XMLDBException on LocalXMLResource.getContentAsDOM()

[Michael-526]

Hello,

I am attempting to convert an application that has been using a server deployment of eXist to embedding eXist right in the application. I have been able to configure the program to start and initialize the embedded database. I can also query the embedded database, however, when parsing the results of a query I am having some difficulty.

When I perform the following actions:

    ResourceSet results = query(RESNAME, query);
    XMLResource resultBlob = (XMLResource) results.getMembersAsResource();
    Node node = resultBlob.getContentAsDOM();

I receive an XMLDBException with error INVALID_RESOURCE (301) thrown from within resultBlob.getContentAsDOM(). This did not cause any exceptions to be thrown when the database was running as a server and not embedded. It appears the LocalXMLResource implementation of getContentAsDOM() differs from the RemoteXMLResource in such a way that the local version causes this exception.

The LocalXMLResource implementation of getContentAsDOM() attempts to retrieve the DOM Document by calling
    document = parent.getCollection().getDocumentWithLock(broker, docId, lock);
Which fails to retrieve a document since the docID is blank.

The RemoteXMLResource implementation of getContentAsDOM() creates and builds the document from scratch using the string field "content". This properly returns the DOM Document without error.

I suppose a solution around this would be to simply call getContent() and then build the DOM Document from the returned string. Though, I am not really sure if I am simply performing an invalid action, or if there is something wrong with my setup, or if this really should just simply work but is not. Any suggestions/info/advise/solutions would be greatly appreciated.


Here is a simplified sample of what is occurring in my application. This is a simple example of the issue which reproduces the same issue that I am seeing in my application. I created this example to best show the problem. I have also hosted the source of this application as a complete eclipse workspace at http://mtbin.com/source/existExample.zip if anyone would like to attempt running this example on their system.


package main;

import java.util.Properties;

import org.exist.xmldb.DatabaseInstanceManager;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xmldb.api.DatabaseManager;
import org.xmldb.api.base.Collection;
import org.xmldb.api.base.Database;
import org.xmldb.api.base.ResourceSet;
import org.xmldb.api.base.XMLDBException;
import org.xmldb.api.modules.CollectionManagementService;
import org.xmldb.api.modules.XMLResource;
import org.xmldb.api.modules.XPathQueryService;

public class DBExample
{
    public static final String DRIVER_NAME = "org.exist.xmldb.DatabaseImpl";
   
    private static String DBPARAM_BASEURI = "exist://";
   
    public static final String USERNAME = "admin";
   
    public static final String PASSWORD = "admin";
   
    // the resource name for system preferences
    private static final String RESNAME_SYSTEM_PREFERENCES_DATABASE =
        "systempreferences.xml";
   
    // the root element of the resource
    private static final String ELEMENTNAME_ROOT = "systempreferences";
   
    // The element name of any preference in the database
    private static final String ELEMENTNAME_SYSTEM_PREFERENCE = "preference";
   
    private Collection rootCollection;
   
    private XPathQueryService queryService;
   
    public void init(String id) throws Exception
    {
        Database database = registerDatabaseByDriver(DRIVER_NAME);
       
        Collection pluginRootCollection =
            database
                .getCollection(DBPARAM_BASEURI + "/db/", USERNAME, PASSWORD);
       
        Collection localCollection =
            pluginRootCollection.getChildCollection(id);
       
        if (localCollection == null)
        {
            CollectionManagementService collectionManagementService =
                (CollectionManagementService) pluginRootCollection.getService(
                    "CollectionManagementService",
                    "1.0");
           
            if (collectionManagementService == null)
            {
                // We need this exception in two places so it must be created
                // ahead of the throw statement.
                NullPointerException ex =
                    new NullPointerException(
                        "collectionManagementService must be supported.");
               
                // Crash time (not really, the davadoc DOES warn clients this
                // may happen)
                throw ex;
            }
           
            // Create the collection
            localCollection = collectionManagementService.createCollection(id);
           
        }
       
        this.rootCollection = localCollection;
       
        this.queryService =
            (XPathQueryService) rootCollection.getService(
                "XPathQueryService",
                "1.0");
    }
   
    public Database registerDatabaseByDriver(String driver)
        throws ClassNotFoundException,
            InstantiationException,
            IllegalAccessException,
            XMLDBException
    {
        Database database = (Database) Class.forName(driver).newInstance();
        database.setProperty("create-database", "true");
        System.setProperty("exist.home", System.getProperty("user.dir"));
       
        DatabaseManager.registerDatabase(database);
       
        return database;
    }
   
    public void deregisterDatabase() throws XMLDBException
    {
        DatabaseInstanceManager manager =
            (DatabaseInstanceManager) rootCollection.getService(
                "DatabaseInstanceManager",
                "1.0");
        manager.shutdown();
    }
   
    public ResourceSet query(String context, String query)
        throws XMLDBException
    {
        // Check if this query is against the collection or a specific resource
        if (context == null || context.equals(""))
        {
            return queryService.query(query);
        }
       
        // Must be a specific resource
        return queryService.queryResource(context, query);
    }
   
    public Properties getPreferences(String group) throws XMLDBException
    {
        // For making the query
        String query;
        ResourceSet results;
       
        // For parsing the results
        XMLResource resultBlob;
        Node node;
        Document document;
        NodeList nodeList;
        Element element;
       
        // To store the results
        Properties preferences = new Properties();
       
        /*
         * /systempreferences/preference[@group='NameHere']
         */
        // Build the query
        query =
            String.format(
                "/%s/%s[@%s='%s']",
                ELEMENTNAME_ROOT,
                ELEMENTNAME_SYSTEM_PREFERENCE,
                "group",
                group);
       
        // Make the query
        results = query(RESNAME_SYSTEM_PREFERENCES_DATABASE, query);
       
        if (results.getSize() == 0)
        {
            // No results
            return null;
        }
       
        // Parse out the results
        resultBlob = (XMLResource) results.getMembersAsResource();
       
        // Display the results to console
        System.out.println(resultBlob.getContent());
       
        // get content as DOM for parsing
        // !!!!!!!!!! an XMLDBException is being thrown here !!!!!!!!!!
        node = resultBlob.getContentAsDOM();
        if (node.getOwnerDocument() == null)
        {
            document = (Document) node;
        }
        else
        {
            document = node.getOwnerDocument();
        }
       
        // create a list of all the preference nodes
        nodeList = document.getElementsByTagName(ELEMENTNAME_SYSTEM_PREFERENCE);
       
        // parse the list into a properties map
        for (int index = 0; index < nodeList.getLength(); index++)
        {
            // grab an element in the list
            element = (Element) nodeList.item(index);
           
            // add "value" to the properties map with the key "name"
            preferences.put(element.getAttribute("name"), element
                .getAttribute("value"));
           
        }
       
        return preferences;
    }
   
    public static void main(String args[]) throws Exception
    {
        DBExample dbExample = null;
        try
        {
            dbExample = new DBExample();
            dbExample.init("preferences");
            dbExample.getPreferences("group1");
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        finally
        {
            if (dbExample != null)
                dbExample.deregisterDatabase();
        }
    }
}

The output of this program is:

log4j:WARN No appenders could be found for logger (org.exist.util.ConfigurationHelper).
log4j:WARN Please initialize the log4j system properly.
<exist:result xmlns:exist="http://exist.sourceforge.net/NS/exist" hitCount="4">
    <preference group="group1" name="preference1" value="50"/>
    <preference group="group1" name="preference2" value="foo"/>
    <preference group="group1" name="preference3" value="200"/>
    <preference group="group1" name="preference4" value="true"/>
</exist:result>
org.xmldb.api.base.XMLDBException:
        at org.exist.xmldb.LocalXMLResource.getDocument(LocalXMLResource.java:496)
        at org.exist.xmldb.LocalXMLResource.getContentAsDOM(LocalXMLResource.java:210)
        at main.DBExample.getPreferences(DBExample.java:170)
        at main.DBExample.main(DBExample.java:205)



Thank you,
Michael


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[Adam Retter-3]

> Here is a simplified sample of what is occurring in my application. This is a simple example of the issue which reproduces the  same issue that I am seeing in my application. I created this example to best show the problem.


I have spent some time and looked over this code and to be honest it
was a mess and a pain! This code is far much more than what you need
to reproduce the problem. For a reproducible test case for this, I
would have liked to have seen a single method with the absolute
minimum required to cause the issue.

Anyways, I have run this code against eXist trunk and can confirm that
there is no problem with eXist. I think the issue is in how you are
retrieving and parsing the output from eXist.

If you look at the code below the comment   "// Parse out the results"
 in the method "getPreferences", as you have said this causes an
exception. Replacing this code with something similar to the following
should work for you - I believe that it does here.

The results reading code was taken from examples freely available in
the eXist documentation on the website.


// Parse out the results
       ResourceIterator i = results.getIterator();
       while(i.hasMoreResources())
       {
            Resource r = i.nextResource();
            if(r.getResourceType().equals("XMLResource"))
            {
                node = ((XMLResource)r).getContentAsDOM();

                if (node.getOwnerDocument() == null)
                {
                   document = (Document) node;
                }
                else
                {
                   document = node.getOwnerDocument();
                }

                // create a list of all the preference nodes
                nodeList =
document.getElementsByTagName(ELEMENTNAME_SYSTEM_PREFERENCE);

               // parse the list into a properties map
               for (int index = 0; index < nodeList.getLength(); index++)
               {
                   // grab an element in the list
                   element = (Element) nodeList.item(index);

                   // add "value" to the properties map with the key "name"
                   preferences.put(element.getAttribute("name"), element
                       .getAttribute("value"));

               }
            }
        }

>
> package main;
>
> import java.util.Properties;
>
> import org.exist.xmldb.DatabaseInstanceManager;
> import org.w3c.dom.Document;
> import org.w3c.dom.Element;
> import org.w3c.dom.Node;
> import org.w3c.dom.NodeList;
> import org.xmldb.api.DatabaseManager;
> import org.xmldb.api.base.Collection;
> import org.xmldb.api.base.Database;
> import org.xmldb.api.base.ResourceSet;
> import org.xmldb.api.base.XMLDBException;
> import org.xmldb.api.modules.CollectionManagementService;
> import org.xmldb.api.modules.XMLResource;
> import org.xmldb.api.modules.XPathQueryService;
>
> public class DBExample
> {
>    public static final String DRIVER_NAME = "org.exist.xmldb.DatabaseImpl";
>
>    private static String DBPARAM_BASEURI = "exist://";
>
>    public static final String USERNAME = "admin";
>
>    public static final String PASSWORD = "admin";
>
>    // the resource name for system preferences
>    private static final String RESNAME_SYSTEM_PREFERENCES_DATABASE =
>        "systempreferences.xml";
>
>    // the root element of the resource
>    private static final String ELEMENTNAME_ROOT = "systempreferences";
>
>    // The element name of any preference in the database
>    private static final String ELEMENTNAME_SYSTEM_PREFERENCE = "preference";
>
>    private Collection rootCollection;
>
>    private XPathQueryService queryService;
>
>    public void init(String id) throws Exception
>    {
>        Database database = registerDatabaseByDriver(DRIVER_NAME);
>
>        Collection pluginRootCollection =
>            database
>                .getCollection(DBPARAM_BASEURI + "/db/", USERNAME, PASSWORD);
>
>        Collection localCollection =
>            pluginRootCollection.getChildCollection(id);
>
>        if (localCollection == null)
>        {
>            CollectionManagementService collectionManagementService =
>                (CollectionManagementService) pluginRootCollection.getService(
>                    "CollectionManagementService",
>                    "1.0");
>
>            if (collectionManagementService == null)
>            {
>                // We need this exception in two places so it must be created
>                // ahead of the throw statement.
>                NullPointerException ex =
>                    new NullPointerException(
>                        "collectionManagementService must be supported.");
>
>                // Crash time (not really, the davadoc DOES warn clients this
>                // may happen)
>                throw ex;
>            }
>
>            // Create the collection
>            localCollection = collectionManagementService.createCollection(id);
>
>        }
>
>        this.rootCollection = localCollection;
>
>        this.queryService =
>            (XPathQueryService) rootCollection.getService(
>                "XPathQueryService",
>                "1.0");
>    }
>
>    public Database registerDatabaseByDriver(String driver)
>        throws ClassNotFoundException,
>            InstantiationException,
>            IllegalAccessException,
>            XMLDBException
>    {
>        Database database = (Database) Class.forName(driver).newInstance();
>        database.setProperty("create-database", "true");
>        System.setProperty("exist.home", System.getProperty("user.dir"));
>
>        DatabaseManager.registerDatabase(database);
>
>        return database;
>    }
>
>    public void deregisterDatabase() throws XMLDBException
>    {
>        DatabaseInstanceManager manager =
>            (DatabaseInstanceManager) rootCollection.getService(
>                "DatabaseInstanceManager",
>                "1.0");
>        manager.shutdown();
>    }
>
>    public ResourceSet query(String context, String query)
>        throws XMLDBException
>    {
>        // Check if this query is against the collection or a specific resource
>        if (context == null || context.equals(""))
>        {
>            return queryService.query(query);
>        }
>
>        // Must be a specific resource
>        return queryService.queryResource(context, query);
>    }
>
>    public Properties getPreferences(String group) throws XMLDBException
>    {
>        // For making the query
>        String query;
>        ResourceSet results;
>
>        // For parsing the results
>        XMLResource resultBlob;
>        Node node;
>        Document document;
>        NodeList nodeList;
>        Element element;
>
>        // To store the results
>        Properties preferences = new Properties();
>
>        /*
>         * /systempreferences/preference[@group='NameHere']
>         */
>        // Build the query
>        query =
>            String.format(
>                "/%s/%s[@%s='%s']",
>                ELEMENTNAME_ROOT,
>                ELEMENTNAME_SYSTEM_PREFERENCE,
>                "group",
>                group);
>
>        // Make the query
>        results = query(RESNAME_SYSTEM_PREFERENCES_DATABASE, query);
>
>        if (results.getSize() == 0)
>        {
>            // No results
>            return null;
>        }
>
>        // Parse out the results
>        resultBlob = (XMLResource) results.getMembersAsResource();
>
>        // Display the results to console
>        System.out.println(resultBlob.getContent());
>
>        // get content as DOM for parsing
>        // !!!!!!!!!! an XMLDBException is being thrown here !!!!!!!!!!
>        node = resultBlob.getContentAsDOM();
>        if (node.getOwnerDocument() == null)
>        {
>            document = (Document) node;
>        }
>        else
>        {
>            document = node.getOwnerDocument();
>        }
>
>        // create a list of all the preference nodes
>        nodeList = document.getElementsByTagName(ELEMENTNAME_SYSTEM_PREFERENCE);
>
>        // parse the list into a properties map
>        for (int index = 0; index < nodeList.getLength(); index++)
>        {
>            // grab an element in the list
>            element = (Element) nodeList.item(index);
>
>            // add "value" to the properties map with the key "name"
>            preferences.put(element.getAttribute("name"), element
>                .getAttribute("value"));
>
>        }
>
>        return preferences;
>    }
>
>    public static void main(String args[]) throws Exception
>    {
>        DBExample dbExample = null;
>        try
>        {
>            dbExample = new DBExample();
>            dbExample.init("preferences");
>            dbExample.getPreferences("group1");
>        }
>        catch (Exception e)
>        {
>            e.printStackTrace();
>        }
>        finally
>        {
>            if (dbExample != null)
>                dbExample.deregisterDatabase();
>        }
>    }
> }
>
> The output of this program is:
>
> log4j:WARN No appenders could be found for logger (org.exist.util.ConfigurationHelper).
> log4j:WARN Please initialize the log4j system properly.
> <exist:result xmlns:exist="http://exist.sourceforge.net/NS/exist" hitCount="4">
>    <preference group="group1" name="preference1" value="50"/>
>    <preference group="group1" name="preference2" value="foo"/>
>    <preference group="group1" name="preference3" value="200"/>
>    <preference group="group1" name="preference4" value="true"/>
> </exist:result>
> org.xmldb.api.base.XMLDBException:
>        at org.exist.xmldb.LocalXMLResource.getDocument(LocalXMLResource.java:496)
>        at org.exist.xmldb.LocalXMLResource.getContentAsDOM(LocalXMLResource.java:210)
>        at main.DBExample.getPreferences(DBExample.java:170)
>        at main.DBExample.main(DBExample.java:205)
>
>
>
> Thank you,
> Michael
>
>
> ------------------------------------------------------------------------------
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>

--
Adam Retter

eXist Developer
{ United Kingdom }
adam@...
irc://irc.freenode.net/existdb

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[Michael-526]

Thank you for spending the time to look into this. I am sorry that the
sample was too complicated and messy. Next time I have an issue I will
spend more time breaking it down to as little code as possible.

The solution you have suggested offers a good work-around for the
problem. I have also created a work-around solution myself which
involved building the DOM Node by parsing the result content string. In
this solution I basically replicated what
RemoteXMLResource.getContentAsDOM() does.

I suppose at this point, it appears to me that my issue is due to how
eXist implements the XML:DB API. I understand that it was probably not
expected that a developer like myself parse the results of a query in
this manner. But I am still not clear if what I am attempting to do is
an illegal action according to the API spec. I guess in the end, the
fact that there are several ways to parse the results differently to
achieve the same result is really all the solution I require. But I did
still feel it was necessary to point out the unexpected behaviour I was
seeing while using eXist.

Again, thank you for your time on this one Adam.


Michael


Adam Retter wrote:

> I have spent some time and looked over this code and to be honest it
> was a mess and a pain! This code is far much more than what you need
> to reproduce the problem. For a reproducible test case for this, I
> would have liked to have seen a single method with the absolute
> minimum required to cause the issue.
>
> Anyways, I have run this code against eXist trunk and can confirm that
> there is no problem with eXist. I think the issue is in how you are
> retrieving and parsing the output from eXist.
>
> If you look at the code below the comment   "// Parse out the results"
>  in the method "getPreferences", as you have said this causes an
> exception. Replacing this code with something similar to the following
> should work for you - I believe that it does here.
>
> The results reading code was taken from examples freely available in
> the eXist documentation on the website.
>
>
> // Parse out the results
>        ResourceIterator i = results.getIterator();
>        while(i.hasMoreResources())
>        {
>             Resource r = i.nextResource();
>             if(r.getResourceType().equals("XMLResource"))
>             {
>                 node = ((XMLResource)r).getContentAsDOM();
>
>                 if (node.getOwnerDocument() == null)
>                 {
>                    document = (Document) node;
>                 }
>                 else
>                 {
>                    document = node.getOwnerDocument();
>                 }
>
>                 // create a list of all the preference nodes
>                 nodeList =
> document.getElementsByTagName(ELEMENTNAME_SYSTEM_PREFERENCE);
>
>                // parse the list into a properties map
>                for (int index = 0; index < nodeList.getLength(); index++)
>                {
>                    // grab an element in the list
>                    element = (Element) nodeList.item(index);
>
>                    // add "value" to the properties map with the key "name"
>                    preferences.put(element.getAttribute("name"), element
>                        .getAttribute("value"));
>
>                }
>             }
>         }
>
>
>
>  
>> package main;
>>
>> import java.util.Properties;
>>
>> import org.exist.xmldb.DatabaseInstanceManager;
>> import org.w3c.dom.Document;
>> import org.w3c.dom.Element;
>> import org.w3c.dom.Node;
>> import org.w3c.dom.NodeList;
>> import org.xmldb.api.DatabaseManager;
>> import org.xmldb.api.base.Collection;
>> import org.xmldb.api.base.Database;
>> import org.xmldb.api.base.ResourceSet;
>> import org.xmldb.api.base.XMLDBException;
>> import org.xmldb.api.modules.CollectionManagementService;
>> import org.xmldb.api.modules.XMLResource;
>> import org.xmldb.api.modules.XPathQueryService;
>>
>> public class DBExample
>> {
>>    public static final String DRIVER_NAME = "org.exist.xmldb.DatabaseImpl";
>>
>>    private static String DBPARAM_BASEURI = "exist://";
>>
>>    public static final String USERNAME = "admin";
>>
>>    public static final String PASSWORD = "admin";
>>
>>    // the resource name for system preferences
>>    private static final String RESNAME_SYSTEM_PREFERENCES_DATABASE =
>>        "systempreferences.xml";
>>
>>    // the root element of the resource
>>    private static final String ELEMENTNAME_ROOT = "systempreferences";
>>
>>    // The element name of any preference in the database
>>    private static final String ELEMENTNAME_SYSTEM_PREFERENCE = "preference";
>>
>>    private Collection rootCollection;
>>
>>    private XPathQueryService queryService;
>>
>>    public void init(String id) throws Exception
>>    {
>>        Database database = registerDatabaseByDriver(DRIVER_NAME);
>>
>>        Collection pluginRootCollection =
>>            database
>>                .getCollection(DBPARAM_BASEURI + "/db/", USERNAME, PASSWORD);
>>
>>        Collection localCollection =
>>            pluginRootCollection.getChildCollection(id);
>>
>>        if (localCollection == null)
>>        {
>>            CollectionManagementService collectionManagementService =
>>                (CollectionManagementService) pluginRootCollection.getService(
>>                    "CollectionManagementService",
>>                    "1.0");
>>
>>            if (collectionManagementService == null)
>>            {
>>                // We need this exception in two places so it must be created
>>                // ahead of the throw statement.
>>                NullPointerException ex =
>>                    new NullPointerException(
>>                        "collectionManagementService must be supported.");
>>
>>                // Crash time (not really, the davadoc DOES warn clients this
>>                // may happen)
>>                throw ex;
>>            }
>>
>>            // Create the collection
>>            localCollection = collectionManagementService.createCollection(id);
>>
>>        }
>>
>>        this.rootCollection = localCollection;
>>
>>        this.queryService =
>>            (XPathQueryService) rootCollection.getService(
>>                "XPathQueryService",
>>                "1.0");
>>    }
>>
>>    public Database registerDatabaseByDriver(String driver)
>>        throws ClassNotFoundException,
>>            InstantiationException,
>>            IllegalAccessException,
>>            XMLDBException
>>    {
>>        Database database = (Database) Class.forName(driver).newInstance();
>>        database.setProperty("create-database", "true");
>>        System.setProperty("exist.home", System.getProperty("user.dir"));
>>
>>        DatabaseManager.registerDatabase(database);
>>
>>        return database;
>>    }
>>
>>    public void deregisterDatabase() throws XMLDBException
>>    {
>>        DatabaseInstanceManager manager =
>>            (DatabaseInstanceManager) rootCollection.getService(
>>                "DatabaseInstanceManager",
>>                "1.0");
>>        manager.shutdown();
>>    }
>>
>>    public ResourceSet query(String context, String query)
>>        throws XMLDBException
>>    {
>>        // Check if this query is against the collection or a specific resource
>>        if (context == null || context.equals(""))
>>        {
>>            return queryService.query(query);
>>        }
>>
>>        // Must be a specific resource
>>        return queryService.queryResource(context, query);
>>    }
>>
>>    public Properties getPreferences(String group) throws XMLDBException
>>    {
>>        // For making the query
>>        String query;
>>        ResourceSet results;
>>
>>        // For parsing the results
>>        XMLResource resultBlob;
>>        Node node;
>>        Document document;
>>        NodeList nodeList;
>>        Element element;
>>
>>        // To store the results
>>        Properties preferences = new Properties();
>>
>>        /*
>>         * /systempreferences/preference[@group='NameHere']
>>         */
>>        // Build the query
>>        query =
>>            String.format(
>>                "/%s/%s[@%s='%s']",
>>                ELEMENTNAME_ROOT,
>>                ELEMENTNAME_SYSTEM_PREFERENCE,
>>                "group",
>>                group);
>>
>>        // Make the query
>>        results = query(RESNAME_SYSTEM_PREFERENCES_DATABASE, query);
>>
>>        if (results.getSize() == 0)
>>        {
>>            // No results
>>            return null;
>>        }
>>
>>        // Parse out the results
>>        resultBlob = (XMLResource) results.getMembersAsResource();
>>
>>        // Display the results to console
>>        System.out.println(resultBlob.getContent());
>>
>>        // get content as DOM for parsing
>>        // !!!!!!!!!! an XMLDBException is being thrown here !!!!!!!!!!
>>        node = resultBlob.getContentAsDOM();
>>        if (node.getOwnerDocument() == null)
>>        {
>>            document = (Document) node;
>>        }
>>        else
>>        {
>>            document = node.getOwnerDocument();
>>        }
>>
>>        // create a list of all the preference nodes
>>        nodeList = document.getElementsByTagName(ELEMENTNAME_SYSTEM_PREFERENCE);
>>
>>        // parse the list into a properties map
>>        for (int index = 0; index < nodeList.getLength(); index++)
>>        {
>>            // grab an element in the list
>>            element = (Element) nodeList.item(index);
>>
>>            // add "value" to the properties map with the key "name"
>>            preferences.put(element.getAttribute("name"), element
>>                .getAttribute("value"));
>>
>>        }
>>
>>        return preferences;
>>    }
>>
>>    public static void main(String args[]) throws Exception
>>    {
>>        DBExample dbExample = null;
>>        try
>>        {
>>            dbExample = new DBExample();
>>            dbExample.init("preferences");
>>            dbExample.getPreferences("group1");
>>        }
>>        catch (Exception e)
>>        {
>>            e.printStackTrace();
>>        }
>>        finally
>>        {
>>            if (dbExample != null)
>>                dbExample.deregisterDatabase();
>>        }
>>    }
>> }
>>
>> The output of this program is:
>>
>> log4j:WARN No appenders could be found for logger (org.exist.util.ConfigurationHelper).
>> log4j:WARN Please initialize the log4j system properly.
>> <exist:result xmlns:exist="http://exist.sourceforge.net/NS/exist" hitCount="4">
>>    <preference group="group1" name="preference1" value="50"/>
>>    <preference group="group1" name="preference2" value="foo"/>
>>    <preference group="group1" name="preference3" value="200"/>
>>    <preference group="group1" name="preference4" value="true"/>
>> </exist:result>
>> org.xmldb.api.base.XMLDBException:
>>        at org.exist.xmldb.LocalXMLResource.getDocument(LocalXMLResource.java:496)
>>        at org.exist.xmldb.LocalXMLResource.getContentAsDOM(LocalXMLResource.java:210)
>>        at main.DBExample.getPreferences(DBExample.java:170)
>>        at main.DBExample.main(DBExample.java:205)
>>
>>
>>
>> Thank you,
>> Michael
>>
>>
>> ------------------------------------------------------------------------------
>> _______________________________________________
>> Exist-open mailing list
>> Exist-open@...
>> https://lists.sourceforge.net/lists/listinfo/exist-open
>>
>>    
>
>
>
>  

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[Adam Retter-3]

> Thank you for spending the time to look into this. I am sorry that the
> sample was too complicated and messy. Next time I have an issue I will spend
> more time breaking it down to as little code as possible.

Thats ok, retrospectively I must appologise as I see now the tone of
my email was less than constructive in places!

However I think the lesson to take away here is that - simple, small
reproducible test cases will be addressed faster by us and receive
more attention as they really get to the crux of the problem.

For completeness of this, in your case, the reporducible example would of been -


public final static void main(String args[]) throws Exception {
        Database database = (Database)
Class.forName("org.exist.xmldb.DatabaseImpl").newInstance();
        database.setProperty("create-database", "true");
        DatabaseManager.registerDatabase(database);

        Collection rootCollection =
database.getCollection("exist:///db", "admin", "admin");
        Collection localCollection =
rootCollection.getChildCollection("preferences");

        XPathQueryService queryService = (XPathQueryService)
rootCollection.getService("XPathQueryService", "1.0");

        String query = "/systempreferences/preference[@group='group1']";

        ResourceSet results =
queryService.queryResource("systempreferences.xml", query);

        if(results.getSize() == 0) {
            // No results
            return;
        }

        // Parse out the results
        XMLResource resultBlob = (XMLResource) results.getMembersAsResource();

       // Display the results to console
       System.out.println(resultBlob.getContent());

       // get content as DOM for parsing
       // !!!!!!!!!! an XMLDBException is being thrown here !!!!!!!!!!
       Node node = resultBlob.getContentAsDOM();
       Document document = null;
       if (node.getOwnerDocument() == null) {
           document = (Document) node;
       }
       else {
           document = node.getOwnerDocument();
       }

       // create a list of all the preference nodes
       NodeList nodeList = document.getElementsByTagName("preference");

       // parse the list into a properties map
       Properties preferences = new Properties();
       for(int index = 0; index < nodeList.getLength(); index++) {
           // grab an element in the list
           Element element = (Element) nodeList.item(index);

           // add "value" to the properties map with the key "name"
           preferences.put(element.getAttribute("name"),
element.getAttribute("value"));

       }
    }



> The solution you have suggested offers a good work-around for the problem. I
> have also created a work-around solution myself which involved building the
> DOM Node by parsing the result content string. In this solution I basically
> replicated what RemoteXMLResource.getContentAsDOM() does.

I dont see it as a work around. I think it is the correct way to do it.
Your problem is really this line -

 resultBlob = (XMLResource) results.getMembersAsResource();


> I suppose at this point, it appears to me that my issue is due to how eXist
> implements the XML:DB API. I understand that it was probably not expected
> that a developer like myself parse the results of a query in this manner.

Are you aware of other xml db implementations that work in this way?

> But I am still not clear if what I am attempting to do is an illegal action
> according to the API spec.

To be honest I am not entirely sure myself, I do not use the xmldb
stuff myself. Some of the other eXist developers may be able to help
you here...

--
Adam Retter

eXist Developer
{ United Kingdom }
adam@...
irc://irc.freenode.net/existdb

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