Slides accompanying a presentation on Dropwizard I gave at the DevIgnition conference ( www.devignition.com ) on April 29, 2016. The sample code is on GitHub at https://github.com/sleberknight/dropwizard-devignition-2016

1. Dropwizard
Scott Leberknight
4/29/2016

2. “…a Java framework for developing ops-
friendly, high-performance, RESTful web
services…”

3. “…pulls together stable, mature libraries
from the Java ecosystem into a simple, light-
weight package that lets you focus on
getting things done…”

4. “…out-of-the-box support for sophisticated
configuration, application metrics, logging,
operational tools…”

5. “…allowing you and your team to ship a
production-quality web service in the shortest
time possible”

6. Key Takeaways…

7. Simple to Build
Simple to Deploy
Simple to Monitor
RESTful web services that are…

8. Main Components
Jetty - Standalone web server
Jackson - JSON processing
Jersey (JAX-RS) - REST
Metrics - Application metrics

9. Other components…
Hibernate Validator - Validation
Logback & SLF4J - Logging
Liquibase - Database migrations
JDBI or Hibernate - Database access

10. And more…
Google Guava - Utilities
HttpClient or Jersey Client - HTTP clients
Joda Time - Date/time API
(*)
(*) Java 8 Date/Time API supersedes Joda
Freemarker & Mustache - Views/templates

11. Dropwizard app
30,000 foot view

12. Configuration
Application (Jetty server)
Resources (Jersey)
Data access (DAOs)
POJOs
reads
registers
access
serialize/
deserialize
JSON
CRUD
(fromYAML file)
(using Jackson)
components

13. basic workflow
HTTP
Request
Incoming
POJO
Resource
method
Logic, data
access, etc.
Outgoing
POJO(s)
HTTP
Response
Deserialize
JSON
Serialize
JSON
CLIENT

14. The Players

15. Class/Component Description
Configuration
Application configuration de-serialized fromYAML file
(via Jackson-annotated class)
Application
Initialize bundles, commands, resources, health checks,
etc. Starts Jetty server.
Resource Annotated Jersey/JAX-RS classes
DAO
Data access layer. Native Hibernate (AbstractDAO) and
JDBI support.
HealthCheck
Defines a runtime test of application behavior,
dependencies, etc.
Managed Objects Components requiring an explicit lifecycle (start / stop)
Command
Define command line actions (e.g. server starts Jetty; db
handles database operations)
POJOs (aka Representations)
Objects representing a service's RESTful API, serialized/
deserialized by Jackson

16. Lets’ build a simple
RESTful service to
control Nest thermostats…

17. Quick Digression - Lombok
“Project Lombok makes java a spicier
language by adding ‘handlers’ that know
how to build and compile simple,
boilerplate-free, not-quite-java code.”
- projectlombok.org

18. Lombok example #1
@Getter
@Setter
@EqualsAndHashCode
@ToString
@RequiredArgsConstructor
@AllArgsConstructor
public class Person {
private String firstName;
private String lastName;
private int age;
}
or use
@Data
{

19. Lombok example #2
@Data
@Builder
@NoArgsConstructor
public class Person {
private String firstName;
private String lastName;
private int age;
}

20. Lombok example #3
val p = Person.builder()
.firstName("Bob")
.lastName("Smith")
.age(36)
.build();
local variable
type inference

21. configuration class
@Getter
@Setter
@ToString
public class NestConfiguration extends Configuration {
@JsonProperty("database")
@Valid
@NotNull
private DataSourceFactory dataSourceFactory;
}

22. config YAML
database:
driverClass: org.h2.Driver
user: nest
password: ${DEVIGNITION_DB_PWD:-DevIg$2016}
url: jdbc:h2:tcp://localhost/~/db/nest
validationQuery: "/* Nest DB Health Check */ SELECT 42"
properties:
hibernate.connection.charSet: UTF-8
hibernate.dialect: org.hibernate.dialect.H2Dialect
hibernate.format_sql: true
hibernate.show_sql: false
logging:
level: INFO
loggers:
com.devignition: DEBUG
org.hibernate.SQL: DEBUG

23. Application
main() - starts app (Jetty server)
initialize() - bundles, configuration options, etc.
run() - register Jersey resources & more

24. application class
public class NestApplication
extends Application<NestConfiguration> {
public static void main(final String[] args) throws Exception {
new NestApplication().run(args);
}
@Override public String getName() { return “Nest Service"; }
@Override
public void initialize(Bootstrap<NestConfiguration> bootstrap) {
// initialize bundles, e.g. migrations, Hibernate, etc.
}
@Override
public void run(NestConfiguration configuration,
Environment environment) {
// register resources, health checks, metrics, etc.
}
}

25. initialize - env var substitution
// in Application#initialize()
bootstrap.setConfigurationSourceProvider(
new SubstitutingSourceProvider(
bootstrap.getConfigurationSourceProvider(),
new EnvironmentVariableSubstitutor(false)));
# config.yml
# Use DEVIGNITION_DB_PWD env var, or
# default to DevIg$2016 if not exists (bash syntax)
password: ${DEVIGNITION_DB_PWD:-DevIg$2016}

26. Bundles
Re-usable functionality
Examples:
- Database migrations bundle
- Hibernate bundle

27. Migrations Bundle
Liquibase (out of box)
Add migrations bundle to application class

28. initialize - add a Bundle
// in Application#initialize()
bootstrap.addBundle(new MigrationsBundle<NestConfiguration>() {
@Override
public PooledDataSourceFactory
getDataSourceFactory(NestConfiguration config) {
return config.getDataSourceFactory();
}
});

29. Liquibase migration
<databaseChangeLog>
<changeSet id="001-create-nests-table" author="batman">
<createTable tableName="nests">
<column name="id" type="bigint" autoIncrement="true">
<constraints primaryKey="true" nullable="false"/>
</column>
<column name="location" type="varchar(256)">
<constraints nullable="false" unique="true"/>
</column>
<column name="temperature" type="int">
<constraints nullable="false"/>
</column>
<column name="mode" type="varchar(256)">
<constraints nullable="false"/>
</column>
</createTable>
</changeSet>
</databaseChangeLog>

30. run - register a resource
@Override
public void run(NestConfiguration configuration,
Environment environment) {
NestDao nestDao = new NestDao(
hibernateBundle.getSessionFactory());
NestResource nestResource = new NestResource(nestDao);
environment.jersey().register(nestResource);
}

31. Hibernate Bundle creates…
- managed connection pool
- database health check
- managed & instrumented SessionFactory

32. Managed Objects
Objects that are tied to the application’s
lifecycle (i.e. to Jetty lifecycle)
start() called before server starts
stop() called after server shuts down
Ideal for thread pools, scheduled executors, etc.

33. managed executor
// Create a Dropwizard-managed executor service
boolean useDaemon = true;
ScheduledExecutorService executor = environment.lifecycle()
.scheduledExecutorService("special-task-%d", useDaemon)
.build();
executor.scheduleAtFixedRate(this::performTask, 1L, 5L,
TimeUnit.MINUTES);

34. Health Checks
Runtime test of behavior, dependencies, etc.
Health checks should lightly test service
dependencies, e.g. databases, downstream
services, etc.

35. health check
public class NestServiceHealthCheck extends HealthCheck {
private NestService nestService;
public NestServiceHealthCheck(NestService service) {
this.nestService = service;
}
@Override
protected Result check() throws Exception {
NestServiceStatus status = nestService.currentStatus();
if (status.ok() {
return Result.healthy();
} else {
return Result.unhealthy(status.problems());
}
}
}

36. Representations
Generally…just POJOs
Use Hibernate Validator, e.g. @NotBlank
Optionally use advanced Jackson features,
e.g. custom serializers or deserializers
Sprinkle in Jackson annotations, e.g. @JsonIgnore

37. representation (POJO)
@Data
@Entity
@Table(name = "nests")
public class NestThermostat {
@Id @GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@NotBlank @Length(max = 256)
private String location;
@NotNull @Min(60) @Max(90)
private Integer temperature;
@NotNull
@Enumerated(EnumType.STRING)
private Mode mode;
@JsonIgnore
private UUID internalGuid;
}

38. Data Access / Application Logic
Use whatever makes sense for a given service
Difference services may use different data stores
- Postgres for relational data
- Neo4J for connected data
- MongoDB for document-oriented data

39. DAO (Hibernate)
public class NestDao extends AbstractDAO<NestThermostat> {
public NestDao(SessionFactory sessionFactory) { super(sessionFactory); }
public NestThermostat getById(long id) { return get(id); }
public List<NestThermostat> getAll() {
Criteria criteria = currentSession().createCriteria(getEntityClass())
.addOrder(Order.asc("location"));
return list(criteria);
}
public long create(NestThermostat nest) {
checkState(nest.getId() == null, "New nests cannot have an id");
return persist(nest).getId();
}
public void update(NestThermostat nest) {
checkState(nest.getId() != null, "Existing Nest must have an id");
persist(nest);
}
public void delete(long id) { currentSession().delete(getById(id)); }
}

40. DAO (JDBI)
public interface NestDao {
@SqlQuery("select * from nests order by location")
@Mapper(NestMapper.class)
ImmutableList<Nest> getAllNests();
@SqlQuery("select * from nests where location = :it")
@Mapper(NestMapper.class)
@SingleValueResult(Nest.class)
Optional<Nest> getNest(@Bind String location);
@GetGeneratedKeys
@SqlUpdate("insert into nests (location, location_id)"
+ " values (:location, :locationId)")
long createNest(@BindBean Nest nest);
@SqlUpdate("delete from nests where location = :it")
void deleteNest(@Bind String location);
}

41. Resource classes
Mostly just Jersey (JAX-RS) resource classes
Dropwizard adds some additional features, e.g.
- validation with @Valid
- AbstractParam and implementations
- Metrics support, e.g. @Timed

42. resource class
@Path("/nests")
@Produces(MediaType.APPLICATION_JSON)
@Consumes(MediaType.APPLICATION_JSON)
public class NestResource {
private NestDao nestDao;
public NestResource(NestDao nestDao) {
this.nestDao = nestDao;
}
// resource methods (see next slide)
}
( dependency injection w/o a framework…amazing what constructors can do ! )

43. example resource methods
@GET
@Path("/{id}")
@Timed
@ExceptionMetered
@UnitOfWork
public Optional<NestThermostat> getById(@PathParam("id") LongParam id) {
return Optional.ofNullable(nestDao.getById(id.get()));
}
@POST
@Timed
@ExceptionMetered
@UnitOfWork
public Response addNest(@Valid NestThermostat nest) {
long id = nestDao.create(nest);
URI location = UriBuilder.fromResource(NestResource.class)
.path("{id}").build(id);
return Response.created(location)
.entity(nest)
.build();
}

45. Now let's put on
our DevOps hat…
https://twitter.com/shu/status/575801992641056768

46. Fat JARs
Maven Shade plugin
Single executable "fat" JAR files
One easily deployable artifact
(*)
(*) POJJ - Plain Old Java JAR

47. <plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>2.6</version>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<mainClass>${mainClass}</mainClass>
<addDefaultImplementationEntries>true</addDefaultImplementationEntries>
</manifest>
</archive>
</configuration>
</plugin>
Versioned JARs
Add Implementation-Version to JAR manifest
Maven jar plugin

48. Manifest-Version: 1.0
Implementation-Title: Nest Example Service
Implementation-Version: 1.0.0
Archiver-Version: Plexus Archiver
Built-By: sleberkn
Implementation-Vendor-Id: com.devignition
3. MANIFEST.MF (in JAR)
<groupId>com.devignition</groupId>
<artifactId>nest-service</artifactId>
<version>1.0.0</version>
<packaging>jar</packaging>
<name>Nest Example Service</name>
1. pom.xml (in project)
nest-service-1.0.0.jar
2. Build JAR file / maven-jar-plugin

49. Deployment steps
Build executable fat JAR
Run database migrations (if any)
Start application (embedded Jetty server)

50. Build JAR
$ mvn clean package
(*) Chicken & egg - database tests will fail without first migrating

52. Commands
$ java -jar nest-service-1.0.0.jar
usage: java -jar nest-service-1.0.0.jar
[-h] [-v] {server,check,db} ...
positional arguments:
{server,check,db} available commands
optional arguments:
-h, --help show this help message and exit
-v, --version show the application version and exit

53. Check, Migrate & Run!
$ java -jar nest-service-1.0.0.jar check config.yml
$ java -jar nest-service-1.0.0.jar db migrate config.yml
$ java -jar nest-service-1.0.0.jar server config.yml

54. Jetty is now listening…
Dropwizard App
(Jetty)
App Port
8080
Admin Port
8081
GET my.nest.com:8080 /nests
GET my.nest.com:8081 /healthcheck
GET my.nest.com:8081 /metrics
GET my.nest.com:8081 /ping
GET my.nest.com:8081 /threads
GET my.nest.com:8080 /nests/2

55. Ping…

56. (HTTP) GET Our Nests

57. DevOps Menu

58. Check our health

59. Metrics (there are a LOT)

60. Console
Metrics reporting
Graphite
CSV files
Ganglia
Custom…SLF4J

61. Monitoring

62. Common OS monitoring tools
ps, top, htop, lsof, iostat, etc.

63. Common OS monitoring tools
ps, top, htop, lsof, iostat, etc.

64. Testing Dropwizard
Fixtures for unit testing representations
Easily unit test resources using mock DAOs
Excellent integration test support…
Prefer AssertJ fluent-assertions

65. Lots of unit tests….

66. Integration testing
ResourceTestRule
DropwizardClientRule
DropwizardAppRule
DropwizardTestSupport

67. ResourceTestRule
public class NestResourceIntegrationTest {
private static final NestDao NEST_DAO = mock(NestDao.class);
@ClassRule
public static final ResourceTestRule RESOURCE = ResourceTestRule.builder()
.addResource(new NestResource(NEST_DAO))
.build();
@After public void tearDown() { reset(NEST_DAO); }
@Test
public void testGetNestById() {
long id = 42;
NestThermostat nest = newNest(id, "Kitchen", 72, Mode.COOL);
when(NEST_DAO.getById(id)).thenReturn(nest);
assertThat(RESOURCE.client()
.target("/nests/42")
.request()
.get(NestThermostat.class))
.isEqualToComparingFieldByField(nest);
}
}
(in-memory Jersey server)

68. DropwizardAppRule
public class NestApplicationIntegrationTest {
@ClassRule
public static final DropwizardAppRule<NestConfiguration> APP =
new DropwizardAppRule<>(NestApplication.class,
ResourceHelpers.resourceFilePath("test-app-config.yml"));
@Test
public void testGetNest() {
Client client = new JerseyClientBuilder(APP.getEnvironment())
.build("app test client");
String url = String.format("http://localhost:%d/nests",
APP.getLocalPort());
Response response = client.target(url)
.request()
.get();
assertThat(response.getStatusInfo()).isEqualTo(Response.Status.OK);
}
}
(full integration test starts your entire app)

69. & more to explore…
Tasks
Authentication
Filters
Simple Views
Form Handling
Clients
Polymorphic Config
Logging HTTP/2
HTTPS/TLS

70. Wrap-up
Production-focused, RESTful web services
DevOps-friendly deployment & monitoring
Make your apps Twelve-Factor apps…

71. The Twelve-Factor App
Dropwizard apps have many
characteristics of 12-Factor apps
http://12factor.net

72. Simple to Build
Simple to Deploy
Simple to Monitor
RESTful web services that are…

73. sample code
available at:
https://github.com/sleberknight/dropwizard-devignition-2016

74. https://jersey.java.net/
References, Act I
http://www.dropwizard.io/
http://wiki.fasterxml.com/JacksonHome
http://www.eclipse.org/jetty/
https://dropwizard.github.io/metrics/

75. References, Act II
http://hibernate.org/validator/
http://www.jdbi.org/
http://www.liquibase.org/
http://www.joda.org/joda-time/
https://github.com/google/guava/wiki

76. Photo Attributions
nest thermostat - http://www.nest.com
bundle - https://www.flickr.com/photos/pembo1781/5477885038/
caduceus - https://www.flickr.com/photos/26672416@N00/4777701981/
DevOps hat - https://twitter.com/shu/status/575801992641056768
coffee in mason jar - https://www.flickr.com/photos/traveloriented/9757236883/
tux - http://powerpcaccess.blogspot.com/2013/03/linux-
on-ppc-mac.html#.VyGHCBMrLdQ
(I own or took all other photos myself)
gunshow comic - http://gunshowcomic.com/316
half moon - https://www.flickr.com/photos/75929731@N08/7044973631/

77. My Info
sleberknight at
fortitudetec.com
www.fortitudetec.com
@sleberknight
scott.leberknight at
gmail

78. Dropwizard???
http://gunshowcomic.com/316