Chapter 58. Servlet
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>{CamelSBVersion}</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.
58.1. URI format
servlet://relative_path[?options]
58.2. Configuring Options
Camel components are configured on two separate levels:
- component level
- endpoint level
58.2.1. 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.
58.2.2. 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 as a type safe way of configuring endpoints.
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.
58.3. 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 means 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 |
| 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 |
| 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 turned off by default as this may require servlet specific configuration to enable this when using Servlets. | 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 |
58.4. Endpoint Options
The Servlet endpoint is configured using URI syntax:
servlet:contextPath
with the following path and query parameters:
58.4.1. Path Parameters (1 parameters)
| Name | Description | Default | Type |
|---|---|---|---|
| contextPath (consumer) | Required The context-path to use. | String |
58.4.2. Query Parameters (22 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 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 this option is set 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 (advanced)) | 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 means 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 sent back serialized in the response as an 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 (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 turned off by default as this may require servlet specific configuration to enable this when using Servlets. | 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:
| 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 |
58.5. 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.
58.6. 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.
58.7. 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> </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 turned 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 means 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.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. | false | 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 |
