Schematron

Since Camel 2.15

Only producer is supported

Schematron is an XML-based language for validating XML instance documents. It is used to make assertions about data in an XML document and it is also used to express operational and business rules. Schematron is an ISO Standard. The schematron component uses the leading implementation of ISO schematron. It is an XSLT based implementation. The schematron rules is run through four XSLT pipelines, which generates a final XSLT which will be used as the basis for running the assertion against the XML document. The component is written in a way that Schematron rules are loaded at the start of the endpoint (only once) this is to minimise the overhead of instantiating a Java Templates object representing the rules.

URI format

schematron://path?[options]

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 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.

Component Options

The Schematron component supports 2 options, which are listed below.

Name Description Default Type

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.

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.

boolean

Endpoint Options

The Schematron endpoint is configured using URI syntax:

schematron:path

with the following path and query parameters:

Path Parameters (1 parameters)

Name Description Default Type

path (producer)

Required The path to the schematron rules file. Can either be in class path or location in the file system.

String

Query Parameters (4 parameters)

Name Description Default Type

abort (producer)

Flag to abort the route and throw a schematron validation exception.

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.

boolean

rules (producer)

To use the given schematron rules instead of loading from the path.

Templates

uriResolver (advanced)

Set the URIResolver to be used for resolving schematron includes in the rules file.

URIResolver

Headers

Name Description Type In/Out

CamelSchematronValidationStatus

The schematron validation status: SUCCESS / FAILED

String

IN

CamelSchematronValidationReport

The schematrion report body in XML format. See an example below

String

IN

URI and path syntax

The following example shows how to invoke the schematron processor in Java DSL. The schematron rules file is sourced from the class path:

from("direct:start").to("schematron://sch/schematron.sch").to("mock:result")

The following example shows how to invoke the schematron processor in XML DSL. The schematrion rules file is sourced from the file system:

<route>
   <from uri="direct:start" />
   <to uri="schematron:///usr/local/sch/schematron.sch" />
   <log message="Schematron validation status: ${in.header.CamelSchematronValidationStatus}" />
   <choice>
      <when>
         <simple>${in.header.CamelSchematronValidationStatus} == 'SUCCESS'</simple>
         <to uri="mock:success" />
      </when>
      <otherwise>
         <log message="Failed schematron validation" />
         <setBody>
            <header>CamelSchematronValidationReport</header>
         </setBody>
         <to uri="mock:failure" />
      </otherwise>
   </choice>
</route>

Where to store schematron rules?

Schematron rules can change with business requirement, as such it is recommended to store these rules somewhere in file system. When the schematron component endpoint is started, the rules are compiled into XSLT as a Java Templates Object. This is done only once to minimise the overhead of instantiating Java Templates object, which can be an expensive operation for large set of rules and given that the process goes through four pipelines of XSLT transformations. So if you happen to store the rules in the file system, in the event of an update, all you need is to restart the route or the component. No harm in storing these rules in the class path though, but you will have to build and deploy the component to pick up the changes.

Schematron rules and report samples

Here is an example of schematron rules

<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://purl.oclc.org/dsdl/schematron">
   <title>Check Sections 12/07</title>
   <pattern id="section-check">
      <rule context="section">
         <assert test="title">This section has no title</assert>
         <assert test="para">This section has no paragraphs</assert>
      </rule>
   </pattern>
</schema>

Here is an example of schematron report:

<?xml version="1.0" encoding="UTF-8"?>
<svrl:schematron-output xmlns:svrl="http://purl.oclc.org/dsdl/svrl"
 xmlns:iso="http://purl.oclc.org/dsdl/schematron"
 xmlns:saxon="http://saxon.sf.net/"
 xmlns:schold="http://www.ascc.net/xml/schematron"
 xmlns:xhtml="http://www.w3.org/1999/xhtml"
 xmlns:xs="http://www.w3.org/2001/XMLSchema"
 xmlns:xsd="http://www.w3.org/2001/XMLSchema" schemaVersion="" title="">

   <svrl:active-pattern document="" />
   <svrl:fired-rule context="chapter" />
   <svrl:failed-assert test="title" location="/doc[1]/chapter[1]">
      <svrl:text>A chapter should have a title</svrl:text>
   </svrl:failed-assert>
   <svrl:fired-rule context="chapter" />
   <svrl:failed-assert test="title" location="/doc[1]/chapter[2]">
      <svrl:text>A chapter should have a title</svrl:text>
   </svrl:failed-assert>
   <svrl:fired-rule context="chapter" />
</svrl:schematron-output>

Useful Links and resources

Spring Boot Auto-Configuration

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

The component supports 3 options, which are listed below.

Name Description Default Type

camel.component.schematron.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.schematron.enabled

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

Boolean

camel.component.schematron.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