SpringCloud—OpenFeign的Http请求源码简析

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Client组件

在Feign中，Client是一个非常重要的组件，Feign最终发送Request请求以及接收Response响应都是由Client组件来完成的。Client在Feign源码中是一个接口，在默认情况下，Client的实现类是Client.Default。Client.Default是由HttpURLConnection来实现网络请求的。另外,Client还支持HttpClient和OkHttp来进行网络请求。

Client的实现类包括：

  1. Client.Default类：默认的Client实现类，内部使用 HttpURLConnnection 完成HTTP URL请求处理；

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    public static class Default implements Client {
            private final SSLSocketFactory sslContextFactory;
            private final HostnameVerifier hostnameVerifier;

            public Default(SSLSocketFactory sslContextFactory, HostnameVerifier hostnameVerifier) {
                this.sslContextFactory = sslContextFactory;
                this.hostnameVerifier = hostnameVerifier;
            }

            public Response execute(Request request, Options options) throws IOException {
                HttpURLConnection connection = this.convertAndSend(request, options);
                return this.convertResponse(connection, request);
            }
            
            ......//代码省略
    }

    由于 HttpURLConnnection 由于缺乏连接池的支持，在达到一定流量的后服务可能会出现性能问题。

  2. ApacheHttpClient 类：内部使用 Apache Httpclient 开源组件完成HTTP URL请求处理的Client实现类；

  3. OkHttpClient类：内部使用 OkHttp3 开源组件完成HTTP URL请求处理的Client实现类。

自动配置 FeignAutoConfiguration

OpenFeign的自动配置类：org.springframework.cloud.openfeign.FeignAutoConfiguration，它配置的最原始的Client。

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@Configuration
@ConditionalOnClass(Feign.class)
@EnableConfigurationProperties({ FeignClientProperties.class,
		FeignHttpClientProperties.class })
public class FeignAutoConfiguration {

        //省略...
}

使用HttpClient

自动配置类中，有一个内部类HttpClientFeignConfiguration.class，它用于配置一个 ApacheHttpClient客户端。其源码如下：

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@Configuration
@ConditionalOnClass({ApacheHttpClient.class})
@ConditionalOnMissingClass({"com.netflix.loadbalancer.ILoadBalancer"})
@ConditionalOnMissingBean({CloseableHttpClient.class})
@ConditionalOnProperty(
    value = {"feign.httpclient.enabled"},
    matchIfMissing = true
)
protected static class HttpClientFeignConfiguration {
    private final Timer connectionManagerTimer = new Timer("FeignApacheHttpClientConfiguration.connectionManagerTimer", true);
    @Autowired(
        required = false
    )
    private RegistryBuilder registryBuilder;
    private CloseableHttpClient httpClient;
 
    protected HttpClientFeignConfiguration() {
    }
 
    @Bean
    @ConditionalOnMissingBean({HttpClientConnectionManager.class})
    public HttpClientConnectionManager connectionManager(ApacheHttpClientConnectionManagerFactory connectionManagerFactory, FeignHttpClientProperties httpClientProperties) {
        final HttpClientConnectionManager connectionManager = connectionManagerFactory.newConnectionManager(httpClientProperties.isDisableSslValidation(), httpClientProperties.getMaxConnections(), httpClientProperties.getMaxConnectionsPerRoute(), httpClientProperties.getTimeToLive(), httpClientProperties.getTimeToLiveUnit(), this.registryBuilder);
        this.connectionManagerTimer.schedule(new TimerTask() {
            public void run() {
                connectionManager.closeExpiredConnections();
            }
        }, 30000L, (long)httpClientProperties.getConnectionTimerRepeat());
        return connectionManager;
    }
 
    @Bean
    public CloseableHttpClient httpClient(ApacheHttpClientFactory httpClientFactory, HttpClientConnectionManager httpClientConnectionManager, FeignHttpClientProperties httpClientProperties) {
        RequestConfig defaultRequestConfig = RequestConfig.custom().setConnectTimeout(httpClientProperties.getConnectionTimeout()).setRedirectsEnabled(httpClientProperties.isFollowRedirects()).build();
        this.httpClient = httpClientFactory.createBuilder().setConnectionManager(httpClientConnectionManager).setDefaultRequestConfig(defaultRequestConfig).build();
        return this.httpClient;
    }
 
    @Bean
    @ConditionalOnMissingBean({Client.class})
    public Client feignClient(HttpClient httpClient) {
        //Client实例是一个ApacheHttpClient对象
        return new ApacheHttpClient(httpClient);
    }
 
    @PreDestroy
    public void destroy() throws Exception {
        this.connectionManagerTimer.cancel();
        if (this.httpClient != null) {
            this.httpClient.close();
        }
 
    }
}

可以看到这个配置生效的条件是：

  • @ConditionalOnClass(ApacheHttpClient.class)： 类路径下存在 ApacheHttpClient 类。
  • @ConditionalOnMissingClass("com.netflix.loadbalancer.ILoadBalancer")：类路径下不存在 ILoadBalancer 类。
  • feign.httpclient.enabled的值是true或者缺省（默认是true）。源码如下：

那么如何在Feign中使用HttpClient的框架呢？根据上面FeignAutoConfiguration.HttpClientFeignConfiguration的源码，可知只需要引入HttpClient的依赖即可，feign.httpclient.enabled可设置为true或者缺省。

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<dependency>
    <groupId>io.github.openfeign</groupId>
    <artifactId>feign-httpclient</artifactId>
    <version>9.4.0</version>
</dependency>

使用OkHttp

自动配置类中，另外一个内部类 OkHttpFeignConfiguration.class，它用于配置一个 OkHttp 客户端。其源码如下：

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@Configuration
@ConditionalOnClass({OkHttpClient.class})
@ConditionalOnMissingClass({"com.netflix.loadbalancer.ILoadBalancer"})
@ConditionalOnMissingBean({okhttp3.OkHttpClient.class})
@ConditionalOnProperty({"feign.okhttp.enabled"})
protected static class OkHttpFeignConfiguration {
    private okhttp3.OkHttpClient okHttpClient;
 
    protected OkHttpFeignConfiguration() {
    }
 
    @Bean
    @ConditionalOnMissingBean({ConnectionPool.class})
    public ConnectionPool httpClientConnectionPool(FeignHttpClientProperties httpClientProperties, OkHttpClientConnectionPoolFactory connectionPoolFactory) {
        Integer maxTotalConnections = httpClientProperties.getMaxConnections();
        Long timeToLive = httpClientProperties.getTimeToLive();
        TimeUnit ttlUnit = httpClientProperties.getTimeToLiveUnit();
        return connectionPoolFactory.create(maxTotalConnections, timeToLive, ttlUnit);
    }
 
    @Bean
    public okhttp3.OkHttpClient client(OkHttpClientFactory httpClientFactory, ConnectionPool connectionPool, FeignHttpClientProperties httpClientProperties) {
        Boolean followRedirects = httpClientProperties.isFollowRedirects();
        Integer connectTimeout = httpClientProperties.getConnectionTimeout();
        Boolean disableSslValidation = httpClientProperties.isDisableSslValidation();
        this.okHttpClient = httpClientFactory.createBuilder(disableSslValidation).connectTimeout((long)connectTimeout, TimeUnit.MILLISECONDS).followRedirects(followRedirects).connectionPool(connectionPool).build();
        return this.okHttpClient;
    }
 
    @Bean
    @ConditionalOnMissingBean({Client.class})
    public Client feignClient(okhttp3.OkHttpClient client) {
        //Client实例是一个OkHttpClient对象
        return new OkHttpClient(client);
    }
}

可以看到这个配置生效的条件是:

  • @ConditionalOnClass(OkHttpClient.class)： 类路径下存在 OkHttpClient 类。
  • @ConditionalOnMissingClass("com.netflix.loadbalancer.ILoadBalancer")：类路径下不存在 ILoadBalancer 类。
  • feign.okhttp.enabled的值是true（默认是false）。

所以同理，如果想要在Feign中使用OkHttp作为网络请求框架，则需要在pom文件中加上OkHttp的依赖，并且feign.okhttp.enabled为ture（这项配置默认是false），代码如下：
pom.xml文件中引入依赖：

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<dependency>
    <groupId>io.github.openfeign</groupId>
    <artifactId>feign-okhttp</artifactId>
    <version>10.2.0</version>
</dependency>

application.yml文件中增加配置项：

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feign:
  okhttp:
    enabled: true

Ribbon的负载均衡自动配置 FeignRibbonClientAutoConfiguration

除了FeignAutoConfiguration，还有一个很重要的自动配置类：org.springframework.cloud.openfeign.ribbon.FeignRibbonClientAutoConfiguration ，这个自动配置类位于Robbin的jar包中，它让Client具备负载均衡的能力。
Robbin的依赖：

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<!-- ribbon-->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
</dependency>

下面分析一下这个类的源码：

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import com.netflix.loadbalancer.ILoadBalancer;
//….
@ConditionalOnClass({ILoadBalancer.class, Feign.class})
@Configuration
@AutoConfigureBefore({FeignAutoConfiguration.class})  // 本配置类具备优先权
@EnableConfigurationProperties({FeignHttpClientProperties.class})
@Import({
HttpClientFeignLoadBalancedConfiguration.class,  //配置：包装ApacheHttpClient实例的负载均衡客户端
OkHttpFeignLoadBalancedConfiguration.class, //配置：包装OkHttpClient 实例的负载均衡客户端
DefaultFeignLoadBalancedConfiguration.class  //配置：包装Client.Default 实例的负载均衡客户端
})
public class FeignRibbonClientAutoConfiguration {

    //空的构造器
    public FeignRibbonClientAutoConfiguration() {
    }

    //...省略
}

  1. 根据类上的注解 @AutoConfigureBefore({FeignAutoConfiguration.class}) 可知，FeignRibbonClientAutoConfiguration 自动配置是优先于 FeignAutoConfiguration 的。所以当包含OpenFeign功能的项目中引入了Robbin之后，FeignRibbonClientAutoConfiguration 自动配置将生效，而 FeignAutoConfiguration.class 的自动配置将会被忽略。

  2. 再根据类上的注解 @ConditionalOnClass({ILoadBalancer.class, Feign.class}) ，可知 FeignRibbonClientAutoConfiguration 的自动配置有两个前提条件：

    1. 当前的类路径中，存在 ILoadBalancer.class 类
    2. 当前的类路径中，存在 Feign.class 类

结论：当我们引入了Ribbon的依赖，FeignRibbonClientAutoConfiguration 自动配置生效，负载均衡功能也就生效了。

LoadBalancerFeignClient

LoadBalancerFeignClient 类：这是Ribbon jar包中一个特殊的 feign.Client 客户端实现类。内部先使用 Ribbon 负载均衡算法计算server服务器，然后使用包装的 delegate 客户端实例，去完成 HTTP URL请求处理。

FeignRibbonClientAutoConfiguration 自动配置类，并没有直接配置 LoadBalancerFeignClient 容器实例，而是使用@Import注解，通过导入其他配置类的方式，完成 LoadBalancerFeignClient 客户端容器实例的配置。

分别导入了以下三个自动配置类：

  1. HttpClientFeignLoadBalancedConfiguration.class
    该配置类，负责配置一个包装 ApacheHttpClient 实例的 LoadBalancerFeignClient负载均衡客户端。
  2. OkHttpFeignLoadBalancedConfiguration.class
    该配置类，负责配置一个包装 OkHttpClient 实例的 LoadBalancerFeignClient负载均衡客户端。
  3. DefaultFeignLoadBalancedConfiguration.class
    该配置类，负责配置一个包装 Client.Default 实例的 LoadBalancerFeignClient负载均衡客户端。

所以原生的 HttpClientFeignConfiguration 配置变成了 HttpClientFeignLoadBalancedConfiguration：

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@Configuration
@ConditionalOnClass(ApacheHttpClient.class)
@ConditionalOnProperty(value = "feign.httpclient.enabled", matchIfMissing = true)
class HttpClientFeignLoadBalancedConfiguration {

	@Bean
	@ConditionalOnMissingBean(Client.class)
	public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory,
			SpringClientFactory clientFactory, HttpClient httpClient) {
		ApacheHttpClient delegate = new ApacheHttpClient(httpClient);
		return new LoadBalancerFeignClient(delegate, cachingFactory, clientFactory);
	}

    //省略...
}

原生的 OkHttpFeignConfiguration 配置变成了 OkHttpFeignLoadBalancedConfiguration：

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@Configuration
@ConditionalOnClass(OkHttpClient.class)
@ConditionalOnProperty("feign.okhttp.enabled")
class OkHttpFeignLoadBalancedConfiguration {

	@Bean
	@ConditionalOnMissingBean(Client.class)
	public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory,
			SpringClientFactory clientFactory, okhttp3.OkHttpClient okHttpClient) {
		OkHttpClient delegate = new OkHttpClient(okHttpClient);
		return new LoadBalancerFeignClient(delegate, cachingFactory, clientFactory);
	}

     //省略...
}

Client实例变成了LoadBalancerFeignClient，只不过LoadBalancerFeignClient中封装了ApacheHttpClient或者OkHttp。

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