Java Source Code Generation

Entities generation

Messages declared in Helium spec can be transformed to Java classes with EntitiesGenerator. This handler create a separate Java class for each message defined in specification. Message fields are turned into class fields. Sequences are represented with class fields of Collection type.

There is a set of generation options that can be set with EntitiesGeneratorOptions:

// set package name for generated classes
options.setPackageName("com.example");
// define modifiers to be applied to class fields declarations
options.setFieldModifiers(EnumSet.of(Modifier.PRIVATE));
// generate setter methods
options.setAddSetters(true);
// generate getter methods
options.setAddGetters(true);
// set collection type to represent sequences (default is List)
options.setSequenceCollectionName("java.util.ArrayList") // will make ArrayList<SomeType> field;
// or use arrays instead
options.useArraysForSequences(); // will make SomeType[] field
// set mapping of custom primitive types to Java classes
options.setCustomPrimitivesMapping(Collections.singletonMap("timestamp", "java.util.Date"));
// ask to prettify Java field names (will make fieldName in Java class from field_name in spec)
options.setPrettifyNames(true);

Default behaviour of the handler is to create a POJO classes. However it's possible to add additional features to generated classes specifying class writer wrapper. Available wrappers can be found in Writers class:

• gson() - will add Google Gson's @SerializedName annotations to generated fields
• androidParcelable() - will make generated classes implement android.os.Parcelable and generate required methods
• chain() - will allow to combine multiple wrappers (like chain(gson(), androidParcelable()), which will both add Gson annotations and implement Android's Parcelable)

Wrapper can be set in generator options:

import static com.stanfy.helium.handler.codegen.java.entity.Writers.*;
options.setWriterWrapper(chain(gson(), androidParcelable()));

Entity generator handler can be used as follows:

helium.processBy(new EntitiesGenerator(new File("output"), options));

Constants generation

Handler JavaConstantsGenerator can generate classes with defined message field names as constants. Considering a message in a spec

type 'Book' message {
  title 'string'
  annotation 'string'
  author 'string'
} 

the handler can generate the following class:

public class BookConstants {
  public static final String TITLE = "title";
  public static final String ANNOTATION = "annotation";
  public static final String AUTHOR = "author";
}

You may also customize how to generate constant names with handler options (ConstantsGeneratorOptions):

options.setPackageName("com.example");
options.setNameConverter(new ConstantNameConverter() {
  @Override
  public String constantFrom(final Field field) {
    return "COLUMN_" + field.getCanonicalName().toUpperCase(Locale.US);
  }
});

Then generated class will be:

public class BookConstants {
  public static final String COLUMN_TITLE = "title";
  public static final String COLUMN_ANNOTATION = "annotation";
  public static final String COLUMN_AUTHOR = "author";
}