How to build a CAP plugin

@ServiceName(value = "*", type = ApplicationService.class)
public class SampleHandler implements EventHandler {

    @After
    public void handleSample(CdsReadEventContext context) {
      // any custom Java code using the event context and CQL APIs
    }
}

public class SampleHandlerRuntimeConfiguration implements CdsRuntimeConfiguration {

  @Override
  public void eventHandlers(CdsRuntimeConfigurer configurer) {
    configurer.eventHandler(new SampleHandler());
  }
}
// listed in src/main/resources/META-INF/services/
//   com.sap.cds.services.runtime.CdsRuntimeConfiguration

<!-- consumer: srv/pom.xml -->
<dependency>
  <groupId>com.sap.capire</groupId>
  <artifactId>bookshop</artifactId>
  <version>1.0.0</version>
</dependency>
<!-- plus the cds-maven-plugin 'resolve' goal; then in CDS:
     using { CatalogService } from 'com.sap.capire/bookshop'; -->

public class SampleAdapterFactory implements ServletAdapterFactory, CdsRuntimeAware {
  static final String PROTOCOL_KEY = "protocol-key";
  private CdsRuntime runtime;

  @Override
  public void setCdsRuntime(CdsRuntime runtime) { this.runtime = runtime; }

  @Override
  public Object create() { return new SampleAdapter(runtime); }
  // isEnabled(), getBasePath(), getMappings(), getServletPath()
}

aspect managed {
  createdAt  : DateTime;
  createdBy  : User;
  modifiedAt : DateTime;
  modifiedBy : User;
}

// consumer
using { cuid, managed, temporal } from 'your-reuse-aspects';
entity Bar : cuid, managed, temporal {...}

using { CodeList, Currencies, Languages } from 'some-reuse-package';
extend CodeList with { descr: localized String }
extend Currencies with { symbol: String(2) }
extend Languages:locale with (length:15);

// after: npm add @cap-js/audit-logging   (Node.js)
//   or: cds-feature-auditlog-v2 dependency  (Java)
annotate Customer with @PersonalData ...;

@SpringBootTest
public class CatalogServiceTest {
    @Autowired
    private CatalogService catalogService;
    @Test
    public void submitOrder() {
        SubmitOrderContext context = SubmitOrderContext.create();
        context.setBook("4a519e61-3c3a-4bd9-ab12-d7e0c5329933");
        context.setQuantity(2);
        catalogService.emit(context);
        assertEquals(22 - context.getQuantity(), context.getResult().getStock());
    }
}

cds add lint
cds lint

cds add github-actions

version = 1
SPDX-PackageName = "audit-logging"
SPDX-PackageDownloadLocation = "https://github.com/cap-js/audit-logging"

[[annotations]]
path = "**"
precedence = "aggregate"
SPDX-FileCopyrightText = "2023 SAP SE or an SAP affiliate company and audit-logging contributors."
SPDX-License-Identifier = "Apache-2.0"

entity Orders @(restrict: [
    { grant: 'READ', to: 'Auditor', where: (AuditBy = $user) }
  ]) {/*...*/}

this.before('*', function (req) {
  const user = new cds.User.Privileged
  return this.tx({ user }, tx => tx.run(
    INSERT.into('RequestLog').entries({
      url: req._.req.url,
      user: req.user.id
    })
  )
})

const entity = <from user input>
const column = <from user input>
validate(entity, column) // for example, by comparing with positive list
SELECT.from(entity).columns(column)

annotate my.Customers with @PersonalData : {
  DataSubjectRole : 'Customer',
  EntitySemantics : 'DataSubject'
} {
  ID           @PersonalData.FieldSemantics: 'DataSubjectID';
  email        @PersonalData.IsPotentiallyPersonal;
  creditCardNo @PersonalData.IsPotentiallySensitive;
};

@Bean
@Order(1) // needs to have higher priority than CAP security config
public SecurityFilterChain appFilterChain(HttpSecurity http) throws Exception {
  return http
    .securityMatcher(AntPathRequestMatcher.antMatcher("/public/**"))
    .csrf(c -> c.disable())
    .authorizeHttpRequests(r -> r.anyRequest().permitAll())
    .build();
}