Stream

Since Camel 1.3

Both producer and consumer are supported

The Stream component provides access to the System.in, System.out and System.err streams as well as allowing streaming of file.

Maven users will need to add the following dependency to their pom.xml for this component:

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

URI format

stream:in[?options]
stream:out[?options]
stream:err[?options]
stream:header[?options]
stream:file?fileName=/foo/bar.txt
stream:http?httpUrl=http:myserver:8080/data

If the stream:header URI is specified, the stream header is used to find the stream to write to. This option is available only for stream producers (that is, it cannot appear in from()).

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 Stream component supports 3 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

lazyStartProducer (producer)

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

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

Endpoint Options

The Stream endpoint is configured using URI syntax:

stream:kind

With the following path and query parameters:

Path Parameters (1 parameters)

Name Description Default Type

kind (common)

Required Kind of stream to use such as System.in, System.out, a file, or a http url.

Enum values:

  • in

  • out

  • err

  • header

  • file

  • http

String

Query Parameters (23 parameters)

Name Description Default Type

encoding (common)

You can configure the encoding (is a charset name) to use text-based streams (for example, message body is a String object). If not provided, Camel uses the JVM default Charset.

String

fileName (common)

When using the stream:file URI format, this option specifies the filename to stream to/from.

String

fileWatcher (consumer)

To use JVM file watcher to listen for file change events to support re-loading files that may be overwritten, somewhat like tail --retry.

false

boolean

groupLines (consumer)

To group X number of lines in the consumer. For example to group 10 lines and therefore only spit out an Exchange with 10 lines, instead of 1 Exchange per line.

int

groupStrategy (consumer)

Allows to use a custom GroupStrategy to control how to group lines.

GroupStrategy

httpHeaders (consumer)

When using stream:http format, this option specifies optional http headers, such as Accept: application/json. Multiple headers can be separated by comma. The format of headers can be either HEADER=VALUE or HEADER:VALUE. In accordance with the HTTP/1.1 specification, leading and/or trailing whitespace is ignored.

String

httpUrl (consumer)

When using stream:http format, this option specifies the http url to stream from.

String

initialPromptDelay (consumer)

Initial delay in milliseconds before showing the message prompt. This delay occurs only once. Can be used during system startup to avoid message prompts being written while other logging is done to the system out.

2000

long

promptDelay (consumer)

Optional delay in milliseconds before showing the message prompt.

long

promptMessage (consumer)

Message prompt to use when reading from stream:in; for example, you could set this to Enter a command:.

String

readLine (consumer)

Whether to read the input stream in line mode (terminate by line breaks). Setting this to false, will instead read the entire stream until EOL.

true

boolean

retry (consumer)

Will retry opening the stream if it’s overwritten, somewhat like tail --retry If reading from files then you should also enable the fileWatcher option, to make it work reliable.

false

boolean

scanStream (consumer)

To be used for continuously reading a stream such as the unix tail command.

false

boolean

scanStreamDelay (consumer)

Delay in milliseconds between read attempts when using scanStream.

long

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

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

appendNewLine (producer)

Whether to append a new line character at end of output.

true

boolean

autoCloseCount (producer)

Number of messages to process before closing stream on Producer side. Never close stream by default (only when Producer is stopped). If more messages are sent, the stream is reopened for another autoCloseCount batch.

int

closeOnDone (producer)

This option is used in combination with Splitter and streaming to the same file. The idea is to keep the stream open and only close when the Splitter is done, to improve performance. Mind this requires that you only stream to the same file, and not 2 or more files.

false

boolean

delay (producer)

Initial delay in milliseconds before producing the stream.

long

lazyStartProducer (producer (advanced))

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

boolean

readTimeout (advanced)

Sets the read timeout to a specified timeout, in milliseconds. A non-zero value specifies the timeout when reading from Input stream when a connection is established to a resource. If the timeout expires before there is data available for read, a java.net.SocketTimeoutException is raised. A timeout of zero is interpreted as an infinite timeout.

int

Message Headers

The Stream component supports 2 message header(s), which is/are listed below:

Name Description Default Type

CamelStreamIndex (consumer)

Constant: STREAM_INDEX

The index.

long

CamelStreamComplete (consumer)

Constant: STREAM_COMPLETE

Is complete.

boolean

Message content

The Stream component supports either String or byte[] for writing to streams. Just add either String or byte[] content to the message.in.body. Messages sent to the stream: producer in binary mode are not followed by the newline character (as opposed to the String messages). Message with null body will not be appended to the output stream.
The special stream:header URI is used for custom output streams. Just add a java.io.OutputStream object to message.in.header in the key header.
See samples for an example.

Examples

In the following sample we route messages from the direct:in endpoint to the System.out stream:

// Route messages to the standard output.
from("direct:in").to("stream:out");

// Send String payload to the standard output.
// Message will be followed by the newline.
template.sendBody("direct:in", "Hello Text World");

// Send byte[] payload to the standard output.
// No newline will be added after the message.
template.sendBody("direct:in", "Hello Bytes World".getBytes());

The following sample demonstrates how the header type can be used to determine which stream to use. In the sample we use our own output stream, MyOutputStream.

The following sample demonstrates how to continuously read a file stream (analogous to the UNIX tail command):

from("stream:file?fileName=/server/logs/server.log&scanStream=true&scanStreamDelay=1000")
  .to("bean:logService?method=parseLogLine");

If you want to re-load the file if it roll over/rewritten then you should also turn on the fileWatcher and retry options.

from("stream:file?fileName=/server/logs/server.log&scanStream=true&scanStreamDelay=1000&retry=true&fileWatcher=true")
  .to("bean:logService?method=parseLogLine");

Reading HTTP server side streaming

The camel-stream component has basic support for connecting to a remote HTTP server and read streaming data (chunk of data separated by new-line).

from("stream:http?scanStream=true&httpUrl=http://localhost:8500")
  .to("log:input");

Spring Boot Auto-Configuration

When using stream 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-stream-starter</artifactId>
  <version>x.x.x</version>
  <!-- use the same version as your Camel core version -->
</dependency>

The component supports 4 options, which are listed below.

Name Description Default Type

camel.component.stream.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.stream.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.stream.enabled

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

Boolean

camel.component.stream.lazy-start-producer

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

Boolean
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