Invalid classpath publish/export dependency /local/eclipse/galileo/plugins/com.google.appengine.eclipse.sdkbundle_1.2.2.v200907291526/appengine-java-sdk-1.2.2/lib/user/orm/jdo2-api-2.3-ea.jar. The project contains another dependency with the same archive name.

The solution for this problem was using the notion of explicit dependency exclusion of Maven 2.x in the pom.xml.

<?xml version="1.0" encoding="UTF-8"?>
<AuditTrail>
    <Entry type="ExecutionReport" msgId="2544804979">
        <field tag="35" val="8"/>
        <field tag="34" val="000023"/>
        <field tag="43" val="N"/>
        <field tag="52" val="20090526-20:08:31"/>
        <field tag="6556" val="today12"/>
        <field tag="17" val="73740.1243368511.0"/>
        <field tag="32" val="*"/>
    </Entry>
    <Entry type="Acknowledged" msgId="1540251818">
    </Entry>
</AuditTrail>

I created three classes AuditTrail, AuditTrailEntry and AuditTrailEntryField for the elements AuditTrail, Entry, and field, respectively. In addition, I set the aliases accordingly:

XStream xStream = new XStream ();
xStream.alias ("AuditTrail", AuditTrail.class);
xStream.alias ("Entry", AuditTrailEntry.class);
xStream.alias ("field", AuditTrailEntryField.class);

A call to the method fromXml() of the XStream object resulted in the following exception:

ConversionException: Element [NAME] of type [TYPE]
                     is not defined as [NAME] in type [TYPE]

Because I did not find a quick solution via a Google search I was forced to read the XStream documentation. ;-) There I learned something about Implicit Collections in XStream. Whenever you have a collection which does not display it’s root tag, you can map it as an implicit collection:

xStream.addImplicitCollection (AuditTrailEntry.class, "fields");
xStream.addImplicitCollection (AuditTrail.class, "entries");

with

private List <AuditTrailEntryField> fields;

in class AuditTrailEntry and

private List <AuditTrailEntry> entries;

in class AuditTrail.

org.hibernate.exception.JDBCConnectionException:
  could not execute query
[...]
com.mysql.jdbc.CommunicationsException:
  Communications link failure due to underlying exception:
[...]

This problem occurs because MySQL drops idle JDBC connection after 8 hours, but the C3P0 connection pooling mechanism still considers these connection as alive and valid.

I found several possible solution on the Internet. Some people recommend to set the “autoReconnect” parameter in the JDBC URL, but this is not recommended by the MySQL team.

Others recommend to set the C3P0 properties accordingly in order to check and close idle database connections. In most cases the proposed solution looks like the “official” configuration provided by the Hibernate crew:

<property name="c3p0.min_size">3</property>
<property name="c3p0.max_size">25</property>
<property name="c3p0.acquire_increment">1</property>
<property name="c3p0.max_statements">50</property>
<property name="c3p0.timeout">14400</property>
<property name="c3p0.idle_test_period">3600</property>

But as I have found in many, many comments in discussion groups this also did not work in a large number of cases. In order to get C3P0 connection pooling in Hibernate3 work correctly with a MySQL database one important property setting is still missing. I found this hint in a comment to the above “official” configuration. In addition one has to explicitly set the connection provider class:

<property name="connection.provider_class">
  org.hibernate.connection.C3P0ConnectionProvider
</property>

After setting this property the above C3P0 configuration works correctly. At least for me.

My GWT application makes RPCs to a server backed by Hibernate. Including Hibernate (org.hibernate:hibernate-core-3.3.1.GA from the JBoss repository) into the classpath via Maven also includes XPP3 and the pull-parser-2 libraries. Then for some reason the Google GWT compiler uses the pull-parser-2 to parse the XML of the inherited modules.

The module com.google.gwt.user.User includes the module com.google.gwt.i18n.I18N which causes an ArrayIndexOutOfBoundsException:

[ERROR] Line 29: Unexpected exception while processing element 'inherits'
java.lang.ArrayIndexOutOfBoundsException: null
    at java.lang.System.arraycopy(Native Method)
    at org.gjt.xpp.impl.tokenizer.Tokenizer.next(Tokenizer.java:1274)
    at org.gjt.xpp.impl.pullparser.PullParser.next(PullParser.java:392)
    at org.gjt.xpp.sax2.Driver.parseSubTree(Driver.java:415)
    at org.gjt.xpp.sax2.Driver.parse(Driver.java:310)
    at com.google.gwt.dev.util.xml.ReflectiveParser$Impl.parse(ReflectiveParser.java:310)

This seems to be a bug in the pull-parser-2. Excluding the pull-parser from the hibernate-core dependency removes it from the class path, but the GWT compiler continues using it for parsing its XML modules. The solution was to include the pull-parser-2.1.10 in the Java Build Path of Eclipse and put it to the first position in the build class path order in Eclipse.