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6.4. HttpClient

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1. 什么是HttpClient?

HttpClient是Java 11中引入的一个新特性,用于支持同步和异步发送HTTP请求以及处理HTTP响应。它提供了简单易用的API,使得发送HTTP请求变得非常简单。

2. HttpClient的主要组件

HttpClient由以下几个主要组件组成:

  • HttpClient:用于发送请求的主要类。
  • HttpRequest:表示一个HTTP请求。
  • HttpResponse:表示一个HTTP响应。

3. 发送GET请求

要使用HttpClient发送GET请求,可以创建一个HttpClient对象,然后创建一个HttpRequest对象并设置请求方法为GET。最后,使用HttpClient的send()方法发送请求并获取响应。以下是一个简单示例:

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

public class HttpClientGetExample {
    public static void main(String[] args) {
        try {
            HttpClient client = HttpClient.newHttpClient();
            HttpRequest request = HttpRequest.newBuilder()
                    .uri(URI.create("https://www.example.com/"))
                    .GET()
                    .build();

            HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
            System.out.println(response.statusCode());
            System.out.println(response.body());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

4. 发送POST请求

要使用HttpClient发送POST请求,可以创建一个HttpClient对象,然后创建一个HttpRequest对象并设置请求方法为POST。还需要设置请求体,例如表单数据或JSON数据。最后,使用HttpClient的send()方法发送请求并获取响应。以下是一个简单示例:

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.nio.charset.StandardCharsets;

public class HttpClientPostExample {
    public static void main(String[] args) {
        try {
            HttpClient client = HttpClient.newHttpClient();
            String postData = "username=user&password=pass";
            HttpRequest request = HttpRequest.newBuilder()
                    .uri(URI.create("https://www.example.com/login"))
                    .header("Content-Type", "application/x-www-form-urlencoded")
                    .POST(HttpRequest.BodyPublishers.ofString(postData))
                    .build();

            HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
            System.out.println(response.statusCode());
            System.out.println(response.body());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

5. 异步请求

HttpClient还支持异步发送HTTP请求。要发送异步请求,可以使用HttpClient的sendAsync()方法。以下是一个简单示例:

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

public class HttpClientAsyncExample {
    public static void main(String[] args) {
        try {
            HttpClient client = HttpClient.newHttpClient();
            HttpRequest request = HttpRequest.newBuilder()
                    .uri(URI.create("https://www.example.com/"))
                    .GET()
                    .build();

            client.sendAsync(request, HttpResponse.BodyHandlers.ofString())
                    .thenApply(HttpResponse::body)
                    .thenAccept(System.out::println)
                    .join();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

6. 自定义HttpClient

可以通过HttpClient.Builder类自定义HttpClient,例如设置超时、代理、重定向策略等。以下是一个简单示例,演示如何设置超时和代理:

import java.net.InetSocketAddress;
import java.net.ProxySelector;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.time.Duration;

public class CustomHttpClientExample {
    public static void main(String[] args) {
        try {
            HttpClient client = HttpClient.newBuilder()
                    .connectTimeout(Duration.ofSeconds(5))
                    .proxy(ProxySelector.of(new InetSocketAddress("myproxy.example.com", 8080)))
                    .build();

            HttpRequest request = HttpRequest.newBuilder()
                    .uri(URI.create("https://www.example.com/"))
                    .GET()
                    .build();

            HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
            System.out.println(response.statusCode());
            System.out.println(response.body());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

现在,您已经了解了Java的HttpClient的基本概念和用法。实际上,还有许多其他功能和配置可以探索。在实际项目中,您可能需要根据具体需求调整HttpClient的配置。希望这些示例能帮助您更好地理解Java网络编程中的HttpClient组件。

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