A Simple Web Server in Java

Overview

This repo contains a simple web server I made with java from scratch without using any external libraries.

Note -: I developed this in linux OS, so it is recommended to run this in the linux OS also. But if you want to run this in windows, follow the step 1.1 in Guidelines section.

Prerequisites

1. The jar file is created with JDK 11. So to run it, make sure you have the same or higher version of jre installed. To check the java version, run the following command in command prompt/terminal.

   • java -version.

2. You should have php-cgi installed in your system. To check it, type the following command.

   • php-cgi -v

If you don't have any of the above, install them before running the program.

Guidelines

Do the following steps to run the program.

1. Clone this repository.

   1. Windows

      If you are in linux or macOS, skip to the step 2.
      1. In PhpInterpreter.java, in function createProcess(String command) change the line 126 as follows.

         env.put("SCRIPT_FILENAME", filename);

         env.put("SCRIPT_FILENAME", "./"+filename);

      2. Then open command prompt and go to the directory that contains htdocs, icons, src folders and execute the following commands.

         del Webserver.jar

         • The above command will delete the existing Webserver.jar file.

         javac -d bin src/*.java

         jar cvfm Webserver.jar src/META-INF/MANIFEST.MF -C bin/ .

         • The above 2 commands will re-create the Webserver.jar file with the updated files.

2. Run the jar file with the following command.

   java -jar Webserver.jar

   Make sure htdocs, icons and Webserver.jar are in the same folder.

3. The server is listening on the port 2728. So in the address-bar, enter the following url. localhost:2728
   You can change the port the server is listening by changing the port in the following line in Main.java

   int port = 2728;

4. You can edit the html, css, js, php files in the htdocs folder.

5. If you have any other html, css, js, php files, you should add them to the htdocs folder.

6. You can change the icon shown in the tab of your web browser by changing the icon in the icons folder.
   The icon with the name favicon.ico will be shown in the browser.

Source Code Review

• I have attached 2 HttpHandler objects to the server.

  server.createContext("/favicon.ico", new FaviconHandler()); // route all requests to resource /favicon.ico to FaviconHandler.
  server.createContext("/", new MainHttpHandler()); // all other requests are handled by the MainHttpHandler.

  • For each request to the resource favicon.ico, a new instance of FaviconHandler class will be created and the request will be handled by it.
  • For any other request to a source that starts from the root, MainHttpHandler class will handle it.

• To interpret the php files, I used the ProcessBuilder class in java.

  String command = "php-cgi"; // this is the command this function runs.
  ProcessBuilder processBuilder = new ProcessBuilder(command);    // create a builder that will build (start) the process.

  • This will make a system call to create a new process according to the given command. In this case it will create a new php-cgi process which is used to interpret php files.

• The user input data we get through the request, either through url query parameters or request body, should be passed to the php interpreter. This is done through the CGI protocol.

  • First we have to set some environmental variables of the created process according to the CGI protocol,

        Map<String, String> env = processBuilder.environment(); // gets a pointer to the environment attached to this process.
    
        // set the relevant environment fields to create the process.
        env.put("REQUEST_METHOD", method);
        env.put("GATEWAY_INTERFACE", "CGI/1.1");    // we are using cgi to interpret php files.
        env.put("REDIRECT_STATUS",  "true");
        env.put("SCRIPT_FILENAME", filename);
    
        if (this.method.equals("POST")) {
            env.put("CONTENT_LENGTH", this.contentLength);  // CONTENT_LENGTH, CONTENT_TYPE should be set only if the request is a POST request.
            env.put("CONTENT_TYPE", contentType);
        }
    
        else if (this.method.equals("GET")) {
            if (params!=null)
                env.put("QUERY_STRING", params);    // if it is a get request, we need to set QUERY_STRING env.
        }

  • After that we pass the data to the process through its input stream.

    BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(phpProcess.getOutputStream()));
        try {
            // if there is data,
            if (params!=null){
                writer.write(params);   // send them to the running process.
                writer.flush();
            }
            writer.close();
        } catch (IOException e) {
            System.out.println(e.getMessage());
        }

Important

Whenever you run the program, the executable file should be in the same folder as the htdocs and icons folders.