JSLT

Since Camel 3.1

Only producer is supported

The Jslt component allows you to process a JSON messages using an JSLT expression. This can be ideal when doing JSON to JSON transformation or querying data.

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

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

URI format

jslt:specName[?options]

Where specName is the classpath-local URI of the specification to invoke; or the complete URL of the remote specification (eg: file://folder/myfile.vm).

Configuring Options

Camel components are configured on two separate levels:

  • component level

  • endpoint level

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.

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 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, 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.

Component Options

The JSLT component supports 5 options, which are listed below.

Name Description Default Type

allowTemplateFromHeader (producer)

Whether to allow to use resource template from header or not (default false). Enabling this allows to specify dynamic templates via message header. However this can be seen as a potential security vulnerability if the header is coming from a malicious user, so use this with care.

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

functions (advanced)

JSLT can be extended by plugging in functions written in Java.

Collection

objectFilter (advanced)

JSLT can be extended by plugging in a custom jslt object filter.

JsonFilter

Endpoint Options

The JSLT endpoint is configured using URI syntax:

jslt:resourceUri

with the following path and query parameters:

Path Parameters (1 parameters)

Name Description Default Type

resourceUri (producer)

Required Path to the resource. You can prefix with: classpath, file, http, ref, or bean. classpath, file and http loads the resource using these protocols (classpath is default). ref will lookup the resource in the registry. bean will call a method on a bean to be used as the resource. For bean you can specify the method name after dot, eg bean:myBean.myMethod.

String

Query Parameters (7 parameters)

Name Description Default Type

allowContextMapAll (producer)

Sets whether the context map should allow access to all details. By default only the message body and headers can be accessed. This option can be enabled for full access to the current Exchange and CamelContext. Doing so impose a potential security risk as this opens access to the full power of CamelContext API.

false

boolean

allowTemplateFromHeader (producer)

Whether to allow to use resource template from header or not (default false). Enabling this allows to specify dynamic templates via message header. However this can be seen as a potential security vulnerability if the header is coming from a malicious user, so use this with care.

false

boolean

contentCache (producer)

Sets whether to use resource content cache or not.

false

boolean

mapBigDecimalAsFloats (producer)

If true, the mapper will use the USE_BIG_DECIMAL_FOR_FLOATS in serialization features.

false

boolean

objectMapper (producer)

Setting a custom JSON Object Mapper to be used.

ObjectMapper

prettyPrint (common)

If true, JSON in output message is pretty printed.

false

boolean

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

Message Headers

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

Name Description Default Type

CamelJsltString (producer)

Constant: HEADER_JSLT_STRING

The JSLT Template as String.

String

CamelJsltResourceUri (producer)

Constant: HEADER_JSLT_RESOURCE_URI

The resource URI.

String

Passing values to JSLT

Camel can supply exchange information as variables when applying a JSLT expression on the body. The available variables from the Exchange are:

name value

headers

The headers of the In message as a json object

variables

The variables

exchange.properties

The Exchange properties as a json object. exchange is the name of the variable and properties is the path to the exchange properties. Available if allowContextMapAll option is true.

All the values that cannot be converted to json with Jackson are denied and will not be available in the jslt expression.

For example, the header named "type" and the exchange property "instance" can be accessed like

{
  "type": $headers.type,
  "instance": $exchange.properties.instance
}

Samples

For example you could use something like

from("activemq:My.Queue").
  to("jslt:com/acme/MyResponse.json");

And a file based resource:

from("activemq:My.Queue").
  to("jslt:file://myfolder/MyResponse.json?contentCache=true").
  to("activemq:Another.Queue");

You can also specify which JSLT expression the component should use dynamically via a header, so for example:

from("direct:in").
  setHeader("CamelJsltResourceUri").constant("path/to/my/spec.json").
  to("jslt:dummy?allowTemplateFromHeader=true");

Or send whole jslt expression via header: (suitable for querying)

from("direct:in").
  setHeader("CamelJsltString").constant(".published").
  to("jslt:dummy?allowTemplateFromHeader=true");

Passing exchange properties to the jslt expression can be done like this

from("direct:in").
  to("jslt:com/acme/MyResponse.json?allowContextMapAll=true");