Running Play! framework JPA from a command line process

If you are using the Play! framework and wanted to run a command line process that uses the Play! JPA enhancements this post is for you.
It requires some classloader magic and is based on reading the source code of Play 1.0.x, I am not sure if this will be supported in future versions.

You need your Main class to prepare the Play! framework classes, set the classloader and load your "real" Main class using the Play! classloader.
This is how it's done:

public class LoaderMain
{
 public static void main( String[] args ) throws Exception
 {
        File root = new File(System.getProperty("application.path"));
        Play.init(root, System.getProperty("play.id", ""));
        Thread.currentThread().setContextClassLoader( Play.classloader );
        Class c = Play.classloader.loadClass( "com.incapsula.batch.PlayLoaderMain" );
        Method m = c.getMethod( "run" );
        m.invoke( c.newInstance() );
 }
}

Now since you are not invoking web services you need to execute the framework methods by yourself, e.g. initializing the plugins and openning a JPA transaction.
You'll have to get yourself familiar with the Play! framework source code for any dependencies your process has on the Play! frameowrk.

public class PlayLoaderMain
{
 public void run() throws Exception
 {
  new DBPlugin().onApplicationStart();
  new JPAPlugin().onApplicationStart();

  JPAPlugin.startTx( true );
  Fixtures.load( "initial-data.yml" );
  System.out.println( User.findAll() );
  JPAPlugin.closeTx( false );
 }
}

There are a few things to notice:

• You need the Play jars in your classpath (play.jar, framework/lib jar files and module/lib jar files for every module you are using)
  
• You need to point the "application.path" JVM property to your Play application
  
• You need to initialize different Play! plugins if you need them (e.g. if you are using the Play! templates in your process you also need to initialize the MessagesPlugin)
  

JAXB, Sun and how to marshal a CDATA element

According to https://jaxb.dev.java.net/faq/index.html#marshalling_cdata there is no direct support in marshalling CDATA blocks, this is vendor specific.
I'll describe how this is done when using the built-in Sun implementation by an example.


Suppose this is my JAXB annotated class:

package org.oded;

import javax.xml.bind.annotation.*;
import javax.xml.bind.annotation.adapters.*;

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Item
{
 @XmlAttribute public int id;
 
 public String text;
}

Next I run the Main class:

package org.oded;

import java.io.*;

import javax.xml.bind.*;

import com.sun.xml.internal.bind.marshaller.CharacterEscapeHandler;

public class Main
{
 public static void main( String[] args ) throws Exception
 {
  Item i1 = new Item();
  i1.text = "hello";
  i1.id = 1;
  
  Item i2 = new Item();
  i2.text = "";
  i2.id = 2;
    
  Marshaller m = JAXBContext.newInstance( Item.class ).createMarshaller();
  
  m.marshal( i1, new OutputStreamWriter( System.out ) );
  System.out.println();
  m.marshal( i2, new OutputStreamWriter( System.out ) );
 }
}

The output is:

hello
<code><helloWorld/></code>

Now suppose I want to wrap the XML value of text in a CDATA element and avoid the escaping, I need to add specify an Adapter for text to surround the value in a CDATA element in the following way:

package org.oded;

import javax.xml.bind.annotation.*;
import javax.xml.bind.annotation.adapters.*;

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Item
{
 @XmlAttribute public int id;
 
 @XmlJavaTypeAdapter(value=Adapter.class) 
 public String text;
 
 private static class Adapter extends XmlAdapter
 {

  @Override
  public String marshal( String v ) throws Exception
  {
   return "<![CDATA[" + v + "]]>";
  }

  @Override
  public String unmarshal( String v ) throws Exception
  {
   return v;
  }
  
 }
}

Now tell the Marshaller, in a Sun-specific way, not to escape the value of text:

package org.oded;

import java.io.*;

import javax.xml.bind.*;

import com.sun.xml.internal.bind.marshaller.CharacterEscapeHandler;

public class Main
{
 public static void main( String[] args ) throws Exception
 {
  Item i1 = new Item();
  i1.text = "hello";
  i1.id = 1;
  
  Item i2 = new Item();
  i2.text = "";
  i2.id = 2;
    
  Marshaller m = JAXBContext.newInstance( Item.class ).createMarshaller();
  m.setProperty( "com.sun.xml.internal.bind.characterEscapeHandler", new CharacterEscapeHandler() {
   @Override
   public void escape( char[] ac, int i, int j, boolean flag, Writer writer ) throws IOException
   {
    // do not escape
    writer.write( ac, i, j );
   }
  });
  
  m.marshal( i1, new OutputStreamWriter( System.out ) );
  System.out.println();
  m.marshal( i2, new OutputStreamWriter( System.out ) );
 }
}

Now the output is:

<![CDATA[hello]]>
<![CDATA[]]>