1. What you will learn

In this short summary you will get an idea how you can transform the format of PAKs output data.

2. Basics

As mentioned in this summary, the IDataTransformer plays a major role in persisting data in PAK. It can be used to map between a specified output format and JSON, which PAK uses internally. By default, the output format is JSON as well.

3. Signature

Before giving a short example on how the interface should be used, this section describes the signature of the IDataTransformer<T> interface, as well as an overview on which methods have to be implemented.

T convertJSONToScheme(final String json) throws ConversionException;

Converts the given JSON to the desired representation

String convertSchemeToJSON(final T scheme) throws ConversionException;

Converts the specified scheme to JSON

boolean isScheme(final Object bean);

Checks if the given object is of the desired output type

Set<String> getExcludeFromConversion();

Returns a set of class names that are excluded from being serialized, defaults to an empty set

In this context, scheme refers to the output format, that is specified by the transformer.

All methods but getExcludeFromConversion have to be implemented.

4. Usage

This section briefly outlines a few examples demonstrating how the implementing Transformer should be used.

4.1. Data Transformation

Let’s suppose our persistence can only handle data stored in xml. In order to reduce the workload of the IPersistenceService, we implement a custom transformer to handle the conversions.

    "name" : "Max",
    "age" : 33,
    "hobbies" : [
            "name" : "Soccer",
            "id" : 0
            "name" : "Coding",
            "id" : 1
            "name" : "Automating Workflows",
            "id" : 2

Any data passing the persistence will be in the JSON format by default. The persistence service then calls IDataTransformer#convertJSONToScheme(…​) to prepare it for the store operation. In our case the result of this would something like follows.

<person name="Max" age="33">
        <hobby name="Soccer" id="0" />
        <hobby name="Coding" id="1" />
        <hobby name="Automating Workflows" id="2" />

We also need to handle the other way around. In order to prepare our data for PAK (after the find operation), IDataTransformer#convertSchemeToJSON(…​) is called and should result in the JSON above.

The IDataTransformer#isScheme(…​) method is solely responsible for detecting if the given data is already in the desired format, so in our case isScheme(json) = false and isScheme(xml) = true.

4.2. Data Exclusion

Sometimes it may be the case that data cannot be converted to json due to limitations. Should such a case be applicable to your environment, you can also choose to exclude specific class/package names to be converted at all.

All referenced classes have to be available at runtime

If this applies to some of your classes, make sure that your persistence can handle the (de-)serialization of java objects.

5. Default Implementations

  • The de.asap.pak.extra.impl.datatransformer.JsonStringDataTransformer: Functions as a NOP implementation which does not transform any data given.

  • The de.asap.pak.core.testutils.datatransformer.DataTransfomerImpl: Does not convert any objects at all. Can be used for migrating tests or to simplify tests, which write content into the persistence.

  • The de.asap.pak.core.testutils.datatransformer.DataTransformerMock: Helps running tests for IDataTransformer. Will fallback to the methods of TestDataTransformer when nothing is explicitly mocked.

  • The de.asap.pak.core.testutils.datatransformer.TestDataTransformer: Provides spy functionality when testing the IDataTransformer.