NullPointerException when using WADL extension

[delor]

While I was running source code from "Restlet in Action" book, I did get NullPointerException after visiting http://localhost:8111/?method=options in web browser.

xalan 2.6.0

java.lang.NullPointerException
    at org.apache.xalan.transformer.TransformerImpl.transform(TransformerImpl.java:606)
    at org.apache.xalan.transformer.TransformerImpl.transform(TransformerImpl.java:1192)
    at org.apache.xalan.transformer.TransformerImpl.transform(TransformerImpl.java:1170)
    at org.restlet.ext.xml.TransformRepresentation.transform(TransformRepresentation.java:572)
    at org.restlet.ext.xml.TransformRepresentation.write(TransformRepresentation.java:589)
    at org.restlet.ext.xml.TransformRepresentation.write(TransformRepresentation.java:599)
    at org.restlet.representation.CharacterRepresentation.write(CharacterRepresentation.java:76)
    at org.restlet.engine.adapter.ServerCall.writeResponseBody(ServerCall.java:509)
    at org.restlet.engine.adapter.ServerCall.sendResponse(ServerCall.java:453)
    at org.restlet.ext.servlet.internal.ServletCall.sendResponse(ServletCall.java:426)
    at org.restlet.engine.adapter.ServerAdapter.commit(ServerAdapter.java:196)
    at org.restlet.engine.adapter.HttpServerHelper.handle(HttpServerHelper.java:153)
    at org.restlet.ext.servlet.ServerServlet.service(ServerServlet.java:1089)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:530)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:426)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:118)
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:495)
    at org.eclipse.jetty.server.session.SessionHandler.handle(SessionHandler.java:179)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:930)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:361)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:864)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:116)
    at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:243)
    at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:126)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:112)
    at org.eclipse.jetty.server.Server.handle(Server.java:337)
    at org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:552)
    at org.eclipse.jetty.server.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:979)
    at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:533)
    at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:203)
    at org.eclipse.jetty.server.HttpConnection.handle(HttpConnection.java:399)
    at org.eclipse.jetty.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:437)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:435)
    at java.lang.Thread.run(Thread.java:662)

xalan 2.7.1

java.lang.NullPointerException
    at org.apache.xalan.transformer.TransformerImpl.transform(TransformerImpl.java:642)
    at org.apache.xalan.transformer.TransformerImpl.transform(TransformerImpl.java:1273)
    at org.apache.xalan.transformer.TransformerImpl.transform(TransformerImpl.java:1251)
    at org.restlet.ext.xml.TransformRepresentation.transform(TransformRepresentation.java:572)
    at org.restlet.ext.xml.TransformRepresentation.write(TransformRepresentation.java:589)
    at org.restlet.ext.xml.TransformRepresentation.write(TransformRepresentation.java:599)
    at org.restlet.representation.CharacterRepresentation.write(CharacterRepresentation.java:76)
    at org.restlet.engine.adapter.ServerCall.writeResponseBody(ServerCall.java:509)
    at org.restlet.engine.adapter.ServerCall.sendResponse(ServerCall.java:453)
    at org.restlet.ext.servlet.internal.ServletCall.sendResponse(ServletCall.java:426)
    at org.restlet.engine.adapter.ServerAdapter.commit(ServerAdapter.java:196)
    at org.restlet.engine.adapter.HttpServerHelper.handle(HttpServerHelper.java:153)
    at org.restlet.ext.servlet.ServerServlet.service(ServerServlet.java:1089)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:530)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:426)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:118)
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:495)
    at org.eclipse.jetty.server.session.SessionHandler.handle(SessionHandler.java:179)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:930)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:361)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:864)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:116)
    at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:243)
    at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:126)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:112)
    at org.eclipse.jetty.server.Server.handle(Server.java:337)
    at org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:552)
    at org.eclipse.jetty.server.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:979)
    at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:533)
    at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:203)
    at org.eclipse.jetty.server.HttpConnection.handle(HttpConnection.java:399)
    at org.eclipse.jetty.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:437)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:435)
    at java.lang.Thread.run(Thread.java:662)

[jlouvel]

This normally works. Could you provide a reproducible sample code (minimal Eclipse project Zip)?

[jlouvel]

I have fixed a NPE error in TransformRepresentation that might help:
50c24de

Could you test with master/2.1 branch or upcoming 2.1.2/2.2 M2 and confirm?

[msmall-cotm]

From my own experience using 2.1.2, the problem still occurs.

[jlouvel]

Are you sure you are using Xalan 2.7 and not the default/bundled Xalan part of the JDK?

[msmall-cotm]

I believe so. Here's the relavant output from CheckEnvironment:

version.xerces2=not-present
version.xerces1=not-present
version.xalan2_2=Xalan Java 2.7.1
version.xalan1=not-present
version.ant=not-present
java.version=1.6.0_43
version.DOM=2.0
version.crimson=not-present
sun.boot.class.path=/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Classes/jsfd.jar:/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Classes/classes.jar:/System/Library/Frameworks/JavaVM.framework/Frameworks/JavaRuntimeSupport.framework/Resources/Java/JavaRuntimeSupport.jar:/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Classes/ui.jar:/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Classes/la f.jar:/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Classes/sunrsasign.jar:/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Classes/jsse.jar:/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Classes/jce.jar:/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Classes/charsets.jar
version.SAX=2.0
version.xalan2x=Xalan Java 2.7.1

[gchatelet]

Same here with our project. I tried 2.2-M1 and 2.2-M2 and we also have this NPE.
Xalan is the one bundled with maven restlet's extension : 2.7.0

SEVERE: An exception occured writing the response entity
java.lang.NullPointerException
at org.apache.xalan.transformer.TransformerImpl.transform(TransformerImpl.java:642)
at org.apache.xalan.transformer.TransformerImpl.transform(TransformerImpl.java:1284)
at org.apache.xalan.transformer.TransformerImpl.transform(TransformerImpl.java:1262)
at org.restlet.ext.xml.TransformRepresentation.transform(TransformRepresentation.java:573)
at org.restlet.ext.xml.TransformRepresentation.write(TransformRepresentation.java:590)
at org.restlet.ext.xml.TransformRepresentation.write(TransformRepresentation.java:600)
at org.restlet.representation.CharacterRepresentation.write(CharacterRepresentation.java:76)
at org.restlet.engine.adapter.ServerCall.writeResponseBody(ServerCall.java:519)
at org.restlet.engine.adapter.ServerCall.sendResponse(ServerCall.java:463)
at org.restlet.ext.servlet.internal.ServletCall.sendResponse(ServletCall.java:430)
at org.restlet.engine.adapter.ServerAdapter.commit(ServerAdapter.java:196)
at org.restlet.engine.adapter.HttpServerHelper.handle(HttpServerHelper.java:153)
at org.restlet.ext.servlet.ServerServlet.service(ServerServlet.java:1087)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
....

the source parameter of this function from org.apache.xalan.transformer.TransformerImpl is null

public void transform(Source source, boolean shouldRelease) throws TransformerException

Also tracking the origin of this null value leads me to org.restlet.ext.xml.TransformRepresentation

public void write(Result result) throws IOException {
transform(getSaxSource(), result);
}

getSaxSource() generates the null value. After a few calls getSaxSource() triggers org.restlet.ext.xml.TransformRepresentation.toSaxSource(...)

public static SAXSource toSaxSource(Representation representation) throws IOException {
SAXSource result = null;
if (representation instanceof XmlRepresentation) {
result = ((XmlRepresentation) representation).getSaxSource(); << enters this function
...

which leads to org.restlet.ext.xml.SaxRepresentation.getSaxSource()

public SAXSource getSaxSource() throws IOException {
if (this.source == null && this.xmlRepresentation != null) {

where this.source and this.xmlRepresentation are both null, yielding a null result.

Two possibilities :

• either what really is intended to be executed is XmlRepresentation.toSaxSource() instead of SaxRepresentation.toSaxSource() ( but WadlRepresentation extends SaxRepresentation extends XmlRepresentation )
• either this.source and this.xmlRepresentation are not setup correctly.

[msmall-cotm]

Any progress on this?

[spraguep]

I was having the same problem. I was able to work around it as follows:

import org.restlet.data.MediaType;
import org.restlet.ext.wadl.WadlRepresentation;
import org.restlet.representation.WriterRepresentation;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.Writer;

import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;

public class Wadl2HtmlRepresentation extends WriterRepresentation {
    private static final String WADL_TO_HTML_XSLT = "/org/restlet/ext/wadl/wadl2html.xslt";
    private final WadlRepresentation representation;

    public Wadl2HtmlRepresentation(final WadlRepresentation representation) {
        super(MediaType.TEXT_HTML);
        this.representation = representation;
    }

    @Override
    public void write(final Writer writer) throws IOException {
        final TransformerFactory transformerFactory = TransformerFactory.newInstance();
        try {
            final Transformer transformer = transformerFactory.newTransformer(new StreamSource(getClass().getResourceAsStream(WADL_TO_HTML_XSLT)));

            final ByteArrayOutputStream wadlOutput = new ByteArrayOutputStream();
            representation.write(wadlOutput);

            final ByteArrayInputStream wadlInput = new ByteArrayInputStream(wadlOutput.toByteArray());

            transformer.transform(new StreamSource(wadlInput), new StreamResult(writer));
        } catch (IOException | TransformerException e) {
            throw new RuntimeException("Transform failed.", e);
        }
    }
}

You need to subclass WadlApplication and override the createHtmlRepresentation() method like this:

    @Override
    protected Representation createHtmlRepresentation(ApplicationInfo applicationInfo) {
        return new Wadl2HtmlRepresentation(new WadlRepresentation(applicationInfo));
    }

[jlouvel]

Several other reports of this NPE:
http://restlet.tigris.org/ds/viewMessage.do?dsForumId=4447&dsMessageId=2974664

@thboileau, @ssfartz, let's increase the priority of this issue.

[thboileau]

Hello,
this should have been fixed, cf #810.

Could you try using the current master branch, or the current 2.1 branch?

[jlouvel]

Do you mean 2.1.6 and 2.2 M6?