multiple-chains-example

Multiple Chains Example

This is an example of how to implement multiple chains of responsibility with COR Bean Processor Spring Boot Starter.

The main objective of this project is to retrieve configuration files of different types - XML, JSON or YAML - from different sources: File system, Java classpath or HTTP server.

Even though both chains extends ChainLink interface, the library knows that there are two different chains to be assembled due to the class informed on the interface parameter.

Highlights

Content Verifier Chain

ContentVerifier interface extends COR Bean Processor Spring Boot Starter ChainLink<T> interface passing a self-reference as parameter. It also contains the entry method used to verify the content type.

public interface ContentVerifier extends ChainLink<ContentVerifier> {

  ContentType verify(String content);
}

AbstractContentVerifier is an abstract class that implements ContentVerifier interface. It also implements verify demanded by ContentVerifier and setNext demanded by ChainLink. The latter is implemented using Lombok @Setter annotation.

public abstract class AbstractContentVerifier implements ContentVerifier {

  @Setter
  private ContentVerifier next;

  @Override
  public ContentType verify(String content) { /* Full logic can be checked in the code implementation. */ }
}

ContentVerifierService encapsulates the components required to verify a content type. It contains a verify method which invokes the first link verify method, starting the chain analysis.

public class ContentVerifierService {

  private final ContentVerifier firstLink;

  public ContentType verify(String content) {
    return contentVerifier.verify(content);
  }
}

COR Bean Processor Spring Boot Starter will be responsible to chain all ContentVerifier implementations and inject the first chain link on firstLink field.

Configuration Retriever Chain

ConfigurationRetriever interface extends COR Bean Processor Spring Boot Starter ChainLink<T> interface passing a self-reference as parameter. It also contains the entry method definition to retrieve the configuration.

public interface ConfigurationRetriever extends ChainLink<ConfigurationRetriever> {
  Map<String, String> retrieve(URI uri);
}

AbstractConfigurationRetriever is an abstract class that implements ConfigurationRetriever interface. It also implements retrieve demanded by ConfigurationRetriever and setNext demanded by ChainLink. The latter is implemented using Lombok @Setter annotation.

public abstract class AbstractConfigurationRetriever implements ConfigurationRetriever {

  @Setter
  private ConfigurationRetriever next;

  @Override
  public Map<String, String> retrieve(URI uri) { /* Full logic can be checked in the code implementation. */ }
}

ConfigurationService encapsulates the components required to retrieve configuration. It contains a retrieve method which invokes the first link retrieve method, starting the chain analysis.

public class ConfigurationService {

  private final ConfigurationRetriever firstLink;

  public Map<String, String> retrieve(URI uri) {
    return configurationRetriever.retrieve(uri);
  }
}

COR Bean Processor Spring Boot Starter will be responsible to chain all ConfigurationRetriever implementations and inject the first chain link on firstLink field.

Execution

The complete integration with Spring Boot can be checked on ContentVerifierServiceIT and ConfigurationServiceIT classes. They are integration tests and can be executed through an IDE like IntelliJ IDEA, Eclipse or Microsoft Visual Studio Code.

Alternatively, the tests can also be executed through a terminal running the following command on this module root directory.

mvn test-compile failsafe:integration-test