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Apache HttpClient 是一个功能强大且灵活的库，用于在Java中处理HTTP请求。

它支持多种HTTP方法，包括GET、POST、PUT和DELETE等。

本教程将演示如何使用Apache HttpClient来执行GET、POST、PUT和DELETE请求。

Maven依赖

要使用Apache HttpClient，您需要在pom.xml文件中添加以下依赖项：

<!-- https://mvnrepository.com/artifact/org.apache.httpcomponents.client5/httpclient5 -->
<dependency><groupId>org.apache.httpcomponents.client5</groupId><artifactId>httpclient5</artifactId><version>5.3</version>
</dependency>

示例场景

我们将创建简单的Java类，这些类将向指定的URL发送GET、POST、PUT和DELETE请求，并打印响应。

JSONPlaceholder API

为了演示目的，我们将使用JSONPlaceholder API，该API提供了一个虚拟的在线RESTful端点，用于测试和原型设计。

GET请求

发送GET请求的Java类

创建一个名为HttpClientGetExample的类，代码如下：

import org.apache.hc.client5.http.classic.methods.HttpGet;
import org.apache.hc.client5.http.classic.methods.CloseableHttpResponse;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.HttpClients;
import org.apache.hc.core5.http.io.entity.EntityUtils;public class HttpClientGetExample {public static void main(String[] args) {String url = "https://jsonplaceholder.typicode.com/posts/1";// 创建HttpClienttry (CloseableHttpClient httpClient = HttpClients.createDefault()) {// 创建HttpGet请求HttpGet request = new HttpGet(url);// 执行请求try (CloseableHttpResponse response = httpClient.execute(request)) {// 获取HTTP响应状态System.out.println("Response Code: " + response.getCode());// 获取HTTP响应内容String content = EntityUtils.toString(response.getEntity());System.out.println("Response Content: \n" + content);}} catch (Exception e) {e.printStackTrace();}}
}

示例输出

Response Code: 200
Response Content: 
{"userId": 1,"id": 1,"title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit","body": "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto"
}

POST请求

发送POST请求的Java类

创建一个名为HttpClientPostExample的类，代码如下：

import org.apache.hc.client5.http.classic.methods.HttpPost;
import org.apache.hc.client5.http.classic.methods.CloseableHttpResponse;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.HttpClients;
import org.apache.hc.core5.http.io.entity.StringEntity;
import org.apache.hc.core5.http.ContentType;
import org.apache.hc.core5.http.io.entity.EntityUtils;public class HttpClientPostExample {public static void main(String[] args) {String url = "https://jsonplaceholder.typicode.com/posts";String json = "{\"title\":\"foo\",\"body\":\"bar\",\"userId\":1}";// 创建HttpClienttry (CloseableHttpClient httpClient = HttpClients.createDefault()) {// 创建HttpPost请求HttpPost request = new HttpPost(url);// 设置JSON负载StringEntity entity = new StringEntity(json, ContentType.APPLICATION_JSON);request.setEntity(entity);// 设置头部request.setHeader("Accept", "application/json");request.setHeader("Content-type", "application/json");// 执行请求try (CloseableHttpResponse response = httpClient.execute(request)) {// 获取HTTP响应状态System.out.println("Response Code: " + response.getCode());// 获取HTTP响应内容String content = EntityUtils.toString(response.getEntity());System.out.println("Response Content: \n" + content);}} catch (Exception e) {e.printStackTrace();}}
}

示例输出

Response Code: 201
Response Content: 
{"title": "foo","body": "bar","userId": 1,"id": 101
}

PUT请求

发送PUT请求的Java类

创建一个名为HttpClientPutExample的类，代码如下：

import org.apache.hc.client5.http.classic.methods.HttpPut;
import org.apache.hc.client5.http.classic.methods.CloseableHttpResponse;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.HttpClients;
import org.apache.hc.core5.http.io.entity.StringEntity;
import org.apache.hc.core5.http.ContentType;
import org.apache.hc.core5.http.io.entity.EntityUtils;public class HttpClientPutExample {public static void main(String[] args) {String url = "https://jsonplaceholder.typicode.com/posts/1";String json = "{\"id\":1,\"title\":\"foo\",\"body\":\"bar\",\"userId\":1}";// 创建HttpClienttry (CloseableHttpClient httpClient = HttpClients.createDefault()) {// 创建HttpPut请求HttpPut request = new HttpPut(url);// 设置JSON负载StringEntity entity = new StringEntity(json, ContentType.APPLICATION_JSON);request.setEntity(entity);// 设置头部request.setHeader("Accept", "application/json");request.setHeader("Content-type", "application/json");// 执行请求try (CloseableHttpResponse response = httpClient.execute(request)) {// 获取HTTP响应状态System.out.println("Response Code: " + response.getCode());// 获取HTTP响应内容String content = EntityUtils.toString(response.getEntity());System.out.println("Response Content: \n" + content);}} catch (Exception e) {e.printStackTrace();}}
}

示例输出

Response Code: 200
Response Content: 
{"id": 1,"title": "foo","body": "bar","userId": 1
}

DELETE请求

发送DELETE请求的Java类

创建一个名为HttpClientDeleteExample的类，代码如下：

import org.apache.hc.client5.http.classic.methods.HttpDelete;
import org.apache.hc.client5.http.classic.methods.CloseableHttpResponse;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.HttpClients;
import org.apache.hc.core5.http.io.entity.EntityUtils;public class HttpClientDeleteExample {public static void main(String[] args) {String url = "https://jsonplaceholder.typicode.com/posts/1";// 创建HttpClienttry (CloseableHttpClient httpClient = HttpClients.createDefault()) {// 创建HttpDelete请求HttpDelete request = new HttpDelete(url);// 执行请求try (CloseableHttpResponse response = httpClient.execute(request)) {// 获取HTTP响应状态System.out.println("Response Code: " + response.getCode());// 获取HTTP响应内容String content = EntityUtils.toString(response.getEntity());System.out.println("Response Content: \n" + content);}} catch (Exception e) {e.printStackTrace();}}
}

示例输出

Response Code: 200
Response Content: 
{}

额外配置

• 设置自定义头部：可以通过调用请求对象（如HttpGet、HttpPost、HttpPut、HttpDelete）上的setHeader方法来设置自定义头部。
• 处理重定向：默认情况下，Apache HttpClient会自动处理重定向。您可以使用自定义的HttpClientBuilder来自定义这种行为。
• 设置超时：可以使用RequestConfig来设置连接和套接字超时。

结论

使用Apache HttpClient来执行GET、POST、PUT和DELETE HTTP请求非常方便。

通过遵循本教程，您现在应该能够创建并执行这些类型的请求，处理响应，并定制HTTP请求和响应过程。

Apache HttpClient提供了一整套功能，使其成为处理Java应用程序中HTTP操作的优秀选择。

JSONPlaceholder API作为一个实用且方便的来源，适合用来测试和原型化您的HTTP请求。