Configuring XStream

Enabling Staging and Export/Import
Step 5 of 7

Configuring XStream for your Guestbook app provides an easy way to customize how entities are serialized to XML and back again. You can use it to enhance the Guestbook’s Staging implementation; however, it’s not required. There are three ways to leverage Liferay’s offering of XStream via the XStreamConfigurator:

• Allowed Types: whitelists entities so everything is forbidden except a certain set of items. All staged models are allowed by default; this would be in addition to the default functionality. Liferay DXP defines a default list of allowed types, which are available in the portlet data context.
• Aliases: helps with the readability and char length of LAR files by creating an alias for an otherwise long winded entity name.
• Converters: converts configured objects to and from XML. This is primarily used to protect sensitive data; when serialized this way, sensitive data cannot be extracted from the generated LAR.

Since Allowed Types don’t make sense in this context (there are no additional entities to allow), you don’t need them for Guestbook. Converters let you re-write the serialization process from scratch—for example, to add encryption. This is a tutorial on Staging, not serialization, so the default serialization implementation is fine. That leaves aliases.

In the Guestbook, you’ll leverage XStream by creating an alias that modifies the XML in the LAR file produced by your app during the staging and export processes.

For example, by default your generated data has this structure:

<com.liferay.docs.guestbook.model.impl.GuestBookImpl>
    <field1>...</field1>
    ...
</com.liferay.docs.guestbook.model.impl.GuestBookImpl>

With an XStream alias configured in your app, that same LAR content has this structure:

<GuestBook>
    <field1>...</field1>
    ...
</GuestBook>

Follow the instructions below to create an XStream alias:

1. In the guestbook-service module, create a package named com.liferay.docs.guestbook.xstream.configurator. In that package, create a class named GuestbookXStreamConfigurator.

2. Modify the class to implement the XStreamConfigurator interface and create an @Component annotation declaring that same class as the implementation service:

   @Component(
       immediate = true, 
       service = XStreamConfigurator.class
   )
   public class GuestbookXStreamConfigurator implements XStreamConfigurator {
   

3. Since the Guestbook won’t leverage the Allowed Types and Converters XStream options, override their associated methods and have them return null:

   @Override
   public List<XStreamType> getAllowedXStreamTypes() {
   
       return null;
   }
   
   @Override
   public List<XStreamConverter> getXStreamConverters() {
   
       return null;
   }
   

4. Override the getXStreamAliases() method to return a list of aliases you want to define. Also, define the list field.

   @Override
   public List<XStreamAlias> getXStreamAliases() {
       return ListUtil.toList(_xStreamAliases);
   }
   
   private XStreamAlias[] _xStreamAliases;
   

   Next, you’ll define the list.

5. Create an activate() method that defines the aliases to use for Guestbook’s generated LAR file. You’ll define an alias for the GuestbookImpl and EntryImpl classes to convert them from their full package names to simple entity names:

   @Activate
   protected void activate() {
   
       _xStreamAliases = new XStreamAlias[] {
           new XStreamAlias(GuestbookImpl.class, "Guestbook"),
           new XStreamAlias(EntryImpl.class, "Entry"),
       };
   }
   

6. Organize your imports ([CTRL]+[SHIFT]+O), and save the file.

Awesome! You implemented an XStream Configurator for the Guestbook and created an alias for your guestbook and entry entity declarations.

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