JAX-WS: javax.xml.bind.UnmarshalException

Question

//HelloWorld.java
import javax.ws.rs.core.Context;
import javax.ws.rs.core.UriInfo;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;
import javax.ws.rs.Consumes;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.PUT;
import javax.ws.rs.core.MediaType;
@Path("generic")
public class HelloWorld {
    @Context
    private UriInfo context;
    public HelloWorld() {
    }
    @GET
    @Produces("text/html")
    public String getHtml() {
        return "Hello World";
    }
}

//ApplicationConfig.java
import java.util.Set;
import javax.ws.rs.core.Application;
@javax.ws.rs.ApplicationPath("webresources")
public class ApplicationConfig extends Application {
    @Override
    public Set<Class<?>> getClasses() {
        Set<Class<?>> resources = new java.util.HashSet<>();
        addRestResourceClasses(resources);
        return resources;
    }
    private void addRestResourceClasses(Set<Class<?>> resources) {
        resources.add(HelloWorld.class);
    } 
}

//JavaApplication3
package javaapplication3;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import sun.misc.IOUtils;
public class JavaApplication3 {
    public static void main(String[] args) throws MalformedURLException, IOException, JAXBException {
        //Get the URI by selecting the RESTful web services folder under the web app project.   Then right click on the underlying node
        //and select: TestResourceURI
        String uri ="http://localhost:8080/HelloRestService/webresources/generic";
        URL url = new URL(uri);
        HttpURLConnection connection =  (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("GET");
        //connection.setRequestProperty("Accept", "application/xml");
        connection.setRequestProperty("Accept", "text/html");
        JAXBContext jc = JAXBContext.newInstance(String.class); 
        InputStream xml = connection.getInputStream();
        String str = (String) jc.createUnmarshaller().unmarshal(xml); //line that throws exception
        connection.disconnect();
    }   
}

I have marked the line, which causes the exception in: JavaApplication3.java. I can browse to the web service here: http://localhost:8080/HelloRestService/webresources/generic

The exception is:

Exception in thread "main" javax.xml.bind.UnmarshalException
 - with linked exception:
[org.xml.sax.SAXParseException; lineNumber: 1; columnNumber: 1; Content is not allowed in prolog.]
    at javax.xml.bind.helpers.AbstractUnmarshallerImpl.createUnmarshalException(AbstractUnmarshallerImpl.java:335)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.createUnmarshalException(UnmarshallerImpl.java:563)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal0(UnmarshallerImpl.java:249)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal(UnmarshallerImpl.java:214)
    at javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal(AbstractUnmarshallerImpl.java:157)
    at javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal(AbstractUnmarshallerImpl.java:204)
    at javaapplication3.JavaApplication3.main(JavaApplication3.java:41)
Caused by: org.xml.sax.SAXParseException; lineNumber: 1; columnNumber: 1; Content is not allowed in prolog.
    at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(ErrorHandlerWrapper.java:203)
    at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.fatalError(ErrorHandlerWrapper.java:177)
    at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:400)
    at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:327)
    at com.sun.org.apache.xerces.internal.impl.XMLScanner.reportFatalError(XMLScanner.java:1465)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(XMLDocumentScannerImpl.java:999)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:606)
    at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(XMLNSDocumentScannerImpl.java:118)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:504)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:848)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:777)
    at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:141)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1213)
    at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:643)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal0(UnmarshallerImpl.java:243)
    ... 4 more
Java Result: 1

What is the problem? I expect the str variable to be populated with HelloWorld!.

Answer 1

You get this error because you try to use JAXB to bind a content that is not even an XML content which simply cannot work (as reminder JAXB stands for Java Architecture for XML Binding). What you really get is plain/text not even text/html as you set in your code while JAXB expects XML.

What you need to do, is to convert your input stream into a String with something like this:

try (
    BufferedReader reader = new BufferedReader(
        new InputStreamReader(connection.getInputStream(), charset)
    )
) {
    String content = reader.lines().collect(Collectors.joining("\n"));
    ...
}