Servlet

Since Camel 2.0

Only consumer is supported

The Servlet component provides HTTP-based endpoints for consuming HTTP requests that arrive at an 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]

Configuring Options

Camel components are configured on two separate levels:

  • component level

  • endpoint level

Configuring Component Options

At the component level, you set general and shared configurations that are, then, inherited by the endpoints. It is the highest configuration level.

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.

You can configure components using:

  • the Component DSL.

  • in a configuration file (application.properties, *.yaml files, etc).

  • directly in the Java code.

Configuring Endpoint Options

You usually spend more time setting up endpoints because they have many options. These options help you customize what you want the endpoint to do. The options are also categorized into whether the endpoint is used as a consumer (from), as a producer (to), or 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.

Property placeholders provide a few benefits:

  • They help prevent using hardcoded urls, port numbers, sensitive information, and other settings.

  • They allow externalizing the configuration from the code.

  • They help the code to become more flexible and reusable.

The following two sections list 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

bridgeErrorHandler (consumer)

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

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.

true

boolean

servletName (consumer)

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

CamelServlet

String

attachmentMultipartBinding (consumer (advanced))

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 (advanced))

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

String

httpRegistry (consumer (advanced))

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

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

contextPath (consumer)

Required The context-path to use.

String

Query Parameters (23 parameters)

Name Description Default Type

disableStreamCache (common)

Determines whether or not the raw input stream is cached or not. The Camel consumer (camel-servlet, camel-jetty etc.) will by default cache the 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 producer (camel-http) 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 (the stream can only be read once) as the message body.

false

boolean

headerFilterStrategy (common (advanced))

To use a custom HeaderFilterStrategy to filter header to and from Camel message.

HeaderFilterStrategy

httpBinding (common (advanced))

To use a custom HttpBinding to control the mapping between Camel message and HttpClient.

HttpBinding

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

transferException (common)

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

async (consumer)

Configure the consumer to work in async mode.

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

logException (consumer)

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

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 jakarta.servlet.ServletResponse.

Integer

servletName (consumer)

Name of the servlet to use.

CamelServlet

String

attachmentMultipartBinding (consumer (advanced))

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

bridgeErrorHandler (consumer (advanced))

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

eagerCheckContentAvailable (consumer (advanced))

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 (advanced))

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 (advanced))

Sets the exchange pattern when the consumer creates an exchange.

Enum values:

  • InOnly

  • InOut

ExchangePattern

fileNameExtWhitelist (consumer (advanced))

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

String

mapHttpMessageBody (consumer (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

mapHttpMessageFormUrlEncodedBody (consumer (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 (consumer (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

optionsEnabled (consumer (advanced))

Specifies whether to enable HTTP OPTIONS for this Servlet consumer. By default OPTIONS is turned off.

false

boolean

traceEnabled (consumer (advanced))

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.

Examples

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.

Example CamelHttpTransportServlet configuration

Camel Spring Boot / Camel Quarkus

When running camel-servlet on the Spring Boot or Camel Quarkus runtimes, CamelHttpTransportServlet is configured for you automatically and is driven by configuration properties. Refer to the camel-servlet configuration documentation for these runtimes.

Servlet container / application server

If you’re running Camel standalone on a Servlet container or application server, you can use web.xml to configure CamelHttpTransportServlet.

For example, to define a route that exposes an HTTP service under the path /services.

<web-app>
  <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>/services/*</url-pattern>
  </servlet-mapping>
</web-app>

Example route

from("servlet:hello").process(new Processor() {
    public void process(Exchange exchange) throws Exception {
        // Access HTTP headers sent by the client
        Message message = exchange.getMessage();
        String contentType = message.getHeader(Exchange.CONTENT_TYPE, String.class);
        String httpUri = message.getHeader(Exchange.HTTP_URI, String.class);

        // Set the response body
        message.setBody("<b>Got Content-Type: " + contentType = ", URI: " + httpUri + "</b>");
    }
});

Camel Servlet HTTP endpoint path

The full path where the camel-servlet HTTP endpoint is published depends on:

  • The Servlet application context path

  • The configured Servlet mapping URL patterns

  • The camel-servlet endpoint URI context path

For example, if the application context path is /camel and CamelHttpTransportServlet is configured with a URL mapping of /services/*. Then a Camel route like from("servlet:hello") would be published to a path like http://localhost:8080/camel/services/hello.

Servlet asynchronous support

To enable Camel to benefit from Servlet asynchronous support, you must enable the async boolean init parameter by setting it to true.

By default, the servlet thread pool is used for exchange processing. However, to use a custom thread pool, you can configure an init parameter named executorRef with the String value set to the name of a bean bound to the Camel registry of type Executor. If no bean was found in the Camel registry, the Servlet component will attempt to fall back on an executor policy or default executor service.

If you want to force exchange processing to wait in another container background thread, you can set the forceAwait boolean init parameter to true.

On the Camel Quarkus runtime, these init parameters can be set via configuration properties. Refer to the Camel Quarkus Servlet extension documentation for more information.

On other runtimes you can configure these parameters in web.xml as follows.

<web-app>
    <servlet>
        <servlet-name>CamelServlet</servlet-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-custom-thread-pool</param-value>
        </init-param>
    </servlet>

    <servlet-mapping>
        <servlet-name>CamelServlet</servlet-name>
        <url-pattern>/services/*</url-pattern>
    </servlet-mapping>
</web-app>

Camel JARs on an application server boot classpath

If deploying into an application server / servlet container and you choose to have Camel JARs such as camel-core, camel-servlet, etc on the boot classpath. Then the servlet mapping list will be shared between multiple deployed Camel application in the app server.

Having Camel JARs on the boot classpath of the application server is not best practice.

In this scenario, you must define a custom and unique servlet name in each of your Camel applications. For example, in web.xml:

<web-app>
    <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>
</web-app>

In your Camel servlet endpoints, include the servlet name:

from("servlet://foo?servletName=MyServlet")

Camel detects duplicate Servlet names and will fail to start the application. You can control and ignore such duplicates 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.

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 15 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 (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

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.mute-exception

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

camel.component.servlet.servlet-name

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

CamelServlet

String

camel.servlet.mapping.context-path

Context path used by the servlet component for automatic mapping.

/camel/*

String

camel.servlet.mapping.enabled

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

true

Boolean

camel.servlet.mapping.servlet-name

The name of the Camel servlet.

CamelServlet

String
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