Java100行弱で10分以内に読める！Tomcat無しでサーブレットを実行する最小コンテナを自作してみた第2回web.xml導入

前回まで

Javaによる簡易HTTPサーバの作り方
Java100行弱で10分以内に読める！Tomcat無しでサーブレットを実行する最小コンテナを自作してみた

今回の実装

web.xmlからパスとサーブレットのクラス名を取得するようにした。
一気にコンテナっぽくなった

MiniContainer.js

        //...略...
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse(new File("web.xml"));

        NodeList list = doc.getElementsByTagName("servlet");
        for (int i = 0; i < list.getLength(); i++) {
            Element el = (Element) list.item(i);
            String path = el.getAttribute("path");
            String clazz = el.getAttribute("class");
            addServletFromClass(path, clazz);
        }
        //...略...

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app>
    <servlet path="/hello" class="HelloServlet"/>
    <servlet path="/bye" class="ByeServlet"/>
</web-app>

動作

見た目は前回までと特に変わらない。

コンテナの実装

MiniContainer.js

import java.io.*;
import java.net.*;
import java.util.*;
import java.lang.reflect.*;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.w3c.dom.Element;

public class MiniContainer {
    private static final Map<String, MyServlet> routes = new HashMap<>();

    public static void main(String[] args) throws Exception {
    
        // ユーザが作ったServletクラスをロードして登録
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse(new File("web.xml"));

        NodeList list = doc.getElementsByTagName("servlet");
        for (int i = 0; i < list.getLength(); i++) {
            Element el = (Element) list.item(i);
            String path = el.getAttribute("path");
            String clazz = el.getAttribute("class");
            addServletFromClass(path, clazz);
        }
        //web.xml導入前
        //addServletFromClass("/hello", "HelloServlet");
        //addServletFromClass("/bye", "ByeServlet");

        ServerSocket server = new ServerSocket(8081);
        System.out.println("Running on http://localhost:8081/");

        while (true) {
            Socket client = server.accept();
            handleClient(client);
        }
    }

    // クラス名からユーザのサーブレットをロードして登録
    private static void addServletFromClass(String path, String className) throws Exception {
        Class<?> clazz = Class.forName(className); // クラスをロード
        MyServlet servlet = (MyServlet) clazz.getDeclaredConstructor().newInstance();
        routes.put(path, servlet);
    }

    private static void handleClient(Socket client) throws Exception {
        InputStream in = client.getInputStream();
        OutputStream out = client.getOutputStream();

        // ブラウザから送られてくるHTTPリクエスト1行目を読む
        char[] buf = new char[1024];
        int idx = 0;
        int c;
        while ((c = in.read()) != -1) {
            if (c == '\r') continue; // HTTPではCRLFなのでCRは無視
            if (c == '\n') break; // LFで1行終わり
    	    buf[idx++] = (char)c;
        }
        String requestLine = new String(buf, 0, idx);
        System.out.println("Request: " + requestLine);

        // 例 "GET /hello HTTP/1.1" → ["GET", "/hello", "HTTP/1.1"]
        // "/hello"だけ取り出す
        String path = "/";
        if (!requestLine.isEmpty()) {
            path = requestLine.split(" ")[1];
        }

        MyServlet servlet = routes.get(path);
        if (servlet != null) {
            servlet.service(in, out); // ユーザが作ったサーブレットを呼び出す
        } else {
            String body = "<h1>404 Not Found</h1>";
            String headers = "HTTP/1.1 404 Not Found\r\n" +
                             "Content-Length: " + body.getBytes("UTF-8").length + "\r\n" +
                             "Content-Type: text/html; charset=UTF-8\r\n\r\n";
            out.write(headers.getBytes("UTF-8"));
            out.write(body.getBytes("UTF-8"));
        }

        out.flush();
        client.close();
    }
}

MyServlet.java

import java.io.*;

public interface MyServlet {
    void service(InputStream in, OutputStream out) throws Exception;
}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app>
    <servlet path="/hello" class="HelloServlet"/>
    <servlet path="/bye" class="ByeServlet"/>
</web-app>

サーブレット

HelloServlet.java

import java.io.*;

public class HelloServlet implements MyServlet {
    @Override
    public void service(InputStream in, OutputStream out) throws Exception {
        String body = "<html><body><h1>Hello from HelloServlet!</h1></body></html>";
        String headers = "HTTP/1.1 200 OK\r\n" +
                         "Content-Length: " + body.getBytes("UTF-8").length + "\r\n" +
                         "Content-Type: text/html; charset=UTF-8\r\n\r\n";
        out.write(headers.getBytes("UTF-8"));
        out.write(body.getBytes("UTF-8"));
    }
}

ByeServlet.java

import java.io.*;

public class ByeServlet implements MyServlet {
    @Override
    public void service(InputStream in, OutputStream out) throws Exception {
        String body = "<html><body><h1>Goodbye!</h1></body></html>";
        String headers = "HTTP/1.1 200 OK\r\n" +
                         "Content-Length: " + body.getBytes("UTF-8").length + "\r\n" +
                         "Content-Type: text/html; charset=UTF-8\r\n\r\n";
        out.write(headers.getBytes("UTF-8"));
        out.write(body.getBytes("UTF-8"));
    }
}