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 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 10 options, which are listed below.

Name Description Default Type

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

servletName (consumer)

Default name of servlet to use. The default name is CamelServlet.

CamelServlet

String

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

fileNameExtWhitelist (consumer)

Whitelist of accepted filename extensions for accepting uploaded files. Multiple extensions can be separated by comma, such as txt,xml.

String

httpRegistry (consumer)

To use a custom org.apache.camel.component.servlet.HttpRegistry.

HttpRegistry

allowJavaSerializedObject (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

autowiredEnabled (advanced)

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

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

headerFilterStrategy (filter)

To use a custom org.apache.camel.spi.HeaderFilterStrategy to filter header to and from Camel message.

HeaderFilterStrategy

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 (23 parameters):

Name Description Default Type

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

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 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

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

muteException (consumer)

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

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 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

exchangePattern (consumer)

Sets the exchange pattern when the consumer creates an exchange. There are 3 enums and the value can be one of: InOnly, InOut, InOptionalOut

ExchangePattern

fileNameExtWhitelist (consumer)

Whitelist of accepted filename extensions for accepting uploaded files. Multiple extensions can be separated by comma, such as txt,xml.

String

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

mapHttpMessageFormUrlEncoded​Body (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>

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:

  1. Enable async boolean init parameter by setting it to true

  2. 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 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

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);
        }
    }

}

Usage with Spring-Boot

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

true

Enables the automatic mapping of the servlet component into the Spring web context

camel.component.servlet.mapping.context-path

/camel/*

Context path used by the servlet component for automatic mapping

camel.component.servlet.mapping.servlet-name

CamelServlet

The name of the Camel servlet

Spring Boot Auto-Configuration

When using servlet with Spring Boot make sure to use the following Maven dependency to have support for auto configuration:

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

The component supports 14 options, which are listed below.

Name Description Default Type

camel.component.servlet.allow-java-serialized-object

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

camel.component.servlet.attachment-multipart-binding

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

camel.component.servlet.autowired-enabled

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

camel.component.servlet.bridge-error-handler

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

camel.component.servlet.enabled

Whether to enable auto configuration of the servlet component. This is enabled by default.

Boolean

camel.component.servlet.file-name-ext-whitelist

Whitelist of accepted filename extensions for accepting uploaded files. Multiple extensions can be separated by comma, such as txt,xml.

String

camel.component.servlet.header-filter-strategy

To use a custom org.apache.camel.spi.HeaderFilterStrategy to filter header to and from Camel message. The option is a org.apache.camel.spi.HeaderFilterStrategy type.

HeaderFilterStrategy

camel.component.servlet.http-binding

To use a custom HttpBinding to control the mapping between Camel message and HttpClient. The option is a org.apache.camel.http.common.HttpBinding type.

HttpBinding

camel.component.servlet.http-configuration

To use the shared HttpConfiguration as base configuration. The option is a org.apache.camel.http.common.HttpConfiguration type.

HttpConfiguration

camel.component.servlet.http-registry

To use a custom org.apache.camel.component.servlet.HttpRegistry. The option is a org.apache.camel.http.common.HttpRegistry type.

HttpRegistry

camel.component.servlet.mapping.context-path

Context path used by the servlet component for automatic mapping.

/camel/*

String

camel.component.servlet.mapping.enabled

Enables the automatic mapping of the servlet component into the Spring web context.

true

Boolean

camel.component.servlet.mapping.servlet-name

The name of the Camel servlet.

CamelServlet

String

camel.component.servlet.servlet-name

Default name of servlet to use. The default name is CamelServlet.

CamelServlet

String
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