Message Size

Camel can track the size of message payloads (body and headers) at the endpoint level. This is useful for observability — understanding how large messages are, detecting payload bloat, and monitoring size trends over time. Sizes are tracked per endpoint for both incoming (IN) and outgoing (OUT) directions.

Message size tracking is disabled by default and must be explicitly enabled. It also requires extended management statistics level.

Message size tracking is a global feature. When enabled, it applies to all endpoints in the CamelContext. There is no fine-grained control to enable or disable it per route or per endpoint.
Streaming message bodies (such as InputStream) are only supported when Stream Caching is enabled. Without stream caching, the body size of streaming payloads cannot be determined and will be reported as -1 (unknown).

How it works

When enabled, Camel computes message body and headers sizes using the RuntimeEndpointRegistry event mechanism:

  • IN direction — sizes are computed when an exchange is created by a consumer endpoint (e.g., an HTTP request arrives, a file is consumed, a JMS message is received). The computed sizes are also stored as exchange properties (CamelMessageBodySize and CamelMessageHeadersSize) for use during routing.

  • OUT direction — sizes are computed when a message is sent to a producer endpoint (e.g., sending to a Kafka topic, writing to a file, calling an HTTP service).

Size statistics (min, max, mean) are collected per endpoint and exposed via JMX as part of the runtime endpoint statistics.

A pluggable MessageSizeStrategy computes the actual sizes.

Enabling Message Size

Message size tracking requires both the messageSizeEnabled option and Extended statistics level:

  • Application Properties

  • Java

camel.main.messageSizeEnabled = true
camel.main.jmxManagementStatisticsLevel = Extended
CamelContext context = ...
context.setMessageSize(true);
context.getManagementStrategy().getManagementAgent()
    .setStatisticsLevel(ManagementStatisticsLevel.Extended);
Message size tracking is automatically enabled when running with the dev profile.
You can run Camel JBang: camel doc main --filter=messageSize from CLI to see message size options.

Default size computation

The default MessageSizeStrategy computes body size using type-specific logic. If the body type is not recognized, it falls back to the Content-Length header (useful for HTTP components where the body is a stream). If size cannot be determined, it returns -1 and the exchange is not included in the size statistics.

Body size

Body type Size computation

null

0

byte[]

Array length

String

UTF-8 encoded byte length

StreamCache

length() method

WrappedFile

getFileLength() method (covers file, FTP, and similar components)

File

length() method

Path

Files.size()

Content-Length header

Fallback: uses the Content-Length message header value

Other

-1 (unknown, not tracked)

Headers size

The total headers size is computed by iterating all message headers and summing:

  • Each header key’s UTF-8 byte length

  • Each header value’s toString() UTF-8 byte length

Returns 0 if there are no headers.

Endpoint statistics via JMX

When JMX is enabled with Extended statistics level, size statistics are available in the runtime endpoint registry MBean alongside the existing endpoint hit counts.

The statistics are part of the endpointStatistics tabular data on the RuntimeEndpointRegistry MBean (under org.apache.camel domain, type services):

Column Description

url

Endpoint URI

routeId

Associated route ID

direction

in for consumer endpoints, out for producer endpoints

hits

Number of messages processed

minBodySize

Smallest message body size observed (bytes), -1 if not tracked

maxBodySize

Largest message body size observed (bytes), -1 if not tracked

meanBodySize

Average message body size observed (bytes), -1 if not tracked

minHeadersSize

Smallest total headers size observed (bytes), -1 if not tracked

maxHeadersSize

Largest total headers size observed (bytes), -1 if not tracked

meanHeadersSize

Average total headers size observed (bytes), -1 if not tracked

The statistics are reset when the endpoint registry statistics are reset.

Exchange properties

For the IN direction, the computed sizes are available as exchange properties during routing. You can use them for logging, content-based routing, or custom processing:

from("seda:start")
    .log("Body size: ${exchangeProperty.CamelMessageBodySize} bytes")
    .choice()
        .when(exchangeProperty("CamelMessageBodySize").isGreaterThan(1048576))
            .to("direct:largeMessage")
        .otherwise()
            .to("direct:normalMessage");
Property Description

CamelMessageBodySize

Body size in bytes, or -1 if unknown

CamelMessageHeadersSize

Total headers size in bytes
Exchange properties are set when the consumer endpoint creates the exchange. They reflect the size of the incoming message as received by the route.

Custom strategy

You can provide a custom MessageSizeStrategy implementation for specialized sizing logic (for example, to handle application-specific body types):

CamelContext context = ...
context.setMessageSizeStrategy(new MyCustomMessageSizeStrategy());
context.setMessageSize(true);

The strategy must implement org.apache.camel.spi.MessageSizeStrategy.

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