Servlet
Since Camel 2.0
Only consumer is supported
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>
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 |
Configuring Options
Camel components are configured on two separate levels:
-
component level
-
endpoint level
Configuring Component Options
The component level is the highest level which holds general and common configurations that are inherited by the endpoints. For example a component may have security settings, credentials for authentication, urls for network connection and so forth.
Some components only have a few options, and others may have many. Because components typically have pre configured defaults that are commonly used, then you may often only need to configure a few options on a component; or none at all.
Configuring components can be done with the Component DSL, in a configuration file (application.properties|yaml), or directly with Java code.
Configuring Endpoint Options
Where you find yourself configuring the most is on endpoints, as endpoints often have many options, which allows you to configure what you need the endpoint to do. The options are also categorized into whether the endpoint is used as consumer (from) or as a producer (to), or used for both.
Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL and DataFormat DSL as a type safe way of configuring endpoints and data formats in Java.
A good practice when configuring options is to use Property Placeholders, which allows to not hardcode urls, port numbers, sensitive information, and other settings. In other words placeholders allows to externalize the configuration from your code, and gives more flexibility and reuse.
The following two sections lists all the options, firstly for the component followed by the endpoint.
Component Options
The Servlet component supports 11 options, which are listed below.
Name | Description | Default | Type |
---|---|---|---|
Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. 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 |
|
If enabled and an Exchange failed processing on the consumer side the response’s body won’t contain the exception’s stack trace. |
true |
boolean |
|
Default name of servlet to use. The default name is CamelServlet. |
CamelServlet |
String |
|
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 |
|
Whitelist of accepted filename extensions for accepting uploaded files. Multiple extensions can be separated by comma, such as txt,xml. |
String |
||
To use a custom org.apache.camel.component.servlet.HttpRegistry. |
HttpRegistry |
||
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 |
|
Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. |
true |
boolean |
|
To use a custom HttpBinding to control the mapping between Camel message and HttpClient. |
HttpBinding |
||
To use the shared HttpConfiguration as base configuration. |
HttpConfiguration |
||
To use a custom org.apache.camel.spi.HeaderFilterStrategy to filter header to and from Camel message. |
HeaderFilterStrategy |
Endpoint Options
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 |
---|---|---|---|
Required The context-path to use. |
String |
Query Parameters (23 parameters)
Name | Description | Default | Type |
---|---|---|---|
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 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 |
|
To use a custom HeaderFilterStrategy to filter header to and from Camel message. |
HeaderFilterStrategy |
||
To use a custom HttpBinding to control the mapping between Camel message and HttpClient. |
HttpBinding |
||
If this option is false the Servlet will disable the HTTP streaming and set the content-length header on the response. |
true |
boolean |
|
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 |
|
Configure the consumer to work in async mode. |
false |
boolean |
|
Used to only allow consuming if the HttpMethod matches, such as GET/POST/PUT etc. Multiple methods can be specified separated by comma. |
String |
||
If enabled and an Exchange failed processing on the consumer side the exception’s stack trace will be logged when the exception stack trace is not sent in the response’s body. |
false |
boolean |
|
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 |
|
If enabled and an Exchange failed processing on the consumer side the response’s body won’t contain the exception’s stack trace. |
false |
boolean |
|
To use a custom buffer size on the jakarta.servlet.ServletResponse. |
Integer |
||
Name of the servlet to use. |
CamelServlet |
String |
|
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 |
|
Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. 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 |
|
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 |
|
To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored. |
ExceptionHandler |
||
Sets the exchange pattern when the consumer creates an exchange. Enum values:
|
ExchangePattern |
||
Whitelist of accepted filename extensions for accepting uploaded files. Multiple extensions can be separated by comma, such as txt,xml. |
String |
||
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 |
|
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 |
|
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 |
|
Specifies whether to enable HTTP OPTIONS for this Servlet consumer. By default OPTIONS is turned off. |
false |
boolean |
|
Specifies whether to enable HTTP TRACE for this Servlet consumer. By default TRACE is turned off. |
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>
Camel detects 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 it is strongly advised to use unique servlet-name
for each Camel
application to avoid this duplication clash, as well any unforeseen
side-effects.
Servlet >= 3.0 and AsyncContext
To enable Camel to benefit from Servlet asynchronous support you must:
-
Enable
async
boolean init parameter by setting it totrue
-
Without more configuration it will reuse servlet thread pool to handle the processing but you can set
executorRef
to an executor service reference to let another pool handle the processing of the exchange. It will use camel context registry by default and potentially fallback on an executor policy or default executor service if no bean matches this name.
Note that to force camel to get back pre-3.7.0 behavior which was to wait in another container background thread, you can set forceAwait
boolean init parameter to true
.
Sample async configuration:
<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>async</param-name>
<param-value>true</param-value>
</init-param>
<init-param>
<param-name>executorRef</param-name>
<param-value>my-threads</param-value>
</init-param>
</servlet>
Sample
Use Servlet in Spring web applications for simplicity’s sake. 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:
<web-app>
<servlet>
<servlet-name>CamelServlet</servlet-name>
<display-name>Camel Http Transport Servlet</display-name>
<servlet-class>org.apache.camel.component.servlet.CamelHttpTransportServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CamelServlet</servlet-name>
<url-pattern>/services/*</url-pattern>
</servlet-mapping>
</web-app>
Then you can define your route as follows:
from("servlet:hello?matchOnUriPrefix=true").process(new Processor() {
public void process(Exchange exchange) throws Exception {
String contentType = exchange.getIn().getHeader(Exchange.CONTENT_TYPE, String.class);
String path = exchange.getIn().getHeader(Exchange.HTTP_URI, String.class);
path = path.substring(path.lastIndexOf("/"));
assertEquals(CONTENT_TYPE, contentType, "Get a wrong content type");
// assert camel http header
String charsetEncoding = exchange.getIn().getHeader(Exchange.HTTP_CHARACTER_ENCODING, String.class);
assertEquals(charsetEncoding, "Get a wrong charset name from the message heaer", "UTF-8");
// assert exchange charset
assertEquals(exchange.getProperty(Exchange.CHARSET_NAME), "Get a wrong charset naem from the exchange property", "UTF-8");
exchange.getOut().setHeader(Exchange.CONTENT_TYPE, contentType + "; charset=UTF-8");
exchange.getOut().setHeader("PATH", path);
exchange.getOut().setBody("<b>Hello World</b>");
}
});
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 |
Sample when using Spring
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
You can publish the CamelHttpTransportServlet as an OSGi service with Blueprint like this:
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.osgi.org/xmlns/blueprint/v1.0.0 https://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd">
<bean id="camelServlet" class="org.apache.camel.component.servlet.CamelHttpTransportServlet" />
<!--
Enlist it in OSGi service registry.
This will cause two things:
1) As the pax web whiteboard extender is running the CamelServlet will
be registered with the OSGi HTTP Service
2) It will trigger the HttpRegistry in other bundles so the servlet is
made known there too
-->
<service ref="camelServlet">
<interfaces>
<value>javax.servlet.Servlet</value>
<value>org.apache.camel.http.common.CamelServlet</value>
</interfaces>
<service-properties>
<entry key="alias" value="/camel/services" />
<entry key="matchOnUriPrefix" value="true" />
<entry key="servlet-name" value="CamelServlet" />
</service-properties>
</service>
</blueprint>
Then use this service in your Camel route like this:
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
xmlns:ext="http://aries.apache.org/blueprint/xmlns/blueprint-ext/v1.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.osgi.org/xmlns/blueprint/v1.0.0 https://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd">
<reference id="servletref" ext:proxy-method="classes" interface="org.apache.camel.http.common.CamelServlet">
<reference-listener ref="httpRegistry" bind-method="register" unbind-method="unregister" />
</reference>
<bean id="httpRegistry" class="org.apache.camel.component.servlet.DefaultHttpRegistry" />
<bean id="servlet" class="org.apache.camel.component.servlet.ServletComponent">
<property name="httpRegistry" ref="httpRegistry" />
</bean>
<bean id="servletProcessor" class="org.apache.camel.example.servlet.ServletProcessor" />
<camelContext xmlns="http://camel.apache.org/schema/blueprint">
<route>
<!-- Notice how we can use the servlet scheme which is that reference above -->
<from uri="servlet://hello" />
<process ref="servletProcessor" />
</route>
</camelContext>
</blueprint>
You can use an Activator
to publish
the
CamelHttpTransportServlet
on the OSGi platform:
import java.util.Dictionary;
import java.util.Hashtable;
import org.apache.camel.component.servlet.CamelHttpTransportServlet;
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;
import org.osgi.service.http.HttpContext;
import org.osgi.service.http.HttpService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.osgi.context.BundleContextAware;
public final class ServletActivator implements BundleActivator, BundleContextAware {
private static final Logger LOG = LoggerFactory.getLogger(ServletActivator.class);
private static boolean registerService;
/**
* HttpService reference.
*/
private ServiceReference<?> httpServiceRef;
/**
* Called when the OSGi framework starts our bundle
*/
public void start(BundleContext bc) throws Exception {
registerServlet(bc);
}
/**
* Called when the OSGi framework stops our bundle
*/
public void stop(BundleContext bc) throws Exception {
if (httpServiceRef != null) {
bc.ungetService(httpServiceRef);
httpServiceRef = null;
}
}
protected void registerServlet(BundleContext bundleContext) throws Exception {
httpServiceRef = bundleContext.getServiceReference(HttpService.class.getName());
if (httpServiceRef != null && !registerService) {
LOG.info("Register the servlet service");
final HttpService httpService = (HttpService)bundleContext.getService(httpServiceRef);
if (httpService != null) {
// create a default context to share between registrations
final HttpContext httpContext = httpService.createDefaultHttpContext();
// register the hello world servlet
final Dictionary<String, String> initParams = new Hashtable<String, String>();
initParams.put("matchOnUriPrefix", "false");
initParams.put("servlet-name", "CamelServlet");
httpService.registerServlet("/camel/services", // alias
new CamelHttpTransportServlet(), // register servlet
initParams, // init params
httpContext // http context
);
registerService = true;
}
}
}
public void setBundleContext(BundleContext bc) {
try {
registerServlet(bc);
} catch (Exception e) {
LOG.error("Cannot register the servlet, the reason is {}", e);
}
}
}