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51.3. ghttp
ghttp Component
The
ghttp component contributes to the Camel Components for Google App Engine (GAE). It provides connectivity to the GAE URL fetch service but can also be used to receive messages from servlets (the only way to receive HTTP requests on GAE). This is achieved by extending the Servlet component. As a consequence, ghttp URI formats and options sets differ on the consumer-side (from) and producer-side (to).
URI format
| Format | Context | Comment |
|---|---|---|
ghttp:///path[?options] |
Consumer | See also Servlet component |
ghttp://hostname[:port][/path][?options] ghttps://hostname[:port][/path][?options] |
Producer | See also Http component |
Options
| Name | Default Value | Context | Description |
|---|---|---|---|
bridgeEndpoint
|
true
|
Producer |
If set to true the Exchange.HTTP_URI header will be ignored. To override the default endpoint URI with the Exchange.HTTP_URI header set this option to false.
|
throwExceptionOnFailure
|
true
|
Producer |
Throw a org.apache.camel.component.gae.http if the response code is >= 400. To disable throwing an exception set this option to false.
|
inboundBindingRef
|
reference to GHttpBinding
|
Consumer |
Reference to an InboundBinding<GHttpEndpoint, HttpServletRequest, HttpServletResponse> in the Registry for customizing the binding of an Exchange to the Servlet API. The referenced binding is used as post-processor to org.apache.camel.component.http.HttpBinding.
|
outboundBindingRef
|
reference to GHttpBinding
|
Producer |
Reference to an OutboundBinding<GHttpEndpoint, HTTPRequest, HTTPResponse> in the Registry for customizing the binding of an Exchange to the URLFetchService.
|
On the consumer-side, all options of the Servlet component are supported.
Message headers
On the producer side, the following headers of the Http component are supported.
| Name | Type | Description |
|---|---|---|
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.
|
Exchange.HTTP_METHOD
|
String
|
The HTTP method to execute. One of GET, POST, PUT and DELETE. If not set, POST will be used if the message body is not null, GET otherwise.
|
Exchange.HTTP_QUERY
|
String
|
Overrides the query part of the endpoint URI or the the query part of Exchange.HTTP_URI (if defined). The query string must be in decoded form.
|
Exchange.HTTP_URI
|
String
|
Overrides the default endpoint URI if the bridgeEndpoint option is set to false. The URI string must be in decoded form.
|
Exchange.RESPONSE_CODE
|
int
|
The HTTP response code from URL fetch service responses. |
On the consumer-side all headers of the Servlet component component are supported.
Message body
On the producer side the
in message body is converted to a byte[]. The out message body is made available as InputStream. If the reponse size exceeds 1 megabyte a ResponseTooLargeException is thrown by the URL fetch service (see quotas and limits).
Receiving messages
For receiving messages via the
ghttp component, a CamelHttpTransportServlet must be configured and mapped in the application's web.xml (see the section called “The web.xml”). For example, to handle requests targeted at http://<appname>.appspot.com/camel/* or http://localhost/camel/* (when using a local development server) the following servlet mapping must be defined:
web.xml
...
<servlet>
<servlet-name>CamelServlet</servlet-name>
<servlet-class>org.apache.camel.component.servlet.CamelHttpTransportServlet</servlet-class>
...
</servlet>
...
<servlet-mapping>
<servlet-name>CamelServlet</servlet-name>
<url-pattern>/camel/*</url-pattern>
</servlet-mapping>
...
Endpoint URI path definitions are relative to this servlet mapping e.g. the route
from("ghttp:///greeting").transform().constant("Hello")
processes requests targeted at
http://<appname>.appspot.com/camel/greeting. In this example, the request body is ignored and the response body is set to Hello. Requests targeted at http://<appname>.appspot.com/camel/greeting/* are not processed by default. This requires setting the option matchOnUriPrefix to true.
from("ghttp:///greeting?matchOnUriPrefix=true").transform().constant("Hello")Sending messages
For sending resquests to external HTTP services the
ghttp component uses the URL fetch service. For example, the Apache Camel homepage can the retrieved with the following endpoint definition on the producer-side.
from(...)
...
.to("ghttp://camel.apache.org")
...
The HTTP method used depends on the
Exchange.HTTP_METHOD message header or on the presence of an in-message body (GET if null, POST otherwise). Retrieving the Camel homepage via a GAE application is as simple as
from("ghttp:///home")
.to("ghttp://camel.apache.org")
Sending a
GET request to http://<appname>.appspot.com/camel/home returns the Camel homepage. HTTPS-based communication with external services can be enabled with the ghttps scheme.
from(...)
...
.to("ghttps://svn.apache.org/repos/asf/camel/trunk/")
...Dependencies
Maven users will need to add the following dependency to their
pom.xml.
pom.xml
<dependency>
<groupId>org.apache.camel</groupId>
<artifactId>camel-gae</artifactId>
<version>${camel-version}</version>
</dependency>
where
${camel-version} must be replaced by the actual version of Apache Camel (2.1.0 or higher).
