Error - org.xml.sax.SAXParseException; systemId: http://schemas.xmlsoap.org/soap/envelope/; lineNumber: 1; columnNumber: 1; Premature end of file - rest-assured

Question

I am getting an error as org.xml.sax.SAXParseException; systemId: http://schemas.xmlsoap.org/soap/envelope/; lineNumber: 1; columnNumber: 1; Premature end of file.
while running a matcher clause in xsd validation in rest assured
The request and the response is successful and getting a status code as 200. But when performing the action as body(matchesXsdInClasspath("addinteger.xsd")); it is showing the above error message.
Not being able to resolve the error.
My Code -
package soap_request.get_request;
import static io.restassured.RestAssured.*;
import static org.hamcrest.Matchers.*;
import java.io.File;
import java.io.FileInputStream;
import org.apache.commons.io.IOUtils;
import org.testng.annotations.Test;
import io.restassured.http.ContentType;
import static io.restassured.matcher.RestAssuredMatchers.matchesXsdInClasspath;
import static org.hamcrest.Matchers.equalTo;
public class get_request {
#Test
public void getListOfUsers() throws Exception {
File xmlFile = new File("C:\\Users\\das_k\\Downloads\\addinteger.xml");
if (xmlFile.exists()) {
FileInputStream oFIS = new FileInputStream(xmlFile);
String requestBody = IOUtils.toString(oFIS,"UTF-8");
oFIS.close();
baseURI = "http://dneonline.com/";
given().
contentType("text/xml").
accept(ContentType.XML).
body(requestBody).
when().
post("calculator.asmx").
then().
statusCode(200).
log().all().
and().
body("//*:AddResult.text()", equalTo("24")).
and().
body(matchesXsdInClasspath("addinteger.xsd"));
} else {
throw new Exception("The xml file specified does not exist");
}
}
}
My response -
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<soap:Body>
<AddResponse xmlns="http://tempuri.org/">
<AddResult>24</AddResult>
</AddResponse>
</soap:Body>
</soap:Envelope>
xsd file -
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"
targetNamespace="http://tempuri.org/">
<xs:import namespace="http://schemas.xmlsoap.org/soap/envelope/"
schemaLocation="http://schemas.xmlsoap.org/soap/envelope/"/>
<xs:element name="AddIntegerResponse">
<xs:complexType>
<xs:sequence>
<xs:element type="xs:byte" name="AddIntegerResult"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>