Unirest-Java 3.x Reference (v3.14.5)

This skill covers the Unirest-Java 3.x HTTP client library for Java 8+. It uses Apache HttpClient 4 as the HTTP engine and includes GSON as the default JSON parser.

Capability Boundaries

✅ Strong Suits

1. Building HTTP requests (GET, POST, PUT, DELETE, PATCH) with fluent API
2. JSON/object mapping with built-in GSON (no extra dependency needed)
3. Async requests with CompletableFuture (via Apache HttpAsyncClient)
4. File uploads with progress monitoring
5. Mock testing for HTTP clients
6. Response caching with configurable eviction
7. Proxy configuration (simple, system, per-request)
8. Request/response interceptors for logging and auth
9. Connection pool tuning (concurrency(total, perRoute))
10. Socket timeout control (independent of connect timeout)
11. Automatic retries on socket errors (automaticRetries())
12. Shutdown hooks for background thread management
13. Custom HostnameVerifier support

⚠️ Requirements

1. Java 8 or higher
2. Apache HttpClient 4 (transitive dependency)
3. Maven/Gradle dependency management

❌ Out of Scope (with alternatives)

1. HTTP/2 → use Unirest 4.x (defaults to HTTP/2)
2. WebSocket via Unirest → use Apache HttpClient WebSocket or dedicated library
3. Server-Sent Events (SSE) → use Unirest 4.x or custom implementation
4. Custom executor support → not available in 3.x
5. Java Authenticator integration → use Apache-specific auth mechanisms
6. ProxySelector support → use per-request proxies or system properties

When to Use This Skill

Use this skill when the user needs to:

• Make HTTP requests to REST APIs in Java 8+ projects
• Use Apache HttpClient as the HTTP engine
• Have built-in GSON without extra dependencies
• Tune connection pools (concurrency())
• Control socket timeout independently
• Use automatic retries on socket errors
• Configure per-request proxies
• Use custom HostnameVerifier

Quick Start

Maven dependency (Unirest 3.14.5):

<dependency>
    <groupId>com.konghq</groupId>
    <artifactId>unirest-java</artifactId>
    <version>3.14.5</version>
</dependency>

✅ No JSON module declaration needed — GSON is included by default.

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 3.x is a single dependency that includes GSON by default:

<dependency>
    <groupId>com.konghq</groupId>
    <artifactId>unirest-java</artifactId>
    <version>3.14.5</version>
</dependency>

✅ No need to declare a separate JSON module — JsonObjectMapper (GSON-based) is included.

Critical: Configuration

All configuration goes through Unirest.config():

Unirest.config()
    .connectTimeout(5000)
    .socketTimeout(10000)
    .concurrency(200, 20)
    .setDefaultHeader("Accept", "application/json")
    .setDefaultBasicAuth("user", "pass")
    .followRedirects(true)
    .verifySsl(true)
    .enableCookieManagement(true)
    .automaticRetries(true)
    .proxy("proxy.com", 8080, "user", "pass");

Key config options:

| Method | Impact | Default | |--------|--------|---------| | connectTimeout(int) | Connection timeout (ms) | 10000 | | socketTimeout(int) | Socket/read timeout (ms) | 60000 | | concurrency(int, int) | Max total connections, max per route | 200/20 | | followRedirects(boolean) | Follow HTTP redirects | true | | verifySsl(boolean) | Enforce SSL verification | true | | enableCookieManagement(boolean) | Accept/store cookies | true | | automaticRetries(boolean) | Auto-retry on socket errors (up to 4 times) | true | | retryAfter(boolean) | Auto-retry on 429/529 with Retry-After header | false | | defaultBaseUrl(String) | Default base URL for all requests | none | | addShutdownHook(boolean) | Register JVM shutdown hook | false | | useSystemProperties(boolean) | Use system properties for proxies etc. | true |

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());
    });

Per-request proxy (3.x only):

Unirest.get("http://localhost/data")
    .proxy("proxy.com", 8080)
    .asString();

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 (GSON included by default)
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: 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 (3.x requires both clients):

UnirestInstance unirest = Unirest.spawnInstance();
MockClient mock = MockClient.register(unirest);
// In 3.x, the mock implements both Client and AsyncClient

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: 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: Proxies

Simple proxy:

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

Per-request proxy (3.x only):

Unirest.get("http://localhost/data")
    .proxy("proxy.com", 8080)
    .asString();

System properties (default: true in 3.x):

System.setProperty("http.proxyHost", "localhost");
System.setProperty("http.proxyPort", "7777");
// useSystemProperties defaults to true in 3.x

See references/proxies.md for details.

Quick Fixes

| Error | Cause | Fix | |-------|-------|-----| | NoClassDefFoundError: kong/unirest/Unirest | Wrong package | Use import kong.unirest.* (not 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 | | SocketTimeoutException | Read timeout exceeded | Increase socketTimeout (default 60000ms) | | SSLHandshakeException | SSL verification failure | Use verifySsl(false) for dev only, fix certs in prod | | Proxy not working | System props may be disabled | Check useSystemProperties(true) (default true in 3.x) | | Too many connections | Connection pool exhausted | Increase concurrency(total, perRoute) | | Automatic retries not working | Disabled or not applicable | Check automaticRetries(true) (default true) |

Gotchas

1. Java 8+ is sufficient — 3.x runs on Java 8 (unlike 4.x which requires Java 11+)
2. GSON included by default — No need to declare a separate JSON module (unlike 4.x)
3. Package is kong.unirest — Not kong.unirest.core (that's 4.x)
4. Single Maven dependency — unirest-java:3.14.5 (unlike 4.x which uses BOM + core + module)
5. Apache HttpClient engine — Uses Apache HttpClient 4 (not java.net.http.HttpClient)
6. Socket timeout is independent — socketTimeout() controls read timeout separately from connectTimeout()
7. Connection pool tuning — concurrency(total, perRoute) lets you tune Apache's connection pool
8. Automatic retries enabled by default — automaticRetries(true) retries socket errors up to 4 times
9. Per-request proxies supported — request.proxy(host, port) works (removed in 4.x)
10. HostnameVerifier supported — hostnameVerifier(verifier) for custom SSL hostname verification
11. Shutdown hooks available — addShutdownHook(true) registers JVM shutdown hooks
12. System proxy props enabled by default — useSystemProperties defaults to true (unlike 4.x)
13. No WebSocket via Unirest — Use Apache HttpClient WebSocket or a dedicated library
14. No SSE support — Unirest.sse() does not exist in 3.x
15. Mock registration requires both clients — MockClient implements both Client and AsyncClient

References

Requests

• requests.md — Route params, query params, headers, auth, body types, file uploads, upload progress, async, paged requests, per-request proxy

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, metrics, Apache-specific options

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

Proxies

• proxies.md — Simple proxy, system properties, per-request proxy