Jackfruit processes annotations on Java interfaces to generate code that can read and write Apache Configuration files. The demo module includes sample code. In the top level directory, run mvn clean package, which will build the annotation library, run the annotation processor on the file demo/src/main/java/jackfruit/demo/DemoConfig.java, and generate the class demo/target/generated-sources/annotations/jackfruit/demo/DemoConfigFactory.java. The file demo/src/main/java/jackfruit/demo/JackfruitDemo.java shows some simple examples of use.

Introduction

Include Jackfruit in your project with the following POM:

<dependency>
    <groupId>edu.jhuapl.ses.srn</groupId>
    <artifactId>jackfruit</artifactId>
    <version>$VERSION</version>
    <type>pom</type>
</dependency>

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An example of an annotated interface is

@Jackfruit(prefix = "prefix")
public interface DemoConfig {

  // default key is field name
  @Key("key")
  @Comment("field comment")
  @DefaultValue("0")
  public int intMethod();

  @DefaultValue("0.")
  public Double doubleMethod();

  @DefaultValue("Default String")
  public String StringMethod();

  @Comment("This string is serialized into an object")
  @DefaultValue("serialized string")
  @ParserClass(SomeRandomClassParser.class)
  public SomeRandomClass randomClass();

  @Comment("List of Doubles")
  @DefaultValue("0. 5.34 17")
  List<Double> doubles();
  
  @Comment("List of RandomClass")
  @DefaultValue("obj1 obj2")
  @ParserClass(SomeRandomClassParser.class)
  List<SomeRandomClass> randoms();
}

This corresponds to this Apache Configuration file:

# field comment
# field comment
prefix.key = 0
prefix.doubleMethod = 0.0
prefix.StringMethod = Default String
# This string is serialized into an object
prefix.randomClass = serialized string
# List of Doubles
prefix.doubles = 0.0
prefix.doubles = 5.34
prefix.doubles = 17.0
# List of RandomClass
prefix.randoms = obj1
prefix.randoms = obj2

The annotation processor generates a class called DemoConfigFactory. An example of use is

    // this factory is built by the annotation processor after reading the DemoConfig interface
    DemoConfigFactory factory = new DemoConfigFactory();

    // get an example config object
    DemoConfig template = factory.getTemplate();

    // generate an Apache PropertiesConfiguration object. This can be written out to a file
    PropertiesConfiguration config = factory.toConfig(template);

    try {
      // this is the template, with comments
      config.write(new PrintWriter(System.out));

      // write to file
      File tmpFile = File.createTempFile("tmp", ".config");
      tmpFile.deleteOnExit();
      // System.out.println("wrote "+tmpFile.getAbsolutePath());
      config.write(new PrintWriter(tmpFile));

      // read from file
      config = new Configurations().properties(tmpFile);

      // print to screen 
      config.write(new PrintWriter(System.out));

    } catch (ConfigurationException | IOException e) {
      e.printStackTrace();
    }

    // create a config object from an Apache PropertiesConfiguration
    template = factory.fromConfig(config);

    // get one of the config object's properties
    System.out.printf("config.StringMethod() = %s\n", template.StringMethod());