Getting Content is not allowed in prolog when running in Java - jmeter

Question

I am facing Content is not allowed in prolog exception when I run my xxx.jmx file from Java (Jmeter 5.0).
I tested the jmx in the GUI mode and everything works fine and in the Java I am just following the standard way to call the jmx file and execute it.
The jmx just have some normal stuff. Sending HTTP request and validate the expected and received XML (I am using this snipped to validate):
import org.apache.commons.io.FileUtils
expect = FileUtils.readFileToString(new File('some_path'))
XmlParser parser = new XmlParser()
expectedXML = new XmlSlurper().parseText(expect)
actualXML = new XmlSlurper().parseText(prev.getResponseDataAsString())
if (expectedXML != actualXML) {
AssertionResult.setFailure(true)
AssertionResult.setFailureMessage('Mismatch between expected and actual XML \n'+ prev.getResponseDataAsString())
and the stack trace:
2018/10/24 15:18:03,386 12675 [ERROR ] [Thread Group 1-1] (JSR223Assertion.java:52) – Problem in JSR223 script: Validate resposne
javax.script.ScriptException: org.xml.sax.SAXParseException; lineNumber: 1; columnNumber: 1; Content is not allowed in prolog.
at org.codehaus.groovy.jsr223.GroovyScriptEngineImpl.eval(GroovyScriptEngineImpl.java:320)
at org.codehaus.groovy.jsr223.GroovyCompiledScript.eval(GroovyCompiledScript.java:72)
at javax.script.CompiledScript.eval(CompiledScript.java:92)
at org.apache.jmeter.util.JSR223TestElement.processFileOrScript(JSR223TestElement.java:221)
at org.apache.jmeter.assertions.JSR223Assertion.getResult(JSR223Assertion.java:49)
at org.apache.jmeter.threads.JMeterThread.processAssertion(JMeterThread.java:901)
at org.apache.jmeter.threads.JMeterThread.checkAssertions(JMeterThread.java:892)
at org.apache.jmeter.threads.JMeterThread.executeSamplePackage(JMeterThread.java:565)
at org.apache.jmeter.threads.JMeterThread.processSampler(JMeterThread.java:486)
at org.apache.jmeter.threads.JMeterThread.run(JMeterThread.java:253)
at java.lang.Thread.run(Thread.java:745)
Caused by: org.xml.sax.SAXParseException; lineNumber: 1; columnNumber: 1; Content is not allowed in prolog.
at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)
at groovy.util.XmlSlurper.parse(XmlSlurper.java:207)
at groovy.util.XmlSlurper.parse(XmlSlurper.java:260)
at groovy.util.XmlSlurper.parseText(XmlSlurper.java:286)
at groovy.util.XmlSlurper$parseText.call(Unknown Source)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
at Script1.run(Script1.groovy:9)
at org.codehaus.groovy.jsr223.GroovyScriptEngineImpl.eval(GroovyScriptEngineImpl.java:317)
... 10 more
UPDATE 1:
The problem of using Response Assertion is it cannot ignore the space or tab. So if the format is not exactly the same when I use equal will always fail. Any ideas how to ignore these things by using Response Assertion?
UPDATE 2:
I found out that the issue is not related to the BOM. Is becasue if I run the jmx from my Java application:
prev.getResponseDataAsString()
above function always return:
${__FileToString(${inputFilePath},,)}
but not the actual response. This function is come from the body data of the HTTP Request sampler!!!!!! If I give the acutal body there then I am able to run the jmx...... Any idea how to deal with this dynamic body data?

Answer 1

It might be the case your "expected" XML file contains BOM and it causes your code failure.
BOM is basically 3 first bytes so you can remove them using code like:
def expect = FileUtils.readFileToString(new File('some_path')).getBytes().flatten()
1.upto(3) {
expect.remove(0)
}
XmlParser parser = new XmlParser()
def expectedXML = parser.parseText(new String(expect.toArray(new Byte[0])))
The rest of your code should work fine.
Check out The Groovy Templates Cheat Sheet for JMeter article to learn more Groovy tips and tricks.
Also be informed that in majority of cases it's easier to use Response Assertion or when it comes to XML - XPath Assertion, Java code will work faster than Groovy in any case.