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Spring Cloud（三）：Web服务客户端之Feign
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<p>前文介绍了实现客户端负载均衡的Ribbon，但直接使用Ribbon的API来实现服务间的调用相对较为繁琐，服务间的调用能否像本地接口调用一样便捷、透明，更符合编程习惯呢？ Feign就是用来干这事的。</p>
<a id="more"></a>
<h2 id="Feign"><a href="#Feign" class="headerlink" title="Feign"></a>Feign</h2><p>Feign是一个声明式的Web服务客户端，让服务之间的调用变得非常简单——定义带@FeignClient注解的接口，本地直接@Autowired 接口，通过调用接口的方法来实现远程服务的调用。</p>
<p>支持的注解包括Feign注解与JAX-RS（Java API for RESTful Web Services）注解。</p>
<p>每一个Feign的客户端都包含一系列对应的组件，Spring Cloud通过FeignClientsConfiguration 为每一个命名的Feign客户端创建一个组件集合，包括feign.Decoder，feign.Encoder，feign.Contract等。</p>
<p>Feign提供的默认bean实现及说明</p>
<table>
<thead>
<tr>
<th align="center">Bean类型</th>
<th align="center">默认实现类</th>
<th align="center">说明</th>
</tr>
</thead>
<tbody><tr>
<td align="center">Decoder</td>
<td align="center">ResponseEntityDecoder</td>
<td align="center">ResponseEntityDecoder封装了SpringDecoder，解码器，将服务的响应消息进行解码</td>
</tr>
<tr>
<td align="center">Encoder</td>
<td align="center">SpringEncoder</td>
<td align="center">编码器</td>
</tr>
<tr>
<td align="center">Logger</td>
<td align="center">Slf4jLogger</td>
<td align="center">日志框架</td>
</tr>
<tr>
<td align="center">Contract</td>
<td align="center">SpringMvcContract</td>
<td align="center">支持注解契约，使用SpringMvcContract可以对Spring MVC注解提供支持</td>
</tr>
<tr>
<td align="center">Feign.Builder</td>
<td align="center">HystrixFeign.Builder</td>
<td align="center">使用断路器来装饰Feign接口</td>
</tr>
<tr>
<td align="center">Client</td>
<td align="center">LoadBalancerFeignClient</td>
<td align="center">如果是ribbon则 LoadBalancerFeignClient， 如果是spring cloud LoadBalancer 则 FeignBlockingLoadBalancerClient，默认ribbon</td>
</tr>
</tbody></table>
<p>跟Ribbon类似，可以通过配置类来自定义Feign客户端，如</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@FeignClient</span>(name = <span class="string">"hello-service"</span>, configuration = CustomConfiguration<span class="class">.<span class="keyword">class</span>)</span></span><br><span class="line"><span class="class"><span class="title">public</span> <span class="title">interface</span> <span class="title">StoreClient</span> </span>{</span><br><span class="line"> <span class="comment">//..</span></span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">CustomConfiguration</span> </span>{</span><br><span class="line"> <span class="meta">@Bean</span></span><br><span class="line"> <span class="function"><span class="keyword">public</span> Contract <span class="title">feignContract</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">new</span> feign.Contract.Default();</span><br><span class="line"> }</span><br><span class="line"> <span class="meta">@Bean</span></span><br><span class="line"> <span class="function"><span class="keyword">public</span> BasicAuthRequestInterceptor <span class="title">basicAuthRequestInterceptor</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">new</span> BasicAuthRequestInterceptor(<span class="string">"user"</span>, <span class="string">"password"</span>);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>这样Feign客户端就包含了FeignClientsConfiguration 与CustomConfiguration 中定义的组件，并且后者会覆盖前者（即自定义配置的优先级高于默认配置）。</p>
<blockquote>
<p>自定义配置类不需要加注解@Configuration，如果加了且被@ComponentScan扫描到，则将成为所有Feign客户端的默认配置</p>
</blockquote>
<p>同样Feign客户端也支持通过配置文件来配置</p>
<figure class="highlight yaml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="attr">feign:</span></span><br><span class="line"> <span class="attr">client:</span></span><br><span class="line"> <span class="attr">config:</span></span><br><span class="line"> <span class="attr">feignName:</span></span><br><span class="line"> <span class="attr">connectTimeout:</span> <span class="number">5000</span></span><br><span class="line"> <span class="attr">readTimeout:</span> <span class="number">5000</span></span><br><span class="line"> <span class="attr">loggerLevel:</span> <span class="string">full</span></span><br><span class="line"> <span class="attr">errorDecoder:</span> <span class="string">com.example.SimpleErrorDecoder</span></span><br><span class="line"> <span class="attr">retryer:</span> <span class="string">com.example.SimpleRetryer</span></span><br><span class="line"> <span class="attr">requestInterceptors:</span></span><br><span class="line"> <span class="bullet">-</span> <span class="string">com.example.FooRequestInterceptor</span></span><br><span class="line"> <span class="bullet">-</span> <span class="string">com.example.BarRequestInterceptor</span></span><br><span class="line"> <span class="attr">decode404:</span> <span class="literal">false</span></span><br><span class="line"> <span class="attr">encoder:</span> <span class="string">com.example.SimpleEncoder</span></span><br><span class="line"> <span class="attr">decoder:</span> <span class="string">com.example.SimpleDecoder</span></span><br><span class="line"> <span class="attr">contract:</span> <span class="string">com.example.SimpleContract</span></span><br></pre></td></tr></table></figure>
<p>对于应用于所有Feign客户端的全局默认配置，也可以通过两种方式</p>
<ol>
<li>通过@EnableFeignClients 的defaultConfiguration 属性指定默认配置类</li>
<li>在配置文件中通过名称为default的配置实现<figure class="highlight yaml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="attr">feign:</span></span><br><span class="line"> <span class="attr">client:</span></span><br><span class="line"> <span class="attr">config:</span></span><br><span class="line"> <span class="attr">default:</span></span><br><span class="line"> <span class="attr">connectTimeout:</span> <span class="number">5000</span></span><br><span class="line"> <span class="attr">readTimeout:</span> <span class="number">5000</span></span><br><span class="line"> <span class="attr">loggerLevel:</span> <span class="string">basic</span></span><br></pre></td></tr></table></figure>
</li>
</ol>
<p>优先级同Ribbon， 配置文件>自定义配置类>默认的FeignClientsConfiguration</p>
<h2 id="案例演示"><a href="#案例演示" class="headerlink" title="案例演示"></a>案例演示</h2><p>本文案例演示基于前面搭建的springcloud-eureka 与 springcloud-eureka-client 两个示例项目。</p>
<ol>
<li><p>新建springcloud-feign项目，pom.xml中加入依赖</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag"><<span class="name">dependency</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">groupId</span>></span>org.springframework.cloud<span class="tag"></<span class="name">groupId</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">artifactId</span>></span>spring-cloud-starter-netflix-eureka-client<span class="tag"></<span class="name">artifactId</span>></span></span><br><span class="line"><span class="tag"></<span class="name">dependency</span>></span></span><br><span class="line"><span class="tag"><<span class="name">dependency</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">groupId</span>></span>org.springframework.cloud<span class="tag"></<span class="name">groupId</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">artifactId</span>></span>spring-cloud-starter-openfeign<span class="tag"></<span class="name">artifactId</span>></span></span><br><span class="line"><span class="tag"></<span class="name">dependency</span>></span></span><br><span class="line"><span class="tag"><<span class="name">dependency</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">groupId</span>></span>org.springframework.boot<span class="tag"></<span class="name">groupId</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">artifactId</span>></span>spring-boot-starter-web<span class="tag"></<span class="name">artifactId</span>></span></span><br><span class="line"><span class="tag"></<span class="name">dependency</span>></span></span><br></pre></td></tr></table></figure>
<p>spring-cloud-starter-openfeign 包含了spring-cloud-starter-netflix-ribbon 与 spring-cloud-starter-loadbalancer。</p>
</li>
<li><p>启动类加上@EnableFeignClients 注解</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@SpringBootApplication</span></span><br><span class="line"><span class="meta">@EnableFeignClients</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">FeignApplication</span> </span>{</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> </span>{</span><br><span class="line"> SpringApplication.run(FeignApplication<span class="class">.<span class="keyword">class</span>, <span class="title">args</span>)</span>;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
</li>
<li><p>定义Feign client（feign client支持继承）</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@FeignClient</span>(<span class="string">"hello-service"</span>)</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">interface</span> <span class="title">HelloClient</span> <span class="keyword">extends</span> <span class="title">BaseHelloClient</span></span>{</span><br><span class="line"></span><br><span class="line"> <span class="meta">@RequestMapping</span>(<span class="string">"hello/param"</span>)</span><br><span class="line"> <span class="function">String <span class="title">hello</span><span class="params">(@SpringQueryMap QueryParam param)</span></span>;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
</li>
<li><p>调用Feign client</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@RestController</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">FeignController</span> </span>{</span><br><span class="line"></span><br><span class="line"> <span class="meta">@Autowired</span></span><br><span class="line"> <span class="keyword">private</span> HelloClient helloClient;</span><br><span class="line"></span><br><span class="line"> <span class="meta">@RequestMapping</span>(<span class="string">"feign"</span>)</span><br><span class="line"> <span class="function"><span class="keyword">public</span> String <span class="title">feignTest</span><span class="params">()</span></span>{</span><br><span class="line"> <span class="keyword">return</span> <span class="string">"调用Hello-service返回： "</span> + helloClient.hello();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="meta">@RequestMapping</span>(<span class="string">"feign/param"</span>)</span><br><span class="line"> <span class="function"><span class="keyword">public</span> String <span class="title">feignTestParam</span><span class="params">(QueryParam param)</span> </span>{</span><br><span class="line"> <span class="keyword">return</span> <span class="string">"调用Hello-service返回： "</span> + helloClient.hello(param);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
</li>
</ol>
<p>依次启动三个项目，调用<a href="http://localhost:8083/feign" target="_blank" rel="noopener">http://localhost:8083/feign</a> 能正常返回调用hello-service的结果。</p>
<p>本示例项目还通过@SrpingQueryMap 注解实现了Feign对 pojo用于GET请求参数的支持。如果不加@SrpingQueryMap， 则pojo参数是无法通过Feign client传递的，可去掉注解自行验证下。</p>
<h2 id="一些知识点"><a href="#一些知识点" class="headerlink" title="一些知识点"></a>一些知识点</h2><ol>
<li><p>如果需要定制化产生的查询参数map，可以实现并注入一个自定义的 QueryMapEncoder bean</p>
</li>
<li><p>Feign client的日志可通过feign client接口的全路径名进行配置，如logging.level.project.user.UserClient: DEBUG，默认为NONE（即不打印日志）。全局设置</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Configuration</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">FooConfiguration</span> </span>{</span><br><span class="line"> <span class="meta">@Bean</span></span><br><span class="line"> Logger.<span class="function">Level <span class="title">feignLoggerLevel</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="keyword">return</span> Logger.Level.FULL;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>可设置的level值</p>
</li>
</ol>
<ul>
<li>NONE： 不记录日志 ，默认</li>
<li>BASIC：只记录请求方法，url，以及响应状态码与执行时间</li>
<li>HEADERS：包括BASIC与请求、响应头</li>
<li>FULL：包括请求与响应的headers，body，metadata</li>
</ul>
<ol start="3">
<li><p>Feign默认使用Ribbon来做负载均衡，可通过配置spring.cloud.loadbalancer.ribbon.enabled=false 来使用spring cloud loadbalancer（目前Ribbon处于维护状态，近期内不做更新）</p>
</li>
<li><p>可通过配置feign.okhttp.enabled=true 或 feign.httpclient.enabled=true 来使用OkHttpClient 或ApacheHttpClient， 默认使用的是JDK 原生的URLConnection 发送HTTP请求，没有连接池</p>
</li>
<li><p>如果需要在RequestInterceptor 中使用ThreadLocal中的变量， 那么要么禁用Hystrix，要么设置hystrix的线程隔离策略为SEMAPHORE</p>
<figure class="highlight yaml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="attr">feign:</span></span><br><span class="line"> <span class="attr">hystrix:</span></span><br><span class="line"> <span class="attr">enabled:</span> <span class="literal">false</span></span><br><span class="line"><span class="comment"># 或者</span></span><br><span class="line"><span class="attr">hystrix:</span></span><br><span class="line"> <span class="attr">command:</span></span><br><span class="line"> <span class="attr">default:</span></span><br><span class="line"> <span class="attr">execution:</span></span><br><span class="line"> <span class="attr">isolation:</span></span><br><span class="line"> <span class="attr">strategy:</span> <span class="string">SEMAPHORE</span></span><br></pre></td></tr></table></figure>
</li>
<li><p>使用有Hystrix fallback的Feign时，会在ApplicationContext中存在多个同类型bean， 导致@Autowired 失效。为了解决这个问题，Spring cloud netflix 将所有feign实例标为@Primary，如果要关闭该特性， 可将@FeignClient的 primary属性置为false。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@FeignClient</span>(name = <span class="string">"hello"</span>, primary = <span class="keyword">false</span>)</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">interface</span> <span class="title">HelloClient</span> </span>{</span><br><span class="line"> <span class="comment">// ...</span></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
</li>
</ol>
<p><a href="https://github.com/ronwxy/springcloud-demos" target="_blank" rel="noopener">本文示例代码</a></p>
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<ol class="toc"><li class="toc-item toc-level-2"><a class="toc-link" href="#Feign"><span class="toc-text">Feign</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#案例演示"><span class="toc-text">案例演示</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#一些知识点"><span class="toc-text">一些知识点</span></a></li></ol>
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