java<\/code>), library (e.g., webclient<\/code>), and config options to fill Mustache template<\/a> files with API metadata and models, producing fully generated source code tailored to that setup. In this example, I will demonstrate how to generate HTTP Client source code from an OpenAPI Spec YAML<\/a> file in a Gradle project.<\/p>\n2. Setup<\/h2>\n2.1 An OpenAPI Spec YAML File<\/h3>\n
In this step, I will create a “demoApi.yaml<\/code>” file that describes a User<\/code> API for POST<\/code>, GET<\/code> APIs.<\/p>\ndemoApi.yaml<\/em><\/span><\/p>\nopenapi: 3.0.0\ninfo:\n title: Sample User API\n description: This is a sample API for managing users.\n version: 1.0.0\nservers:\n - url: https:\/\/api.example.com\/v1\n description: Production server\n - url: https:\/\/staging.example.com\/v1\n description: Staging server\ntags:\n - name: users\n description: Operations related to users\npaths:\n \/users:\n get:\n tags:\n - users\n summary: Get all users\n operationId: getUsers\n description: Retrieves a list of all registered users.\n responses:\n '200':\n description: A list of users\n content:\n application\/json:\n schema:\n type: array\n items:\n $ref: '#\/components\/schemas\/User'\n '500':\n description: Internal server error\n post:\n tags:\n - users\n summary: Create a new user\n operationId: createUser\n description: Creates a new user with the provided details.\n requestBody:\n required: true\n content:\n application\/json:\n schema:\n $ref: '#\/components\/schemas\/User'\n responses:\n '201':\n description: User created successfully\n content:\n application\/json:\n schema:\n $ref: '#\/components\/schemas\/User'\n '400':\n description: Invalid input\n \/users\/{userId}:\n get:\n tags:\n - users\n summary: Get user by ID\n operationId: getUserById\n description: Retrieves a single user by their ID.\n parameters:\n - in: path\n name: userId\n schema:\n type: string\n required: true\n description: The ID of the user to retrieve.\n responses:\n '200':\n description: User found\n content:\n application\/json:\n schema:\n $ref: '#\/components\/schemas\/User'\n '404':\n description: User not found\ncomponents:\n schemas:\n User:\n type: object\n properties:\n id:\n type: string\n format: uuid\n description: Unique identifier for the user.\n name:\n type: string\n description: Name of the user.\n email:\n type: string\n format: email\n description: Email address of the user.\n required:\n - id\n - name\n - email\n <\/pre>\n\n- Line 15,16: GET \/users<\/strong> to fetch all users.<\/li>\n
- Line 33: POST \/users<\/strong> to create a new user<\/li>\n
- Line 54, 55: GET \/users\/{id}<\/strong> to retrieve a user by ID<\/li>\n
- Line 79: a
User<\/code> schema.<\/li>\n<\/ul>\n2.2 Build.gradle<\/h3>\n
In this step, I will edit the “build.gradle<\/code>” file to generate HTTP WebClient<\/code> via the “org.openapi.generator<\/code>” plugin..<\/p>\nbuild.gradle<\/em><\/span><\/p>\nplugins {\n\tid 'java'\n\tid 'org.springframework.boot' version '3.5.7'\n\tid 'io.spring.dependency-management' version '1.1.7'\n\tid 'org.openapi.generator' version '7.5.0'\n}\n\ngroup = 'org.jcg.zheng.demo'\nversion = '0.0.1-SNAPSHOT'\ndescription = 'Demo project for Spring Boot'\n\njava {\n\ttoolchain {\n\t\tlanguageVersion = JavaLanguageVersion.of(21)\n\t}\n}\n\nrepositories {\n\tmavenCentral()\n}\n\ndef openApiOutputDir = \"$buildDir\/generated\"\n\ntask openApiGenerateJavaWebClient( type: org.openapitools.generator.gradle.plugin.tasks.GenerateTask) {\n inputSpec = file(\"$projectDir\/src\/main\/resources\/demoApi.yaml\").path\n outputDir = \"${openApiOutputDir}\/java\/webclient\"\n apiPackage = \"org.jcg.zheng.demo.javawebclient.api\"\n modelPackage = \"org.jcg.zheng.demo.javawebclient.model\"\n \tgeneratorName = \"java\" \/\/general-purpose java client library \n library = \"webclient\" \/\/other options: webclient, resttemplate, feign, jersey2\n enablePostProcessFile = true\n configOptions = [\n useJakartaEe: \"true\",\n dateLibrary: \"java8\",\n reactive: \"false\",\n hideGenerationTimestamp: \"true\"\n ]\n}\n\ndependencies {\n\timplementation 'org.springframework.boot:spring-boot-starter-web'\n\timplementation 'org.springframework.boot:spring-boot-starter-validation'\n\t\n\t\/\/here are dependencies for webclient\n\timplementation 'org.springframework.boot:spring-boot-starter-webflux'\n\timplementation 'org.openapitools:jackson-databind-nullable:0.2.6'\n\t\n\ttestImplementation 'org.springframework.boot:spring-boot-starter-test'\n\ttestRuntimeOnly 'org.junit.platform:junit-platform-launcher'\n}\n\ntasks.named('test') {\n\tuseJUnitPlatform()\n}\n\ntasks.named('compileJava') { \n dependsOn(tasks.openApiGenerateJavaWebClient)\n source(\"$buildDir\/generated\/src\/main\/java\")\n}\n\nsourceSets{\n main { \n java { \n srcDir(\"${openApiOutputDir}\/java\/webclient\/src\/main\/java\")\n }\n }\n\n}\n\n<\/pre>\n\n- Line 5: imports the “
org.openapi.generator<\/code>” plugin.<\/li>\n- Line 22: defines the
openApiOutputDir<\/code> to \"$buildDir\/generated\"<\/code>.<\/li>\n- Line 24: defines the
openApiGenerateJavaWebClient<\/code> task to generate webclient<\/code><\/li>\n- Line 25: sets the
inputSpec<\/code> file path.<\/li>\n- Line 26: sets up the
outputDir<\/code>.<\/li>\n- Line 27: sets the
apiPackage<\/code> name. Note<\/strong>: the best practice is to name it as the project’s base package.<\/li>\n- Line 28: sets the
modelPackage<\/code> name.<\/li>\n- Line 29: sets the
generatorName=java <\/code> for general-purpose java client.<\/li>\n- Line 30: sets the library to
webclient<\/code> for generating Spring WebFlux WebClient<\/code>.<\/li>\n- Line 32: sets additional configuration options.<\/li>\n
- Line 57: invokes the
openApiGeneratorJavaWebClient<\/code> before the compileJava<\/code> task.<\/li>\n- Line 64: adds the generated source directory to the
sourceSets<\/code>.<\/li>\n<\/ul>\n2.3 HttpclientWebclientApplication<\/h3>\n
No change to the generated HttpclientWebclientApplication.java<\/code> class.<\/p>\nHttpclientWebclientApplication.java<\/em><\/span><\/p>\npackage org.jcg.zheng.demo.httpclient_webclient;\n\nimport org.springframework.boot.SpringApplication;\nimport org.springframework.boot.autoconfigure.SpringBootApplication;\n\n@SpringBootApplication\npublic class HttpclientWebclientApplication {\n\n\tpublic static void main(String[] args) {\n\t\tSpringApplication.run(HttpclientWebclientApplication.class, args);\n\t}\n}\n<\/pre>\n3. Generate HTTP Client from Openapi Spec.<\/h2>\n
In this step, I will execute the gradlew build<\/code> command to generate the HTTP WebClient<\/code>.<\/p>\ngradlew build output<\/em><\/span><\/p>\nC:\\MaryZheng\\workspace\\httpclient-webclient>gradlew build\n\n> Task :openApiGenerateJavaWebClient\n################################################################################\n# Thanks for using OpenAPI Generator. #\n# Please consider donation to help us maintain this project \u2261\u0192\u00d6\u00c5 #\n# https:\/\/opencollective.com\/openapi_generator\/donate #\n################################################################################\nSuccessfully generated code to C:\\MaryZheng\\workspace\\httpclient-webclient\\build\/generated\/java\/webclient\n\n> Task :compileJava\nNote: C:\\MaryZheng\\workspace\\httpclient-webclient\\build\\generated\\java\\webclient\\src\\main\\java\\org\\jcg\\zheng\\demo\\javawebclient\\ApiClient.java uses or overrides a deprecated API.\nNote: Recompile with -Xlint:deprecation for details.\nJava HotSpot(TM) 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended\n\n[Incubating] Problems report is available at: file:\/\/\/C:\/MaryZheng\/workspace\/httpclient-webclient\/build\/reports\/problems\/problems-report.html\n\nBUILD SUCCESSFUL in 9s\n8 actionable tasks: 8 executed\nC:\\MaryZheng\\workspace\\httpclient-webclient><\/pre>\n
\n- Line 9: the source code is generated successfully.<\/li>\n<\/ul>\n
4. View Generated Files<\/h2>\n\n![\"http](\"https:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2025\/11\/projectPackages.jpg\")
<\/a>Figure 1 Project Setting<\/figcaption><\/figure>\n<\/div>\nFigure 1 shows four packages generated from the gradlew build<\/code> command. <\/p>\nWe will review the following classes:<\/p>\n
\nApiClient.java<\/code>: this is the core helper class that wraps org.springframework.web.reactive.function.client.WebClient<\/code> and manages HTTP communication, including creates and configures the Spring WebClient<\/code> instance, handles JSON encoding\/decoding, converts Java objects to query\/form params, authentication, and error handling. All generated API classes(UsersApi<\/code>, etc.) depend on it.<\/li>\nUsersApi.java<\/code>: this is generated API client class that represents all HTTP operations(GET, POST, PUT, DELETE, etc.) based on the openApi Specification’s endpoints \u2014 e.g. \/users<\/code>, \/users\/{id}<\/code>.<\/li>\nUser.java<\/code>: this is Plain Old Java Object(POJO)<\/code> generated from the OpenAPI schema definition for the User<\/code> model.<\/li>\n<\/ul>\n4.1 Generated ApiClient<\/h3>\n
In this step, I will view the generated ApiClient.java<\/code> class.<\/p>\nApiClient.java<\/em><\/span><\/p>\npackage org.jcg.zheng.demo.javawebclient;\n\nimport com.fasterxml.jackson.databind.DeserializationFeature;\nimport com.fasterxml.jackson.databind.ObjectMapper;\nimport com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;\nimport org.openapitools.jackson.nullable.JsonNullableModule;\nimport org.springframework.core.ParameterizedTypeReference;\nimport org.springframework.http.HttpHeaders;\nimport org.springframework.http.HttpMethod;\nimport org.springframework.http.HttpRequest;\nimport org.springframework.http.HttpStatus;\nimport org.springframework.http.InvalidMediaTypeException;\nimport org.springframework.http.MediaType;\nimport org.springframework.http.RequestEntity;\nimport org.springframework.http.RequestEntity.BodyBuilder;\nimport org.springframework.http.ResponseEntity;\nimport org.springframework.http.client.BufferingClientHttpRequestFactory;\nimport org.springframework.http.client.ClientHttpRequestExecution;\nimport org.springframework.http.client.ClientHttpRequestInterceptor;\nimport org.springframework.http.client.ClientHttpResponse;\nimport org.springframework.http.codec.json.Jackson2JsonDecoder;\nimport org.springframework.http.codec.json.Jackson2JsonEncoder;\nimport org.springframework.util.CollectionUtils;\nimport org.springframework.util.LinkedMultiValueMap;\nimport org.springframework.util.MultiValueMap;\nimport org.springframework.util.StringUtils;\nimport org.springframework.http.client.reactive.ClientHttpRequest;\nimport org.springframework.web.client.RestClientException;\nimport org.springframework.web.util.UriComponentsBuilder;\nimport org.springframework.web.reactive.function.client.WebClient;\nimport org.springframework.web.reactive.function.client.WebClient.ResponseSpec;\nimport org.springframework.web.reactive.function.client.ClientResponse;\nimport org.springframework.web.reactive.function.BodyInserter;\nimport org.springframework.web.reactive.function.BodyInserters;\nimport org.springframework.web.reactive.function.client.ExchangeStrategies;\nimport reactor.core.publisher.Mono;\nimport reactor.core.publisher.Flux;\nimport java.util.Optional;\n\nimport java.io.BufferedReader;\nimport java.io.IOException;\nimport java.io.InputStream;\nimport java.io.InputStreamReader;\nimport java.io.UnsupportedEncodingException;\nimport java.net.URLEncoder;\nimport java.nio.charset.StandardCharsets;\nimport java.text.DateFormat;\nimport java.text.ParseException;\nimport java.util.Arrays;\nimport java.util.ArrayList;\nimport java.util.Collection;\nimport java.util.Collections;\nimport java.util.Date;\nimport java.util.HashMap;\nimport java.util.Iterator;\nimport java.util.List;\nimport java.util.Map;\nimport java.util.Map.Entry;\nimport java.util.TimeZone;\n\nimport jakarta.annotation.Nullable;\n\nimport java.time.OffsetDateTime;\n\nimport org.jcg.zheng.demo.javawebclient.auth.Authentication;\nimport org.jcg.zheng.demo.javawebclient.auth.HttpBasicAuth;\nimport org.jcg.zheng.demo.javawebclient.auth.HttpBearerAuth;\nimport org.jcg.zheng.demo.javawebclient.auth.ApiKeyAuth;\n\n@jakarta.annotation.Generated(value = \"org.openapitools.codegen.languages.JavaClientCodegen\", comments = \"Generator version: 7.5.0\")\npublic class ApiClient extends JavaTimeFormatter {\n public enum CollectionFormat {\n CSV(\",\"), TSV(\"\\t\"), SSV(\" \"), PIPES(\"|\"), MULTI(null);\n\n private final String separator;\n private CollectionFormat(String separator) {\n this.separator = separator;\n }\n\n private String collectionToString(Collection<?> collection) {\n return StringUtils.collectionToDelimitedString(collection, separator);\n }\n }\n\n private static final String URI_TEMPLATE_ATTRIBUTE = WebClient.class.getName() + \".uriTemplate\";\n\n private HttpHeaders defaultHeaders = new HttpHeaders();\n private MultiValueMap<String, String> defaultCookies = new LinkedMultiValueMap<String, String>();\n\n private String basePath = \"https:\/\/api.example.com\/v1\";\n\n private final WebClient webClient;\n private final DateFormat dateFormat;\n private final ObjectMapper objectMapper;\n\n private Map<String, Authentication> authentications;\n\n\n public ApiClient() {\n this.dateFormat = createDefaultDateFormat();\n this.objectMapper = createDefaultObjectMapper(this.dateFormat);\n this.webClient = buildWebClient(this.objectMapper);\n this.init();\n }\n\n public ApiClient(WebClient webClient) {\n this(Optional.ofNullable(webClient).orElseGet(() -> buildWebClient()), createDefaultDateFormat());\n }\n\n public ApiClient(ObjectMapper mapper, DateFormat format) {\n this(buildWebClient(mapper.copy()), format);\n }\n\n public ApiClient(WebClient webClient, ObjectMapper mapper, DateFormat format) {\n this(Optional.ofNullable(webClient).orElseGet(() -> buildWebClient(mapper.copy())), format);\n }\n\n private ApiClient(WebClient webClient, DateFormat format) {\n this.webClient = webClient;\n this.dateFormat = format;\n this.objectMapper = createDefaultObjectMapper(format);\n this.init();\n }\n\n public static DateFormat createDefaultDateFormat() {\n DateFormat dateFormat = new RFC3339DateFormat();\n dateFormat.setTimeZone(TimeZone.getTimeZone(\"UTC\"));\n return dateFormat;\n }\n\n public static ObjectMapper createDefaultObjectMapper(@Nullable DateFormat dateFormat) {\n if (null == dateFormat) {\n dateFormat = createDefaultDateFormat();\n }\n ObjectMapper mapper = new ObjectMapper();\n mapper.setDateFormat(dateFormat);\n mapper.registerModule(new JavaTimeModule());\n mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);\n JsonNullableModule jnm = new JsonNullableModule();\n mapper.registerModule(jnm);\n return mapper;\n }\n\n protected void init() {\n \/\/ Setup authentications (key: authentication name, value: authentication).\n authentications = new HashMap<String, Authentication>();\n \/\/ Prevent the authentications from being modified.\n authentications = Collections.unmodifiableMap(authentications);\n }\n\n \/**\n * Build the WebClientBuilder used to make WebClient.\n * @param mapper ObjectMapper used for serialize\/deserialize\n * @return WebClient\n *\/\n public static WebClient.Builder buildWebClientBuilder(ObjectMapper mapper) {\n ExchangeStrategies strategies = ExchangeStrategies\n .builder()\n .codecs(clientDefaultCodecsConfigurer -> {\n clientDefaultCodecsConfigurer.defaultCodecs().jackson2JsonEncoder(new Jackson2JsonEncoder(mapper, MediaType.APPLICATION_JSON));\n clientDefaultCodecsConfigurer.defaultCodecs().jackson2JsonDecoder(new Jackson2JsonDecoder(mapper, MediaType.APPLICATION_JSON));\n }).build();\n WebClient.Builder webClientBuilder = WebClient.builder().exchangeStrategies(strategies);\n return webClientBuilder;\n }\n\n \/**\n * Build the WebClientBuilder used to make WebClient.\n * @return WebClient\n *\/\n public static WebClient.Builder buildWebClientBuilder() {\n return buildWebClientBuilder(createDefaultObjectMapper(null));\n }\n\n \/**\n * Build the WebClient used to make HTTP requests.\n * @param mapper ObjectMapper used for serialize\/deserialize\n * @return WebClient\n *\/\n public static WebClient buildWebClient(ObjectMapper mapper) {\n return buildWebClientBuilder(mapper).build();\n }\n\n \/**\n * Build the WebClient used to make HTTP requests.\n * @return WebClient\n *\/\n public static WebClient buildWebClient() {\n return buildWebClientBuilder(createDefaultObjectMapper(null)).build();\n }\n\n \/**\n * Get the current base path\n * @return String the base path\n *\/\n public String getBasePath() {\n return basePath;\n }\n\n \/**\n * Set the base path, which should include the host\n * @param basePath the base path\n * @return ApiClient this client\n *\/\n public ApiClient setBasePath(String basePath) {\n this.basePath = basePath;\n return this;\n }\n\n \/**\n * Get authentications (key: authentication name, value: authentication).\n * @return Map the currently configured authentication types\n *\/\n public Map<String, Authentication> getAuthentications() {\n return authentications;\n }\n\n \/**\n * Get authentication for the given name.\n *\n * @param authName The authentication name\n * @return The authentication, null if not found\n *\/\n public Authentication getAuthentication(String authName) {\n return authentications.get(authName);\n }\n\n \/**\n * Helper method to set access token for the first Bearer authentication.\n * @param bearerToken Bearer token\n *\/\n public void setBearerToken(String bearerToken) {\n for (Authentication auth : authentications.values()) {\n if (auth instanceof HttpBearerAuth) {\n ((HttpBearerAuth) auth).setBearerToken(bearerToken);\n return;\n }\n }\n throw new RuntimeException(\"No Bearer authentication configured!\");\n }\n\n \/**\n * Helper method to set username for the first HTTP basic authentication.\n * @param username the username\n *\/\n public void setUsername(String username) {\n for (Authentication auth : authentications.values()) {\n if (auth instanceof HttpBasicAuth) {\n ((HttpBasicAuth) auth).setUsername(username);\n return;\n }\n }\n throw new RuntimeException(\"No HTTP basic authentication configured!\");\n }\n\n \/**\n * Helper method to set password for the first HTTP basic authentication.\n * @param password the password\n *\/\n public void setPassword(String password) {\n for (Authentication auth : authentications.values()) {\n if (auth instanceof HttpBasicAuth) {\n ((HttpBasicAuth) auth).setPassword(password);\n return;\n }\n }\n throw new RuntimeException(\"No HTTP basic authentication configured!\");\n }\n\n \/**\n * Helper method to set API key value for the first API key authentication.\n * @param apiKey the API key\n *\/\n public void setApiKey(String apiKey) {\n for (Authentication auth : authentications.values()) {\n if (auth instanceof ApiKeyAuth) {\n ((ApiKeyAuth) auth).setApiKey(apiKey);\n return;\n }\n }\n throw new RuntimeException(\"No API key authentication configured!\");\n }\n\n \/**\n * Helper method to set API key prefix for the first API key authentication.\n * @param apiKeyPrefix the API key prefix\n *\/\n public void setApiKeyPrefix(String apiKeyPrefix) {\n for (Authentication auth : authentications.values()) {\n if (auth instanceof ApiKeyAuth) {\n ((ApiKeyAuth) auth).setApiKeyPrefix(apiKeyPrefix);\n return;\n }\n }\n throw new RuntimeException(\"No API key authentication configured!\");\n }\n\n \/**\n * Set the User-Agent header's value (by adding to the default header map).\n * @param userAgent the user agent string\n * @return ApiClient this client\n *\/\n public ApiClient setUserAgent(String userAgent) {\n addDefaultHeader(\"User-Agent\", userAgent);\n return this;\n }\n\n \/**\n * Add a default header.\n *\n * @param name The header's name\n * @param value The header's value\n * @return ApiClient this client\n *\/\n public ApiClient addDefaultHeader(String name, String value) {\n if (defaultHeaders.containsKey(name)) {\n defaultHeaders.remove(name);\n }\n defaultHeaders.add(name, value);\n return this;\n }\n\n \/**\n * Add a default cookie.\n *\n * @param name The cookie's name\n * @param value The cookie's value\n * @return ApiClient this client\n *\/\n public ApiClient addDefaultCookie(String name, String value) {\n if (defaultCookies.containsKey(name)) {\n defaultCookies.remove(name);\n }\n defaultCookies.add(name, value);\n return this;\n }\n\n \/**\n * Get the date format used to parse\/format date parameters.\n * @return DateFormat format\n *\/\n public DateFormat getDateFormat() {\n return dateFormat;\n }\n\n \/**\n * Parse the given string into Date object.\n *\/\n public Date parseDate(String str) {\n try {\n return dateFormat.parse(str);\n } catch (ParseException e) {\n throw new RuntimeException(e);\n }\n }\n\n \/**\n * Format the given Date object into string.\n *\/\n public String formatDate(Date date) {\n return dateFormat.format(date);\n }\n\n \/**\n * Get the ObjectMapper used to make HTTP requests.\n * @return ObjectMapper objectMapper\n *\/\n public ObjectMapper getObjectMapper() {\n return objectMapper;\n }\n\n \/**\n * Get the WebClient used to make HTTP requests.\n * @return WebClient webClient\n *\/\n public WebClient getWebClient() {\n return webClient;\n }\n\n \/**\n * Format the given parameter object into string.\n * @param param the object to convert\n * @return String the parameter represented as a String\n *\/\n public String parameterToString(Object param) {\n if (param == null) {\n return \"\";\n } else if (param instanceof Date) {\n return formatDate( (Date) param);\n } else if (param instanceof OffsetDateTime) {\n return formatOffsetDateTime((OffsetDateTime) param);\n } else if (param instanceof Collection) {\n StringBuilder b = new StringBuilder();\n for(Object o : (Collection<?>) param) {\n if(b.length() > 0) {\n b.append(\",\");\n }\n b.append(String.valueOf(o));\n }\n return b.toString();\n } else {\n return String.valueOf(param);\n }\n }\n\n \/**\n * Converts a parameter to a {@link MultiValueMap} for use in REST requests\n * @param collectionFormat The format to convert to\n * @param name The name of the parameter\n * @param value The parameter's value\n * @return a Map containing the String value(s) of the input parameter\n *\/\n public MultiValueMap<String, String> parameterToMultiValueMap(CollectionFormat collectionFormat, String name, Object value) {\n final MultiValueMap<String, String> params = new LinkedMultiValueMap<String, String>();\n\n if (name == null || name.isEmpty() || value == null) {\n return params;\n }\n\n if(collectionFormat == null) {\n collectionFormat = CollectionFormat.CSV;\n }\n\n if (value instanceof Map) {\n @SuppressWarnings(\"unchecked\")\n final Map<String, Object> valuesMap = (Map<String, Object>) value;\n for (final Entry<String, Object> entry : valuesMap.entrySet()) {\n params.add(entry.getKey(), parameterToString(entry.getValue()));\n }\n return params;\n }\n\n Collection<?> valueCollection = null;\n if (value instanceof Collection) {\n valueCollection = (Collection<?>) value;\n } else {\n params.add(name, parameterToString(value));\n return params;\n }\n\n if (valueCollection.isEmpty()){\n return params;\n }\n\n if (collectionFormat.equals(CollectionFormat.MULTI)) {\n for (Object item : valueCollection) {\n params.add(name, parameterToString(item));\n }\n return params;\n }\n\n List<String> values = new ArrayList<String>();\n for(Object o : valueCollection) {\n values.add(parameterToString(o));\n }\n params.add(name, collectionFormat.collectionToString(values));\n\n return params;\n }\n\n \/**\n * Check if the given {@code String} is a JSON MIME.\n * @param mediaType the input MediaType\n * @return boolean true if the MediaType represents JSON, false otherwise\n *\/\n public boolean isJsonMime(String mediaType) {\n \/\/ \"* \/ *\" is default to JSON\n if (\"*\/*\".equals(mediaType)) {\n return true;\n }\n\n try {\n return isJsonMime(MediaType.parseMediaType(mediaType));\n } catch (InvalidMediaTypeException e) {\n }\n return false;\n }\n\n \/**\n * Check if the given MIME is a JSON MIME.\n * JSON MIME examples:\n * application\/json\n * application\/json; charset=UTF8\n * APPLICATION\/JSON\n * @param mediaType the input MediaType\n * @return boolean true if the MediaType represents JSON, false otherwise\n *\/\n public boolean isJsonMime(MediaType mediaType) {\n return mediaType != null && (MediaType.APPLICATION_JSON.isCompatibleWith(mediaType) || mediaType.getSubtype().matches(\"^.*(\\\\+json|ndjson)[;]?\\\\s*$\"));\n }\n\n \/**\n * Check if the given {@code String} is a Problem JSON MIME (RFC-7807).\n * @param mediaType the input MediaType\n * @return boolean true if the MediaType represents Problem JSON, false otherwise\n *\/\n public boolean isProblemJsonMime(String mediaType) {\n return \"application\/problem+json\".equalsIgnoreCase(mediaType);\n }\n\n \/**\n * Select the Accept header's value from the given accepts array:\n * if JSON exists in the given array, use it;\n * otherwise use all of them (joining into a string)\n *\n * @param accepts The accepts array to select from\n * @return List The list of MediaTypes to use for the Accept header\n *\/\n public List<MediaType> selectHeaderAccept(String[] accepts) {\n if (accepts.length == 0) {\n return null;\n }\n for (String accept : accepts) {\n MediaType mediaType = MediaType.parseMediaType(accept);\n if (isJsonMime(mediaType) && !isProblemJsonMime(accept)) {\n return Collections.singletonList(mediaType);\n }\n }\n return MediaType.parseMediaTypes(StringUtils.arrayToCommaDelimitedString(accepts));\n }\n\n \/**\n * Select the Content-Type header's value from the given array:\n * if JSON exists in the given array, use it;\n * otherwise use the first one of the array.\n *\n * @param contentTypes The Content-Type array to select from\n * @return MediaType The Content-Type header to use. If the given array is empty, null will be returned.\n *\/\n public MediaType selectHeaderContentType(String[] contentTypes) {\n if (contentTypes.length == 0) {\n return null;\n }\n for (String contentType : contentTypes) {\n MediaType mediaType = MediaType.parseMediaType(contentType);\n if (isJsonMime(mediaType)) {\n return mediaType;\n }\n }\n return MediaType.parseMediaType(contentTypes[0]);\n }\n\n \/**\n * Select the body to use for the request\n * @param obj the body object\n * @param formParams the form parameters\n * @param contentType the content type of the request\n * @return Object the selected body\n *\/\n protected BodyInserter<?, ? super ClientHttpRequest> selectBody(Object obj, MultiValueMap<String, Object> formParams, MediaType contentType) {\n if(MediaType.APPLICATION_FORM_URLENCODED.equals(contentType)) {\n MultiValueMap<String, String> map = new LinkedMultiValueMap<>();\n\n formParams\n .toSingleValueMap()\n .entrySet()\n .forEach(es -> map.add(es.getKey(), String.valueOf(es.getValue())));\n\n return BodyInserters.fromFormData(map);\n } else if(MediaType.MULTIPART_FORM_DATA.equals(contentType)) {\n return BodyInserters.fromMultipartData(formParams);\n } else {\n return obj != null ? BodyInserters.fromValue(obj) : null;\n }\n }\n\n \/**\n * Invoke API by sending HTTP request with the given options.\n *\n * @param <T> the return type to use\n * @param path The sub-path of the HTTP URL\n * @param method The request method\n * @param pathParams The path parameters\n * @param queryParams The query parameters\n * @param body The request body object\n * @param headerParams The header parameters\n * @param formParams The form parameters\n * @param accept The request's Accept header\n * @param contentType The request's Content-Type header\n * @param authNames The authentications to apply\n * @param returnType The return type into which to deserialize the response\n * @return The response body in chosen type\n *\/\n public <T> ResponseSpec invokeAPI(String path, HttpMethod method, Map<String, Object> pathParams, MultiValueMap<String, String> queryParams, Object body, HttpHeaders headerParams, MultiValueMap<String, String> cookieParams, MultiValueMap<String, Object> formParams, List<MediaType> accept, MediaType contentType, String[] authNames, ParameterizedTypeReference<T> returnType) throws RestClientException {\n final WebClient.RequestBodySpec requestBuilder = prepareRequest(path, method, pathParams, queryParams, body, headerParams, cookieParams, formParams, accept, contentType, authNames);\n return requestBuilder.retrieve();\n }\n\n \/**\n * Include queryParams in uriParams taking into account the paramName\n * @param queryParams The query parameters\n * @param uriParams The path parameters\n * return templatized query string\n *\/\n private String generateQueryUri(MultiValueMap<String, String> queryParams, Map<String, Object> uriParams) {\n StringBuilder queryBuilder = new StringBuilder();\n queryParams.forEach((name, values) -> {\n if (CollectionUtils.isEmpty(values)) {\n if (queryBuilder.length() != 0) {\n queryBuilder.append('&');\n }\n queryBuilder.append(name);\n } else {\n int valueItemCounter = 0;\n for (Object value : values) {\n if (queryBuilder.length() != 0) {\n queryBuilder.append('&');\n }\n queryBuilder.append(name);\n if (value != null) {\n String templatizedKey = name + valueItemCounter++;\n uriParams.put(templatizedKey, value.toString());\n queryBuilder.append('=').append(\"{\").append(templatizedKey).append(\"}\");\n }\n }\n }\n });\n return queryBuilder.toString();\n }\n\n private WebClient.RequestBodySpec prepareRequest(String path, HttpMethod method, Map<String, Object> pathParams,\n MultiValueMap<String, String> queryParams, Object body, HttpHeaders headerParams,\n MultiValueMap<String, String> cookieParams, MultiValueMap<String, Object> formParams, List<MediaType> accept,\n MediaType contentType, String[] authNames) {\n updateParamsForAuth(authNames, queryParams, headerParams, cookieParams);\n\n final UriComponentsBuilder builder = UriComponentsBuilder.fromHttpUrl(basePath).path(path);\n\n String finalUri = builder.build(false).toUriString();\n Map<String, Object> uriParams = new HashMap<>();\n uriParams.putAll(pathParams);\n\n if (queryParams != null && !queryParams.isEmpty()) {\n \/\/Include queryParams in uriParams taking into account the paramName\n String queryUri = generateQueryUri(queryParams, uriParams);\n \/\/Append to finalUri the templatized query string like \"?param1={param1Value}&.......\n finalUri += \"?\" + queryUri;\n }\n\n final WebClient.RequestBodySpec requestBuilder = webClient.method(method).uri(finalUri, uriParams);\n\n if (accept != null) {\n requestBuilder.accept(accept.toArray(new MediaType[accept.size()]));\n }\n if(contentType != null) {\n requestBuilder.contentType(contentType);\n }\n\n addHeadersToRequest(headerParams, requestBuilder);\n addHeadersToRequest(defaultHeaders, requestBuilder);\n addCookiesToRequest(cookieParams, requestBuilder);\n addCookiesToRequest(defaultCookies, requestBuilder);\n\n requestBuilder.attribute(URI_TEMPLATE_ATTRIBUTE, path);\n\n requestBuilder.body(selectBody(body, formParams, contentType));\n return requestBuilder;\n }\n\n \/**\n * Add headers to the request that is being built\n * @param headers The headers to add\n * @param requestBuilder The current request\n *\/\n protected void addHeadersToRequest(HttpHeaders headers, WebClient.RequestBodySpec requestBuilder) {\n for (Entry<String, List<String>> entry : headers.entrySet()) {\n List<String> values = entry.getValue();\n for(String value : values) {\n if (value != null) {\n requestBuilder.header(entry.getKey(), value);\n }\n }\n }\n }\n\n \/**\n * Add cookies to the request that is being built\n * @param cookies The cookies to add\n * @param requestBuilder The current request\n *\/\n protected void addCookiesToRequest(MultiValueMap<String, String> cookies, WebClient.RequestBodySpec requestBuilder) {\n for (Entry<String, List<String>> entry : cookies.entrySet()) {\n List<String> values = entry.getValue();\n for(String value : values) {\n if (value != null) {\n requestBuilder.cookie(entry.getKey(), value);\n }\n }\n }\n }\n\n \/**\n * Update query and header parameters based on authentication settings.\n *\n * @param authNames The authentications to apply\n * @param queryParams The query parameters\n * @param headerParams The header parameters\n * @param cookieParams the cookie parameters\n *\/\n protected void updateParamsForAuth(String[] authNames, MultiValueMap<String, String> queryParams, HttpHeaders headerParams, MultiValueMap<String, String> cookieParams) {\n for (String authName : authNames) {\n Authentication auth = authentications.get(authName);\n if (auth == null) {\n throw new RestClientException(\"Authentication undefined: \" + authName);\n }\n auth.applyToParams(queryParams, headerParams, cookieParams);\n }\n }\n\n \/**\n * Formats the specified collection path parameter to a string value.\n *\n * @param collectionFormat The collection format of the parameter.\n * @param values The values of the parameter.\n * @return String representation of the parameter\n *\/\n public String collectionPathParameterToString(CollectionFormat collectionFormat, Collection<?> values) {\n \/\/ create the value based on the collection format\n if (CollectionFormat.MULTI.equals(collectionFormat)) {\n \/\/ not valid for path params\n return parameterToString(values);\n }\n\n \/\/ collectionFormat is assumed to be \"csv\" by default\n if(collectionFormat == null) {\n collectionFormat = CollectionFormat.CSV;\n }\n\n return collectionFormat.collectionToString(values);\n }\n}\n\n<\/pre>\n\n- The generated
ApiClient<\/code> class has 731 lines.<\/li>\n<\/ul>\n4.2 Generated UserApi<\/h3>\n
In this step, I will view the generated UserApi.java<\/code> class. <\/div> <\/div><\/p>\nUserApi.java<\/em><\/span><\/p>\npackage org.jcg.zheng.demo.javawebclient.api;\n\nimport org.jcg.zheng.demo.javawebclient.ApiClient;\n\nimport org.jcg.zheng.demo.javawebclient.model.User;\n\nimport java.util.HashMap;\nimport java.util.List;\nimport java.util.Locale;\nimport java.util.Map;\nimport java.util.stream.Collectors;\n\nimport org.springframework.beans.factory.annotation.Autowired;\nimport org.springframework.util.LinkedMultiValueMap;\nimport org.springframework.util.MultiValueMap;\nimport org.springframework.core.ParameterizedTypeReference;\nimport org.springframework.web.reactive.function.client.WebClient.ResponseSpec;\nimport org.springframework.web.reactive.function.client.WebClientResponseException;\nimport org.springframework.core.io.FileSystemResource;\nimport org.springframework.http.HttpHeaders;\nimport org.springframework.http.HttpMethod;\nimport org.springframework.http.HttpStatus;\nimport org.springframework.http.MediaType;\nimport org.springframework.http.ResponseEntity;\nimport reactor.core.publisher.Mono;\nimport reactor.core.publisher.Flux;\n\n@jakarta.annotation.Generated(value = \"org.openapitools.codegen.languages.JavaClientCodegen\", comments = \"Generator version: 7.5.0\")\npublic class UsersApi {\n private ApiClient apiClient;\n\n public UsersApi() {\n this(new ApiClient());\n }\n\n @Autowired\n public UsersApi(ApiClient apiClient) {\n this.apiClient = apiClient;\n }\n\n public ApiClient getApiClient() {\n return apiClient;\n }\n\n public void setApiClient(ApiClient apiClient) {\n this.apiClient = apiClient;\n }\n\n \/**\n * Create a new user\n * Creates a new user with the provided details.\n * <p><b>201<\/b> - User created successfully\n * <p><b>400<\/b> - Invalid input\n * @param user The user parameter\n * @return User\n * @throws WebClientResponseException if an error occurs while attempting to invoke the API\n *\/\n private ResponseSpec createUserRequestCreation(User user) throws WebClientResponseException {\n Object postBody = user;\n \/\/ verify the required parameter 'user' is set\n if (user == null) {\n throw new WebClientResponseException(\"Missing the required parameter 'user' when calling createUser\", HttpStatus.BAD_REQUEST.value(), HttpStatus.BAD_REQUEST.getReasonPhrase(), null, null, null);\n }\n \/\/ create path and map variables\n final Map<String, Object> pathParams = new HashMap<String, Object>();\n\n final MultiValueMap<String, String> queryParams = new LinkedMultiValueMap<String, String>();\n final HttpHeaders headerParams = new HttpHeaders();\n final MultiValueMap<String, String> cookieParams = new LinkedMultiValueMap<String, String>();\n final MultiValueMap<String, Object> formParams = new LinkedMultiValueMap<String, Object>();\n\n final String[] localVarAccepts = { \n \"application\/json\"\n };\n final List<MediaType> localVarAccept = apiClient.selectHeaderAccept(localVarAccepts);\n final String[] localVarContentTypes = { \n \"application\/json\"\n };\n final MediaType localVarContentType = apiClient.selectHeaderContentType(localVarContentTypes);\n\n String[] localVarAuthNames = new String[] { };\n\n ParameterizedTypeReference<User> localVarReturnType = new ParameterizedTypeReference<User>() {};\n return apiClient.invokeAPI(\"\/users\", HttpMethod.POST, pathParams, queryParams, postBody, headerParams, cookieParams, formParams, localVarAccept, localVarContentType, localVarAuthNames, localVarReturnType);\n }\n\n \/**\n * Create a new user\n * Creates a new user with the provided details.\n * <p><b>201<\/b> - User created successfully\n * <p><b>400<\/b> - Invalid input\n * @param user The user parameter\n * @return User\n * @throws WebClientResponseException if an error occurs while attempting to invoke the API\n *\/\n public Mono<User> createUser(User user) throws WebClientResponseException {\n ParameterizedTypeReference<User> localVarReturnType = new ParameterizedTypeReference<User>() {};\n return createUserRequestCreation(user).bodyToMono(localVarReturnType);\n }\n\n \/**\n * Create a new user\n * Creates a new user with the provided details.\n * <p><b>201<\/b> - User created successfully\n * <p><b>400<\/b> - Invalid input\n * @param user The user parameter\n * @return ResponseEntity<User>\n * @throws WebClientResponseException if an error occurs while attempting to invoke the API\n *\/\n public Mono<ResponseEntity<User>> createUserWithHttpInfo(User user) throws WebClientResponseException {\n ParameterizedTypeReference<User> localVarReturnType = new ParameterizedTypeReference<User>() {};\n return createUserRequestCreation(user).toEntity(localVarReturnType);\n }\n\n \/**\n * Create a new user\n * Creates a new user with the provided details.\n * <p><b>201<\/b> - User created successfully\n * <p><b>400<\/b> - Invalid input\n * @param user The user parameter\n * @return ResponseSpec\n * @throws WebClientResponseException if an error occurs while attempting to invoke the API\n *\/\n public ResponseSpec createUserWithResponseSpec(User user) throws WebClientResponseException {\n return createUserRequestCreation(user);\n }\n \/**\n * Get user by ID\n * Retrieves a single user by their ID.\n * <p><b>200<\/b> - User found\n * <p><b>404<\/b> - User not found\n * @param userId The ID of the user to retrieve.\n * @return User\n * @throws WebClientResponseException if an error occurs while attempting to invoke the API\n *\/\n private ResponseSpec getUserByIdRequestCreation(String userId) throws WebClientResponseException {\n Object postBody = null;\n \/\/ verify the required parameter 'userId' is set\n if (userId == null) {\n throw new WebClientResponseException(\"Missing the required parameter 'userId' when calling getUserById\", HttpStatus.BAD_REQUEST.value(), HttpStatus.BAD_REQUEST.getReasonPhrase(), null, null, null);\n }\n \/\/ create path and map variables\n final Map<String, Object> pathParams = new HashMap<String, Object>();\n\n pathParams.put(\"userId\", userId);\n\n final MultiValueMap<String, String> queryParams = new LinkedMultiValueMap<String, String>();\n final HttpHeaders headerParams = new HttpHeaders();\n final MultiValueMap<String, String> cookieParams = new LinkedMultiValueMap<String, String>();\n final MultiValueMap<String, Object> formParams = new LinkedMultiValueMap<String, Object>();\n\n final String[] localVarAccepts = { \n \"application\/json\"\n };\n final List<MediaType> localVarAccept = apiClient.selectHeaderAccept(localVarAccepts);\n final String[] localVarContentTypes = { };\n final MediaType localVarContentType = apiClient.selectHeaderContentType(localVarContentTypes);\n\n String[] localVarAuthNames = new String[] { };\n\n ParameterizedTypeReference<User> localVarReturnType = new ParameterizedTypeReference<User>() {};\n return apiClient.invokeAPI(\"\/users\/{userId}\", HttpMethod.GET, pathParams, queryParams, postBody, headerParams, cookieParams, formParams, localVarAccept, localVarContentType, localVarAuthNames, localVarReturnType);\n }\n\n \/**\n * Get user by ID\n * Retrieves a single user by their ID.\n * <p><b>200<\/b> - User found\n * <p><b>404<\/b> - User not found\n * @param userId The ID of the user to retrieve.\n * @return User\n * @throws WebClientResponseException if an error occurs while attempting to invoke the API\n *\/\n public Mono<User> getUserById(String userId) throws WebClientResponseException {\n ParameterizedTypeReference<User> localVarReturnType = new ParameterizedTypeReference<User>() {};\n return getUserByIdRequestCreation(userId).bodyToMono(localVarReturnType);\n }\n\n \/**\n * Get user by ID\n * Retrieves a single user by their ID.\n * <p><b>200<\/b> - User found\n * <p><b>404<\/b> - User not found\n * @param userId The ID of the user to retrieve.\n * @return ResponseEntity<User>\n * @throws WebClientResponseException if an error occurs while attempting to invoke the API\n *\/\n public Mono<ResponseEntity<User>> getUserByIdWithHttpInfo(String userId) throws WebClientResponseException {\n ParameterizedTypeReference<User> localVarReturnType = new ParameterizedTypeReference<User>() {};\n return getUserByIdRequestCreation(userId).toEntity(localVarReturnType);\n }\n\n \/**\n * Get user by ID\n * Retrieves a single user by their ID.\n * <p><b>200<\/b> - User found\n * <p><b>404<\/b> - User not found\n * @param userId The ID of the user to retrieve.\n * @return ResponseSpec\n * @throws WebClientResponseException if an error occurs while attempting to invoke the API\n *\/\n public ResponseSpec getUserByIdWithResponseSpec(String userId) throws WebClientResponseException {\n return getUserByIdRequestCreation(userId);\n }\n \/**\n * Get all users\n * Retrieves a list of all registered users.\n * <p><b>200<\/b> - A list of users\n * <p><b>500<\/b> - Internal server error\n * @return List<User>\n * @throws WebClientResponseException if an error occurs while attempting to invoke the API\n *\/\n private ResponseSpec getUsersRequestCreation() throws WebClientResponseException {\n Object postBody = null;\n \/\/ create path and map variables\n final Map<String, Object> pathParams = new HashMap<String, Object>();\n\n final MultiValueMap<String, String> queryParams = new LinkedMultiValueMap<String, String>();\n final HttpHeaders headerParams = new HttpHeaders();\n final MultiValueMap<String, String> cookieParams = new LinkedMultiValueMap<String, String>();\n final MultiValueMap<String, Object> formParams = new LinkedMultiValueMap<String, Object>();\n\n final String[] localVarAccepts = { \n \"application\/json\"\n };\n final List<MediaType> localVarAccept = apiClient.selectHeaderAccept(localVarAccepts);\n final String[] localVarContentTypes = { };\n final MediaType localVarContentType = apiClient.selectHeaderContentType(localVarContentTypes);\n\n String[] localVarAuthNames = new String[] { };\n\n ParameterizedTypeReference<User> localVarReturnType = new ParameterizedTypeReference<User>() {};\n return apiClient.invokeAPI(\"\/users\", HttpMethod.GET, pathParams, queryParams, postBody, headerParams, cookieParams, formParams, localVarAccept, localVarContentType, localVarAuthNames, localVarReturnType);\n }\n\n \/**\n * Get all users\n * Retrieves a list of all registered users.\n * <p><b>200<\/b> - A list of users\n * <p><b>500<\/b> - Internal server error\n * @return List<User>\n * @throws WebClientResponseException if an error occurs while attempting to invoke the API\n *\/\n public Flux<User> getUsers() throws WebClientResponseException {\n ParameterizedTypeReference<User> localVarReturnType = new ParameterizedTypeReference<User>() {};\n return getUsersRequestCreation().bodyToFlux(localVarReturnType);\n }\n\n \/**\n * Get all users\n * Retrieves a list of all registered users.\n * <p><b>200<\/b> - A list of users\n * <p><b>500<\/b> - Internal server error\n * @return ResponseEntity<List<User>>\n * @throws WebClientResponseException if an error occurs while attempting to invoke the API\n *\/\n public Mono<ResponseEntity<List<User>>> getUsersWithHttpInfo() throws WebClientResponseException {\n ParameterizedTypeReference<User> localVarReturnType = new ParameterizedTypeReference<User>() {};\n return getUsersRequestCreation().toEntityList(localVarReturnType);\n }\n\n \/**\n * Get all users\n * Retrieves a list of all registered users.\n * <p><b>200<\/b> - A list of users\n * <p><b>500<\/b> - Internal server error\n * @return ResponseSpec\n * @throws WebClientResponseException if an error occurs while attempting to invoke the API\n *\/\n public ResponseSpec getUsersWithResponseSpec() throws WebClientResponseException {\n return getUsersRequestCreation();\n }\n}\n<\/pre>\n\n- The generated
UserApi<\/code> has 273 lines.<\/li>\n<\/ul>\n4.3 Generated User<\/h3>\n
In this step, I will view the generated User.java<\/code> class.<\/p>\nUser.java<\/em><\/span><\/p>\n\/*\n * Sample User API\n * This is a sample API for managing users.\n *\n * The version of the OpenAPI document: 1.0.0\n * \n *\n * NOTE: This class is auto generated by OpenAPI Generator (https:\/\/openapi-generator.tech).\n * https:\/\/openapi-generator.tech\n * Do not edit the class manually.\n *\/\n\n\npackage org.jcg.zheng.demo.javawebclient.model;\n\nimport java.util.Objects;\nimport java.util.Arrays;\nimport com.fasterxml.jackson.annotation.JsonInclude;\nimport com.fasterxml.jackson.annotation.JsonProperty;\nimport com.fasterxml.jackson.annotation.JsonCreator;\nimport com.fasterxml.jackson.annotation.JsonTypeName;\nimport com.fasterxml.jackson.annotation.JsonValue;\nimport java.util.UUID;\nimport com.fasterxml.jackson.annotation.JsonPropertyOrder;\nimport com.fasterxml.jackson.annotation.JsonTypeName;\n\n\/**\n * User\n *\/\n@JsonPropertyOrder({\n User.JSON_PROPERTY_ID,\n User.JSON_PROPERTY_NAME,\n User.JSON_PROPERTY_EMAIL\n})\n@jakarta.annotation.Generated(value = \"org.openapitools.codegen.languages.JavaClientCodegen\", comments = \"Generator version: 7.5.0\")\npublic class User {\n public static final String JSON_PROPERTY_ID = \"id\";\n private UUID id;\n\n public static final String JSON_PROPERTY_NAME = \"name\";\n private String name;\n\n public static final String JSON_PROPERTY_EMAIL = \"email\";\n private String email;\n\n public User() {\n }\n\n public User id(UUID id) {\n \n this.id = id;\n return this;\n }\n\n \/**\n * Unique identifier for the user.\n * @return id\n **\/\n @jakarta.annotation.Nonnull\n @JsonProperty(JSON_PROPERTY_ID)\n @JsonInclude(value = JsonInclude.Include.ALWAYS)\n\n public UUID getId() {\n return id;\n }\n\n\n @JsonProperty(JSON_PROPERTY_ID)\n @JsonInclude(value = JsonInclude.Include.ALWAYS)\n public void setId(UUID id) {\n this.id = id;\n }\n\n\n public User name(String name) {\n \n this.name = name;\n return this;\n }\n\n \/**\n * Name of the user.\n * @return name\n **\/\n @jakarta.annotation.Nonnull\n @JsonProperty(JSON_PROPERTY_NAME)\n @JsonInclude(value = JsonInclude.Include.ALWAYS)\n\n public String getName() {\n return name;\n }\n\n\n @JsonProperty(JSON_PROPERTY_NAME)\n @JsonInclude(value = JsonInclude.Include.ALWAYS)\n public void setName(String name) {\n this.name = name;\n }\n\n\n public User email(String email) {\n \n this.email = email;\n return this;\n }\n\n \/**\n * Email address of the user.\n * @return email\n **\/\n @jakarta.annotation.Nonnull\n @JsonProperty(JSON_PROPERTY_EMAIL)\n @JsonInclude(value = JsonInclude.Include.ALWAYS)\n\n public String getEmail() {\n return email;\n }\n\n\n @JsonProperty(JSON_PROPERTY_EMAIL)\n @JsonInclude(value = JsonInclude.Include.ALWAYS)\n public void setEmail(String email) {\n this.email = email;\n }\n\n @Override\n public boolean equals(Object o) {\n if (this == o) {\n return true;\n }\n if (o == null || getClass() != o.getClass()) {\n return false;\n }\n User user = (User) o;\n return Objects.equals(this.id, user.id) &&\n Objects.equals(this.name, user.name) &&\n Objects.equals(this.email, user.email);\n }\n\n @Override\n public int hashCode() {\n return Objects.hash(id, name, email);\n }\n\n @Override\n public String toString() {\n StringBuilder sb = new StringBuilder();\n sb.append(\"class User {\\n\");\n sb.append(\" id: \").append(toIndentedString(id)).append(\"\\n\");\n sb.append(\" name: \").append(toIndentedString(name)).append(\"\\n\");\n sb.append(\" email: \").append(toIndentedString(email)).append(\"\\n\");\n sb.append(\"}\");\n return sb.toString();\n }\n\n \/**\n * Convert the given object to string with each line indented by 4 spaces\n * (except the first line).\n *\/\n private String toIndentedString(Object o) {\n if (o == null) {\n return \"null\";\n }\n return o.toString().replace(\"\\n\", \"\\n \");\n }\n\n}\n\n<\/pre>\n\n- The generated
User<\/code> class is lengthy comparing to a class with Lombok<\/a> annotations.<\/li>\n<\/ul>\n5. Invoke Generated Class<\/h2>\n5.1 Invoke Generated Class<\/h3>\n
In this step, I will create a JavaWebClientService.java<\/code> to invoke the generated UserApi<\/code>.<\/p>\nJavaWebClientService.java<\/em><\/span><\/p>\npackage org.jcg.zheng.demo.httpclient_webclient;\n\nimport org.jcg.zheng.demo.javawebclient.ApiClient;\nimport org.jcg.zheng.demo.javawebclient.api.UsersApi;\nimport org.jcg.zheng.demo.javawebclient.model.User;\nimport org.springframework.stereotype.Service;\n\nimport reactor.core.publisher.Flux;\nimport reactor.core.publisher.Mono;\n\n@Service\npublic class JavaWebClientService {\n\n\tprivate final UsersApi usersApi;\n\n\tpublic JavaWebClientService() {\n\t\tsuper();\n\t\tthis.usersApi = new UsersApi(new ApiClient());\n\t\tthis.usersApi.getApiClient().setBasePath(\"http:\/\/localhost:8080\");\n\t}\n\n\tpublic Mono<User> createUser(User user) {\n\t\treturn usersApi.createUser(user);\n\t}\n\n\tpublic Mono<User> getUser(String userId) {\n\t\treturn usersApi.getUserById(userId);\n\t}\n\n\tpublic Flux<User> getUsers() {\n\t\treturn usersApi.getUsers();\n\t}\n\n}\n<\/pre>\n\n- Line 18: initiates new
UsersApi<\/code> and integrated with the JavaWebClientService<\/code> bean.<\/li>\n- Line 19: sets the
basePath<\/code> for the apiClient<\/code>.<\/li>\n<\/ul>\n5.2 Demonstrate<\/h3>\n
In this step, I will start the Spring Boot application and capture the server log.<\/p>\n
Spring Boot Server Log<\/em><\/span><\/p>\n\n . ____ _ __ _ _\n \/\\\\ \/ ___'_ __ _ _(_)_ __ __ _ \\ \\ \\ \\\n( ( )\\___ | '_ | '_| | '_ \\\/ _` | \\ \\ \\ \\\n \\\\\/ ___)| |_)| | | | | || (_| | ) ) ) )\n ' |____| .__|_| |_|_| |_\\__, | \/ \/ \/ \/\n =========|_|==============|___\/=\/_\/_\/_\/\n\n :: Spring Boot :: (v3.5.7)\n\n2025-11-09T09:42:44.729-06:00 INFO 8360 --- [httpclient-webclient] [ main] o.j.z.d.h.HttpclientWebclientApplication : Starting HttpclientWebclientApplication using Java 21.0.8 with PID 8360 (C:\\MaryZheng\\workspace\\httpclient-webclient\\bin\\main started by zzhen in C:\\MaryZheng\\workspace\\httpclient-webclient)\n2025-11-09T09:42:44.732-06:00 INFO 8360 --- [httpclient-webclient] [ main] o.j.z.d.h.HttpclientWebclientApplication : No active profile set, falling back to 1 default profile: \"default\"\n2025-11-09T09:42:45.851-06:00 INFO 8360 --- [httpclient-webclient] [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port 8080 (http)\n2025-11-09T09:42:45.864-06:00 INFO 8360 --- [httpclient-webclient] [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]\n2025-11-09T09:42:45.864-06:00 INFO 8360 --- [httpclient-webclient] [ main] o.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat\/10.1.48]\n2025-11-09T09:42:45.912-06:00 INFO 8360 --- [httpclient-webclient] [ main] o.a.c.c.C.[Tomcat].[localhost].[\/] : Initializing Spring embedded WebApplicationContext\n2025-11-09T09:42:45.914-06:00 INFO 8360 --- [httpclient-webclient] [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1131 ms\n2025-11-09T09:42:46.548-06:00 INFO 8360 --- [httpclient-webclient] [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port 8080 (http) with context path '\/'\n2025-11-09T09:42:46.557-06:00 INFO 8360 --- [httpclient-webclient] [ main] o.j.z.d.h.HttpclientWebclientApplication : Started HttpclientWebclientApplication in 2.344 seconds (process running for 2.808)\n<\/pre>\n
\n- Line 18: the Spring Boot application is started successfully.<\/li>\n<\/ul>\n
6. Advantages & Drawbacks of OpenAPI<\/h2>\n
Using OpenAPI for client generation offers the following advantages:<\/p>\n
\n- Automation and Consistency<\/strong> \u2013 Clients are generated from a single source of truth, reducing human error.<\/li>\n
- Faster Development<\/strong> \u2013 No need to manually write HTTP clients or data transfer objects.<\/li>\n
- Language Flexibility<\/strong> \u2013 OpenAPI Generator supports over 50 programming languages.<\/li>\n
- Strong Typing<\/strong> \u2013 Generated models enforce schema validation and make code more robust.<\/li>\n
- Up-to-Date Integration<\/strong> \u2013 When the API changes, simply regenerate the client for immediate updates.<\/li>\n<\/ol>\n
However, the static Mustache template triggers the following drawbacks:<\/p>\n
\n- Complex Configuration<\/strong> \u2013 The generator can be tricky to configure for large or legacy APIs.<\/li>\n
- Code Overhead<\/strong> \u2013 Generated code may include unnecessary or verbose classes.<\/li>\n
- Customization Difficulty<\/strong> \u2013 Modifying generated code directly is discouraged; templates or post-processing scripts may be needed.<\/li>\n
- Regeneration Risks<\/strong> \u2013 Regenerating code can overwrite manual changes if not properly separated.<\/li>\n<\/ol>\n
7. Conclusion<\/h2>\n
Generating HTTP clients from an OpenAPI specification provides a reliable, consistent, and maintainable approach to API integration in Spring Boot applications. It reduces manual effort, eliminates boilerplate code, and helps maintain contract alignment between services. For the “java<\/code>” generator, beside the “webclient<\/code>” library used in this example, here are a few other common libraries supported by OpenAPI generator.<\/p>\n\n\n\n\nLibrary for Generator=”java”<\/strong><\/td>\nDescription<\/strong><\/td>\nMustache Template Link<\/strong><\/td>\nMethod to Get Client<\/strong><\/td>\n<\/tr>\n\nwebclient<\/td>\n Spring WebFlux HttpClient<\/td>\n https:\/\/github.com\/OpenAPITools\/openapi-generator\/tree\/master\/modules\/openapi-generator\/src\/main\/resources\/Java\/libraries\/webclient<\/a><\/td>\n new UserApi(new ApiClient)<\/td>\n<\/tr>\n \nfeign<\/td>\n Feign Client<\/td>\n https:\/\/github.com\/OpenAPITools\/openapi-generator\/tree\/master\/modules\/openapi-generator\/src\/main\/resources\/Java\/libraries\/feign<\/a><\/td>\n Feign.builder().target(UserApi.class, basePath)<\/td>\n<\/tr>\n \nresttemplate<\/td>\n RestTemplate Client<\/td>\n https:\/\/github.com\/OpenAPITools\/openapi-generator\/tree\/master\/modules\/openapi-generator\/src\/main\/resources\/Java\/libraries\/feign<\/a><\/td>\n new UserApi(new ApiClient)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n8. Download<\/h2>\n
This was an example of a Gradle project that generated the HTTP Webclient<\/code> in a Spring Boot project<\/p>\n