Chapter 3. AHC

Async Http Client (AHC) Component

Available as of Camel 2.8

The ahc: component provides HTTP-based endpoints for consuming external HTTP resources (as a client to call external servers using HTTP). The component uses the Async Http Client library.

Maven users will need to add the following dependency to their pom.xml for this component:

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-ahc</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

URI format

ahc:http://hostname[:port][/resourceUri][?options]
ahc:https://hostname[:port][/resourceUri][?options]

Will by default use port 80 for HTTP and 443 for HTTPS.

You can append query options to the URI in the following format, ?option=value&option=value&...

AhcEndpoint Options

Name	Default Value	Description
`throwExceptionOnFailure`	`true`	Option to disable throwing the `AhcOperationFailedException` in case of failed responses from the remote server. This allows you to get all responses regardless of the HTTP status code.
`bridgeEndpoint`	`false`	If the option is true, then the Exchange.HTTP_URI header is ignored, and use the endpoint's URI for request. You may also set the throwExcpetionOnFailure to be false to let the AhcProducer send all the fault response back.
`transferException`	`false`	If enabled and an Exchange failed processing on the consumer side, and if the caused `Exception` was send back serialized in the response as a `application/x-java-serialized-object` content type (for example using Jetty or Servlet Camel components). On the producer side the exception will be deserialized and thrown as is, instead of the `AhcOperationFailedException`. The caused exception is required to be serialized.
`client`	`null`	To use a custom `com.ning.http.client.AsyncHttpClient`.
`clientConfig`	`null`	To configure the `AsyncHttpClient` to use a custom `com.ning.http.client.AsyncHttpClientConfig`.
`clientConfig.x`	`null`	To configure additional properties of the `com.ning.http.client.AsyncHttpClientConfig` instance used by the endpoint. Note that configuration options set using this parameter will be merged with those set using the `clientConfig` parameter or the instance set at the component level with properties set using this parameter taking priority.
`clientConfig.realm.x`	`null`	Camel 2.11: To configure realm properties of the `com.ning.http.client.AsyncHttpClientConfig` The options which can be used are the options from `com.ning.http.client.Realm.RealmBuilder`. eg to set scheme, you can configure `"clientConfig.realm.scheme=DIGEST"`
`binding`	`null`	To use a custom `org.apache.camel.component.ahc.AhcBinding`.
`sslContextParameters`	`null`	Camel 2.9: Reference to an `org.apache.camel.util.jsse.SSLContextParameters` object in the CAMEL:Registry. This reference overrides any configured SSLContextParameters at the component level. See chapter "Configuring Transport Security for Camel Components" in "Security Guide" and Using the JSSE Configuration Utility. Note that configuring this option will override any SSL/TLS configuration options provided through the clientConfig option at the endpoint or component level.
`bufferSize`	`4096`	Camel 2.10.3: The initial in-memory buffer size used when transferring data between Camel and AHC Client.

AhcComponent Options

Name	Default Value	Description
`client`	`null`	To use a custom `com.ning.http.client.AsyncHttpClient`.
`clientConfig`	`null`	To configure the `AsyncHttpClient`s use a custom `com.ning.http.client.AsyncHttpClientConfig`.
`binding`	`null`	To use a custom `org.apache.camel.component.ahc.AhcBinding`.
`sslContextParameters`	`null`	Camel 2.9: To configure custom SSL/TLS configuration options at the component level. See chapter "Configuring Transport Security for Camel Components" in "Security Guide" and Using the JSSE Configuration Utility for more details. Note that configuring this option will override any SSL/TLS configuration options provided through the clientConfig option at the endpoint or component level.

Notice that setting any of the options on the AhcComponent will propagate those options to AhcEndpoints being created. However the AhcEndpoint can also configure/override a custom option. Options set on endpoints will always take precedence over options from the AhcComponent.

Message Headers

Name	Type	Description
`Exchange.HTTP_URI`	`String`	URI to call. Will override existing URI set directly on the endpoint.
`Exchange.HTTP_PATH`	`String`	Request URI's path, the header will be used to build the request URI with the HTTP_URI. If the path is start with "/", http producer will try to find the relative path based on the Exchange.HTTP_BASE_URI header or the `exchange.getFromEndpoint().getEndpointUri();`
`Exchange.HTTP_QUERY`	`String`	URI parameters. Will override existing URI parameters set directly on the endpoint.
`Exchange.HTTP_RESPONSE_CODE`	`int`	The HTTP response code from the external server. Is 200 for OK.
`Exchange.HTTP_CHARACTER_ENCODING`	`String`	Character encoding.
`Exchange.CONTENT_TYPE`	`String`	The HTTP content type. Is set on both the IN and OUT message to provide a content type, such as `text/html`.
`Exchange.CONTENT_ENCODING`	`String`	The HTTP content encoding. Is set on both the IN and OUT message to provide a content encoding, such as `gzip`.

Message Body

Camel will store the HTTP response from the external server on the OUT body. All headers from the IN message will be copied to the OUT message, so headers are preserved during routing. Additionally Camel will add the HTTP response headers as well to the OUT message headers.

Response code

Camel will handle according to the HTTP response code:

Response code is in the range 100..299, Camel regards it as a success response.
Response code is in the range 300..399, Camel regards it as a redirection response and will throw a AhcOperationFailedException with the information.
Response code is 400+, Camel regards it as an external server failure and will throw a AhcOperationFailedException with the information. The option, throwExceptionOnFailure, can be set to false to prevent the AhcOperationFailedException from being thrown for failed response codes. This allows you to get any response from the remote server.

AhcOperationFailedException

This exception contains the following information:

The HTTP status code
The HTTP status line (text of the status code)
Redirect location, if server returned a redirect
Response body as a java.lang.String, if server provided a body as response

Calling using GET or POST

The following algorithm is used to determine if either GET or POST HTTP method should be used: 1. Use method provided in header. 2. GET if query string is provided in header. 3. GET if endpoint is configured with a query string. 4. POST if there is data to send (body is not null). 5. GET otherwise.

Configuring URI to call

You can set the HTTP producer's URI directly form the endpoint URI. In the route below, Camel will call out to the external server, oldhost, using HTTP.

from("direct:start")
	    .to("ahc:http://oldhost");

And the equivalent Spring sample:

<camelContext xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="direct:start"/>
    <to uri="ahc:http://oldhost"/>
  </route>
</camelContext>

You can override the HTTP endpoint URI by adding a header with the key, Exchange.HTTP_URI, on the message.

from("direct:start")
    .setHeader(Exchange.HTTP_URI, constant("http://newhost"))
    .to("ahc:http://oldhost");

Configuring URI Parameters

The ahc producer supports URI parameters to be sent to the HTTP server. The URI parameters can either be set directly on the endpoint URI or as a header with the key Exchange.HTTP_QUERY on the message.

from("direct:start")
	    .to("ahc:http://oldhost?order=123&detail=short");

Or options provided in a header:

from("direct:start")
            .setHeader(Exchange.HTTP_QUERY, constant("order=123&detail=short"))
	    .to("ahc:http://oldhost");

How to set the http method (GET/POST/PUT/DELETE/HEAD/OPTIONS/TRACE) to the HTTP producer

The HTTP component provides a way to set the HTTP request method by setting the message header. Here is an example;

from("direct:start")
            .setHeader(Exchange.HTTP_METHOD, constant("POST"))
	    .to("ahc:http://www.google.com")
            .to("mock:results");

And the equivalent Spring sample:

<camelContext xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="direct:start"/>
    <setHeader headerName="CamelHttpMethod">
        <constant>POST</constant>
    </setHeader>
    <to uri="ahc:http://www.google.com"/>
    <to uri="mock:results"/>
  </route>
</camelContext>

Configuring charset

If you are using POST to send data you can configure the charset using the Exchange property:

exchange.setProperty(Exchange.CHARSET_NAME, "iso-8859-1");

URI Parameters from the endpoint URI

In this sample we have the complete URI endpoint that is just what you would have typed in a web browser. Multiple URI parameters can of course be set using the & character as separator, just as you would in the web browser. Camel does no tricks here.

// we query for Camel at the Google page
template.sendBody("ahc:http://www.google.com/search?q=Camel", null);

URI Parameters from the Message

Map headers = new HashMap();
headers.put(Exchange.HTTP_QUERY, "q=Camel&lr=lang_en");
// we query for Camel and English language at Google
template.sendBody("ahc:http://www.google.com/search", null, headers);

In the header value above notice that it should not be prefixed with ? and you can separate parameters as usual with the & char.

Getting the Response Code

You can get the HTTP response code from the AHC component by getting the value from the Out message header with Exchange.HTTP_RESPONSE_CODE.

Exchange exchange = template.send("ahc:http://www.google.com/search", new Processor() {
            public void process(Exchange exchange) throws Exception {
                exchange.getIn().setHeader(Exchange.HTTP_QUERY, constant("hl=en&q=activemq"));
            }
   });
   Message out = exchange.getOut();
   int responseCode = out.getHeader(Exchange.HTTP_RESPONSE_CODE, Integer.class);

Configuring AsyncHttpClient

The AsyncHttpClient client uses a AsyncHttpClientConfig to configure the client. See the documentation at Async Http Client for more details.

The example below shows how to use a builder to create the AsyncHttpClientConfig which we configure on the AhcComponent.

// create a client config builder
AsyncHttpClientConfig.Builder builder = new AsyncHttpClientConfig.Builder();
// use the builder to set the options we want, in this case we want to follow redirects and try
// at most 3 retries to send a request to the host
AsyncHttpClientConfig config = builder.setFollowRedirects(true).setMaxRequestRetry(3).build();

// lookup AhcComponent
AhcComponent component = context.getComponent("ahc", AhcComponent.class);
// and set our custom client config to be used
component.setClientConfig(config);

In Camel 2.9, the AHC component uses Async HTTP library 1.6.4. This newer version provides added support for plain bean style configuration. The AsyncHttpClientConfigBean class provides getters and setters for the configuration options available in AsyncHttpClientConfig. An instance of AsyncHttpClientConfigBean may be passed directly to the AHC component or referenced in an endpoint URI using the clientConfig URI parameter.

Also available in Camel 2.9 is the ability to set configuration options directly in the URI. URI parameters starting with "clientConfig." can be used to set the various configurable properties of AsyncHttpClientConfig. The properties specified in the endpoint URI are merged with those specified in the configuration referenced by the "clientConfig" URI parameter with those being set using the "clientConfig." parameter taking priority. The AsyncHttpClientConfig instance referenced is always copied for each endpoint such that settings on one endpoint will remain independent of settings on any previously created endpoints. The example below shows how to configure the AHC component using the "clientConfig." type URI parameters.

from("direct:start")
    .to("ahc:http://localhost:8080/foo?clientConfig.maxRequestRetry=3&clientConfig.followRedirects=true")

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