Servlet Component
Available as of Camel version 2.0
The servlet: component provides HTTP based endpoints for consuming HTTP requests that arrive at a HTTP endpoint that is bound to a published Servlet.
Maven users will need to add the following dependency to their pom.xml
for this component:
<dependency>
<groupId>org.apache.camel</groupId>
<artifactId>camel-servlet</artifactId>
<version>x.x.x</version>
<\!-\- use the same version as your Camel core version \-->
</dependency>
INFO: Stream.
Servlet is stream based, which means the input it receives is submitted
to Camel as a stream. That means you will only be able to read the
content of the stream once. If you find a situation where the message
body appears to be empty or you need to access the data multiple times
(eg: doing multicasting, or redelivery error handling) you should use
Stream caching or convert the message body to
a String
which is safe to be read multiple times.
URI format
servlet://relative_path[?options]
You can append query options to the URI in the following format,
?option=value&option=value&…
Options
The Servlet component supports 8 options which are listed below.
Name | Description | Default | Type |
---|---|---|---|
servletName (consumer) |
Default name of servlet to use. The default name is CamelServlet. |
String |
|
httpRegistry (consumer) |
To use a custom org.apache.camel.component.servlet.HttpRegistry. |
HttpRegistry |
|
attachmentMultipart Binding (consumer) |
Whether to automatic bind multipart/form-data as attachments on the Camel Exchange. The options attachmentMultipartBinding=true and disableStreamCache=false cannot work together. Remove disableStreamCache to use AttachmentMultipartBinding. This is turn off by default as this may require servlet specific configuration to enable this when using Servlet’s. |
false |
boolean |
httpBinding (advanced) |
To use a custom HttpBinding to control the mapping between Camel message and HttpClient. |
HttpBinding |
|
httpConfiguration (advanced) |
To use the shared HttpConfiguration as base configuration. |
HttpConfiguration |
|
allowJavaSerialized Object (advanced) |
Whether to allow java serialization when a request uses context-type=application/x-java-serialized-object. This is by default turned off. If you enable this then be aware that Java will deserialize the incoming data from the request to Java and that can be a potential security risk. |
false |
boolean |
headerFilterStrategy (filter) |
To use a custom org.apache.camel.spi.HeaderFilterStrategy to filter header to and from Camel message. |
HeaderFilterStrategy |
|
resolveProperty Placeholders (advanced) |
Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders. |
true |
boolean |
The Servlet endpoint is configured using URI syntax:
servlet:contextPath
with the following path and query parameters:
Path Parameters (1 parameters):
Name | Description | Default | Type |
---|---|---|---|
contextPath |
Required The context-path to use |
String |
Query Parameters (21 parameters):
Name | Description | Default | Type |
---|---|---|---|
disableStreamCache (common) |
Determines whether or not the raw input stream from Servlet is cached or not (Camel will read the stream into a in memory/overflow to file Stream caching) cache. By default Camel will cache the Servlet input stream to support reading it multiple times to ensure it Camel can retrieve all data from the stream. However you can set this option to true when you for example need to access the raw stream such as streaming it directly to a file or other persistent store. DefaultHttpBinding will copy the request input stream into a stream cache and put it into message body if this option is false to support reading the stream multiple times. If you use Servlet to bridge/proxy an endpoint then consider enabling this option to improve performance in case you do not need to read the message payload multiple times. The http/http4 producer will by default cache the response body stream. If setting this option to true then the producers will not cache the response body stream but use the response stream as-is as the message body. |
false |
boolean |
headerFilterStrategy (common) |
To use a custom HeaderFilterStrategy to filter header to and from Camel message. |
HeaderFilterStrategy |
|
httpBinding (common) |
To use a custom HttpBinding to control the mapping between Camel message and HttpClient. |
HttpBinding |
|
async (consumer) |
Configure the consumer to work in async mode |
false |
boolean |
bridgeErrorHandler (consumer) |
Allows for bridging the consumer to the Camel routing Error Handler which mean any exceptions occurred while the consumer is trying to pickup incoming messages or the likes will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions that will be logged at WARN or ERROR level and ignored. |
false |
boolean |
chunked (consumer) |
If this option is false the Servlet will disable the HTTP streaming and set the content-length header on the response |
true |
boolean |
httpMethodRestrict (consumer) |
Used to only allow consuming if the HttpMethod matches such as GET/POST/PUT etc. Multiple methods can be specified separated by comma. |
String |
|
matchOnUriPrefix (consumer) |
Whether or not the consumer should try to find a target consumer by matching the URI prefix if no exact match is found. |
false |
boolean |
responseBufferSize (consumer) |
To use a custom buffer size on the javax.servlet.ServletResponse. |
Integer |
|
servletName (consumer) |
Name of the servlet to use |
CamelServlet |
String |
transferException (consumer) |
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. On the producer side the exception will be deserialized and thrown as is instead of the HttpOperationFailedException. The caused exception is required to be serialized. This is by default turned off. If you enable this then be aware that Java will deserialize the incoming data from the request to Java and that can be a potential security risk. |
false |
boolean |
attachmentMultipartBinding (consumer) |
Whether to automatic bind multipart/form-data as attachments on the Camel Exchange. The options attachmentMultipartBinding=true and disableStreamCache=false cannot work together. Remove disableStreamCache to use AttachmentMultipartBinding. This is turn off by default as this may require servlet specific configuration to enable this when using Servlet’s. |
false |
boolean |
eagerCheckContentAvailable (consumer) |
Whether to eager check whether the HTTP requests has content if the content-length header is 0 or not present. This can be turned on in case HTTP clients do not send streamed data. |
false |
boolean |
exceptionHandler (consumer) |
To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this options is not in use. By default the consumer will deal with exceptions that will be logged at WARN or ERROR level and ignored. |
ExceptionHandler |
|
exchangePattern (consumer) |
Sets the exchange pattern when the consumer creates an exchange. |
ExchangePattern |
|
optionsEnabled (consumer) |
Specifies whether to enable HTTP OPTIONS for this Servlet consumer. By default OPTIONS is turned off. |
false |
boolean |
traceEnabled (consumer) |
Specifies whether to enable HTTP TRACE for this Servlet consumer. By default TRACE is turned off. |
false |
boolean |
mapHttpMessageBody (advanced) |
If this option is true then IN exchange Body of the exchange will be mapped to HTTP body. Setting this to false will avoid the HTTP mapping. |
true |
boolean |
mapHttpMessageFormUrl EncodedBody (advanced) |
If this option is true then IN exchange Form Encoded body of the exchange will be mapped to HTTP. Setting this to false will avoid the HTTP Form Encoded body mapping. |
true |
boolean |
mapHttpMessageHeaders (advanced) |
If this option is true then IN exchange Headers of the exchange will be mapped to HTTP headers. Setting this to false will avoid the HTTP Headers mapping. |
true |
boolean |
synchronous (advanced) |
Sets whether synchronous processing should be strictly used or Camel is allowed to use asynchronous processing (if supported). |
false |
boolean |
Message Headers
Camel will apply the same Message Headers as the HTTP component.
Camel will also populate all request.parameter
and
request.headers
. For example, if a client request has the URL,
http://myserver/myserver?orderid=123
, the exchange will contain a
header named orderid
with the value 123.
Usage
You can consume only from endpoints generated by the Servlet component. Therefore, it should be used only as input into your Camel routes. To issue HTTP requests against other HTTP endpoints, use the HTTP Component
Putting Camel JARs in the app server boot classpath
If you put the Camel JARs such as camel-core
, camel-servlet
, etc. in
the boot classpath of your application server (eg usually in its lib
directory), then mind that the servlet mapping list is now shared
between multiple deployed Camel application in the app server.
Mind that putting Camel JARs in the boot classpath of the application server is generally not best practice!
So in those situations you must define a custom and unique servlet
name in each of your Camel application, eg in the web.xml
define:
<servlet>
<servlet-name>MyServlet</servlet-name>
<servlet-class>org.apache.camel.component.servlet.CamelHttpTransportServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>MyServlet</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
And in your Camel endpoints then include the servlet name as well
<route>
<from uri="servlet://foo?servletName=MyServlet"/>
...
</route>
From Camel 2.11 onwards Camel will detect this duplicate and fail to start the application. You can control to ignore this duplicate by setting the servlet init-parameter ignoreDuplicateServletName to true as follows:
<servlet>
<servlet-name>CamelServlet</servlet-name>
<display-name>Camel Http Transport Servlet</display-name>
<servlet-class>org.apache.camel.component.servlet.CamelHttpTransportServlet</servlet-class>
<init-param>
<param-name>ignoreDuplicateServletName</param-name>
<param-value>true</param-value>
</init-param>
</servlet>
But its strongly advised to use unique servlet-name for each Camel application to avoid this duplication clash, as well any unforeseen side-effects.
Sample
INFO: From Camel 2.7 onwards it’s easier to use Servlet in Spring web applications. See Servlet Tomcat Example for details.
In this sample, we define a route that exposes a HTTP service at
http://localhost:8080/camel/services/hello
.
First, you need to publish the
CamelHttpTransportServlet
through the normal Web Container, or OSGi Service.
Use the Web.xml
file to publish the
CamelHttpTransportServlet
as follows:
Then you can define your route as follows:
Note
|
Specify the relative path for camel-servlet endpoint
Since we are binding the Http transport with a published servlet, and we
don’t know the servlet’s application context path, the camel-servlet
endpoint uses the relative path to specify the endpoint’s URL. A client
can access the camel-servlet endpoint through the servlet publish
address: ("http://localhost:8080/camel/services") + RELATIVE_PATH("/hello") .
|
Sample when using Spring 3.x
Sample when using Spring 2.x
When using the Servlet component in a Camel/Spring application it’s
often required to load the Spring ApplicationContext after the Servlet
component has started. This can be accomplished by using Spring’s
ContextLoaderServlet
instead of ContextLoaderListener
. In that case
you’ll need to start ContextLoaderServlet
after
CamelHttpTransportServlet
like this:
<web-app>
<servlet>
<servlet-name>CamelServlet</servlet-name>
<servlet-class>
org.apache.camel.component.servlet.CamelHttpTransportServlet
</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet>
<servlet-name>SpringApplicationContext</servlet-name>
<servlet-class>
org.springframework.web.context.ContextLoaderServlet
</servlet-class>
<load-on-startup>2</load-on-startup>
</servlet>
<web-app>
Sample when using OSGi
From Camel 2.6.0, you can publish the CamelHttpTransportServlet as an OSGi service with help of SpringDM like this.
Then use this service in your camel route like this:
For versions prior to Camel 2.6 you can use an Activator
to publish
the
CamelHttpTransportServlet
on the OSGi platform
Usage with Spring-Boot
From Camel 2.19.0 onwards, the camel-servlet-starter library binds automatically all the rest endpoints under the "/camel/*" context path. The following table summarizes the additional configuration properties available in the camel-servlet-starter library. The automatic mapping of the Camel servlet can also be disabled.
Spring-Boot Property | Default | Description |
---|---|---|
camel.component.servlet.mapping.enabled |
|
Enables the automatic mapping of the servlet component into the Spring web context |
camel.component.servlet.mapping.context-path |
|
Context path used by the servlet component for automatic mapping |
camel.component.servlet.mapping.servlet-name |
|
The name of the Camel servlet |