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« Return to Thread: XMLDBException on LocalXMLResource.getContentAsDOM()
Re: XMLDBException on LocalXMLResource.getContentAsD
by Michael-526
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Rate this Message:
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
>>
>>
>
>
>
>
------------------------------------------------------------------------------
_______________________________________________
Exist-open mailing list
Exist-open@...
https://lists.sourceforge.net/lists/listinfo/exist-open
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
>>
>>
>
>
>
>
------------------------------------------------------------------------------
_______________________________________________
Exist-open mailing list
Exist-open@...
https://lists.sourceforge.net/lists/listinfo/exist-open
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