Helidon

https://helidon.io/docs/v4
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### Start a WebServer and define a route

Source: https://helidon.io/docs/v4/se/introduction

This example demonstrates how to initialize a WebServer and define a simple GET route that returns 'Hello World!'.

```java
WebServer.builder()
    .addRouting(HttpRouting.builder()
        .get("/greet", (req, res)
            -> res.send("Hello World!")))
    .build()
    .start();
```

--------------------------------

### Simple WebServer Setup

Source: https://helidon.io/docs/v4/se/guides/upgrade-2x

Example of a basic WebServer setup using the WebServer builder.

```java
WebServer.builder()
    .port(8001)
    .host("localhost")
    .routing(createRouting())
    .build();
```

--------------------------------

### Build and run the QuickStart application

Source: https://helidon.io/docs/v4/se/cors

Commands to package and start the Helidon SE application.

```bash
mvn package
java -jar target/helidon-quickstart-se.jar
```

```text
WEB server is up! http://localhost:8080/greet
```

--------------------------------

### Start Server with Default Configuration

Source: https://helidon.io/docs/v4/mp/guides/config

Example of starting the server without a custom Config object, which triggers the use of default configuration.

```java
static Server startServer() {
    return Server.create().start();1
}
```

--------------------------------

### Emitter.create and send example

Source: https://helidon.io/docs/v4/apidocs/io.helidon.messaging/io/helidon/messaging/Emitter.html

Example showing how to create an Emitter for a channel, build a Messaging instance with the emitter and a listener, and start messaging.

```APIDOC
## Emitter<PAYLOAD>

### Description
Emitter is a convenience publisher for one or multiple channels. Publishing is as easy as calling the send(Object) method.

### Type Parameters
- `PAYLOAD` - message payload type

### All Implemented Interfaces
- `Emitter<PAYLOAD>`
- `Publisher<Message<PAYLOAD>>`

### Example
```java
Channel<String> simpleChannel = Channel.create();

Emitter<String> emitter = Emitter.create(simpleChannel);

Messaging messaging = Messaging.builder()
        .emitter(emitter)
        .listener(simpleChannel, System.out::println)
        .build();

messaging.start();
```
```

--------------------------------

### Build and Run Application

Source: https://helidon.io/docs/v4/mp/cors

Commands to build and start the Helidon MP QuickStart application.

```bash
mvn package
java -jar target/helidon-quickstart-mp.jar
```

```text
2020.05.12 05:44:08 INFO io.helidon.microprofile.server.ServerCdiExtension Thread[main,5,main]: Server started on http://localhost:8080 (and all other host addresses) in 5280 milliseconds (since JVM startup).
```

--------------------------------

### start()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.webserver/io/helidon/webserver/WebServer.html

Starts the server.

```APIDOC
## start()

### Description
Starts the server.

### Method
instance

### Signature
WebServer start()

### Returns
WebServer - this server instance.
```

--------------------------------

### Run the Helidon quickstart application

Source: https://helidon.io/docs/v4/se/guides/dbclient

Start the application with this command. Ensure H2 is running before executing.

```bash
java -jar target/helidon-quickstart-se.jar

```

--------------------------------

### start()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.messaging/io/helidon/messaging/Messaging.html

Connects all channels and starts streaming. Returns the started messaging instance.

```APIDOC
## start()

### Description
Connects all channels and starts streaming.

### Method
start()

### Returns
Started messaging instance.
```

--------------------------------

### start()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.webserver/io/helidon/webserver/WebServer.html

Starts the server. Has no effect if the server is already running. Fails if the server is shut down or failed to start.

```APIDOC
## start()

### Description
Starts the server. Has no effect if the server is already running. Fails if the server is shut down or failed to start.

### Method
WebServer start()

### Returns
A started server

### Throws
- `IllegalStateException` - when startup fails, in such a case all channels are shut down
```

--------------------------------

### Observe Server Startup Output

Source: https://helidon.io/docs/v4/mp/guides/testing

Example of the console output indicating that the Helidon MicroProfile server has successfully started for the test suite.

```text
INFO io.helidon.microprofile.server.ServerCdiExtension: Server started on http://localhost:56293 (and all other host addresses) in 1893 milliseconds (since JVM startup).
```

--------------------------------

### start()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.microprofile.server/io/helidon/microprofile/server/ServerImpl.html

Starts the server. This method can only be used once and blocks until the operation is done. Returns the started Server instance.

```APIDOC
## start()

### Description
Starts the server. This method can only be used once and blocks until the operation is done.

### Method
start

### Signature
public Server start()

### Returns
Server instance, started

```

--------------------------------

### Security configuration example

Source: https://helidon.io/docs/v4/apidocs/io.helidon.security/io/helidon/security/package-summary.html

Example configuration for Google login and HTTP signatures.

```yaml
 security:
   provider-policy:
     # Composite policy when using more than one provider
     type: "COMPOSITE"
     authentication:
       # This is a frontend service - only allow google authentication
       - name: "google-login"
     outbound:
       # Propagate the goole token and this service's identity to backend
       - name: "google-login"
       - name: "http-signatures"
   providers:
     # Google login button support - authentication and identity propagation provider
     - google-login:
         client-id: "your-google-application-id"
     # Attribute based access control authorization provider
     - abac:
     # HTTP signatures - authentication and identity propagation provider (for service identity)
     - http-signatures:
         outbound:
         - name: "backend"
           hosts: ["localhost"]
           signature:
             key-id: "frontend"
             # password may be encrypted when using secure filter for Helidon config
             hmac.secret: "..."
```

--------------------------------

### get()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.security.integration.common/io/helidon/security/integration/common/SecurityTracing.html

Static method to get a SecurityTracing instance from the current Context or create a new one and start the security span.

```APIDOC
## get()

### Description
Gets an instance from the current Context or creates a new instance and starts the security span.

### Method
static get()

### Returns
- existing or a new tracing instance to be used for tracing security events
```

--------------------------------

### GET /health/started

Source: https://helidon.io/docs/v4/se/observability

Returns whether the service is started.

```APIDOC
## GET /health/started

### Description
Returns whether the service is started.

### Method
GET

### Endpoint
/health/started

### Response
#### Success Response (200)
Returns whether the service is started.

```

--------------------------------

### Run client application

Source: https://helidon.io/docs/v4/se/guides/webclient

Execute the ClientExample class and view the output.

```bash
java -cp target/helidon-quickstart-se.jar io.helidon.examples.quickstart.se.ClientExample
```

```text
{"message":"Hello World!"}
```

--------------------------------

### Build and run the application

Source: https://helidon.io/docs/v4/mp/guides/config

Package the application and start the JAR file.

```bash
mvn package -DskipTests=true
java -jar target/helidon-quickstart-mp.jar
```

--------------------------------

### setup(HttpRules rules, String docPath, Function<MediaType,String> content)

Source: https://helidon.io/docs/v4/apidocs/io.helidon.integrations.openapi.ui/io/helidon/integrations/openapi/ui/OpenApiUi.html

Sets up the service with routing rules, document path, and content function.

```APIDOC
## setup(HttpRules rules, String docPath, Function<MediaType,String> content)

### Description
Sets up the service.

### Method
setup

### Signature
public void setup(HttpRules rules, String docPath, Function<MediaType,String> content)

### Parameters
- rules (HttpRules) - Required - routing
- docPath (String) - Required - document context path
- content (Function<MediaType,String>) - Required - content function
```

--------------------------------

### Create ClientExample class

Source: https://helidon.io/docs/v4/se/guides/webclient

Initial structure for the ClientExample class in the io.helidon.examples.quickstart.se package.

```java
public class ClientExample {

    public static void main(String[] args) {

    }
}
```

--------------------------------

### GET /health/started/{name}

Source: https://helidon.io/docs/v4/se/observability

Returns whether the specified service is started.

```APIDOC
## GET /health/started/{name}

### Description
Returns whether the specified service is started.

### Method
GET

### Endpoint
/health/started/{name}

### Parameters
#### Path Parameters
- **name** (string) - Required - The name of the service.

### Response
#### Success Response (200)
Returns whether the specified service is started.

```

--------------------------------

### OpenApiUi.setup(HttpRules rules, String docPath, Function<MediaType,String> content)

Source: https://helidon.io/docs/v4/apidocs/io.helidon.common.media.type/io/helidon/common/media/type/class-use/MediaType.html

Sets up the OpenAPI UI service.

```APIDOC
## OpenApiUi.setup(HttpRules rules, String docPath, Function<MediaType,String> content)

### Description
Sets up the OpenAPI UI service.

### Method
void setup(HttpRules rules, String docPath, Function<MediaType,String> content)

### Parameters
- **rules** (HttpRules) - Required - The HTTP routing rules.
- **docPath** (String) - Required - The path to the OpenAPI document.
- **content** (Function<MediaType,String>) - Required - A function that returns content for a given media type.

### Return Type
void
```

--------------------------------

### instance()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.microprofile.cdi/io/helidon/microprofile/cdi/HelidonContainer.html

Static method to get the (initialized or started) container singleton instance.

```APIDOC
## instance()

### Description
Static method to get the (initialized or started) container singleton instance.

### Method
static instance()

### Returns
HelidonContainer - the singleton instance of container
```

--------------------------------

### WebLogic JMS Connector Configuration Example

Source: https://helidon.io/docs/v4/mp/reactive-messaging/weblogic

An example YAML configuration for the helidon-weblogic-jms connector, demonstrating both incoming and outgoing channel setups with JNDI and CDI destination syntax.

```yaml
mp:
  messaging:
    connector:
      helidon-weblogic-jms:
        # JMS factory configured in WebLogic
        jms-factory: jms/TestConnectionFactory
        # Path to the WLS Thin T3 client jar
        thin-jar: wlthint3client.jar
        url: t3://localhost:7001
    incoming:
      from-wls:
        connector: helidon-weblogic-jms
        # WebLogic CDI Syntax(CDI stands for Create Destination Identifier)
        destination: ./TestJMSModule!TestQueue
    outgoing:
      to-wls:
        connector: helidon-weblogic-jms
        # JNDI identifier for the same queue
        jndi.destination: jms/TestQueue
```

--------------------------------

### start()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.service.registry/io/helidon/service/registry/ServiceRegistryManager.html

Creates a new manager with default configuration and initializes all services that have a Service.RunLevel defined in ascending order (only singletons are initialized).

```APIDOC
## start()

### Description
Creates a new manager with default configuration, and initializes all services that have a Service.RunLevel defined in ascending order (only singletons are initialized).

### Method
start

### Signature
static ServiceRegistryManager start()

### Returns
- ServiceRegistryManager - A new manager instance with services started according to run levels.
```

--------------------------------

### HTTP Server Endpoint Example

Source: https://helidon.io/docs/v4/se/injection/declarative

A basic example of an HTTP endpoint class annotated with @RestServer.Endpoint, demonstrating path configuration, dependency injection, and a GET method returning JSON.

```java
@RestServer.Endpoint // identifies this class as a server endpoint
@Http.Path("/greet") // serve this endpoint on /greet context root (path)
@Service.Singleton   // a singleton service (single instance within a service registry)
static class GreetEndpoint {
    private static final JsonBuilderFactory JSON = Json.createBuilderFactory(Map.of());
    private final String greeting;

    // inject app.greeting configuration value, use "Hello" if not configured
    GreetEndpoint(@Configuration.Value("app.greeting") @Default.Value("Hello") String greeting) {
        this.greeting = greeting;
    }

    @Http.GET   // HTTP GET endpoint
    @Http.Produces(MediaTypes.APPLICATION_JSON_VALUE) // produces entity of application/json media type
    public JsonObject getDefaultMessageHandler() {
        // build the JSON object (requires `helidon-http-media-jsonp` on classpath)
        return JSON.createObjectBuilder()
                .add("message", greeting + " World!")
                .build();
    }
}
```

--------------------------------

### setup(ServerFeature.ServerFeatureContext featureContext)

Source: https://helidon.io/docs/v4/apidocs/io.helidon.openapi/io/helidon/openapi/OpenApiFeature.html

Sets up a server feature.

```APIDOC
## setup(ServerFeature.ServerFeatureContext featureContext)

### Description
Sets up a server feature.

### Method
void setup(ServerFeature.ServerFeatureContext featureContext)

### Parameters
- **featureContext** (ServerFeature.ServerFeatureContext) - Required - The server feature context
```

--------------------------------

### startingPhase()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.service.registry/io/helidon/service/registry/ActivationRequest.BuilderBase.html

Gets the phase to start activation. Typically, this should be left as the default (i.e., PENDING).

```APIDOC
## startingPhase()

### Description
Gets the phase to start activation. Typically, this should be left as the default (i.e., PENDING).

### Method
startingPhase

### Signature
public Optional<ActivationPhase> startingPhase()

### Returns
Phase to start

```

--------------------------------

### OpenApiService.setup(HttpRules routing, String docPath, Function<MediaType,String> content)

Source: https://helidon.io/docs/v4/apidocs/io.helidon.common.media.type/io/helidon/common/media/type/class-use/MediaType.html

Sets up the OpenAPI service.

```APIDOC
## OpenApiService.setup(HttpRules routing, String docPath, Function<MediaType,String> content)

### Description
Set up the service.

### Method
void setup(HttpRules routing, String docPath, Function<MediaType,String> content)

### Parameters
- **routing** (HttpRules) - Required - The HTTP routing rules.
- **docPath** (String) - Required - The path to the OpenAPI document.
- **content** (Function<MediaType,String>) - Required - A function that returns content for a given media type.

### Return Type
void
```

--------------------------------

### WebClient Runtime Configuration Example

Source: https://helidon.io/docs/v4/se/webclient

Demonstrates how to initialize a WebClient instance using a configuration object.

```java
Config config = Config.create();
WebClient client = WebClient.builder()
    .baseUri("http://localhost")
    .config(config.get("client"))
    .build();
```

--------------------------------

### get(int index)

Source: https://helidon.io/docs/v4/apidocs/io.helidon.data.codegen.query/io/helidon/data/codegen/query/CriteriaParameters.html

Returns the parameter at the specified index. Index values start from 0.

```APIDOC
## get(int index)

### Description
Returns the parameter at the specified index. Index values start from 0.

### Method
get(int index)

### Parameters
- **index** (int) - Required - parameter index

### Returns
- CharSequence - the parameter with the provided index
```

--------------------------------

### Initialize a Helidon SE project

Source: https://helidon.io/docs/v4

Use the Helidon CLI to generate a new project with the quickstart flavor.

```bash
helidon init --batch -Dflavor=se -Dapp-type=quickstart
```

--------------------------------

### kubectl get service - Output

Source: https://helidon.io/docs/v4/mp/guides/health

Example output showing the NodePort service with port 8080:30116/TCP.

```bash
NAME             TYPE       CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
helidon-health   NodePort   10.107.226.62   <none>        8080:30116/TCP   4s
```

--------------------------------

### Full Server Configuration Example

Source: https://helidon.io/docs/v4/mp/server

A complete YAML configuration example including port settings and management socket routing.

```yaml
server:
  port: 8080
  sockets:
   management:
   port: 8090

io.helidon.examples.AdminApplication:
  routing-name:
    name: "management"
    required: true
  routing-path:
    path: "/management"
```

--------------------------------

### Trigger the batch job via REST

Source: https://helidon.io/docs/v4/mp/guides/jbatch

Send a GET request to the batch endpoint to start the job.

```bash
curl -X GET http://localhost:8080/batch
```

--------------------------------

### SecurityTracing.get(Context context)

Source: https://helidon.io/docs/v4/apidocs/io.helidon.common.context/io/helidon/common/context/class-use/Context.html

Gets an instance from the provided Context or creates a new instance, registers it, and starts the security span.

```APIDOC
## SecurityTracing.get(Context context)

### Description
Gets an instance from the provided Context or creates a new instance, registers it, and starts the security span.

### Method
get(Context context)

### Parameters
- **context** (Context) - Required - The context to get or create the instance from.

### Returns
SecurityTracing - the SecurityTracing instance.
```

--------------------------------

### Build and Run Application

Source: https://helidon.io/docs/v4/mp/guides/oidc

Commands to package the application skipping unit tests and start the server.

```bash
mvn package -DskipTests
java -jar target/helidon-quickstart-mp.jar
```

--------------------------------

### Build and Run Second Service

Source: https://helidon.io/docs/v4/mp/guides/tracing

Compile the application and start the server.

```bash
mvn package -DskipTests=true
java -jar target/helidon-quickstart-mp-2.jar
```

--------------------------------

### Producing and Consuming with Oracle AQ

Source: https://helidon.io/docs/v4/se/reactive-messaging

Example demonstrating how to configure a PoolDataSource, set up an AqConnector, define channels for sending and receiving, and start the messaging system.

```java
PoolDataSource pds = PoolDataSourceFactory.getPoolDataSource();1
pds.setConnectionFactoryClassName("oracle.jdbc.pool.OracleDataSource");
pds.setURL(jdbcUrl);
pds.setUser("frank");
pds.setPassword("frank");
AqConnector connector = AqConnector.builder()2
        .dataSource("test-ds", pds)
        .build();
Channel<String> toAq = Channel.<String>builder()3
        .name("toAq")
        .subscriberConfig(AqConnector.configBuilder()
                                  .queue("example_queue_1")
                                  .dataSource("test-ds")
                                  .build())
        .build();

Channel<String> fromAq = Channel.<String>builder()4
        .name("fromAq")
        .publisherConfig(AqConnector.configBuilder()
                                 .queue("example_queue_1")
                                 .dataSource("test-ds")
                                 .build())
        .build();

Messaging.builder()5
        .connector(connector)
        .publisher(toAq,
                   Multi.just("Hello", "world", "from", "Oracle", "DB!")
                           .map(Message::of))6
        .listener(fromAq, s -> System.out.println("Message received: " + s))7
        .build()
        .start();
```

--------------------------------

### static Timer.Sample start()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.metrics.api/io/helidon/metrics/api/Timer.html

Starts a timing sample using the default system clock. For new code, prefer MetricsFactory.timerStart().

```APIDOC
## static Timer.Sample start()

### Description
Starts a timing sample using the default system clock. For new code, prefer MetricsFactory.timerStart() on the MetricsFactory instance used by the application.

### Method
start

### Returns
new sample
```

--------------------------------

### Configure Data Source via System Properties

Source: https://helidon.io/docs/v4/mp/persistence

Example of passing data source configuration as system properties when starting the application via the command line.

```bash
java \
  -Djavax.sql.DataSource.yourDataSourceName.somePropertyOfYourConnectionPoolAndDataSource=itsValue \
  -Djavax.sql.DataSource.yourDataSourceName.someOtherPropertyOfYourConnectionPoolAndDataSource=anotherValue \
  # ...
```

--------------------------------

### Build and Run Application

Source: https://helidon.io/docs/v4/mp/openapi

Use Maven to package the application and then execute the resulting JAR file.

```bash
mvn package
java -jar target/helidon-examples-microprofile-openapi.jar
```

--------------------------------

### Method with Indexed Parameters in @Data.Query

Source: https://helidon.io/docs/v4/mp/data

Example of using indexed parameters in a JPQL query where arguments must match the order of the query parameters starting at 1.

```java
@Data.Query("SELECT p.keeper FROM Pet p WHERE k.name = $1 AND p.category.name = $2")
Optional<Keeper> selectKeeper(String name, String category);
```

--------------------------------

### Initialize WebServer from Configuration File

Source: https://helidon.io/docs/v4/se/webserver

Load server configuration from the application.yaml file located on the classpath.

```java
Config config = Config.create();1
WebServer.builder()
        .config(config.get("server"));2
```

--------------------------------

### Expose a REST endpoint with Jakarta RESTful Web Services

Source: https://helidon.io/docs/v4/mp/introduction

A basic example of a REST resource class using the @Path and @GET annotations to define a simple endpoint.

```java
@Path("hello")
public class HelloWorld {
    @GET
    public String hello() {
        return "Hello World";
    }
}
```

--------------------------------

### HelidonTest setup with disabled discovery

Source: https://helidon.io/docs/v4/mp/lra

When CDI bean auto-discovery is not desired, add the LRA and Config CDI extensions manually. This example uses @DisableDiscovery, @AddJaxRs, @AddBean(TestLraCoordinator.class), @AddExtension(LraCdiExtension.class), @AddExtension(ConfigCdiExtension.class), and @AddBean(WithdrawResource.class).

```java
@HelidonTest
@DisableDiscovery
@AddJaxRs
@AddBean(TestLraCoordinator.class)
@AddExtension(LraCdiExtension.class)
@AddExtension(ConfigCdiExtension.class)
@AddBean(WithdrawResource.class)
public class LraNoDiscoveryTest {
}
```

--------------------------------

### started()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.microprofile.server/io/helidon/microprofile/server/ServerCdiExtension.html

Returns the state of the server.

```APIDOC
## Method: started()

### Description
State of the server.

### Signature
`public boolean started()`

### Returns
- **boolean** - True if the server is started, false otherwise.
```

--------------------------------

### Testing LRA-enabled JAX-RS resources with TestLraCoordinator

Source: https://helidon.io/docs/v4/apidocs/io.helidon.microprofile.testing.lra/io/helidon/microprofile/testing/lra/package-summary.html

Demonstrates how to use @HelidonTest and TestLraCoordinator to test LRA-enabled JAX-RS resources. The example includes the setup of the test class, LRA lifecycle methods, and a test case verifying the LRA status.

```java
 @HelidonTest
 @AddBean(TestLraCoordinator.class)
 @Path("/test")
 public class LraTest {

     private final WebTarget target;
     private final Set<String> completedLras;
     private final Set<String> cancelledLras;
     private final TestLraCoordinator coordinator;

     @Inject
     public LraTest(WebTarget target,
                    TestLraCoordinator coordinator) {
         this.target = target;
         this.coordinator = coordinator;
         this.completedLras = new CopyOnWriteArraySet<>();
         this.cancelledLras = new CopyOnWriteArraySet<>();
     }

     @PUT
     @Path("/withdraw")
     @LRA(LRA.Type.REQUIRES_NEW)
     public Response withdraw(@HeaderParam(LRA.LRA_HTTP_CONTEXT_HEADER) Optional<URI> lraId, String content) {
         ...
         return Response.ok().build();
     }

     @Complete
     public void complete(URI lraId) {
         completedLras.add(lraId.toString());
     }

     @Compensate
     public void rollback(URI lraId) {
         cancelledLras.add(lraId.toString());
     }

     @Test
     public void testLra() {
         try (Response res = target
                 .path("/test/withdraw")
                 .request()
                 .put(Entity.entity("test", MediaType.TEXT_PLAIN_TYPE))) {
             assertThat(res.getStatus(), is(200));
             String lraId = res.getHeaderString(LRA.LRA_HTTP_CONTEXT_HEADER);
             Lra lra = coordinator.lra(lraId);
             assertThat(lra.status(), is(LRAStatus.Closed));
             assertThat(completedLras, contains(lraId));
         }
     }
 }
```

--------------------------------

### started()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.microprofile.server/io/helidon/microprofile/server/ServerCdiExtension.html

Returns the state of the server.

```APIDOC
## started()

### Description
Returns the state of the server.

### Returns
- **boolean** - true if the server is already started, false otherwise
```

--------------------------------

### Build and Run Application

Source: https://helidon.io/docs/v4/mp/integrations/neo4j

Commands to package and execute the application.

```bash
mvn package
java -jar target/helidon-examples-integration-neo4j-mp.jar
```

--------------------------------

### setup(ServerFeature.ServerFeatureContext featureContext)

Source: https://helidon.io/docs/v4/apidocs/io.helidon.openapi/io/helidon/openapi/OpenApiFeature.html

Sets up a server feature, allowing modification of server configuration before the server is created.

```APIDOC
## setup(ServerFeature.ServerFeatureContext featureContext)

### Description
Sets up a server feature. Server features can modify server configuration, right before the server is created. To access listener configuration, or routing, a list of all listeners is provided. Specified by setup in interface ServerFeature.

### Method
setup

### Signature
public void setup(ServerFeature.ServerFeatureContext featureContext)

### Parameters
- featureContext (ServerFeature.ServerFeatureContext) - Required - to access builders of webserver, listeners, and routing
```

--------------------------------

### start()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.tracing/io/helidon/tracing/Span.Builder.html

Builds and starts the span with the current timestamp. Returns the newly created and started span.

```APIDOC
## start()

### Description
Builds and starts the span with the current timestamp.

### Method
start

### Returns
Newly created and started span.
```

--------------------------------

### Restore application from snapshot with output

Source: https://helidon.io/docs/v4/mp/guides/crac

Restore the application and observe the fast startup time.

```bash
java -XX:CRaCEngine=warp -XX:CRaCRestoreFrom=./target/cr
```

```text
warp: Restore successful!
[0x501ce1b2] http://0.0.0.0:8080 bound for socket '@default'
Restored all channels in 3 milliseconds. 43 milliseconds since JVM snapshot restore. Java 23.0.1
```

--------------------------------

### start()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.microprofile.cdi/io/helidon/microprofile/cdi/HelidonContainer.html

Starts the container, finishing the lifecycle of the CDI implementation. If already started, this method is a noop.

```APIDOC
## start()

### Description
Starts the container, finishing the lifecycle of the CDI implementation. If already started, this method is a noop.

### Method
start()

### Returns
SeContainer - the started container
```

--------------------------------

### Run greeting application

Source: https://helidon.io/docs/v4/se/guides/webclient

Start the main greeting application.

```bash
java -cp target/helidon-quickstart-se.jar io.helidon.examples.quickstart.se.Main
```

--------------------------------

### start(Instant instant)

Source: https://helidon.io/docs/v4/apidocs/io.helidon.tracing/io/helidon/tracing/Span.Builder.html

Starts the span with an explicit timestamp. Returns the newly created and started span.

```APIDOC
## start(Instant instant)

### Description
Starts the span with an explicit timestamp.

### Method
start

### Parameters
- `instant` (Instant) - Required - When the span started.

### Returns
Newly created and started span.
```

--------------------------------

### Build and Run the Application

Source: https://helidon.io/docs/v4/se/guides/tracing

Package the application skipping tests and start the JAR file.

```bash
mvn package -DskipTests=true
java -jar target/helidon-quickstart-se-2.jar
```

--------------------------------

### start()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.service.registry/io/helidon/service/registry/ServiceRegistryManager.html

Creates a new manager with default configuration and initializes all services that have a Service.RunLevel defined in ascending order (only singletons are initialized). Registers the registry as the GlobalServiceRegistry.

```APIDOC
## start()

### Description
Creates a new manager with default configuration, and initializes all services that have a `Service.RunLevel` defined in ascending order (only singletons are initialized). Registers the registry as the GlobalServiceRegistry.

### Method
static start

### Signature
public static ServiceRegistryManager start()

### Returns
A new registry manager with an initialized registry
```

--------------------------------

### get()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.webclient.grpc/io/helidon/webclient/grpc/GrpcClientConfig.BuilderBase.GrpcClientConfigImpl.html

Gets the GrpcClient instance.

```APIDOC
## Method: get

### Description
Gets the GrpcClient instance.

### Signature
public GrpcClient get()
```

--------------------------------

### range(int start, int count)

Source: https://helidon.io/docs/v4/apidocs/io.helidon.common.reactive/io/helidon/common/reactive/Multi.html

Creates a Multi that emits a range of integers starting from start with the given count.

```APIDOC
## range(int start, int count)

### Description
Create a Multi that emits a range of integers.

### Method
range

### Parameters
- start (int) - Required - The starting value.
- count (int) - Required - The number of values to emit.

### Returns
Multi<Integer> - A Multi that emits the range of integers.
```

--------------------------------

### create()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.webserver.observe.log/io/helidon/webserver/observe/log/LogObserver.html

Creates a new LogObserver with default configuration.

```APIDOC
## create()

### Description
Creates a new LogObserver with default configuration.

### Method
create

### Returns
A new LogObserver instance.
```

--------------------------------

### get(HeaderName name)

Source: https://helidon.io/docs/v4/apidocs/io.helidon.http/io/helidon/http/Headers.html

Get a header value.

```APIDOC
## get(HeaderName name)

### Description
Get a header value.

### Method
get

### Parameters
- **name** (HeaderName) - Required - name of the header

### Returns
Header - value if present
```

--------------------------------

### get()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.webclient.api/io/helidon/webclient/api/HttpClient.html

Shortcut for creating a GET request with the default path.

```APIDOC
## get()

### Description
Shortcut for creating a GET request with the default path.

### Method
get

### Signature
default REQ get()

### Returns
A new request (not thread safe).
```

--------------------------------

### Start the development loop

Source: https://helidon.io/docs/v4/cli

Navigate to the project directory and start the development loop to automatically recompile and restart the application on changes.

```bash
cd myproject
helidon dev
```

--------------------------------

### get(String path)

Source: https://helidon.io/docs/v4/apidocs/io.helidon.integrations.vault.secrets.kv/io/helidon/integrations/vault/secrets/kv2/Kv2Secrets.html

Gets the latest version of a secret.

```APIDOC
## get(String path)

### Description
Gets the latest version of a secret.

### Method
get

### Parameters
- **path** (String) - Required - The path of the secret.

### Returns
Optional<Kv2Secret> - The secret data if present.
```

--------------------------------

### get()

Source: https://helidon.io/docs/v4/apidocs/io.helidon.common.reactive/io/helidon/common/reactive/RequestedCounter.html

Gets the current requested event counter value.

```APIDOC
## Method: get()

### Description
Gets the current requested event counter value.

### Signature
public long get()

### Parameters
None.

### Returns
- **long** - current value of the requested event counter.
```

--------------------------------

### Lookup services by RunLevel.STARTUP

Source: https://helidon.io/docs/v4/apidocs/io.helidon.service.registry/io/helidon/service/registry/Service.RunLevel.html

Demonstrates how to retrieve all services configured with the STARTUP run level using the registry lookup builder.

```java
registry.all(Lookup.builder()
    .runLevel(Service.RunLevel.STARTUP)
    .build());
```

--------------------------------

### Bootstrap Client and execute a GET request

Source: https://helidon.io/docs/v4/mp/jaxrs/jaxrs-client

Obtain a Client instance to create a WebTarget and execute a synchronous GET request returning a Response object.

```java
Client client = ClientBuilder.newClient();
Response res = client
    .target("http://localhost:8080/greet")
    .request("text/plain")
    .get();
```

--------------------------------

### OpenTelemetry Configuration Example

Source: https://helidon.io/docs/v4/mp/tracing

Example configuration for OpenTelemetry in microprofile-config.properties.

```properties
tracing.service=helidon-otel-tracing-example1
tracing.global=false2
tracing.int-tags.0.example=13
tracing.tags.0.direction=north4
```

--------------------------------

### setup(HttpRouting.Builder routing)

Source: https://helidon.io/docs/v4/apidocs/io.helidon.security.providers.oidc/io/helidon/security/providers/oidc/OidcFeature.html

Sets up the feature by configuring the routing builder.

```APIDOC
## setup(HttpRouting.Builder routing)

### Description
Method to set up a feature. This method is specified by the HttpFeature interface.

### Method
setup

### Parameters
- **routing** (HttpRouting.Builder) - Required - Routing builder
```
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