Object Flattener

A java library which helps you flatten java object to single-layer-dot-annotated properties and back to json and/or java object.

Why properties?

This is helpful when we need to convert a Java object to config properties file or backwards;
Or, if you're planning to write structured logs in JSON line, it will be handy to store key-value pairs in MDC and then unflatten them into object and eventually format it to JSON line.

How to Use

Include following dependency in your pom.xml

<dependency>
    <groupId>io.sgr</groupId>
    <artifactId>object-flattener-jackson</artifactId>
    <version>1.0.0</version>
</dependency>

Gradle is similar, I'm pretty sure you will know what to do.

Examples

For instance if you have a Java class defined like this:

public class User {

  private final String username;
  private final String password;
  private final List<String> roles;
  
  @JsonCreator
  public User(
    @JsonProperty("username") final String username,
    @JsonProperty("password") final String password,
    @JsonProperty("roles") final List<String> roles
  ) {
    // Details are omitted
  }
  
  // Getters are omitted
}

You can call ObjectFlattener.flatten() to get a flattened single-layer Map like this:

Map<String, String> flattened = ObjectFlattener.flatten(
  new User("John", "Dow", Arrays.asList("User", "Reporter"))
);

The content on the map will be:

username=John
password=Dow
roles.[0]=User
roles.[1]=Reporter

You can also unflatten it to JsonNode:

  JsonNode node = ObjectFlattener.unflatten(flattened);

or Java object:

  User user = ObjectFlattener.unflatten(flattened, User.class);

Advanced Usage

You can pass your own ObjectMapper in case you want additional controll of the serialization/deserialization process.
You can pass a prefix string when flattening to append prefix to generated properties.
You can pass a prefix string when unflattening so you could only read a subset of the properties.

License