Spring Integration - XML Schema validator - Dynamic schema file selection - spring-integration

Question

I am trying to implement XML validation using Spring Integration <int-xml:validating-filter />. I followed the discussion in usage of spring integration's schema validator?. The problem statement is the same but with an additional parameter. Instead to hard coding the value in schema-location="xyz.xsd", rather I want to dynamically select the appropriate xsd file for respective incoming xml or DOMSource inputs.
I also followed http://forum.spring.io/forum/spring-projects/integration/121115-dynamic-schema-location-for-xml-validating-filter-component where Gary Russell mentioned:
There's no direct support for dynamic schemas, but you can provide a
custom XmlValidator using the xml-validator attribute (mutually
exclusive with schema location)
Once you've introspected your document to find the schema you wish to
validate against, simply delegate to a validator that has been
configured to validate against that schema.
You can use a XmlValidatorFactory to create each validator; see the
XmlValidatingMessageSelector for how to create a validator, once you
know the schema location
Since the comments dates back to the year 2012, is there an approach now in spring integration to validate input xml by dynamically selecting appropriate schema? If not can anyone provide an example on how to implement?
Following is my spring integration configuration:
<int:gateway id="applicationServiceGateway" service-interface="abc.IGateway"
default-request-channel="applicationRequestChannel" default-reply-channel="applicationResponseChannel"
error-channel="errorProcessingChannel" />
<int:chain id="serviceRequestValidation" input-channel="applicationRequestChannel" output-channel="responseChannel">
<!-- How to do -->
<int-xml:validating-filter xml-validator="xmlValidator"
schema-type="xml-schema"
throw-exception-on-rejection="true" />
<int:service-activator id="schematronValidationActivator" ref="schematronValidator" method="validate" />
</int:chain>
<bean id="xmlValidator" class="abc.validator.DomSourceValidator" />
Here is my Validator class defined:
import org.springframework.xml.validation.ValidationErrorHandler;
import org.springframework.xml.validation.XmlValidator;
import org.xml.sax.SAXParseException;
public class DomSourceValidator implements XmlValidator {
#Override
public SAXParseException[] validate(Source source) throws IOException {
/* How to implement this method?
Using XPath I can identify the root node from 'source' and then load
the appropriate XSD file. But don't know how to proceed
or what should be 'return'(ed) from here.
Any example is much appreciated.
*/
return null;
}
#Override
public SAXParseException[] validate(Source source, ValidationErrorHandler errorHandler) throws IOException {
// TODO Auto-generated method stub
return null;
}
}
Which is the best way of implementing the XML validator using Spring Integration?

Answer 1

There have been no changes since that comment.
As I said there, your validator needs to use XmlValidatorFactory to create a validator for each schema; then call a specific validator for each message; something like:
String schema = determineSchema(source);
XmlValidator val = lookupValidatorForSchema(schema);
if (val == null) {
// create a new one and add it to the map.
}
return val.validate(source);

Answer 2

If it helps other folks who are trying to do the same
Based on Gary's suggestion, I have come out with an implementation of XmlValidator by dynamically identifying input XML and then selecting appropriate Schema file to apply the validation.
Below is my spring integration configuration:
<int:gateway id="applicationServiceGateway" service-interface="abc.IGateway" default-request-channel="applicationRequestChannel" default-reply-channel="applicationResponseChannel" error-channel="errorProcessingChannel" />
<int:chain id="serviceRequestValidation" input-channel="applicationRequestChannel" output-channel="responseChannel">
<int-xml:validating-filter xml-validator="xmlValidator"
schema-type="xml-schema"
throw-exception-on-rejection="true" /> <!-- a MessageRejectedException is thrown in case validation fails -->
<int:service-activator id="schematronValidationActivator" ref="schematronValidator" method="validate" />
</int:chain>
<bean id="xmlValidator" class="abc.validator.DomSourceValidator">
<constructor-arg>
<map key-type="java.lang.String" value-type="java.lang.String">
<entry key="OTA_AirAvailRQ" value="common/schemas/FS_OTA_AirAvailRQ.xsd" />
<entry key="OTA_AirBookModifyRQ" value="common/schemas/FS_OTA_AirBookModifyRQ.xsd" />
<entry key="OTA_AirBookRQ" value="common/schemas/FS_OTA_AirBookRQ.xsd" />
</map>
</constructor-arg>
</bean>
To demonstrate I have used the OTA schema files to construct a map as constructor-arg. The map key is the root node from the XML file from the gateway and value is the location of the xsd file; and form the key-value pair map.
Refer to the below implementation class how this map is being used to identify the input XML and apply the validation.
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import javax.annotation.PostConstruct;
import javax.xml.transform.Source;
import javax.xml.transform.dom.DOMSource;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.core.io.ClassPathResource;
import org.springframework.util.Assert;
import org.springframework.xml.validation.ValidationErrorHandler;
import org.springframework.xml.validation.XmlValidator;
import org.springframework.xml.validation.XmlValidatorFactory;
import org.xml.sax.SAXParseException;
public class DomSourceValidator implements XmlValidator {
private static final Log LOGGER = LogFactory.getLog(DomSourceValidator.class);
private Map<String, String> schemaMap;
private static Map<String, XmlValidator> validatorMap = new HashMap<>();
public DomSourceValidator(Map<String, String> schemaMap) {
this.schemaMap = schemaMap;
}
#PostConstruct
private void init() throws IOException {
LOGGER.info("Constructing Validators from schema resource list ...");
Assert.notEmpty(schemaMap, "No schema resource map found");
if (validatorMap.isEmpty()) {
XmlValidator validator = null;
for (Map.Entry<String, String> entry : schemaMap.entrySet()) {
validator = createValidatorFromResourceUri(entry.getValue());
validatorMap.put(entry.getKey(), validator);
}
}
}
#Override
public SAXParseException[] validate(Source source) throws IOException {
Assert.notNull(schemaMap, "No validator(s) defined");
XmlValidator validator = lookupValidator(source);
return validator.validate(source);
}
#Override
public SAXParseException[] validate(Source source, ValidationErrorHandler errorHandler) throws IOException {
// Skip implementation
return null;
}
private XmlValidator lookupValidator(Source source) {
String reqType = determineRequestType(source);
LOGGER.info("Loading validator for type: " + reqType);
XmlValidator xmlValidator = validatorMap.get(reqType);
Assert.notNull(xmlValidator, "No validator found for type: " + reqType);
return xmlValidator;
}
private String determineRequestType(Source source) {
if (source instanceof DOMSource) {
return ((DOMSource) source).getNode().getFirstChild().getNodeName();
}
return null;
}
private XmlValidator createValidatorFromResourceUri(String schemaResource) throws IOException {
Assert.notNull(schemaResource);
return XmlValidatorFactory.createValidator(new ClassPathResource(schemaResource), XmlValidatorFactory.SCHEMA_W3C_XML);
}
}
As soon as the spring bean id="xmlValidator" is initialized, the #PostConstruct kicks in to create Validator instances using XmlValidatorFactory from the resource URIs to have a pre-initialized validators.
If there is a validation error, a org.springframework.integration.MessageRejectedException: Message was rejected due to XML Validation errors is thrown (ref. throw-exception-on-rejection="true" in the <int-xml:validating-filter />).
The above implementation works perfectly fine for me. One can customize it further, or post another version to achieve the same.
Note
Instead of using a <int-xml:validating-filter />, one can also use a <int:service-activator /> in the <int-chain />, as logically <int-xml:validating-filter /> does not actually do any filter logic. But it serves the purpose.