Unirest-Java 4.x Reference (v4.10.0)

This skill covers the Unirest-Java 4.x HTTP client library for Java 11+. It uses the built-in java.net.http.HttpClient (replacing Apache HttpClient in 3.x) and defaults to HTTP/2.

Capability Boundaries

✅ Strong Suits

1. Building HTTP requests (GET, POST, PUT, DELETE, PATCH) with fluent API
2. JSON/object mapping with GSON or Jackson (must declare module explicitly)
3. Async requests with CompletableFuture (built into java.net.http.HttpClient)
4. File uploads with progress monitoring
5. Server-Sent Events (SSE) consumption via Unirest.sse(url)
6. WebSocket connections via Unirest.webSocket(url)
7. Mock testing for HTTP clients
8. Response caching with configurable eviction
9. Proxy configuration (simple, system, ProxySelector)
10. HTTP/2 by default (configurable via config.version())
11. Custom executor support via config.executor()
12. Java Authenticator support via config.authenticator()

⚠️ Requirements

1. Java 11 or higher (uses java.net.http.HttpClient)
2. Must declare a JSON module (unirest-modules-gson or unirest-modules-jackson) for object mapping
3. Maven/Gradle dependency management with BOM

❌ Out of Scope (with alternatives)

1. Per-request proxies → use global Unirest.config().proxy() (removed in 4.x)
2. Custom HostnameVerifier → use disableHostNameVerification() system property
3. Socket timeout (independent of connect timeout) → use requestTimeout() instead
4. Connection pool tuning (concurrency(total, perRoute)) → not supported (java.net.http manages this)
5. Automatic retries on socket errors → use retryAfter() for 429/529 only
6. Shutdown hooks → not needed (no background threads to manage)
7. Apache HttpClient integration → use 3.x if you need Apache-specific features

When to Use This Skill

Use this skill when the user needs to:

• Make HTTP requests to REST APIs in Java
• Upload or download files via HTTP
• Consume Server-Sent Event streams
• Mock HTTP calls in unit tests
• Configure proxies for HTTP requests
• Cache HTTP responses
• Migrate from Unirest 3.x to 4.x

Quick Start

Maven dependency (Unirest 4.10.0):

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>com.konghq</groupId>
            <artifactId>unirest-java-bom</artifactId>
            <version>4.10.0</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

<dependencies>
    <dependency>
        <groupId>com.konghq</groupId>
        <artifactId>unirest-java-core</artifactId>
    </dependency>
    <!-- Choose ONE JSON module: -->
    <dependency>
        <groupId>com.konghq</groupId>
        <artifactId>unirest-modules-gson</artifactId>
    </dependency>
</dependencies>

Minimal GET request:

String body = Unirest.get("https://api.example.com/users")
    .asString()
    .getBody();

Minimal POST with JSON:

HttpResponse<JsonNode> response = Unirest.post("https://api.example.com/users")
    .header("Content-Type", "application/json")
    .body(new User("Alice", "[email protected]"))
    .asJson();

Critical: Installation

Unirest 4 is modular. You must declare:

1. unirest-java-core — the HTTP client engine
2. A JSON module — unirest-modules-gson OR unirest-modules-jackson (required for object mapping/JSON parsing)

⚠️ Without a JSON module, calls to asObject(), asJson(), and JSON Patch will fail at runtime.

See references/configuration.md for full installation details.

Critical: Configuration

All configuration goes through Unirest.config():

Unirest.config()
    .connectTimeout(5000)
    .setDefaultHeader("Accept", "application/json")
    .setDefaultBasicAuth("user", "pass")
    .followRedirects(true)
    .verifySsl(true)
    .enableCookieManagement(true)
    .proxy("proxy.com", 8080, "user", "pass");

Key config options:

| Method | Impact | Default | |--------|--------|---------| | connectTimeout(int) | Connection timeout (ms) | 10000 | | requestTimeout(int) | Request timeout (ms) | infinite | | followRedirects(boolean) | Follow HTTP redirects | true | | verifySsl(boolean) | Enforce SSL verification | true | | enableCookieManagement(boolean) | Accept/store cookies | true | | retryAfter(boolean) | Auto-retry on 429/529 | false | | defaultBaseUrl(String) | Default base URL for all requests | none |

Multiple configurations:

// Primary instance (same as static Unirest)
UnirestInstance unirest = Unirest.primaryInstance();

// Spawn a new independent instance
UnirestInstance custom = Unirest.spawnInstance();
custom.config().connectTimeout(3000);

⚠️ If you spawn a new instance, YOU are responsible for shutting it down.

See references/configuration.md for full config table, interceptors, object mappers, and metrics.

Critical: Making Requests

Basic request types:

Unirest.get("http://localhost/users").asString();
Unirest.post("http://localhost/users").body(json).asJson();
Unirest.put("http://localhost/users/1").body(user).asEmpty();
Unirest.delete("http://localhost/users/1").asEmpty();

Route parameters:

Unirest.get("http://localhost/users/{id}")
    .routeParam("id", "42")
    .asString();
// Results in http://localhost/users/42

Query parameters:

Unirest.get("http://localhost/search")
    .queryString("q", "unirest")
    .queryString("page", 1)
    .asString();

Headers and auth:

Unirest.get("http://localhost/protected")
    .header("X-Custom", "value")
    .basicAuth("user", "pass")
    .asString();

Form data:

Unirest.post("http://localhost/form")
    .field("name", "Alice")
    .field("age", 30)
    .asEmpty();

File upload:

Unirest.post("http://localhost/upload")
    .field("file", new File("/path/to/file.zip"))
    .asEmpty();

Async request:

CompletableFuture<HttpResponse<JsonNode>> future = Unirest.get("http://localhost/data")
    .asJsonAsync(response -> {
        System.out.println(response.getBody());
    });

JSON Patch (RFC-6902):

Unirest.jsonPatch("http://localhost/resource")
    .add("/fruits/-", "Apple")
    .remove("/bugs")
    .replace("/name", "Updated")
    .asJson();

See references/requests.md for upload progress, paged requests, client certificates, and more.

Critical: Handling Responses

Response types:

// String
String body = Unirest.get(url).asString().getBody();

// Object mapping
Book book = Unirest.get(url).asObject(Book.class).getBody();

// Generic types
List<Book> books = Unirest.get(url)
    .asObject(new GenericType<List<Book>>(){}).getBody();

// JSON
JsonNode json = Unirest.get(url).asJson().getBody();

// File
File file = Unirest.get(url).asFile("/tmp/download.zip").getBody();

// Empty (status/headers only)
HttpResponse resp = Unirest.delete(url).asEmpty();

Error handling:

Unirest.get("http://localhost/data")
    .asJson()
    .ifSuccess(response -> handleSuccess(response))
    .ifFailure(response -> {
        log.error("Status: " + response.getStatus());
        response.getParsingError().ifPresent(e -> {
            log.error("Parse error: " + e.getMessage());
        });
    });

Parsing errors:

response.getParsingError().ifPresent(ex -> {
    String originalBody = ex.getOriginalBody();
    String message = ex.getMessage();
});

Map error objects:

HttpResponse<Book> book = Unirest.get(url).asObject(Book.class);
Error err = book.mapError(Error.class);

See references/responses.md for download progress, large responses, body mapping, and more.

Critical: Server-Sent Events (SSE)

Async SSE consumption:

var future = Unirest.sse("https://stream.example.com/events")
    .connect(event -> {
        var data = event.asObject(MyEvent.class);
        System.out.println("Event: " + data.getTitle());
    });

Synchronous SSE consumption:

Unirest.sse("https://stream.example.com/events")
    .connect()
    .map(event -> event.asObject(MyEvent.class))
    .forEach(data -> System.out.println("Event: " + data.getTitle()));

⚠️ SSE connections are persistent. Use async mode in production systems. ⚠️ Object mapping requires an ObjectMapper to be configured.

See references/sse.md for full details.

Critical: Caching

Basic caching:

Unirest.config().cacheResponses(true);

Advanced caching with options:

Unirest.config().cacheResponses(Cache.builder()
    .depth(100)                      // Max entries
    .maxAge(5, TimeUnit.MINUTES));   // Entry TTL

Custom cache (e.g., Guava):

Unirest.config().cacheResponses(
    Cache.builder().backingCache(new MyGuavaCache()));

See references/caching.md for custom cache implementation details.

Critical: Mocking

Static mock:

MockClient mock = MockClient.register();

mock.expect(HttpMethod.GET, "http://api.example.com/users")
    .thenReturn("{\"name\":\"Alice\"}")
    .withStatus(200);

String body = Unirest.get("http://api.example.com/users")
    .asString().getBody();
// body == "{\"name\":\"Alice\"}"

mock.verifyAll(); // Verify all expects were called

Instance mock:

UnirestInstance unirest = Unirest.spawnInstance();
MockClient mock = MockClient.register(unirest);

Body matching:

mock.expect(HttpMethod.POST, "http://api.example.com/users")
    .body(FieldMatcher.of("name", "Alice", "role", "admin"))
    .thenReturn()
    .withStatus(201);

Verify with times:

var expect = mock.expect(HttpMethod.GET, "http://api.example.com/users").thenReturn();
expect.verify();              // At least once
expect.verify(Times.never()); // Never called

See references/mocking.md for POJO responses, multiple expects, and more.

Critical: Proxies

Simple proxy:

Unirest.config().proxy("proxy.com", 8080, "user", "pass");

System properties:

System.setProperty("http.proxyHost", "localhost");
System.setProperty("http.proxyPort", "7777");
Unirest.config().useSystemProperties(true);

Multiple proxies (ProxySelector):

Unirest.config()
    .proxy(new ProxySelector() {
        @Override
        public List<Proxy> select(URI uri) {
            if (uri.getHost().equals("internal.com")) {
                return List.of(new Proxy(HTTP,
                    InetSocketAddress.createUnresolved("internal-proxy.com", 8080)));
            }
            return List.of(new Proxy(HTTP,
                InetSocketAddress.createUnresolved("default-proxy.com", 8080)));
        }
        @Override
        public void connectFailed(URI uri, SocketAddress sa, IOException ioe) {}
    });

See references/proxies.md for authenticator setup and details.

Critical: WebSocket

Connect to a WebSocket:

Unirest.webSocket("ws://localhost/socket")
    .connect(ws -> {
        ws.sendText("Hello!");
        ws.onMessage(message -> {
            System.out.println("Received: " + message);
        });
    });

WebSocket with POJO mapping:

Unirest.webSocket("ws://localhost/events")
    .connect(ws -> {
        ws.onMessage(event -> {
            MyEvent data = event.asObject(MyEvent.class);
            processEvent(data);
        });
    });

⚠️ WebSocket is a 4.x-only feature. Not available in 3.x.

See references/websocket.md for full details.

Quick Fixes

| Error | Cause | Fix | |-------|-------|-----| | NoClassDefFoundError: JsonObject | Missing JSON module | Add unirest-modules-gson or unirest-modules-jackson dependency | | java.lang.NoClassDefFoundError: kong/unirest/Unirest | Wrong package in 4.x | Change import from kong.unirest.* to kong.unirest.core.* | | asObject() returns null body | Response parsing failed | Check response.getParsingError() for details | | ConnectException: Connection timed out | Server unreachable or timeout too low | Increase connectTimeout or check network | | SSLHandshakeException | SSL verification failure | Use verifySsl(false) for dev only, fix certs in prod | | Host header override not allowed | Java 11+ HttpClient restriction | Set system property jdk.httpclient.allowRestrictedHeaders=host | | Proxy not working in 4.x | System props disabled by default in 4.x | Call useSystemProperties(true) explicitly |

Gotchas

1. Java 11+ is mandatory — Unirest 4.x uses java.net.http.HttpClient and will not run on Java 8
2. JSON module must be declared — Unlike 3.x, 4.x has NO default JSON parser. Without unirest-modules-gson or unirest-modules-jackson, JSON parsing will fail at runtime
3. Package rename — kong.unirest (3.x) → kong.unirest.core (4.x), JSON modules at kong.unirest.modules.gson/jackson (4.3+)
4. HTTP/2 by default — 4.x defaults to HttpClient.Version.HTTP_2. Use config.version(HttpClient.Version.HTTP_1_1) to downgrade
5. No per-request proxies — 3.x allowed request.proxy(host, port). 4.x only supports global proxy via Unirest.config().proxy()
6. No socketTimeout — 3.x had independent socketTimeout(). 4.x uses requestTimeout() which covers the entire request lifecycle
7. No concurrency tuning — concurrency(total, perRoute) was Apache-specific. java.net.http manages connection pools internally
8. No automatic retries — automaticRetries(true) was Apache-specific. 4.x only has retryAfter() for 429/529 responses
9. No HostnameVerifier — 3.x had hostnameVerifier(verifier). 4.x uses disableHostNameVerification() system property (JVM-wide)
10. System proxy props disabled by default — Unlike 3.x (default true), 4.x defaults useSystemProperties to false
11. SSE and WebSocket are 4.x-only — Unirest.sse() and Unirest.webSocket() do not exist in 3.x
12. Mock registration simplified — 3.x: MockClient.register() required .httpClient(client).asyncClient(client). 4.x: only .httpClient(client)
13. Config changes require reset — Once Unirest is activated, changing client-creation config requires config().reset() first
14. isRunning() removed — 3.x had Unirest.isRunning(). 4.x removed it (no background threads to monitor)

References

Requests

• requests.md — Route params, query params, headers, auth, body types, file uploads, upload progress, async, paged requests, client certificates

Responses

• responses.md — asEmpty/asString/asObject/asJson/asFile, GenericType, parsing errors, error object mapping, download progress, large responses, error handling

Configuration

• configuration.md — Full config options table, global interceptors, multiple configurations, object mappers (Jackson/GSON), metrics

Mocking

• mocking.md — Static/instance mocks, multiple expects (scoring), verification, body matching, form params, POJO responses

Caching

• caching.md — Basic/advanced caching, custom cache implementations

Server-Sent Events

• sse.md — Async/sync SSE consumption, object mapping requirements

WebSocket

• websocket.md — WebSocket connections, message handling, POJO mapping

Proxies

• proxies.md — Simple proxy, system properties, ProxySelector with Authenticator

Upgrade Guide

• upgrade-guide.md — 3.x→4.x migration, package renames, Maven coordinate changes, behavior differences