+= "Content-Type: text/html\r\n";
    header+= "Content-length: "+resp.length()+"\r\n";
    header+="\r\n";
    this.resp=start+header+resp;
}

How about Apache Commons HttpCore project?

From the web site:... HttpCore Goals

• Implementation of the most fundamental HTTP transport aspects
• Balance between good performance and the clarity & expressiveness of API
• Small (predictable) memory footprint
• Self contained library (no external dependencies beyond JRE)

An example of a very basic HTTP server on TCP sockets level:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;

public class NaiveHttpServer {

  public static void main(String[] args) throws IOException {
    String hostname = InetAddress.getLocalHost().getHostName();
    ServerSocket serverSocket = new ServerSocket(8089);
    while (true) {
      Socket clientSocket = serverSocket.accept();
      PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
      BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
      String s = in.readLine();
      System.out.println(s);
      while ("\r\n".equals(in.readLine())); 
      if ("GET /hostname HTTP/1.1".equals(s)) {
        out.println("HTTP/1.1 200 OK");
        out.println("Connection: close");
        out.println("Content-Type: text/plain");
        out.println("Content-Length:" + hostname.length());
        out.println();
        out.println(hostname);
      } else {
        out.println("HTTP/1.1 404 Not Found");
        out.println("Connection: close");
        out.println();    
      }
      out.flush();
    }
  }
}

The example serves the hostname of the computer.

You can write a pretty simple embedded Jetty Java server.

Embedded Jetty means that the server (Jetty) shipped together with the application as opposed of deploying the application on external Jetty server.

So if in non-embedded approach your webapp built into WAR file which deployed to some external server (Tomcat / Jetty / etc), in embedded Jetty, you write the webapp and instantiate the jetty server in the same code base.

An example for embedded Jetty Java server you can git clone and use: https://github.com/stas-slu/embedded-jetty-java-server-example

The old com.sun.net.httpserver is again a public and accepted API, since Java 11. You can get it as HttpServer class, available as part of jdk.httpserver module. See https://docs.oracle.com/en/java/javase/11/docs/api/jdk.httpserver/com/sun/net/httpserver/HttpServer.html

> This class implements a simple HTTP server. A HttpServer is bound to an IP address and port number and listens for incoming TCP connections from clients on this address. The sub-class HttpsServer implements a server which handles HTTPS requests.

So, apart from its limitations, there is no reason to avoid its use anymore.

I use it to publish a control interface in server applications. Reading the User-agent header from a client request I even respond in text/plain to CLI tools like curl or in more elegant HTML way to any other browser.

Cool and easy.

Starting in Java 18, you can create simple web servers with the Java standard library:

class Main {
    public static void main(String[] args) {
        var port = 8000;
        var rootDirectory = Path.of("C:/Users/Mahozad/Desktop/");
        var outputLevel = OutputLevel.VERBOSE;
        var server = SimpleFileServer.createFileServer(
                new InetSocketAddress(port),
                rootDirectory,
                outputLevel
        );
        server.start();
    }
}

This will, by default, show a directory listing of the root directory you specified. You can place an index.html file (and other assets like CSS and JS files) in that directory to show them instead.

Example (I put these in Desktop which was specified as my directory root above):

index.html:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>Java 18 Simple Web Server</title>
  <link rel="stylesheet" href="styles.css">
  <script src="scripts.js" defer></script>
</head>
<body>
  <h1>I'm <i>index.html</i> in the root directory.</h1>
</body>
</html>

styles.css:

h1 { color: blue; }

scripts.js:

let element = document.getElementsByTagName("h1")[0];
element.style.fontSize = "48px";

Sidenote

For Java standard library HTTP client, see this post.