sonallux · sonallux · Dec 6, 2025 · Dec 6, 2025
@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Update to okhttp `5.3.2`
 - Requiring Java 21
 - Remove implicit grant flow (see [blog post from Spotify](https://developer.spotify.com/blog/2025-10-14-reminder-oauth-migration-27-nov-2025))
+- Add JSpecify nullness annotations 
 
 ## [4.3.2]
 - Remove `followers` property from `PlaylistUser` object

@@ -62,6 +62,7 @@
 
         <!-- Dependencies -->
         <lombok.version>1.18.42</lombok.version>
+        <jspecify.version>1.0.0</jspecify.version>
 
         <!-- Test Dependencies -->
         <junit.version>5.13.4</junit.version>

@@ -31,6 +31,11 @@
     </properties>
 
     <dependencies>
+        <dependency>
+            <groupId>org.jspecify</groupId>
+            <artifactId>jspecify</artifactId>
+            <version>${jspecify.version}</version>
+        </dependency>
         <dependency>
             <groupId>io.swagger.parser.v3</groupId>
             <artifactId>swagger-parser</artifactId>

@@ -32,7 +32,7 @@ public class CLI implements Runnable {
     boolean shouldClean = false;
 
     @Option(names = {"-p", "--package"}, required = true, description = "The Java package name")
-    String packageName = null;
+    String packageName;
 
     @Option(names = { "-h", "--help" }, usageHelp = true, description = "Print usage help")
     boolean helpRequested = false;

@@ -6,7 +6,6 @@
 import io.swagger.v3.oas.models.OpenAPI;
 import lombok.extern.slf4j.Slf4j;
 
-import java.io.IOException;
 import java.nio.file.Path;
 
 @Slf4j
@@ -17,7 +16,7 @@ public JavaGenerator() {
         this.mustacheFactory = new NoEscapingMustacheFactory();
     }
 
-    public void generate(OpenAPI openAPI, Path outputDirectory, JavaPackage javaPackage) throws IOException, GeneratorException {
+    public void generate(OpenAPI openAPI, Path outputDirectory, JavaPackage javaPackage) throws GeneratorException {
         var generationContext = new GenerationContext(this.mustacheFactory, openAPI, javaPackage, outputDirectory);
 
         new BaseObjectGenerator(generationContext).generateBaseObject();
@@ -30,8 +29,7 @@ public void generate(OpenAPI openAPI, Path outputDirectory, JavaPackage javaPack
 
         EndpointSplitter.splitEndpoints(spotifyWebApi);
 
-        var apiTemplate = new ApiGenerator(generationContext);
-        apiTemplate.generateEndpoints(spotifyWebApi);
+        ApiGenerator.generateEndpoints(generationContext, spotifyWebApi);
 
         new SpotifyWebApiGenerator(generationContext).generate();
 

@@ -9,6 +9,7 @@
 import de.sonallux.spotify.generator.java.util.JavaPackage;
 import de.sonallux.spotify.generator.java.util.JavaUtils;
 import de.sonallux.spotify.generator.java.util.Markdown2Html;
+import lombok.AccessLevel;
 import lombok.RequiredArgsConstructor;
 
 import java.util.*;
@@ -17,16 +18,17 @@
 import static java.util.stream.Collectors.joining;
 import static java.util.stream.Collectors.toList;
 
-@RequiredArgsConstructor
+@RequiredArgsConstructor(access = AccessLevel.PRIVATE)
 public class ApiGenerator {
     private final GenerationContext generationContext;
 
-    private JavaPackage apisJavaPackage;
+    private final JavaPackage apisJavaPackage;
 
-    public void generateEndpoints(SpotifyWebApi spotifyWebApi) {
-        apisJavaPackage = generationContext.childPackage("apis");
+    public static void generateEndpoints(GenerationContext generationContext, SpotifyWebApi spotifyWebApi) {
+        final var apisJavaPackage = generationContext.childPackage("apis");
+        final var apiGenerator = new ApiGenerator(generationContext, apisJavaPackage);
 
-        spotifyWebApi.getCategories().forEach(this::generateApiClasses);
+        spotifyWebApi.getCategories().forEach(apiGenerator::generateApiClasses);
     }
 
     private void generateApiClasses(ApiCategory category) {

@@ -10,6 +10,7 @@
 import io.swagger.v3.oas.models.media.ComposedSchema;
 import io.swagger.v3.oas.models.media.ObjectSchema;
 import io.swagger.v3.oas.models.media.Schema;
+import org.jspecify.annotations.Nullable;
 
 import java.nio.file.Path;
 import java.util.HashMap;
@@ -41,6 +42,7 @@ public ObjectGenerator(GenerationContext generationContext) {
         this.schemaNameToObjectName = new ConcurrentHashMap<>();
     }
 
+    @Nullable
     public String getObjectNameForResponse(String responseName) {
         return responseNameToObjectName.get(responseName);
     }
@@ -71,78 +73,80 @@ public void generateAllObjects() {
      * @param schema the OpenAPI schema
      * @return an object name to use for this schema
      */
-    private String generateApiObject(String openApiName, Schema schema) {
+    private String generateApiObject(String openApiName, Schema<?> schema) {
         if (schema.get$ref() != null) {
             var schemaName = OpenApiUtils.getSchemaName(schema.get$ref());
             return getObjectNameOrGenerate(schemaName, generationContext.resolveSchema(schema.get$ref()));
         }
 
         var objectName = getObjectNameFromSchemaName(openApiName);
 
-        if (schema instanceof ObjectSchema objectSchema) {
-            var apiObject = generateApiObject(objectSchema, objectName);
-            apiObject.setOpenApiName(openApiName);
-            return objectName;
-        }
-        if (schema instanceof ArraySchema arraySchema) {
-            var itemsSchema = arraySchema.getItems();
-            var itemsType = JavaUtils.getTypeOfSchema(itemsSchema).orElse("Object");
-
-            return "java.util.List<" + itemsType + ">";
-        }
-        if (schema instanceof ComposedSchema composedSchema) {
-            if (composedSchema.getAllOf() != null) {
-                var allOf = composedSchema.getAllOf();
-                if (allOf.size() == 1) {
-                    var ref = allOf.getFirst().get$ref();
-                    if (ref.equals("#/components/schemas/PagingObject")) {
-                        var itemsSchema = (ArraySchema) composedSchema.getProperties().get("items");
-                        var itemsSchemaName = OpenApiUtils.getSchemaName(itemsSchema.getItems().get$ref());
-                        var itemsObjectName = getObjectNameOrGenerate(itemsSchemaName, itemsSchema.getItems());
-                        return "Paging<" + itemsObjectName + ">";
-                    }
-
-                    var referencedSchemaName = OpenApiUtils.getSchemaName(ref);
-                    var referencedObjectName = getObjectNameOrGenerate(referencedSchemaName, allOf.getFirst());
-                    var apiObject = ApiObject.builder()
+        switch (schema) {
+            case ObjectSchema objectSchema -> {
+                var apiObject = generateApiObject(objectSchema, objectName);
+                apiObject.setOpenApiName(openApiName);
+                return objectName;
+            }
+            case ArraySchema arraySchema -> {
+                var itemsSchema = arraySchema.getItems();
+                var itemsType = JavaUtils.getTypeOfSchema(itemsSchema).orElse("Object");
+                return  "java.util.List<" + itemsType + ">";
+            }
+            case ComposedSchema composedSchema -> {
+                if (composedSchema.getAllOf() != null) {
+                    var allOf = composedSchema.getAllOf();
+                    if (allOf.size() == 1) {
+                        var ref = allOf.getFirst().get$ref();
+                        if (ref.equals("#/components/schemas/PagingObject")) {
+                            var itemsSchema = (ArraySchema) composedSchema.getProperties().get("items");
+                            var itemsSchemaName = OpenApiUtils.getSchemaName(itemsSchema.getItems().get$ref());
+                            var itemsObjectName = getObjectNameOrGenerate(itemsSchemaName, itemsSchema.getItems());
+                            return  "Paging<" + itemsObjectName + ">";
+                        }
+
+                        var referencedSchemaName = OpenApiUtils.getSchemaName(ref);
+                        var referencedObjectName = getObjectNameOrGenerate(referencedSchemaName, allOf.getFirst());
+                        var apiObject = ApiObject.builder()
                             .name(objectName)
                             .openApiName(openApiName)
                             .superClassName(referencedObjectName)
                             .description(composedSchema.getDescription())
                             .build();
-                    this.schemaObjects.put(objectName, apiObject);
-                    return objectName;
-                }
-                if (allOf.size() == 2) {
-                    if (allOf.get(0).get$ref().equals("#/components/schemas/PagingObject")) {
-                        var itemsSchema = (ArraySchema) allOf.get(1).getProperties().get("items");
-                        var itemsSchemaName = OpenApiUtils.getSchemaName(itemsSchema.getItems().get$ref());
-                        var itemsObjectName = getObjectNameOrGenerate(itemsSchemaName, itemsSchema.getItems());
-                        return "Paging<" + itemsObjectName + ">";
-                    }
-                    if (allOf.get(0).get$ref().equals("#/components/schemas/CursorPagingObject")) {
-                        var itemsSchema = (ArraySchema) allOf.get(1).getProperties().get("items");
-                        var itemsSchemaName = OpenApiUtils.getSchemaName(itemsSchema.getItems().get$ref());
-                        var itemsObjectName = getObjectNameOrGenerate(itemsSchemaName, itemsSchema.getItems());
-                        return "CursorPaging<" + itemsObjectName + ">";
-                    }
-
-                    if (allOf.get(1) instanceof ObjectSchema objectSchema) {
-                        var referencedSchemaName = OpenApiUtils.getSchemaName(allOf.get(0).get$ref());
-                        var referencedObjectName = getObjectNameOrGenerate(referencedSchemaName, allOf.get(0));
-
-                        var apiObject = generateApiObject(objectSchema, objectName);
-                        apiObject.setDescription(composedSchema.getDescription());
-                        apiObject.setOpenApiName(openApiName);
-                        apiObject.setSuperClassName(referencedObjectName);
+                        this.schemaObjects.put(objectName, apiObject);
                         return objectName;
                     }
+                    if (allOf.size() == 2) {
+                        if (allOf.get(0).get$ref().equals("#/components/schemas/PagingObject")) {
+                            var itemsSchema = (ArraySchema) allOf.get(1).getProperties().get("items");
+                            var itemsSchemaName = OpenApiUtils.getSchemaName(itemsSchema.getItems().get$ref());
+                            var itemsObjectName = getObjectNameOrGenerate(itemsSchemaName, itemsSchema.getItems());
+                            return  "Paging<" + itemsObjectName + ">";
+                        }
+                        if (allOf.get(0).get$ref().equals("#/components/schemas/CursorPagingObject")) {
+                            var itemsSchema = (ArraySchema) allOf.get(1).getProperties().get("items");
+                            var itemsSchemaName = OpenApiUtils.getSchemaName(itemsSchema.getItems().get$ref());
+                            var itemsObjectName = getObjectNameOrGenerate(itemsSchemaName, itemsSchema.getItems());
+                            return  "CursorPaging<" + itemsObjectName + ">";
+                        }
+
+                        if (allOf.get(1) instanceof ObjectSchema objectSchema) {
+                            var referencedSchemaName = OpenApiUtils.getSchemaName(allOf.getFirst().get$ref());
+                            var referencedObjectName = getObjectNameOrGenerate(referencedSchemaName, allOf.getFirst());
+
+                            var apiObject = generateApiObject(objectSchema, objectName);
+                            apiObject.setDescription(composedSchema.getDescription());
+                            apiObject.setOpenApiName(openApiName);
+                            apiObject.setSuperClassName(referencedObjectName);
+                            return objectName;
+                        }
+                    }
                 }
+                return objectName;
+            }
+            default -> {
+                return objectName;
             }
         }
-
-
-        return objectName;
     }
 
     private ApiObject generateApiObject(ObjectSchema objectSchema, String objectName) {
@@ -180,7 +184,7 @@ private ApiObject.Property generateApiObjectProperty(String objectName, String n
         return new ApiObject.Property(name, type, resolvedSchema.getDescription());
     }
 
-    private String getObjectNameOrGenerate(String openApiName, Schema schema) {
+    private String getObjectNameOrGenerate(String openApiName, Schema<?> schema) {
         if (schemaNameToObjectName.containsKey(openApiName)) {
             return schemaNameToObjectName.get(openApiName);
         }
@@ -260,7 +264,7 @@ private void fixContextForPaging(Map<String, Object> context) {
         ));
     }
 
-    private static String firstNonNull(String... strings) {
+    private static @Nullable String firstNonNull(@Nullable String... strings) {
         for (var s : strings) {
             if (s != null) {
                 return s;

@@ -13,15 +13,16 @@
 import io.swagger.v3.oas.models.media.Schema;
 import io.swagger.v3.oas.models.responses.ApiResponse;
 import lombok.RequiredArgsConstructor;
+import org.jspecify.annotations.Nullable;
 
 import java.util.function.Function;
 
 @RequiredArgsConstructor
 public class ObjectModelCreator {
     private final GenerationContext generationContext;
-    private final Function<String, String> responseTypeMapper;
+    private final Function<String, @Nullable String> responseTypeMapper;
 
-    private SpotifyWebApi spotifyWebApi;
+    private SpotifyWebApi spotifyWebApi = new SpotifyWebApi();
 
     public SpotifyWebApi createSpotifyWebApiModel(OpenAPI openAPI) {
         spotifyWebApi = new SpotifyWebApi();

@@ -0,0 +1,4 @@
+@NullMarked
+package de.sonallux.spotify.generator.java.generators;
+
+import org.jspecify.annotations.NullMarked;
@@ -4,6 +4,7 @@
 import de.sonallux.spotify.generator.java.util.Markdown2Html;
 import lombok.Getter;
 import lombok.Setter;
+import org.jspecify.annotations.Nullable;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -25,7 +26,7 @@ public class ApiEndpoint {
     private final List<Parameter> optionalPathParameters;
     private final List<Parameter> optionalQueryParameters;
     private final List<Parameter> optionalBodyParameters;
-    private RawBodyParameter rawBodyParameter = null;
+    private @Nullable RawBodyParameter rawBodyParameter = null;
 
     public ApiEndpoint(String endpointId, String name, String description, String path, String httpMethod, String responseType, String responseDescription, List<String> scopes, boolean deprecated) {
         this.endpointId = endpointId;
@@ -72,7 +73,7 @@ public static class Parameter {
         private String type;
         private boolean commaSeparatedListType;
         private String description;
-        private String defaultValue;
+        private @Nullable String defaultValue;
 
         public Parameter(String name, String type, String description) {
             this.name = name;

@@ -3,7 +3,7 @@
 import lombok.AllArgsConstructor;
 import lombok.Builder;
 import lombok.Data;
-import lombok.NonNull;
+import org.jspecify.annotations.Nullable;
 
 import java.util.Comparator;
 import java.util.HashMap;
@@ -17,11 +17,10 @@ public class ApiObject {
     /**
      * Name of the schema object from OpenAPI. Is null if this object is extracted from a complex OpenAPI schema
      */
-    private String openApiName;
-    @NonNull
+    private @Nullable String openApiName;
     private String name;
-    private String description;
-    private String superClassName;
+    private @Nullable String description;
+    private @Nullable String superClassName;
     @Builder.Default
     private Map<String, Property> properties = new HashMap<>();
 
@@ -39,10 +38,9 @@ public List<Property> getPropertyList() {
     @Data
     @AllArgsConstructor
     public static class Property {
-        @NonNull
         private String name;
-        @NonNull
         private String type;
+        @Nullable
         private String description;
     }
 }
@@ -0,0 +1,4 @@
+@NullMarked
+package de.sonallux.spotify.generator.java.model;
+
+import org.jspecify.annotations.NullMarked;
@@ -0,0 +1,4 @@
+@NullMarked
+package de.sonallux.spotify.generator.java;
+
+import org.jspecify.annotations.NullMarked;
@@ -3,6 +3,7 @@
 import com.google.common.base.Preconditions;
 import com.google.common.base.Strings;
 import lombok.EqualsAndHashCode;
+import org.jspecify.annotations.Nullable;
 
 import java.nio.file.Path;
 import java.util.Arrays;
@@ -15,18 +16,18 @@ private JavaPackage(String... packageNames) {
         this.packageNames = packageNames;
     }
 
-    public static JavaPackage fromNames(String... packageNames) {
+    public static JavaPackage fromNames(@Nullable String... packageNames) {
         Preconditions.checkArgument(isValidJavaPackageName(packageNames), "Invalid java package");
         return new JavaPackage(packageNames);
     }
 
-    public static JavaPackage fromPackage(String packageName) {
+    public static JavaPackage fromPackage(@Nullable String packageName) {
         Preconditions.checkArgument(packageName != null);
         var packageNames = packageName.split("\\.");
         return fromNames(packageNames);
     }
 
-    private static boolean isValidJavaPackageName(String[] packageNames) {
+    private static boolean isValidJavaPackageName(@Nullable String[] packageNames) {
         if (packageNames.length == 0) {
             return false;
         }