实施GenerationConfig.java或扩展DefaultGenerationConfig.java

...
    @Override
    public AnnotationStyle getAnnotationStyle() {
        return AnnotationStyle.GSON;
    }
    ...

如果它能帮助别人，全面实施：

public void convertJsonToJavaClass(String inputJsonStr, File outputJavaClassDirectory,
                                   String packageName, String javaClassName)
        throws IOException {
    JCodeModel jcodeModel = new JCodeModel();

    GenerationConfig config = new DefaultGenerationConfig() {
        @Override
        public boolean isGenerateBuilders() {
            return true;
        }
        @Override
        public SourceType getSourceType() {
            return SourceType.JSON;
        }
        @Override
        public AnnotationStyle getAnnotationStyle() {
            return AnnotationStyle.GSON;
        }
    };

    SchemaMapper mapper = new SchemaMapper(new RuleFactory(config, new GsonAnnotator(config),
            new SchemaStore()), new SchemaGenerator());
    mapper.generate(jcodeModel, javaClassName, packageName, inputJsonStr);

    jcodeModel.build(outputJavaClassDirectory);

}