Auto-configuration — Bu Bean Nereden Geldi?

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@AutoConfiguration(after = JacksonAutoConfiguration.class)
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@ConditionalOnClass(AuditClient.class)                       // the library is on the classpath
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@ConditionalOnProperty(prefix = "audit", name = "enabled", havingValue = "true", matchIfMissing = true)
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@EnableConfigurationProperties(AuditProperties.class)
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public class AuditAutoConfiguration {
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    // Back off if the application defines its own sink.
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    @Bean
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    @ConditionalOnMissingBean
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    AuditSink auditSink(AuditProperties props, ObjectMapper json) {
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        return new HttpAuditSink(props.endpoint(), props.timeout(), json);
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    }
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    @Bean
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    @ConditionalOnMissingBean
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    AuditClient auditClient(AuditSink sink, AuditProperties props) {
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        return new AuditClient(sink, props.serviceName());
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    }
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    // Only in servlet web apps: record every request automatically.
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    @Bean
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    @ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
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    @ConditionalOnMissingBean
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    AuditRequestFilter auditRequestFilter(AuditClient client) {
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        return new AuditRequestFilter(client);
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    }
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}

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@ConfigurationProperties("audit")
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public record AuditProperties(
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        @DefaultValue("true") boolean enabled,
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        @DefaultValue("http://audit-service/events") URI endpoint,
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        @DefaultValue("500ms") Duration timeout,
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        @DefaultValue("unknown-service") String serviceName) {
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}

com.bank.audit.autoconfigure.AuditAutoConfiguration

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// The payments service must not lose an audit event when the audit service is down:
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// it writes them to Kafka, which keeps them until they are consumed.
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// Because the starter's sink is @ConditionalOnMissingBean, this one wins
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// and the starter quietly keeps its AuditClient, wired to this sink.
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@Configuration
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class AuditOverride {
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    @Bean
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    AuditSink kafkaAuditSink(KafkaTemplate<String, AuditEvent> kafka) {
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        // Keyed by subject (the customer), so one customer's events stay in order.
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        // join(): the payment waits for the broker's ack instead of fire-and-forget.
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        return event -> kafka.send("audit-events", event.subject(), event).join();
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    }
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}

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class AuditAutoConfigurationTest {
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    private final ApplicationContextRunner runner = new ApplicationContextRunner()
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            .withConfiguration(AutoConfigurations.of(AuditAutoConfiguration.class, JacksonAutoConfiguration.class));
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    @Test
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    void createsDefaultBeans() {
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        runner.run(context -> {
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            assertThat(context).hasSingleBean(AuditClient.class);
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            assertThat(context).getBean(AuditSink.class).isInstanceOf(HttpAuditSink.class);
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        });
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    }
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    @Test
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    void backsOffWhenTheApplicationDefinesItsOwnSink() {
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        runner.withBean(AuditSink.class, () -> event -> {})
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                .run(context -> assertThat(context).getBean(AuditSink.class).isNotInstanceOf(HttpAuditSink.class));
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    }
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    @Test
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    void canBeSwitchedOff() {
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        runner.withPropertyValues("audit.enabled=false")
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                .run(context -> assertThat(context).doesNotHaveBean(AuditClient.class));
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    }
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    @Test
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    void staysAwayWhenTheLibraryIsMissing() {
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        runner.withClassLoader(new FilteredClassLoader(AuditClient.class))
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                .run(context -> assertThat(context).doesNotHaveBean(AuditClient.class));
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    }
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}

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audit:
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  service-name: payments-service
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  timeout: 300ms
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# Prints the conditions evaluation report at startup: every auto-configuration,
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# whether it matched, and which condition decided it. Development only.
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debug: true