pom引入依赖

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.3.1</version>
</dependency>

在配置文件中加入httpclient需要的一些配置参数

#最大连接数
http.maxTotal = 100
#并发数
http.defaultMaxPerRoute = 20
#创建连接的最长时间
http.connectTimeout=1000
#从连接池中获取到连接的最长时间
http.connectionRequestTimeout=500
#数据传输的最长时间
http.socketTimeout=10000
#提交请求前测试连接是否可用
http.staleConnectionCheckEnabled=true

新建配置文件

@Configuration
public class HttpClient {
 
    @Value("${http.maxTotal}")
    private Integer maxTotal;
 
    @Value("${http.defaultMaxPerRoute}")
    private Integer defaultMaxPerRoute;
 
    @Value("${http.connectTimeout}")
    private Integer connectTimeout;
 
    @Value("${http.connectionRequestTimeout}")
    private Integer connectionRequestTimeout;
 
    @Value("${http.socketTimeout}")
    private Integer socketTimeout;
 
    @Value("${http.staleConnectionCheckEnabled}")
    private boolean staleConnectionCheckEnabled;
 
    /**
     * 首先实例化一个连接池管理器，设置最大连接数、并发连接数
     * @return
     */
    @Bean(name = "httpClientConnectionManager")
    public PoolingHttpClientConnectionManager getHttpClientConnectionManager(){
        PoolingHttpClientConnectionManager httpClientConnectionManager = new PoolingHttpClientConnectionManager();
        //最大连接数
        httpClientConnectionManager.setMaxTotal(maxTotal);
        //并发数
        httpClientConnectionManager.setDefaultMaxPerRoute(defaultMaxPerRoute);
        return httpClientConnectionManager;
    }
 
    /**
     * 实例化连接池，设置连接池管理器。
     * 这里需要以参数形式注入上面实例化的连接池管理器
     * @param httpClientConnectionManager
     * @return
     */
    @Bean(name = "httpClientBuilder")
    public HttpClientBuilder getHttpClientBuilder(@Qualifier("httpClientConnectionManager")PoolingHttpClientConnectionManager httpClientConnectionManager){
 
        //HttpClientBuilder中的构造方法被protected修饰，所以这里不能直接使用new来实例化一个HttpClientBuilder，可以使用HttpClientBuilder提供的静态方法create()来获取HttpClientBuilder对象
        HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();
 
        httpClientBuilder.setConnectionManager(httpClientConnectionManager);
 
        return httpClientBuilder;
    }
 
    /**
     * 注入连接池，用于获取httpClient
     * @param httpClientBuilder
     * @return
     */
    @Bean
    public CloseableHttpClient getCloseableHttpClient(@Qualifier("httpClientBuilder") HttpClientBuilder httpClientBuilder){
        return httpClientBuilder.build();
    }
 
    /**
     * Builder是RequestConfig的一个内部类
     * 通过RequestConfig的custom方法来获取到一个Builder对象
     * 设置builder的连接信息
     * 这里还可以设置proxy，cookieSpec等属性。有需要的话可以在此设置
     * @return
     */
    @Bean(name = "builder")
    public RequestConfig.Builder getBuilder(){
        RequestConfig.Builder builder = RequestConfig.custom();
        return builder.setConnectTimeout(connectTimeout)
                .setConnectionRequestTimeout(connectionRequestTimeout)
                .setSocketTimeout(socketTimeout)
                .setStaleConnectionCheckEnabled(staleConnectionCheckEnabled);
    }
 
    /**
     * 使用builder构建一个RequestConfig对象
     * @param builder
     * @return
     */
    @Bean
    public RequestConfig getRequestConfig(@Qualifier("builder") RequestConfig.Builder builder){
        return builder.build();
    }
 
}

4.编写一个案例Controller层

@RestController
public class HttpClientController {
 
    @Resource
    private HttpAPIService httpAPIService;
 
    @RequestMapping("httpclient")
    public String test() throws Exception {
        String str = httpAPIService.doGet("http://www.baidu.com");
        System.out.println(str);
        return "hello";
    }
}