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@earthen94

Java約215行で15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3回jsp導入

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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
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

今回の肝

コンテナ起動時に自動的にJSPをサーブレット(classファイル)へコンパイルできるようにしました。
JspCompiler.javaの中でjspの中身をwrite.out()へ書き込む簡単なjavaのソースへ変換します。
その後MiniContainer.jsのaddJspメソッドの中でclassファイルへ変換し、インスタンスを生成しています。

動作

image.png

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 javax.tools.*;
import java.net.URLClassLoader;
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 {
    
        // JSPを登録
        addJsp("/hello.jsp", "hello.jsp");
    
        // 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();
    }
    
    private static void addJsp(String path, String jspFile) throws Exception {
        String className = jspFile.replace(".jsp", "_jsp");

        // JSP→Java生成
        String javaFile = JspCompiler.compile(jspFile, className);

        // 実行時コンパイル
        JavaCompiler compiler = javax.tools.ToolProvider.getSystemJavaCompiler();
        if (compiler == null) {
            throw new IllegalStateException("JDKで実行してください (JREでは不可)");
        }
        int result = compiler.run(null, null, null, javaFile);
        if (result != 0) throw new RuntimeException("コンパイル失敗: " + javaFile);

        // .classをロード
        URLClassLoader loader = URLClassLoader.newInstance(new URL[]{new File(".").toURI().toURL()});
        Class<?> clazz = Class.forName(className, true, loader);

        // インスタンス化して登録
        MyServlet servlet = (MyServlet) clazz.getDeclaredConstructor().newInstance();
        routes.put(path, servlet);
    }
}
MyServlet.java
import java.io.*;

public interface MyServlet {
    void service(InputStream in, OutputStream out) throws Exception;
}
JspCompiler.java
import java.nio.file.*;
import java.io.*;

public class JspCompiler {
    public static String compile(String jspFile, String className) throws Exception {
        String jsp = Files.readString(Paths.get(jspFile));
        StringBuilder javaSrc = new StringBuilder();

        javaSrc.append("import java.io.*;\n");
        javaSrc.append("public class " + className + " implements MyServlet {\n");
        javaSrc.append("  @Override\n");
        javaSrc.append("  public void service(InputStream in, OutputStream out) throws Exception {\n");
        javaSrc.append("    StringBuilder sb = new StringBuilder();\n");


        //replaceはややこしいが" を \" に置換している。エスケープ
        for (String line : jsp.split("\n")) {
            javaSrc.append("    sb.append(\"" + line.replace("\"", "\\\"") + "\\n\");\n");
        }

        javaSrc.append("    String body = sb.toString();\n");
        javaSrc.append("    String headers = \"HTTP/1.1 200 OK\\r\\n\" +\n");
        javaSrc.append("                     \"Content-Length: \" + body.getBytes(\"UTF-8\").length + \"\\r\\n\" +\n");
        javaSrc.append("                     \"Content-Type: text/html; charset=UTF-8\\r\\n\\r\\n\";\n");
        javaSrc.append("    out.write(headers.getBytes(\"UTF-8\"));\n");
        javaSrc.append("    out.write(body.getBytes(\"UTF-8\"));\n");
        javaSrc.append("  }\n");
        javaSrc.append("}\n");

        // Javaファイル出力
        String fileName = className + ".java";
        Files.writeString(Paths.get(fileName), javaSrc.toString());
        return fileName;
    }
}
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"));
    }
}

JSP

まだ変数やJavaコードには対応していないため、実質まだHTMLと何も変わらない

hello.jsp
<html>
<body>
    <h1>Hello JSP World!</h1>
    <p>This page is compiled at runtime</p>
</body>
</html>
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"));
    }
}
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