spring-boot-demo/project-structure/src/test/java/com/ankurm/structure/StructureTests.java

package com.ankurm.structure;

import com.ankurm.structure.byfeature.ByFeatureApp;
import com.ankurm.structure.bylayer.ByLayerApp;
import org.junit.jupiter.api.Test;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.context.ConfigurableApplicationContext;

import javax.tools.*;
import java.io.IOException;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.nio.file.*;
import java.util.*;
import java.util.stream.Stream;

import static org.assertj.core.api.Assertions.assertThat;

/** Each test writes one transcript under output/; the article quotes those files verbatim. */
class StructureTests {

    static final Path SRC = Path.of("src/main/java/com/ankurm/structure");
    static final Path CLASSES = Path.of("target/classes");

    // ---------------------------------------------------------------- 01 the two trees
    @Test
    void packageTrees() throws IOException {
        try (Transcript t = new Transcript("01-package-trees.txt", "The same application, two layouts (src/main/java/com/ankurm/structure)")) {
            for (String variant : List.of("bylayer", "byfeature")) {
                t.section(variant);
                Path root = SRC.resolve(variant);
                List<Path> all;
                try (Stream<Path> s = Files.walk(root)) {
                    all = s.sorted().toList();
                }
                int files = 0;
                for (Path p : all) {
                    int depth = root.relativize(p).getNameCount();
                    String indent = "  ".repeat(depth);
                    if (p.equals(root)) {
                        t.line("%s/", variant);
                    } else if (Files.isDirectory(p)) {
                        t.line("%s%s/", indent, p.getFileName());
                    } else {
                        t.line("%s%s", indent, p.getFileName());
                        files++;
                    }
                }
                t.line("(%d source files)", files);
                assertThat(files).isGreaterThan(8);
            }
        }
    }

    // ---------------------------------------------------------------- 02 what is public
    @Test
    void visibility() throws Exception {
        Map<String, Integer> publicCount = new LinkedHashMap<>();
        try (Transcript t = new Transcript("02-public-surface.txt", "Top-level types per layout and whether each one is public")) {
            for (String variant : List.of("bylayer", "byfeature")) {
                t.section(variant);
                Path root = CLASSES.resolve("com/ankurm/structure").resolve(variant);
                List<String> names = new ArrayList<>();
                try (Stream<Path> s = Files.walk(root)) {
                    s.filter(p -> p.toString().endsWith(".class") && !p.getFileName().toString().contains("$"))
                            .sorted().forEach(p -> names.add(CLASSES.relativize(p).toString()
                                    .replace('/', '.').replaceAll("\\.class$", "")));
                }
                int pub = 0;
                for (String n : names) {
                    Class<?> c = Class.forName(n, false, getClass().getClassLoader());
                    boolean isPublic = java.lang.reflect.Modifier.isPublic(c.getModifiers());
                    if (isPublic) pub++;
                    t.line("%-14s %s", isPublic ? "public" : "package-private",
                            n.substring("com.ankurm.structure.".length()));
                }
                t.line("%d of %d top-level types are public", pub, names.size());
                publicCount.put(variant, pub);
            }
        }
        // package-by-feature exposes strictly less
        assertThat(publicCount.get("byfeature")).isLessThan(publicCount.get("bylayer"));
    }

    // ---------------------------------------------------------------- 03 what the compiler enforces
    @Test
    void compilerBoundary() throws Exception {
        try (Transcript t = new Transcript("03-compiler-boundary.txt", "Can code in one package reach another package's repository?")) {
            t.section("by layer: controller/Shortcut.java reaches into repository/");
            List<String> layer = compile("com.ankurm.structure.bylayer.controller.Shortcut",
                    "package com.ankurm.structure.bylayer.controller;\n"
                            + "class Shortcut {\n"
                            + "    Object repo = new com.ankurm.structure.bylayer.repository.BookRepository();\n"
                            + "}\n");
            layer.forEach(t::line);
            assertThat(layer).containsExactly("compiled with 0 errors");

            t.section("by feature: loan/Shortcut.java reaches into book/");
            List<String> feature = compile("com.ankurm.structure.byfeature.loan.Shortcut",
                    "package com.ankurm.structure.byfeature.loan;\n"
                            + "class Shortcut {\n"
                            + "    Object repo = new com.ankurm.structure.byfeature.book.BookRepository();\n"
                            + "}\n");
            feature.forEach(t::line);
            assertThat(feature.get(0)).contains("is not public").contains("cannot be accessed from outside package");
        }
    }

    private List<String> compile(String className, String source) throws IOException {
        JavaCompiler javac = ToolProvider.getSystemJavaCompiler();
        DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<>();
        JavaFileObject file = new SimpleJavaFileObject(URI.create("string:///" + className.replace('.', '/') + ".java"),
                JavaFileObject.Kind.SOURCE) {
            @Override public CharSequence getCharContent(boolean ignore) { return source; }
        };
        Path out = Files.createTempDirectory("shortcut");
        List<String> opts = List.of("-proc:none", "-d", out.toString(), "-classpath", CLASSES.toString());
        boolean ok = javac.getTask(null, null, diagnostics, opts, null, List.of(file)).call();
        List<String> lines = new ArrayList<>();
        for (Diagnostic<? extends JavaFileObject> d : diagnostics.getDiagnostics()) {
            if (d.getKind() == Diagnostic.Kind.ERROR) {
                lines.add("error: " + d.getMessage(Locale.ENGLISH));
            }
        }
        if (ok) lines.add("compiled with 0 errors");
        return lines;
    }

    // ---------------------------------------------------------------- 04 both layouts expose one API
    @Test
    void sameApiBothLayouts() throws Exception {
        HttpClient http = HttpClient.newHttpClient();
        Map<String, List<String>> results = new LinkedHashMap<>();
        try (Transcript t = new Transcript("04-same-api-both-layouts.txt", "The same requests against both layouts")) {
            for (var variant : List.of("bylayer", "byfeature")) {
                Class<?> app = variant.equals("bylayer") ? ByLayerApp.class : ByFeatureApp.class;
                try (ConfigurableApplicationContext ctx = new SpringApplicationBuilder(app)
                        .properties("server.port=0", "spring.main.banner-mode=off", "logging.level.root=WARN").run()) {
                    String base = "http://localhost:" + ctx.getEnvironment().getProperty("local.server.port");
                    t.section(variant);
                    List<String> seen = new ArrayList<>();
                    for (String[] call : new String[][]{
                            {"GET", "/books", null},
                            {"GET", "/books/1", null},
                            {"GET", "/books/99", null},
                            {"POST", "/books", "{\"title\":\"Clean Code\",\"author\":\"Robert Martin\",\"pages\":464}"},
                            {"POST", "/books", "{\"title\":\"\",\"author\":\"x\",\"pages\":0}"}}) {
                        HttpRequest.Builder rb = HttpRequest.newBuilder(URI.create(base + call[1]));
                        if (call[2] == null) rb.GET();
                        else rb.header("Content-Type", "application/json").POST(HttpRequest.BodyPublishers.ofString(call[2]));
                        HttpResponse<String> r = http.send(rb.build(), HttpResponse.BodyHandlers.ofString());
                        String line = call[0] + " " + call[1] + " -> " + r.statusCode();
                        t.line(line);
                        t.line("    %s", r.body());
                        seen.add(call[0] + " " + call[1] + " " + r.statusCode()
                                + (r.statusCode() == 400 ? "" : " " + r.body().replaceAll("\"instance\":\"[^\"]*\",?", "")));
                    }
                    if (variant.equals("byfeature")) {
                        for (String[] call : new String[][]{
                                {"POST", "/loans", "{\"bookId\":2,\"member\":\"Asha\"}"},
                                {"POST", "/loans", "{\"bookId\":7,\"member\":\"Asha\"}"},
                                {"GET", "/loans", null}}) {
                            HttpRequest.Builder rb = HttpRequest.newBuilder(URI.create(base + call[1]));
                            if (call[2] == null) rb.GET();
                            else rb.header("Content-Type", "application/json").POST(HttpRequest.BodyPublishers.ofString(call[2]));
                            HttpResponse<String> r = http.send(rb.build(), HttpResponse.BodyHandlers.ofString());
                            t.line(call[0] + " " + call[1] + " -> " + r.statusCode());
                            t.line("    %s", r.body());
                        }
                    }
                    results.put(variant, seen);
                }
            }
            t.section("comparison");
            boolean same = results.get("bylayer").equals(results.get("byfeature"));
            t.line("status codes and bodies identical for the five shared requests: %s", same);
            assertThat(same).isTrue();
        }
    }
}