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

package com.ankurm.structure;

import com.ankurm.structure.scan.broken.app.BrokenApp;
import com.ankurm.structure.scan.fixed.FixedApp;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.springframework.boot.WebApplicationType;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.test.system.CapturedOutput;
import org.springframework.boot.test.system.OutputCaptureExtension;
import org.springframework.context.ConfigurableApplicationContext;

import javax.tools.*;
import java.net.URI;
import java.net.URL;
import java.net.URLClassLoader;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.List;

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

/** The two ways a project layout silently breaks component scanning. */
@ExtendWith(OutputCaptureExtension.class)
class ScanTrapTests {

    @Test
    void appClassInTheWrongPackage() throws Exception {
        HttpClient http = HttpClient.newHttpClient();
        try (Transcript t = new Transcript("05-scan-starts-at-the-app-class.txt",
                "The controller is found only if it is in or below the @SpringBootApplication class's package")) {
            for (var c : List.of(
                    new Object[]{"broken", BrokenApp.class, "app class in scan.broken.app, controller in scan.broken.web (a sibling)"},
                    new Object[]{"fixed", FixedApp.class, "app class in scan.fixed, controller in scan.fixed.web (below it)"})) {
                try (ConfigurableApplicationContext ctx = new SpringApplicationBuilder((Class<?>) c[1])
                        .properties("server.port=0", "spring.main.banner-mode=off", "logging.level.root=WARN").run()) {
                    String base = "http://localhost:" + ctx.getEnvironment().getProperty("local.server.port");
                    HttpResponse<String> r = http.send(HttpRequest.newBuilder(URI.create(base + "/hello")).GET().build(),
                            HttpResponse.BodyHandlers.ofString());
                    t.section((String) c[2]);
                    t.line("GET /hello -> %d", r.statusCode());
                    t.line("HelloController registered as a bean: %s", ctx.getBeanNamesForType(Object.class).length > 0
                            && java.util.Arrays.stream(ctx.getBeanDefinitionNames()).anyMatch(n -> n.equals("helloController")));
                    if (c[0].equals("broken")) assertThat(r.statusCode()).isEqualTo(404);
                    else assertThat(r.statusCode()).isEqualTo(200);
                }
            }
        }
    }

    @Test
    void appClassInTheDefaultPackage(CapturedOutput output) throws Exception {
        String source = "import org.springframework.boot.autoconfigure.SpringBootApplication;\n"
                + "@SpringBootApplication\n"
                + "public class DefaultPackageApp {\n"
                + "}\n";
        Path out = Files.createTempDirectory("defaultpkg");
        JavaCompiler javac = ToolProvider.getSystemJavaCompiler();
        JavaFileObject file = new SimpleJavaFileObject(URI.create("string:///DefaultPackageApp.java"), JavaFileObject.Kind.SOURCE) {
            @Override public CharSequence getCharContent(boolean ignore) { return source; }
        };
        boolean compiled = javac.getTask(null, null, null,
                List.of("-proc:none", "-d", out.toString(), "-classpath", System.getProperty("java.class.path")), null, List.of(file)).call();
        assertThat(compiled).isTrue();

        try (Transcript t = new Transcript("06-default-package.txt", "A @SpringBootApplication class in the default package (no package statement)")) {
            t.line("source compiled:");
            for (String l : source.split("\n")) t.line("    %s", l);
            t.blank();
            Class<?> app;
            try (URLClassLoader cl = new URLClassLoader(new URL[]{out.toUri().toURL()}, getClass().getClassLoader())) {
                app = Class.forName("DefaultPackageApp", true, cl);
                String result;
                try (ConfigurableApplicationContext ctx = new SpringApplicationBuilder(app)
                        .web(WebApplicationType.NONE).properties("spring.main.banner-mode=off").run()) {
                    result = "context started with " + ctx.getBeanDefinitionCount() + " bean definitions";
                } catch (Throwable e) {
                    Throwable root = e;
                    while (root.getCause() != null) root = root.getCause();
                    result = "context FAILED to start: " + e.getClass().getSimpleName() + " / root cause "
                            + root.getClass().getSimpleName() + ": " + String.valueOf(root.getMessage()).lines().findFirst().orElse("");
                }
                t.section("what Spring Boot logged about the default package");
                output.getAll().lines().filter(l -> l.contains("default package") || l.contains("WARNING"))
                        .map(l -> l.replaceFirst("^\\S+\\s+", "")).forEach(t::line);
                t.section("result");
                t.line(result);
            }
            assertThat(output.getAll()).contains("default package");
        }
    }
}