openapi generation - initialize objects

Question

Iam using openapi-generator-maven-plugin for generating code from my yml files.

<groupId>org.openapitools</groupId>
<artifactId>openapi-generator-maven-plugin</artifactId>
<version>3.3.4</version>

When generating objects from the yml the generated code always generate objects and initilize them with null.

For example:

public class Foo   {
  @JsonProperty("bar")
  private Bar bar = null;
}

Is there a way that the object is initialized with the object itself like:

public class Foo   {
  @JsonProperty("bar")
  private Bar bar = new Bar();
}

Answer 1

Some snippets and links which can help You.

Plugin config in pom.xml :

<plugin>
    <groupId>org.openapitools</groupId>
    <artifactId>openapi-generator-maven-plugin</artifactId>
    <version>4.2.2</version>
    <executions>
        <execution>
            <goals>
                <goal>generate</goal>
            </goals>
            <configuration>
                <inputSpec>${project.basedir}/docs/openapi/api.yml</inputSpec>
                <generatorName>java</generatorName>
                <templateDirectory>docs/openapi/template</templateDirectory>
            </configuration>
        </execution>
    </executions>
</plugin>

Copy default templates eg from Java module of OpenAPI generator and put all mustache files inside some directory in Your project - check plugin configuration (in my case it is docs/openapi/template ).

Find the file pojo.mustache which is a template to generate a POJO files.

You need to understand some basic Mustache syntax at this point. Find sych a fragment:

[...]
{{^isContainer}}
  private {{{datatypeWithEnum}}} {{name}}{{#defaultValue}} = {{{.}}}{{/defaultValue}};
{{/isContainer}}
[...]

Change to whatever You want, eg:

[...]
{{^isContainer}}
private {{{datatypeWithEnum}}} {{name}}{{#defaultValue}} = {{{.}}}{{/defaultValue}}{{^defaultValue}}{{^isPrimitiveType}} = new {{datatypeWithEnum}}(){{/isPrimitiveType}}{{/defaultValue}};
{{/isContainer}}
[...]

This template snippet will generate new TypeYouWantToUse() parts for every non primitive datatype.

Be aware that this is just a simple example how to proceed further. There are many corner cases eg enum handling.

FUrther readings:

• OpenApi generator

• OpenApi generator templating documentation