httpclient版本：

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.1</version>
</dependency>

spring配置如下:

<bean id="pollingConnectionManager"
class="org.apache.http.impl.conn.PoolingHttpClientConnectionManager"
 
>
<property name="maxTotal" value="10" />
<property name="defaultMaxPerRoute" value="5" />
</bean>

<bean id="httpClientBuilder" class="org.apache.http.impl.client.HttpClientBuilder"
factory-method="create">
<property name="connectionManager" ref="pollingConnectionManager" />
 

</bean>

<bean id="httpClient" factory-bean="httpClientBuilder"
factory-method="build" />

<!-- -->
<bean id="clientHttpRequestFactory"
class="org.springframework.http.client.HttpComponentsClientHttpRequestFactory">
<constructor-arg ref="httpClient" />
<property name="connectTimeout"
 
 value="30000" />
<property name="readTimeout" value="30000" />
</bean>

配置帶有連線池的org.springframework.web.client.RestTemplate

<bean id="restTemplate" class="org.springframework.web.client.RestTemplate">
<constructor-arg ref="clientHttpRequestFactory" />
<property name="messageConverters">
<list>
<bean
class="org.springframework.http.converter.StringHttpMessageConverter" />
<bean
class="org.springframework.http.converter.xml.SourceHttpMessageConverter" />
<bean class="org.springframework.http.converter.FormHttpMessageConverter" />
<bean
class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter" />
<bean
class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter" />
</list>
</property>
</bean>

  @Bean(name = "poolingHttpClientConnectionManager")
    public PoolingHttpClientConnectionManager poolingHttpClientConnectionManager() {
        PoolingHttpClientConnectionManager poolingHttpClientConnectionManager = new PoolingHttpClientConnectionManager();
        poolingHttpClientConnectionManager.setMaxTotal(10);
        poolingHttpClientConnectionManager.setDefaultMaxPerRoute(5);
        return poolingHttpClientConnectionManager;
    }

    @Bean(name = "httpClientBuilder")
    public HttpClientBuilder httpClientBuilder() {
        HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();
        httpClientBuilder.setConnectionManager(poolingHttpClientConnectionManager());
        return httpClientBuilder;
    }


    @Bean(name = "httpClient")
    public CloseableHttpClient httpClient() {

        return httpClientBuilder().build();

    }