Validating XML message in Mule 3

a common use case mule esb flows is validating if an xml document is valid against a corresponding xsd . it can be quite annoying to find out you have spent a lot of time fixing an issue when it was actually caused by another system that was supplying invalid xml, especially if a project is in the development/test stage.

the ‘standard’ way to do this in mule is by using the schema-validation-filter , usually in combination with the message-filter . for example, the following configuration will send all non-valid messages to the ‘process-invalid-xml’ flow:

<message-filter onunaccepted="process-invalid-xml" throwonunaccepted="true">
    <xml:schema-validation-filter .../>
</message-filter>

in the ‘process-invalid-xml’ flow you can then create a response message (if applicable) to tell the sender of the original message that it contains invalid xml. this was the case in my situation and i also wanted to show the user what was wrong in the xml. to do this, i created my own sax errorhandler and supplied that to the schema-validation-filter like this:

<spring:bean id="xmlerrorhandler" class="net.pascalalma.xml.handlers.mysaxerrorhandler" />
 <message-filter onunaccepted="invalidrelationxmlflow" throwonunaccepted="false">
     <mulexml:schema-validation-filter errorhandler-ref="xmlerrorhandler"  schemalocations="xsd/my-schema.xsd"/>
</message-filter>

however, no matter what i did my error handler wasn’t being called by the filter. after some debugging i only got it working by extending the original schema-validation-filter and set the error-handler on the created validator like this:

public class myschemavalidationfilter extends schemavalidationfilter
{
  static logger logger = logger.getlogger(myschemavalidationfilter.class);
 
  public validator createvalidator() throws saxexception
  {
    validator validator = super.createvalidator();
    validator.seterrorhandler(geterrorhandler());
    return validator;
  }
}

i am not sure if this is a bug in the original schema-validation-filter or if there is another way to make use of the errorhandler, but this was the only way for me to get it working.

i use my version of the filter with the following configuration:

<custom-filter class="net.pascalalma.xml.filters.myschemavalidationfilter" >
  <spring:property name="schemalocations" value="xsd/my-schema.xsd"/>
  <spring:property name="returnresult" value="false"/>
  <spring:property name="errorhandler" ref="xmlerrorhandler"/>
</custom-filter>

this way i can collect all errors in my error handler and put them with a outbound property on the message and return them to the calling client.

here is the source code of my error handler:

public class myerrorhandler implements errorhandler {
 
    static logger logger = logger.getlogger(myerrorhandler.class);
 
    public list<string> geterrors() {
        return errors;
    }
    public void seterrors(list<string> errors) {
        this.errors = errors;
    }
    private list<string> errors = new arraylist<string>();
    @override
    public void warning(saxparseexception e) throws saxexception {
        logger.warn(e.getlinenumber() + "/" + e.getcolumnnumber() + ": " + e.getmessage());
    }
    @override
    public void fatalerror(saxparseexception e) throws saxexception {
        logger.debug("fatalerror occurred: " + e.tostring());
        errors.add(e.getlinenumber() +"/" + e.getcolumnnumber() + ": " + e.getmessage());
    }
    @override
    public void error(saxparseexception e) throws saxexception {
        logger.debug("error occurred: " + e.tostring());
        errors.add(e.getlinenumber() +"/" + e.getcolumnnumber() + ": " + e.getmessage());
    }
}