如何通过Swagger Code Generator为生成的POJO添加@JsonInclude(Include.ALWAYS)注解

需求说明 #

需要在Swagger Code Generator生成的POJO类和字段级别添加@JsonInclude(Include.ALWAYS)注解，期望生成的POJO示例如下：

@JsonInclude(Include.ALWAYS)
public class Pet {
    @JsonInclude(Include.ALWAYS)
    @JsonProperty("name")
    private String name = null;
}

当前配置问题 #

你当前的Maven插件配置仅设置了类级别的注解，且未覆盖字段级别需求，导致无法生成符合预期的代码：

<plugin>
    <groupId>io.swagger.codegen.v3</groupId>
    <artifactId>swagger-codegen-maven-plugin</artifactId>
    <configuration>
        <inputSpec>${project.basedir}/src/main/resources/openapi.yaml</inputSpec>
        <configOptions>                
            <additionalModelTypeAnnotations>@com.fasterxml.jackson.annotation.JsonInclude(com.fasterxml.jackson.annotation.JsonInclude.Include.ALWAYS)</additionalModelTypeAnnotations>
        </configOptions>
    </plugin>

修复方案 #

1. 同时配置类和字段级别注解 #

添加additionalPropertyAnnotations配置项，实现字段级别注解的生成，完整配置如下：

<plugin>
    <groupId>io.swagger.codegen.v3</groupId>
    <artifactId>swagger-codegen-maven-plugin</artifactId>
    <configuration>
        <inputSpec>${project.basedir}/src/main/resources/openapi.yaml</inputSpec>
        <configOptions>
            <!-- 类级别注解 -->
            <additionalModelTypeAnnotations>@com.fasterxml.jackson.annotation.JsonInclude(com.fasterxml.jackson.annotation.JsonInclude.Include.ALWAYS)</additionalModelTypeAnnotations>
            <!-- 字段级别注解 -->
            <additionalPropertyAnnotations>@com.fasterxml.jackson.annotation.JsonInclude(com.fasterxml.jackson.annotation.JsonInclude.Include.ALWAYS)</additionalPropertyAnnotations>
        </configOptions>
    </configuration>
</plugin>

2. 简化注解写法（可选） #

如果希望生成的注解是短写形式@JsonInclude(Include.ALWAYS)，可以通过importMappings配置自动导入Jackson相关类，避免全限定类名：

<plugin>
    <groupId>io.swagger.codegen.v3</groupId>
    <artifactId>swagger-codegen-maven-plugin</artifactId>
    <configuration>
        <inputSpec>${project.basedir}/src/main/resources/openapi.yaml</inputSpec>
        <!-- 自动导入注解相关类 -->
        <importMappings>
            <importMapping>JsonInclude=com.fasterxml.jackson.annotation.JsonInclude</importMapping>
            <importMapping>Include=com.fasterxml.jackson.annotation.JsonInclude.Include</importMapping>
        </importMappings>
        <configOptions>
            <additionalModelTypeAnnotations>@JsonInclude(Include.ALWAYS)</additionalModelTypeAnnotations>
            <additionalPropertyAnnotations>@JsonInclude(Include.ALWAYS)</additionalPropertyAnnotations>
        </configOptions>
    </configuration>
</plugin>

验证 #

执行Maven代码生成命令：mvn swagger-codegen:generate，生成的POJO类会同时在类和字段级别添加目标注解，与预期示例一致。

内容的提问来源于stack exchange，提问作者P V REDDY