Java 11及以上版本內(nèi)置的HttpClient提供了簡潔的REST客戶端實現(xiàn)，1. 使用HttpClient.newBuilder()配置超時、代理等並創(chuàng)建可重用的客戶端實例；2. 通過HttpRequest.newBuilder()設(shè)置URI、GET/POST/PUT/DELETE方法、請求頭及BodyPublisher發(fā)送同步或異步請求；3. 使用HttpResponse.BodyHandlers處理響應(yīng)體，支持字符串、文件或字節(jié)數(shù)組；4. 異步請求通過sendAsync()結(jié)合thenApply和thenAccept實現(xiàn)非阻塞調(diào)用；5. 添加請求頭、查詢參數(shù)並處理HTTP錯誤狀態(tài)碼以確保健壯性；6. 推薦復(fù)用HttpClient、設(shè)置超時、集成Jackson等序列化庫以提升效率，該客戶端支持HTTP/2、同步異步模式且無需第三方依賴，適用於大多數(shù)REST場景。

Creating a REST client in Java has become much simpler since the introduction of the modern HttpClient API in Java 11. This built-in client supports both synchronous and asynchronous requests, HTTP/2, and provides a fluent, easy-to-use interface. Here's how you can build a practical REST client using java.net.http.HttpClient .

? Setting Up the HttpClient

The HttpClient is part of the java.net.http module. Make sure your project runs on Java 11 or higher .

You create a shared HttpClient instance (it's thread-safe and reusable):

 import java.net.http.HttpClient;
import java.time.Duration;

HttpClient client = HttpClient.newBuilder()
    .connectTimeout(Duration.ofSeconds(10))
    .build();

This client can be used for all requests. Common configurations include:

• Connection timeout
• Redirect policy
• Proxy settings
• SSL context (for HTTPS)

? Making GET Requests

To retrieve data from a REST API (eg, JSON):

 import java.net.URI;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;

HttpRequest request = HttpRequest.newBuilder()
    .uri(URI.create("https://jsonplaceholder.typicode.com/posts/1"))
    .GET() // Optional, GET is default
    .header("Accept", "application/json")
    .build();

try {
    HttpResponse<String> response = client.send(request, 
        HttpResponse.BodyHandlers.ofString());

    System.out.println("Status: " response.statusCode());
    System.out.println("Body: " response.body());
} catch (Exception e) {
    e.printStackTrace();
}

? Use HttpResponse.BodyHandlers.ofString() for text/JSON responses. You can also use ofFile() or ofByteArray() .

? Asynchronous GET Request

For non-blocking calls, use sendAsync() :

 client.sendAsync(request, HttpResponse.BodyHandlers.ofString())
    .thenApply(HttpResponse::body)
    .thenAccept(System.out::println)
    .join(); // Wait for completion (for demo only)

This is useful in high-throughput applications where you don't want to block threads.

? Making POST Requests with JSON

To send data (eg, create a resource):

 String json = """
    {
        "title": "New Post",
        "body": "This is the content",
        "userId": 1
    }
    """;

HttpRequest request = HttpRequest.newBuilder()
    .uri(URI.create("https://jsonplaceholder.typicode.com/posts"))
    .header("Content-Type", "application/json")
    .POST(HttpRequest.BodyPublishers.ofString(json))
    .build();

HttpResponse<String> response = client.send(request, 
    HttpResponse.BodyHandlers.ofString());

System.out.println("Status: " response.statusCode());
System.out.println("Response: " response.body());

? Key parts:

• POST() method with BodyPublisher
• Set correct Content-Type header
• Use raw JSON strings or integrate with Jackson/Gson for object serialization

? PUT and DELETE Requests

Update a resource with PUT :

 HttpRequest request = HttpRequest.newBuilder()
    .uri(URI.create("https://jsonplaceholder.typicode.com/posts/1"))
    .header("Content-Type", "application/json")
    .PUT(HttpRequest.BodyPublishers.ofString(json))
    .build();

Delete a resource:

 HttpRequest request = HttpRequest.newBuilder()
    .uri(URI.create("https://jsonplaceholder.typicode.com/posts/1"))
    .DELETE()
    .build();

? Handling Headers, Query Params, and Errors

Add multiple headers:

 .header("Authorization", "Bearer token123")
.header("User-Agent", "MyApp/1.0");

Add query parameters:

 UriBuilder builder = UriBuilder.fromUri("https://api.example.com/search")
    .queryParam("q", "java")
    .queryParam("limit", 10);
HttpRequest request = HttpRequest.newBuilder()
    .uri(builder.build())
    .GET()
    .build();

?? UriBuilder is from Jakarta/Java EE or use manual string building or URIBuilder from Apache Commons if needed.

Handle HTTP errors:

 if (response.statusCode() == 404) {
    System.out.println("Resource not found");
} else if (response.statusCode() >= 400) {
    System.err.println("Error: " response.statusCode());
}

? Reuse and Best Practices

• ? Reuse HttpClient — it's designed to be long-lived
• ? Use sendAsync() for performance-sensitive apps
• ? Set timeouts to avoid hanging connections
• ? Use ObjectMapper (eg, Jackson) to serialize/deserialize POJOs

Example with Jackson:

 ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(postObject);
// Use in request body

? Summary

With Java 11 , you no longer need external libraries like Apache HttpClient or OkHttp for basic REST interactions. The built-in HttpClient offers:

• Clean, fluent API
• Synchronous and asynchronous support
• HTTP/2 by default (if server supports it)
• Modern features with minimal dependencies

Just remember:

• Run on Java 11
• Handle exceptions and HTTP error codes
• Prefer async for scalability

Basically, it's simple, standard, and sufficient for most REST client needs.

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