Core Application Framework

/**
 * The base class for Dropwizard applications.
 * @param <T> the type of configuration class for this application
 */
public abstract class Application<T extends Configuration> {
    /**
     * Returns the name of the application.
     * @return the application's name
     */
    public String getName();
    
    /**
     * Returns the Class of the configuration class type parameter.
     * @return the configuration class
     */
    public Class<T> getConfigurationClass();
    
    /**
     * Initializes the application bootstrap.
     * @param bootstrap the application bootstrap
     */
    public void initialize(Bootstrap<T> bootstrap);
    
    /**
     * When the application runs, this is called after the bundles are run.
     * Override to add providers, resources, etc. for your application.
     * @param configuration the parsed Configuration object
     * @param environment the application's Environment
     * @throws Exception if something goes wrong
     */
    public abstract void run(T configuration, Environment environment) throws Exception;
    
    /**
     * Parses command-line arguments and runs the application.
     * Call this method from a public static void main entry point.
     * @param arguments the command-line arguments  
     * @throws Exception if something goes wrong
     */
    public void run(String... arguments) throws Exception;
    
    /**
     * The log level at which to bootstrap logging on application startup.
     * @return the bootstrap log level (default: Level.WARN)
     */
    protected Level bootstrapLogLevel();
    
    /**
     * Called by run(String...) to add the standard "server" and "check" commands
     * @param bootstrap the bootstrap instance
     */
    protected void addDefaultCommands(Bootstrap<T> bootstrap);
    
    /**
     * Called by run(String...) to indicate there was a fatal error running the requested command.
     * @param t The Throwable instance which caused the command to fail
     */
    protected void onFatalError(Throwable t);
}

public class MyApplication extends Application<MyConfiguration> {
    public static void main(String[] args) throws Exception {
        new MyApplication().run(args);
    }

    @Override
    public String getName() {
        return "my-service";
    }

    @Override
    public void initialize(Bootstrap<MyConfiguration> bootstrap) {
        // Add bundles during initialization
        bootstrap.addBundle(new AssetsBundle("/assets/", "/", "index.html"));
        bootstrap.addBundle(new SslReloadBundle());
    }

    @Override
    public void run(MyConfiguration configuration, Environment environment) {
        // Register resources
        environment.jersey().register(new MyResource());
        
        // Register health checks
        environment.healthChecks().register("database", new DatabaseHealthCheck());
        
        // Register admin tasks
        environment.admin().addTask(new MyAdminTask());
    }
}

/**
 * An object representation of the YAML configuration file.
 * Extend this with your own configuration properties.
 */
public class Configuration {
    /**
     * Returns the server-specific section of the configuration file.
     * @return server-specific configuration parameters
     */
    @JsonProperty("server")
    public ServerFactory getServerFactory();
    
    /**
     * Sets the HTTP-specific section of the configuration file.
     * @param factory the server factory
     */
    @JsonProperty("server")
    public void setServerFactory(ServerFactory factory);
    
    /**
     * Returns the logging-specific section of the configuration file.
     * @return logging-specific configuration parameters
     */
    @JsonProperty("logging")
    public synchronized LoggingFactory getLoggingFactory();
    
    /**
     * Sets the logging-specific section of the configuration file.
     * @param factory the logging factory
     */
    @JsonProperty("logging")
    public synchronized void setLoggingFactory(LoggingFactory factory);
    
    /**
     * Returns the metrics-specific section of the configuration file.
     * @return metrics configuration parameters
     */
    @JsonProperty("metrics")
    public MetricsFactory getMetricsFactory();
    
    /**
     * Sets the metrics-specific section of the configuration file.
     * @param metrics the metrics factory
     */
    @JsonProperty("metrics")
    public void setMetricsFactory(MetricsFactory metrics);
    
    /**
     * Returns the admin interface-specific section of the configuration file.
     * @return admin interface-specific configuration parameters
     */
    @JsonProperty("admin")
    public AdminFactory getAdminFactory();
    
    /**
     * Sets the admin interface-specific section of the configuration file.
     * @param admin the admin factory
     */
    @JsonProperty("admin")  
    public void setAdminFactory(AdminFactory admin);
    
    /**
     * Returns the health interface-specific section of the configuration file.
     * @return health interface-specific configuration parameters
     */
    @JsonProperty("health")
    public Optional<HealthFactory> getHealthFactory();
    
    /**
     * Sets the health interface-specific section of the configuration file.
     * @param health the health factory
     */
    @JsonProperty("health")
    public void setHealthFactory(HealthFactory health);
}

public class MyConfiguration extends Configuration {
    @NotEmpty
    private String databaseUrl;
    
    @Min(1)
    @Max(100)
    private int connectionPoolSize = 10;
    
    @Valid
    @NotNull
    private RedisConfiguration redis = new RedisConfiguration();
    
    @JsonProperty
    public String getDatabaseUrl() {
        return databaseUrl;
    }
    
    @JsonProperty
    public void setDatabaseUrl(String databaseUrl) {
        this.databaseUrl = databaseUrl;
    }
    
    @JsonProperty
    public int getConnectionPoolSize() {
        return connectionPoolSize;
    }
    
    @JsonProperty
    public void setConnectionPoolSize(int connectionPoolSize) {
        this.connectionPoolSize = connectionPoolSize;
    }
    
    @JsonProperty
    public RedisConfiguration getRedis() {
        return redis;
    }
    
    @JsonProperty
    public void setRedis(RedisConfiguration redis) {
        this.redis = redis;
    }
}

# Server configuration
server:
  type: default
  applicationConnectors:
    - type: http
      port: 8080
  adminConnectors:
    - type: http
      port: 8081

# Logging configuration      
logging:
  level: INFO
  loggers:
    com.example: DEBUG
    
# Custom application configuration
databaseUrl: "jdbc:postgresql://localhost/mydb"
connectionPoolSize: 20
redis:
  host: localhost
  port: 6379

// Log level enumeration used by bootstrapLogLevel()
public enum Level {
    ERROR, WARN, INFO, DEBUG, TRACE
}