Apache HttpClient是一个功能强大的Java库，用于发送HTTP请求和处理响应。对于GET请求，HttpClient提供了简单易用的API。以下是关于在Apache HttpClient中处理GET请求的详细说明。

基本GET请求实现

1. 使用HttpClient发送简单GET请求

import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class SimpleGetRequest {
    public static void main(String[] args) {
        // 创建HttpClient实例
        try (CloseableHttpClient httpClient = HttpClients.createDefault()) {
            // 创建HttpGet实例，设置请求URL
            HttpGet httpGet = new HttpGet("http://example.com/api");
            
            // 执行请求并获取响应
            try (CloseableHttpResponse response = httpClient.execute(httpGet)) {
                // 获取响应状态码
                int statusCode = response.getStatusLine().getStatusCode();
                System.out.println("响应状态码: " + statusCode);
                
                // 获取响应内容
                String responseBody = EntityUtils.toString(response.getEntity());
                System.out.println("响应内容: " + responseBody);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

2. 带查询参数的GET请求

import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.utils.URIBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

public class GetWithQueryParams {
    public static void main(String[] args) {
        try (CloseableHttpClient httpClient = HttpClients.createDefault()) {
            // 使用URIBuilder构建带参数的URL
            URIBuilder uriBuilder = new URIBuilder("http://example.com/api");
            uriBuilder.addParameter("param1", "value1");
            uriBuilder.addParameter("param2", "value2");
            
            HttpGet httpGet = new HttpGet(uriBuilder.build());
            
            // 执行请求...
            // (与前面示例相同的执行和响应处理代码)
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

高级用法

1. 设置请求头

HttpGet httpGet = new HttpGet("http://example.com/api");
httpGet.setHeader("User-Agent", "MyHttpClient/1.0");
httpGet.setHeader("Accept", "application/json");

2. 配置连接超时

import org.apache.http.client.config.RequestConfig;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

RequestConfig requestConfig = RequestConfig.custom()
        .setConnectTimeout(5000) // 连接超时时间(毫秒)
        .setSocketTimeout(5000)  // 读取超时时间(毫秒)
        .build();

try (CloseableHttpClient httpClient = HttpClients.custom()
        .setDefaultRequestConfig(requestConfig)
        .build()) {
    // 执行请求...
}

3. 处理重定向

RequestConfig requestConfig = RequestConfig.custom()
        .setRedirectsEnabled(true) // 启用自动重定向
        .setMaxRedirects(5)        // 最大重定向次数
        .build();

try (CloseableHttpClient httpClient = HttpClients.custom()
        .setDefaultRequestConfig(requestConfig)
        .build()) {
    // 执行请求...
}

最佳实践

  1. 资源管理：始终使用try-with-resources语句确保CloseableHttpClient和CloseableHttpResponse被正确关闭
  2. 连接池：对于频繁请求，考虑使用连接池管理
PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
cm.setMaxTotal(200); // 最大连接数
cm.setDefaultMaxPerRoute(20); // 每个路由的最大连接数

try (CloseableHttpClient httpClient = HttpClients.custom()
        .setConnectionManager(cm)
        .build()) {
    // 执行请求...
}
  1. 异常处理：妥善处理可能出现的IOException和HttpException
  2. 响应处理：确保读取完整的响应体，可以使用EntityUtils.consume(response.getEntity())确保资源释放

完整示例

import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.protocol.HttpClientContext;
import org.apache.http.client.utils.URIBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

import java.net.URI;

public class AdvancedGetExample {
    public static void main(String[] args) {
        // 配置请求
        RequestConfig requestConfig = RequestConfig.custom()
                .setConnectTimeout(5000)
                .setSocketTimeout(5000)
                .setRedirectsEnabled(true)
                .build();
        
        // 创建带连接池的HttpClient
        try (CloseableHttpClient httpClient = HttpClients.custom()
                .setDefaultRequestConfig(requestConfig)
                .build()) {
            
            HttpClientContext context = HttpClientContext.create();
            
            // 构建带参数的URL
            URI uri = new URIBuilder("http://example.com/api")
                    .addParameter("key1", "value1")
                    .addParameter("key2", "value2")
                    .build();
            
            HttpGet httpGet = new HttpGet(uri);
            httpGet.setHeader("Accept", "application/json");
            
            // 执行请求
            try (CloseableHttpResponse response = httpClient.execute(httpGet, context)) {
                System.out.println("响应状态: " + response.getStatusLine());
                
                // 处理响应
                String responseBody = EntityUtils.toString(response.getEntity());
                System.out.println("响应内容: " + responseBody);
                
                // 打印重定向历史(如果有)
                System.out.println("重定向次数: " + context.getRedirectLocations().size());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

通过以上示例和说明，您应该能够掌握在Apache HttpClient中处理GET请求的各种方法。根据实际需求，您可以调整配置参数和请求处理逻辑。