How to debug a remote Java application

It is not worth an entry but... I always forgot how to remotely debug a jvm :

Firstly, jvm options :
-Xdebug : Enables debugging support in the VM
-Xrunjdwp:<options> : Loads in-process debugging libraries and specifies the kind of connection to be made (Xrunjdwp parameters)
I use -Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=8000

JDOM 2.X and Maven

I was asked to contribute to a side project at work. This small java project should handle XML file from an external repository, modify and reinject them in an ETL.

XML and Java ? A tumultuous love story...
Since I am not a big fan of JAXP and SAX, I searched for another XML manipulation library and found JDOM.
JDOM is a powerful Java library which aim to ease XML manipulation. It was once included in JSR 102 however the JSR is now withdrawn (more information can be found in the JDOM mailing list).

Since it is not the main purpose, if you want to learn more about the library there is a great primer writen in github wiki's page : https://github.com/hunterhacker/jdom/wiki/JDOM2-A-Primer

One of the downside of current JDOM version 2.0.2 is maven integration. When you want to include JDOM in your project, you add the following dependency :

<dependency>
  <groupId>org.jdom</groupId>
  <artifactId>jdom</artifactId>
  <version>2.0.2</version>
</dependency>

And JDOM pom.xml references those dependencies :

<dependencies>
  <dependency>
    <groupId>jaxen</groupId>
    <artifactId>jaxen</artifactId>
    <version>1.1.3</version>
    <optional>true</optional>
  </dependency>
  <dependency>
    <groupId>xerces</groupId>
    <artifactId>xercesImpl</artifactId>
    <version>2.10.0</version>
    <optional>true</optional>
  </dependency>
  <dependency>
    <groupId>xalan</groupId>
    <artifactId>xalan</artifactId>
    <version>2.7.1</version>
    <optional>true</optional>
  </dependency>
</dependencies>

Now if you try to perform mvn install, you will face one of the following errors :

• The following artifacts could not be resolved: maven-plugins:maven-cobertura-plugin:plugin:1.3, maven-plugins:maven-findbugs-plugin:plugin:1.3.1, Failure to find maven-plugins:maven-cobertura-plugin:plugin:1.3 in ...

This error is caused by a broken artifact on Jaxen 1.1.3. The work-around is to use the "exlusions" tags in order to avoid loading of unfound dependencies.

<dependency>
  <groupId>jaxen</groupId>
  <artifactId>jaxen</artifactId>
  <version>1.1.3</version>
  <optional>true</optional>
  <!-- http://jira.codehaus.org/browse/JAXEN-217 -->
  <exclusions>
    <exclusion>
      <groupId>maven-plugins</groupId>
      <artifactId>maven-cobertura-plugin</artifactId>
    </exclusion>
    <exclusion>
      <groupId>maven-plugins</groupId>
      <artifactId>maven-findbugs-plugin</artifactId>
    </exclusion>
  </exclusions>
</dependency>

• java.lang.ExceptionInInitializerError
      at org.jdom2.input.SAXBuilder.(SAXBuilder.java:338)
      at org.jdom2.input.SAXBuilder.(SAXBuilder.java:221)
      at [...]
  Caused by: java.lang.UnsupportedOperationException: This parser does not support specification "null" version "null"
      at javax.xml.parsers.SAXParserFactory.setSchema(SAXParserFactory.java:421)
      at org.jdom2.input.sax.XMLReaders.(XMLReaders.java:122)
      at org.jdom2.input.sax.XMLReaders.(XMLReaders.java:95)
      ... 30 more

This error is caused by an old version of xercesImpl specified in the resolved dependencies. Once again, we will use the "exclusions" tag to avoid this error.

<dependency>
  <groupId>jaxen</groupId>
  <artifactId>jaxen</artifactId>
  <version>1.1.3</version>
  <optional>true</optional>
  <!-- Use JDK xerces version -->
  <exclusions>
    <exclusion>
      <groupId>xerces</groupId>
      <artifactId>xercesImpl</artifactId>
    </exclusion>
  </exclusions>
</dependency>

This should not work if your JDK is lesser than 1.5.


In summary, here is the depency set I currently use for JDOM 2.0.2 :

<dependency>
  <groupId>org.jdom</groupId>
  <artifactId>jdom</artifactId>
  <version>2.0.2</version>
</dependency>
<dependency>
  <groupId>jaxen</groupId>
  <artifactId>jaxen</artifactId>
  <version>1.1.3</version>
  <exclusions>
    <!-- Use JDK xerces version -->
    <exclusion>
      <groupId>xerces</groupId>
      <artifactId>xercesImpl</artifactId>
    </exclusion>
    <!-- http://jira.codehaus.org/browse/JAXEN-217 -->
    <exclusion>
      <groupId>maven-plugins</groupId>
      <artifactId>maven-cobertura-plugin</artifactId>
    </exclusion>
    <exclusion>
      <groupId>maven-plugins</groupId>
      <artifactId>maven-findbugs-plugin</artifactId>
    </exclusion>
  </exclusions>
</dependency>
<dependency>
  <groupId>xalan</groupId>
  <artifactId>xalan</artifactId>
  <version>2.7.1</version>
</dependency>

Blog opened

Hello everyone,

I never thought I would open a blog but now it's done.
Enjoy !