# Java Hello World
This section provides step by step instructions on how to write and run a HelloWorld with Java.
For complete, ready to build samples covering all the key Cadence concepts go to Cadence-Java-Samples (opens new window).
You can also review Java-Client and java-docs (opens new window) for more documentation.
# Include Cadence Java Client Dependency
Go to the Maven Repository Uber Cadence Java Client Page (opens new window) and find the latest version of the library. Include it as a dependency into your Java project. For example if you are using Gradle the dependency looks like:
compile group: 'com.uber.cadence', name: 'cadence-client', version: '<latest_version>'
Also add the following dependencies that cadence-client relies on:
compile group: 'commons-configuration', name: 'commons-configuration', version: '1.9'
compile group: 'ch.qos.logback', name: 'logback-classic', version: '1.2.3'
Make sure that the following code compiles:
import com.uber.cadence.workflow.Workflow;
import com.uber.cadence.workflow.WorkflowMethod;
import org.slf4j.Logger;
public class GettingStarted {
private static Logger logger = Workflow.getLogger(GettingStarted.class);
public interface HelloWorld {
@WorkflowMethod
void sayHello(String name);
}
}
If you are having problems setting up the build files use the Cadence Java Samples (opens new window) GitHub repository as a reference.
Also add the following logback config file somewhere in your classpath:
<configuration>
<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
<!-- encoders are assigned the type
ch.qos.logback.classic.encoder.PatternLayoutEncoder by default -->
<encoder>
<pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
</encoder>
</appender>
<logger name="io.netty" level="INFO"/>
<root level="INFO">
<appender-ref ref="STDOUT" />
</root>
</configuration>
# Implement Hello World Workflow
Let's add HelloWorldImpl with the sayHello method that just logs the "Hello ..." and returns.
import com.uber.cadence.worker.Worker;
import com.uber.cadence.workflow.Workflow;
import com.uber.cadence.workflow.WorkflowMethod;
import org.slf4j.Logger;
public class GettingStarted {
private static Logger logger = Workflow.getLogger(GettingStarted.class);
public interface HelloWorld {
@WorkflowMethod
void sayHello(String name);
}
public static class HelloWorldImpl implements HelloWorld {
@Override
public void sayHello(String name) {
logger.info("Hello " + name + "!");
}
}
}
To link the workflow implementation to the Cadence framework, it should be registered with a worker that connects to a Cadence Service. By default the worker connects to the locally running Cadence service.
public static void main(String[] args) {
WorkflowClient workflowClient =
WorkflowClient.newInstance(
new WorkflowServiceTChannel(ClientOptions.defaultInstance()),
WorkflowClientOptions.newBuilder().setDomain(DOMAIN).build());
// Get worker to poll the task list.
WorkerFactory factory = WorkerFactory.newInstance(workflowClient);
Worker worker = factory.newWorker(TASK_LIST);
worker.registerWorkflowImplementationTypes(HelloWorldImpl.class);
factory.start();
}
The code is slightly different if you are using client version prior to 3.0.0:
public static void main(String[] args) {
Worker.Factory factory = new Worker.Factory("test-domain");
Worker worker = factory.newWorker("HelloWorldTaskList");
worker.registerWorkflowImplementationTypes(HelloWorldImpl.class);
factory.start();
}
# Execute Hello World Workflow using the CLI
Now run the worker program. Following is an example log:
13:35:02.575 [main] INFO c.u.c.s.WorkflowServiceTChannel - Initialized TChannel for service cadence-frontend, LibraryVersion: 2.2.0, FeatureVersion: 1.0.0
13:35:02.671 [main] INFO c.u.cadence.internal.worker.Poller - start(): Poller{options=PollerOptions{maximumPollRateIntervalMilliseconds=1000, maximumPollRatePerSecond=0.0, pollBackoffCoefficient=2.0, pollBackoffInitialInterval=PT0.2S, pollBackoffMaximumInterval=PT20S, pollThreadCount=1, pollThreadNamePrefix='Workflow Poller taskList="HelloWorldTaskList", domain="test-domain", type="workflow"'}, identity=45937@maxim-C02XD0AAJGH6}
13:35:02.673 [main] INFO c.u.cadence.internal.worker.Poller - start(): Poller{options=PollerOptions{maximumPollRateIntervalMilliseconds=1000, maximumPollRatePerSecond=0.0, pollBackoffCoefficient=2.0, pollBackoffInitialInterval=PT0.2S, pollBackoffMaximumInterval=PT20S, pollThreadCount=1, pollThreadNamePrefix='null'}, identity=81b8d0ac-ff89-47e8-b842-3dd26337feea}
No Hello printed. This is expected because a worker is just a workflow code host. The workflow has to be started to execute. Let's use Cadence CLI to start the workflow:
> docker run --network=host --rm ubercadence/cli:master --do test-domain workflow start --tasklist HelloWorldTaskList --workflow_type HelloWorld::sayHello --execution_timeout 3600 --input \"World\"
Started Workflow Id: bcacfabd-9f9a-46ac-9b25-83bcea5d7fd7, run Id: e7c40431-8e23-485b-9649-e8f161219efe
The output of the program should change to:
13:35:02.575 [main] INFO c.u.c.s.WorkflowServiceTChannel - Initialized TChannel for service cadence-frontend, LibraryVersion: 2.2.0, FeatureVersion: 1.0.0
13:35:02.671 [main] INFO c.u.cadence.internal.worker.Poller - start(): Poller{options=PollerOptions{maximumPollRateIntervalMilliseconds=1000, maximumPollRatePerSecond=0.0, pollBackoffCoefficient=2.0, pollBackoffInitialInterval=PT0.2S, pollBackoffMaximumInterval=PT20S, pollThreadCount=1, pollThreadNamePrefix='Workflow Poller taskList="HelloWorldTaskList", domain="test-domain", type="workflow"'}, identity=45937@maxim-C02XD0AAJGH6}
13:35:02.673 [main] INFO c.u.cadence.internal.worker.Poller - start(): Poller{options=PollerOptions{maximumPollRateIntervalMilliseconds=1000, maximumPollRatePerSecond=0.0, pollBackoffCoefficient=2.0, pollBackoffInitialInterval=PT0.2S, pollBackoffMaximumInterval=PT20S, pollThreadCount=1, pollThreadNamePrefix='null'}, identity=81b8d0ac-ff89-47e8-b842-3dd26337feea}
13:40:28.308 [workflow-root] INFO c.u.c.samples.hello.GettingStarted - Hello World!
Let's start another workflow execution
> docker run --network=host --rm ubercadence/cli:master --do test-domain workflow start --tasklist HelloWorldTaskList --workflow_type HelloWorld::sayHello --execution_timeout 3600 --input \"Cadence\"
Started Workflow Id: d2083532-9c68-49ab-90e1-d960175377a7, run Id: 331bfa04-834b-45a7-861e-bcb9f6ddae3e
And the output changed to:
13:35:02.575 [main] INFO c.u.c.s.WorkflowServiceTChannel - Initialized TChannel for service cadence-frontend, LibraryVersion: 2.2.0, FeatureVersion: 1.0.0
13:35:02.671 [main] INFO c.u.cadence.internal.worker.Poller - start(): Poller{options=PollerOptions{maximumPollRateIntervalMilliseconds=1000, maximumPollRatePerSecond=0.0, pollBackoffCoefficient=2.0, pollBackoffInitialInterval=PT0.2S, pollBackoffMaximumInterval=PT20S, pollThreadCount=1, pollThreadNamePrefix='Workflow Poller taskList="HelloWorldTaskList", domain="test-domain", type="workflow"'}, identity=45937@maxim-C02XD0AAJGH6}
13:35:02.673 [main] INFO c.u.cadence.internal.worker.Poller - start(): Poller{options=PollerOptions{maximumPollRateIntervalMilliseconds=1000, maximumPollRatePerSecond=0.0, pollBackoffCoefficient=2.0, pollBackoffInitialInterval=PT0.2S, pollBackoffMaximumInterval=PT20S, pollThreadCount=1, pollThreadNamePrefix='null'}, identity=81b8d0ac-ff89-47e8-b842-3dd26337feea}
13:40:28.308 [workflow-root] INFO c.u.c.samples.hello.GettingStarted - Hello World!
13:42:34.994 [workflow-root] INFO c.u.c.samples.hello.GettingStarted - Hello Cadence!
# List Workflows and Workflow History
Let's list our workflow in the CLI
> docker run --network=host --rm ubercadence/cli:master --do test-domain workflow list
WORKFLOW TYPE | WORKFLOW ID | RUN ID | START TIME | EXECUTION TIME | END TIME
HelloWorld::sayHello | d2083532-9c68-49ab-90e1-d960175377a7 | 331bfa04-834b-45a7-861e-bcb9f6ddae3e | 20:42:34 | 20:42:34 | 20:42:35
HelloWorld::sayHello | bcacfabd-9f9a-46ac-9b25-83bcea5d7fd7 | e7c40431-8e23-485b-9649-e8f161219efe | 20:40:28 | 20:40:28 | 20:40:29
Now let's look at the workflow execution history:
> docker run --network=host --rm ubercadence/cli:master --do test-domain workflow showid 1965109f-607f-4b14-a5f2-24399a7b8fa7
1 WorkflowExecutionStarted {WorkflowType:{Name:HelloWorld::sayHello},
TaskList:{Name:HelloWorldTaskList},
Input:["World"],
ExecutionStartToCloseTimeoutSeconds:3600,
TaskStartToCloseTimeoutSeconds:10,
ContinuedFailureDetails:[],
LastCompletionResult:[],
Identity:cadence-cli@linuxkit-025000000001,
Attempt:0,
FirstDecisionTaskBackoffSeconds:0}
2 DecisionTaskScheduled {TaskList:{Name:HelloWorldTaskList},
StartToCloseTimeoutSeconds:10,
Attempt:0}
3 DecisionTaskStarted {ScheduledEventId:2,
Identity:45937@maxim-C02XD0AAJGH6,
RequestId:481a14e5-67a4-436e-9a23-7f7fb7f87ef3}
4 DecisionTaskCompleted {ExecutionContext:[],
ScheduledEventId:2,
StartedEventId:3,
Identity:45937@maxim-C02XD0AAJGH6}
5 WorkflowExecutionCompleted {Result:[],
DecisionTaskCompletedEventId:4}
Even for such a trivial workflow, the history gives a lot of useful information. For complex workflows this is a really useful tool for production and development troubleshooting. History can be automatically archived to a long-term blob store (for example Amazon S3) upon workflow completion for compliance, analytical, and troubleshooting purposes.
# What is Next
Now you have completed the tutorials. You can continue to explore the key concepts in Cadence, and also how to use them with Java Client