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Chapter 62. 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.

62.1. Dependencies

When using jslt with Red Hat build of Camel 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-jslt-starter</artifactId>
</dependency>
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62.2. URI format

jslt:specName[?options]
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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).

62.3. Configuring Options

Camel components are configured on two separate levels:

  • component level
  • endpoint level

62.3.1. 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.

62.3.2. 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.

62.4. Component Options

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

NameDescriptionDefaultType

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

62.4.1. Endpoint Options

The JSLT endpoint is configured using URI syntax: 

jslt:resourceUri
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with the following path and query parameters:

62.4.1.1. Path Parameters (1 parameters)

NameDescriptionDefaultType

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

62.4.1.2. Query Parameters (7 parameters)

NameDescriptionDefaultType

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

62.5. Message Headers

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

NameDescriptionDefaultType

CamelJsltString (producer)

Constant: HEADER_JSLT_STRING

The JSLT Template as String.

 

String

CamelJsltResourceUri (producer)

Constant: HEADER_JSLT_RESOURCE_URI

The resource URI.

 

String

62.6. 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:

namevalue

headers

The headers of the In message as a json object

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
}
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62.7. Samples

The sample example is as given below. 

from("activemq:My.Queue").
  to("jslt:com/acme/MyResponse.json");
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And a file based resource: 

from("activemq:My.Queue").
  to("jslt:file://myfolder/MyResponse.json?contentCache=true").
  to("activemq:Another.Queue");
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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");
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Or send whole jslt expression via header: (suitable for querying) 

from("direct:in").
  setHeader("CamelJsltString").constant(".published").
  to("jslt:dummy?allowTemplateFromHeader=true");
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Passing exchange properties to the jslt expression can be done like this 

from("direct:in").
  to("jslt:com/acme/MyResponse.json?allowContextMapAll=true");
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62.8. Spring Boot Auto-Configuration

The component supports 6 options, which are listed below.

NameDescriptionDefaultType

camel.component.jslt.allow-template-from-header

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

camel.component.jslt.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.jslt.enabled

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

 

Boolean

camel.component.jslt.functions

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

 

Collection

camel.component.jslt.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

camel.component.jslt.object-filter

JSLT can be extended by plugging in a custom jslt object filter. The option is a com.schibsted.spt.data.jslt.filters.JsonFilter type.

 

JsonFilter

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