文章首发：Spring Cloud OpenFeign入门和实战

OpenFeign是什么

Feign是一个声明式的Web Service客户端，是一种声明式、模板化的HTTP客户端。而OpenFeign是Spring Cloud 在Feign的基础上支持了Spring MVC的注解，如@RequesMapping等等。
OpenFeign的@FeignClient可以解析SpringMVC的@RequestMapping注解下的接口，并通过动态代理的方式产生实现类，实现类中做负载均衡并调用其他服务。
Feign可以把Rest的请求进行隐藏，伪装成类似SpringMVC的Controller一样。你不用再自己拼接url，拼接参数等等操作，一切都交给Feign去做。

可插拔的注解支持，包括Feign注解和JSX-RS注解
支持可插拔的HTTP编码器和解码器
支持Hystrix和它的Fallback
支持Ribbon的负载均衡
支持HTTP请求和响应的压缩。

OpenFeign入门

创建父Pom工程：cloud-openfeign-practice

此工程用于存放所有关于openfeign的示例。

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.msr.better</groupId>
    <artifactId>cloud-openfeign-practice</artifactId>
    <version>1.0</version>
    <packaging>pom</packaging>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.3.RELEASE</version>
        <relativePath></relativePath> <!-- lookup parent from repository -->
    </parent>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <spring.cloud-version>Hoxton.SR3</spring.cloud-version>
    </properties>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring.cloud-version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

创建模块：cloud-openfeign-hehllo

pom.xml

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
    </dependencies>

配置文件

application.xml

server:
  port: 8010
spring:
  application:
    name: openfeign-hello
# 日志
logging:
  level:
    com.msr.better.feign.service.HelloFeignService: debug

配置类

@Configuration
public class HelloFeignServiceConfig {
    /**
     * Logger.Level 的具体级别如下：
     * NONE：不记录任何信息
     * BASIC：仅记录请求方法、URL以及响应状态码和执行时间
     * HEADERS：除了记录 BASIC级别的信息外，还会记录请求和响应的头信息
     * FULL：记录所有请求与响应的明细，包括头信息、请求体、元数据
     */
    @Bean
    Logger.Level feignLoggerLevel() {
        return Logger.Level.FULL;
    }
}

serivce

@FeignClient(name = "github-client", url = "https://api.github.com", configuration = HelloFeignServiceConfig.class)
public interface HelloFeignService {
    /**
     * content:
     * {
     *  "message":"Validation Failed",
     *  "errors":[{"resource":"Search","field":"q","code":"missing"}],
     *  "documentation_url":"https://developer.github.com/v3/search"
     *  }
     *
     * @param queryStr
     * @return
     */
    @GetMapping(value = "/search/repositories")
    String searchRepo(@RequestParam("q") String queryStr);
}

在上面的HelloFeignService中通过@FeignClient注解手动指定了该接口要访问的URL(https://api.github.com)，调用searchGithubRepoByStr方法时，最终会发起GET请求https://api.github.com/search/repositories?q=输入的参数。

controller

@RestController
public class HelloFeignController {
    @Autowired
    private HelloFeignService helloFeignService;
    @GetMapping(value = "/search/github")
    public String searchGithubRepoByStr(@RequestParam("searchStr") String searchStr) {
        return helloFeignService.searchRepo(searchStr);
    }
}

启动类

@SpringBootApplication
@EnableFeignClients
public class OpenFeignHelloApplication {
    public static void main(String[] args) {
        SpringApplication.run(OpenFeignHelloApplication.class, args);
    }
}

@EnableFeignClients包扫描时，扫描所有@FeignClient。

启动测试

运行启动类之后，在浏览器或者PostMan之类的工具访问http://localhost:8010/search/github?searchStr=spring-cloud

OpenFeign工作原理

添加@EnableFeignClients注解开启对@FeignClient注解的扫描加载处理。根据Feign Client的开发规范，定义接口并添加@FeiginClient注解
当程序启动之后，会进行包扫描，扫描所有@FeignClient注解的接口，并将这些信息注入到IOC容器中。当定义的Feign接口被调用时，通过JDK的代理的方式生成具体的RequestTemplate。Feign会为每个接口方法创建一个RequestTemplate对象。该对象封装了HTTP请求需要的所有信息，例如请求参数名、请求方法等信息。
然后由RequestTemplate生成Request，把Request交给Client去处理，这里的Client可以是JDK原生的URLConnection、HttpClient或Okhttp。最后Client被封装到LoadBalanceClient类，看这个类的名字既可以知道是结合Ribbon负载均衡发起服务之间的调用，因为在OpenFeign中默认是已经整合了Ribbon了。

OpenFiegn的基础功能

剖析@FeignClient注解

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface FeignClient {...}

从FeignClient的注解可以看得出，ElementType.TYPE说明FeignClient的作用目标是接口。其常用的属性如下：

name：执行FeignClient的名称，如果项目中使用Ribbon，name属性会作为微服务的名称，用作服务发现。
url：url一般用于调试，可以手动指定@FeignClient调用的地址
decode404：当发生404错误时，如果该字段为true，会调用decoder进行解码，否则抛出FeignException。
configuration：Feigin配置类，可自定义Feign的Encode，Decode，LogLevel，Contract。
fallback：定义容错的类，当远程调用的接口失败或者超时的时候，会调用对应接口的容错罗杰，fallback执行的类必须实现@FeignClient标记的接口。在OpenFeign的依赖中可以发现，集成Hystrix。
fallbackFactory：工厂类，用于生成fallback类实例，通过此属性可以实现每个接口通用的容错逻辑，以达到减少重复的代码。
path：定义当前FeignClient的统一前缀。

OpenFeign开始GZIP压缩

OpenFeign支持对请求和响应进行GZIP压缩，以此来提供通信效率。只需在配置文件中配置即可，比较简单。

server:
  port: 8011
spring:
  application:
    name: openfeign-gzip
logging:
  level:
    com.msr.better.feign.service.HelloFeignService: debug
feign:
  # 压缩配置
  compression:
    request:
      enabled: true
      # 配置压缩支持的MIME TYPE
      mime-types: text/xml,application/xml,application/json
      min-request-size: 2048  # 配置压缩数据大小的下限
    response:
      enabled: true # 配置响应GZIP压缩

等价的properties配置

feign.compression.request.enabled=true
# 配置压缩支持的MIME TYPE
feign.compression.request.mime-types=text/xml,application/xml,application/json
# 配置压缩数据大小的下限
feign.compression.request.min-request-size=2048
# 配置响应GZIP压缩
feign.compression.response.enabled=true

支持属性文件配置

对单个特定名称的FeignClient进行配置

@FeignClientde的配置信息可以通过配置文件的方式来配置

server:
  port: 8011
spring:
  application:
    name: openfeign-gzip
logging:
  level:
    com.msr.better.feign.service.HelloFeignService: debug
feign:
  # 压缩配置
  compression:
    request:
      enabled: true
      # 配置压缩支持的MIME TYPE
      mime-types: text/xml,application/xml,application/json
      min-request-size: 2048  # 配置压缩数据大小的下限
    response:
      enabled: true # 配置响应GZIP压缩
  client:
    config:
      # 需要配置的FeignName
      github-client:
        # 连接超时时间
        connectTimout: 5000
        # 读超时时间
        readTimeut: 5000
        # Feign的日志级别
        loggerLevel: full
        # Feign的错误解码器
        errorDecode: com.example.SimpleErrorDecoder
        # 设置重试
        retryer: com.example.SimpleRetryer
        # 拦截前
        requestInterceptors:
          - com.example.FirstInterceptor
          - com.example.SecondInterceptor
        decode404: false
        # Feign的编码器
        encoder: com.example.SimpleEncoder
        # Feign的解码器
        decoder: com.example.SimpleDecoder
        # Feign的contract配置
        contract: com.example.SimpleContract

作用于所有FeignClient的配置

在@EnableFeignClients注解上有一个defaultConfiguration属性，可以将默认设置写成一个配置类，例如这个类叫做DefaultFeignClientConfiguration。

@SpringBootApplication
@EnableFeignClients(defaultConfiguration = DefaultFeignClientConfiguration.class)
public class FeignClientConfigApplication{
    SpringApplication.run(FeignClientConfigApplication.class, args);
}

同时也可以在配置文件中配置

feign:
  client:
    config:
      default:
        # 连接超时时间
        connectTimout: 5000
        # 读超时时间
        readTimeut: 5000
        # Feign的日志级别
        loggerLevel: full
        ...

但是如果以上两种方式(在配置文件和在注解中配置FeignClient的全局配置)，最后配置文件会覆盖注解上执行配置类的方式。但是可以在配置文件中添加feign.client.default-to-properties=false来改变Feigin配置的优先级。

FeignClient开启日志

其实在上面的就已经是配置了FeignClient的日志了。Feign为每一个Feign都提供了一个fegin.Logger实例。可以在配置中开启日志输出，开启的步骤也很简单。

第一步：在配置文件中配置日志输出

logging:
  level:
    # 指定那个FeignClient接口的请求需要输出日志，以及日志级别
    com.msr.better.feign.service.HelloFeignService: debug

第二步：通过Java代码的方式在主程序入口配置日志Bean


    @Bean
    Logger.Level feignLoggerLevel() {
        return Logger.Level.FULL;
    }

又或者通过配置类配置，并在@FeignClient注解中执行改配置类。

@Configuration
public class HelloFeignServiceConfig {
    /**
     * Logger.Level 的具体级别如下：
     * NONE：不记录任何信息
     * BASIC：仅记录请求方法、URL以及响应状态码和执行时间
     * HEADERS：除了记录 BASIC级别的信息外，还会记录请求和响应的头信息
     * FULL：记录所有请求与响应的明细，包括头信息、请求体、元数据
     */
    @Bean
    Logger.Level feignLoggerLevel() {
        return Logger.Level.FULL;
    }
}

FeignClient超时配置

Feign的调用分为两层，Ribbon的调用和Hystrix的调用。但是高版本的Hystrix默认是关闭的。一般出现想这样的异常：Read timed out executing POST http://***，是由Ribbon引起，这样可以适当得调大一下Ribbon的超时时间

ribbon:
  ConnectTimeout: 2000
  ReadTimeout: 5000

HystrixRuntimeException: XXX timed -out and no fallback available .这就是Hystrix的超时报错

feign:
  hystrix:
    enabled: true
# 设置hystrix超时时间
hystrix:
  shareSecurityContext: true
  command:
    default:
      circuitBreaker:
        sleepWindowinMilliseconds: 10000
        forceClosed: true
      execution:
        isolation:
          thread:
            timeoutinMilliseconds: 10000

OpenFeign实战

替换默认的Client

Feign默认是使用JDK原生的URLConnection发送HTTP请求，没有连接池，但是对每个地址会保持一个长连接，就是利用HTTP的persistence connection.。这样可以使用其他优秀的Client去替换。这样可以设置连接池，超时时间等对服务之间的调用调优。下面介绍使用Http Client和Okhttp替换Feign默认的Client。步骤也很简单。

使用Http Client替换默认的Client

pom.xml

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!-- Spring Cloud OpenFeign的Starter的依赖 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <!-- 使用Apache HttpClient替换Feign原生httpclient -->
        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpclient</artifactId>
        </dependency>
        <dependency>
            <groupId>io.github.openfeign</groupId>
            <artifactId>feign-httpclient</artifactId>
        </dependency>
    </dependencies>

application.yml

server:
  port: 8010
spring:
  application:
    name: openfeign-httpclient
feign:
  httpclient:
    enabled: true

关于Http Client的一些配置也是可以在配置文件中配置的

在org.springframework.cloud.openfeign.clientconfig.HttpClientFeignConfiguration中是关于HttpClient的配置：

@Configuration(
    proxyBeanMethods = false
)
@ConditionalOnMissingBean({CloseableHttpClient.class})
public class HttpClientFeignConfiguration {
    private final Timer connectionManagerTimer = new Timer("FeignApacheHttpClientConfiguration.connectionManagerTimer", true);
    private CloseableHttpClient httpClient;
    @Autowired(
        required = false
    )
    private RegistryBuilder registryBuilder;
    public 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
    @ConditionalOnProperty(
        value = {"feign.compression.response.enabled"},
        havingValue = "true"
    )
    public CloseableHttpClient customHttpClient(HttpClientConnectionManager httpClientConnectionManager, FeignHttpClientProperties httpClientProperties) {
        HttpClientBuilder builder = HttpClientBuilder.create().disableCookieManagement().useSystemProperties();
        this.httpClient = this.createClient(builder, httpClientConnectionManager, httpClientProperties);
        return this.httpClient;
    }
    @Bean
    @ConditionalOnProperty(
        value = {"feign.compression.response.enabled"},
        havingValue = "false",
        matchIfMissing = true
    )
    public CloseableHttpClient httpClient(ApacheHttpClientFactory httpClientFactory, HttpClientConnectionManager httpClientConnectionManager, FeignHttpClientProperties httpClientProperties) {
        this.httpClient = this.createClient(httpClientFactory.createBuilder(), httpClientConnectionManager, httpClientProperties);
        return this.httpClient;
    }
    private CloseableHttpClient createClient(HttpClientBuilder builder, HttpClientConnectionManager httpClientConnectionManager, FeignHttpClientProperties httpClientProperties) {
        RequestConfig defaultRequestConfig = RequestConfig.custom().setConnectTimeout(httpClientProperties.getConnectionTimeout()).setRedirectsEnabled(httpClientProperties.isFollowRedirects()).build();
        CloseableHttpClient httpClient = builder.setDefaultRequestConfig(defaultRequestConfig).setConnectionManager(httpClientConnectionManager).build();
        return httpClient;
    }
    @PreDestroy
    public void destroy() throws Exception {
        this.connectionManagerTimer.cancel();
        if (this.httpClient != null) {
            this.httpClient.close();
        }
    }
}

很明显当没有CloseableHttpClient这个bean的时候，就是会由这个类来生成Http Client的默认配置。所以说对于HttpClient的自定义配置可以通过自己注入CloseableHttpClient。还有HttpClientConnectionManager管理连接的bean。其实OpenFeign对HttpClient的支持很好，因为它的一些属性可以在配置文件中配置。

使用Okhttp替换默认的Client

其实和Http Client一样的配置，也是在配置文件中开启

pom.xml

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!-- Spring Cloud OpenFeign的Starter的依赖 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <dependency>
            <groupId>io.github.openfeign</groupId>
            <artifactId>feign-okhttp</artifactId>
        </dependency>
    </dependencies>

application.yml

server:
  port: 8011
spring:
  application:
    name: openfeign-okhttp
feign:
  okhttp:
    enabled: true
# 日志
logging:
  level:
    com.msr.better.feign.service.HelloFeignService: debug

这样开启之后，Client就被替换了。同理在org.springframework.cloud.openfeign.clientconfig包下，也有一个关于Okhttp的配置类。

@Configuration(
    proxyBeanMethods = false
)
@ConditionalOnMissingBean({OkHttpClient.class})
public class OkHttpFeignConfiguration {
    private OkHttpClient okHttpClient;
    public 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 OkHttpClient client(OkHttpClientFactory httpClientFactory, ConnectionPool connectionPool, FeignHttpClientProperties httpClientProperties) {
        Boolean followRedirects = httpClientProperties.isFollowRedirects();
        Integer connectTimeout = httpClientProperties.getConnectionTimeout();
        this.okHttpClient = httpClientFactory.createBuilder(httpClientProperties.isDisableSslValidation()).connectTimeout((long)connectTimeout, TimeUnit.MILLISECONDS).followRedirects(followRedirects).connectionPool(connectionPool).build();
        return this.okHttpClient;
    }
    @PreDestroy
    public void destroy() {
        if (this.okHttpClient != null) {
            this.okHttpClient.dispatcher().executorService().shutdown();
            this.okHttpClient.connectionPool().evictAll();
        }
    }
}

很明显OkHttpClient是核心功能执行的类。因为OpenFeign中有一个类FeignHttpClientProperties，有了这个类关于HttpClient的属性就可以在配置文件中设置了。但是Okhttp没有这一个类似的类，所以一般可以自己注入一个OkHttpClient去设置这些属性

@Configuration
@ConditionalOnClass(Feign.class)
@AutoConfigureBefore(FeignAutoConfiguration.class)
public class OkHttpConfig {
    @Bean
    public okhttp3.OkHttpClient okHttpClient() {
        return new okhttp3.OkHttpClient.Builder()
                //设置连接超时
                .connectTimeout(60, TimeUnit.SECONDS)
                //设置读超时
                .readTimeout(60, TimeUnit.SECONDS)
                //设置写超时
                .writeTimeout(60, TimeUnit.SECONDS)
                //是否自动重连
                .retryOnConnectionFailure(true)
                .connectionPool(new ConnectionPool())
                //构建OkHttpClient对象
                .build();
    }
}

关于自定义OkHttpClient的配置，可以参考OpenFeign里OkHttpFeignConfiguration的配置，例如ConnectionPool这个bean。

Post和Get的多参数传递

在使用OpenFeign实现服务之间的调用时，很多时候是要传递多个参数。

创建cloud-openfeign-eureka-server模块

Eureka Server注册中心

    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <!-- springboot web -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <exclusions>
                <exclusion>
                    <artifactId>spring-boot-starter-tomcat</artifactId>
                    <groupId>org.springframework.boot</groupId>
                </exclusion>
            </exclusions>
        </dependency>
        <!--不用Tomcat,使用undertow -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-undertow</artifactId>
        </dependency>
        <dependency>
            <groupId>io.undertow</groupId>
            <artifactId>undertow-servlet</artifactId>
        </dependency>
    </dependencies>

配置文件application.yml

server:
  port: 8761
eureka:
  instance:
    hostname: localhost
  server :
    enable-self-preservation: false
  client:
    registerWithEureka: false
    fetchRegistry: false
    serviceUrl:
      defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/

启动类

@SpringBootApplication
@EnableEurekaServer
public class EurekaApplication {
    public static void main(String[] args) {
        SpringApplication.run(EurekaApplication.class, args);
    }
}

创建cloud-openfeign-provider模块

服务提提供者

    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
    </dependencies>

配置文件application.yml

server:
  port: 8012
spring:
  application:
    name: openfeign-provider
eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
  #eureka.instance.prefer-ip-address  表示将自己的IP注册到Eureka Server上，
  #如果不配置,会将当前服务提供者所在的主机名注册到Eureka Server上。
  instance:
    prefer-ip-address: true

实体类和控制器

public class Order {
    private Long id;
    private String name;
    private int age;
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
}

@RestController
@RequestMapping("/order")
public class OrderController {
    @GetMapping(value = "/add")
    public String addUser(Order order, HttpServletRequest request) {
        String token = request.getHeader("oauthToken");
        return "hello," + order.getName();
    }
    @PostMapping(value = "/update")
    public String updateUser(@RequestBody Order order) {
        return "hello," + order.getName();
    }
}

启动类

@SpringBootApplication
@EnableDiscoveryClient
public class ProviderApplication {
    public static void main(String[] args) {
        SpringApplication.run(ProviderApplication.class, args);
    }
}

创建cloud-openfeign-consumer模块

消费者服务

<dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <!-- 使用Apache HttpClient替换Feign原生httpclient -->
        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpclient</artifactId>
        </dependency>
        <dependency>
            <groupId>io.github.openfeign</groupId>
            <artifactId>feign-httpclient</artifactId>
        </dependency>
    </dependencies>

配置文件application.yml

server:
  port: 8011
spring:
  application:
    name: openfeign-consumer
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka
feign:
  httpclient:
    enabled: true

实体类

package com.msr.better.feign.model;
public class Order {
    private Long id;
    private String name;
    private int nums;
    // 此处省略了getter和setter
}

FeignClient接口

@FeignClient("openfeign-provider")
public interface OrderApiService {
    @GetMapping(value = "/order/add")
    String addUser(@SpringQueryMap Order order);
    @PostMapping(value = "/order/update")
    String updateUser(@RequestBody Order order);
}

此处的Client接口中对于GET请求传递实体类使用了注解@SpringQueryMap。OpenFeign@QueryMap批注支持将POJO用作GET参数映射。但是默认的OpenFeign QueryMap注释与Spring不兼容，因为它缺少value属性。

Spring Cloud OpenFeign提供了等效的@SpringQueryMap注释，该注释用于将POJO或Map参数注释为查询参数映射。

在一些资料中说什么OpenFeign的什么GET不能传递POJO，写了个拦截器把实体类转换了，估计是OpenFeign的版本低，在新的OpenFeign中是有了对QueryMap的支持了。

配置类

@Configuration
public class CoreAutoConfiguration {
    @Autowired
    private HttpClient httpClient;
    @Bean
    public HttpComponentsClientHttpRequestFactory httpComponentsClientHttpRequestFactory() {
        HttpComponentsClientHttpRequestFactory factory = new HttpComponentsClientHttpRequestFactory();
        factory.setHttpClient(httpClient);
        factory.setReadTimeout(3000);
        factory.setConnectTimeout(3000);
        factory.setConnectionRequestTimeout(3000);
        return factory;
    }
    /**
     * {@link RestTemplate }的setRequestFactory方法支持HttpClient和Okhttp等Client
     * 默认是使用{@link SimpleClientHttpRequestFactory } Http的请求是使用原生的URLConnection
     *
     * @return RestTemplate的bean
     */
    @LoadBalanced
    @Bean
    public RestTemplate restTemplate() {
        RestTemplate restTemplate = new RestTemplate();
        restTemplate.setRequestFactory(httpComponentsClientHttpRequestFactory());
        return restTemplate;
    }
}

上面是替换了RestTemplate的Client。因为RestTemplate默认是使用URLConnection。这里是使用HttpClient替换了。

控制器

@RestController
@RequestMapping("api")
public class OrderController {
    @Autowired
    private OrderApiService orderApiService;
    /**
     * @param order
     * @return
     */
    @PostMapping("/get/pojo")
    public String getPojo(@RequestBody Order order) {
        return orderApiService.addUser(order);
    }
    @PostMapping("/post/pojo")
    String postPojo(@RequestBody Order order){
        return orderApiService.updateUser(order);
    }
}

最后就可以测试http://localhost:8011/get/pojo和http://localhost:8011/post/pojo了。

文件上传

继续使用上一节创建的Eureka Server。然后创建一下两个模块用作文件上传。

想要实现文件上传功能，需要编写Encoder去实现文件上传。现在OpenFeign提供了子项目feign-form(https://github.com/OpenFeign/feign-form)

创建cloud-openfeign-fileupload-server

文件上传接口的提供者

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
    </dependencies>

配置文件application.yml

server:
  port: 8012
spring:
  application:
    name: openfeign-file-server
eureka:
  server:
    enableSelfPreservation: false
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
  instance:
    prefer-ip-address: true

启动类

@SpringBootApplication
@EnableDiscoveryClient
public class UploadServerApplication {
    public static void main(String[] args) {
        SpringApplication.run(UploadServerApplication.class, args);
    }
}

上传接口

@RestController
public class FileController {
    @PostMapping(value = "/uploadFile/server", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    public String fileUploadServer(MultipartFile file) {
        // save file and return file address
        return "http://localhost/" + file.getOriginalFilename();
    }
}

创建cloud-openfeign-fileupload-client

文件上传接口的调用者

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <!-- Spring Cloud OpenFeign的Starter的依赖 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <!-- Feign文件上传依赖-->
        <dependency>
            <groupId>io.github.openfeign.form</groupId>
            <artifactId>feign-form</artifactId>
            <version>3.8.0</version>
        </dependency>
        <dependency>
            <groupId>io.github.openfeign.form</groupId>
            <artifactId>feign-form-spring</artifactId>
        </dependency>
    </dependencies>

配置文件application.yml

server:
  port: 8011
spring:
  application:
    name: openfeign-upload-client
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka

启动类：

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class UploadClientApplication {
    public static void main(String[] args) {
        SpringApplication.run(UploadClientApplication.class, args);
    }
}

配置类

@Configuration
public class FeignMultipartSupportConfig {
    @Bean
    @Primary
    @Scope("prototype")
    public Encoder multipartFormEncoder() {
        return new SpringFormEncoder();
    }
}

控制器

@RestController
@RequestMapping("file")
public class FeignUploadController {
    @Autowired
    private FileUploadApiService fileUploadApiService;
    @PostMapping(value = "/upload", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    public String imageUpload(MultipartFile file) throws Exception {
        return fileUploadApiService.fileUpload(file);
    }
}

FeignClient

@FeignClient(value = "openfeign-file-server", configuration = FeignMultipartSupportConfig.class)
public interface FileUploadApiService {
    /***
     * 1.produces,consumes必填
     * 2.注意区分@RequestPart和RequestParam，不要将
     * @RequestPart(value = "file") 写成@RequestParam(value = "file")
     * @param file
     * @return
     */
    @PostMapping(value = "/uploadFile/server",
            produces = {MediaType.APPLICATION_JSON_UTF8_VALUE},
            consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    String fileUpload(@RequestPart(value = "file") MultipartFile file);
}

测试

先启动cloud-openfeign-eureka-server
后启动cloud-openfeign-fileupload-server和cloud-openfeign-fileupload-client
使用PostMan进行测试。最后成功返回文件的名字，文件成功的上传到server上了。如下图：

解决首次请求失败问题

由于OpenFeign整合了Ribbon和Hystrix，可能会出现首次调用失败的问题。

主要原因是：Hystrix默认的超时时间是1秒，如果超过这个时间没有响应，就会进入fallback代码。由于Bean的装配和懒加载的机制，Feign首次请求都会比较慢。如此一来当响应时间大于1秒就会进入fallback而导致请求失败。解决方法：

将Hystrix的超时时间调大，此方法比较好

hystrix:
  command:
    default:
   execution:
        isolation:
          thread:
            timeoutInMillseconds: 5000 # 5秒

禁用Hystrix的超时时间

hystrix:
  command:
    default:
      execution:
        timout:
          enable: false

使用Feign的时候关闭Hystrix，这是不推荐的
```
feign:
  hystrix:
    enable: false
```

返回图片流的处理方式

对于返回的是图片，一般都是字节数组。但是Contrller不能直接返回byte，所以被调用的API返回的类型应该使用Response。

使用上面的文件上传创建的模块中添加一个返回图片的接口。以生成一个二维码为例。

cloud-openfeign-fileupload-server的一些修改

添加新的依赖，使用hutool快速生成二维码

        <dependency>
            <groupId>cn.hutool</groupId>
            <artifactId>hutool-all</artifactId>
            <version>5.6.3</version>
        </dependency>
        <dependency>
            <groupId>com.google.zxing</groupId>
            <artifactId>core</artifactId>
            <version>3.3.3</version>
        </dependency>
        <dependency>
            <groupId>io.github.openfeign</groupId>
            <artifactId>feign-core</artifactId>
        </dependency>

controller的接口，这里仅简单的生成了一个二维码，二维码还可以添加更加多的信息。这里就不详细介绍，hutool的QrCodeUtil有很多方法，有兴趣的可以自行研究。

    @GetMapping(value = "/qrcode")
    public byte[] image() {
        return generateQrCode();
    }
    /**
     * 先简单的生成一个url的二维码,指向百度
     * @return
     */
    private byte[] generateQrCode() {
        return QrCodeUtil.generatePng("https://www.baidu.cn/", 300, 300);
    }

cloud-openfeign-fileupload-client的一些修改

添加新依赖

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.6</version>
</dependency>

feignclient添加新接口

    @GetMapping("/qrcode")
    Response getQrCode();

controller的修改，对于要在前端页面显示图片，一般用的最多的是返回页面一个url，但是这都是存储好的图片，但是每次生成验证码和二维码这些，服务端可能并不会存储起来。所以并不能返回一个url地址，对于验证码用的返回前端Base64编码。二维码的话可以基于HttpServletResponse，produces返回字节流和Base64图片。

这里使用HttpServletResponse，添加方法：

    @GetMapping("/qrcode")
    public void getQrCode(HttpServletResponse response) {
        Response res = fileUploadApiService.getQrCode();
        try {
            InputStream inputStream = res.body().asInputStream();
            response.setContentType(MediaType.IMAGE_PNG_VALUE);
            IOUtils.copy(inputStream,response.getOutputStream());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

浏览器访问:http://localhost:8011/file/qrcode，结果

调用传递token

正常的来说，系统都是有认证鉴权的功能，不管是JWT还是security，在外部请求到A服务时，是带有token过来的，但是此请求在A服务内部通过Feign调用B服务时，就会发生token的丢失。

解决方法也是不难，就是在使用Feign远程调用时，在请求头里携带一下token，一般token是放在请求头里面。

Feign提供的拦截器RequestInterceptor，这样可以拦截Feign的请求，在请求头里添加token。对于这部分代码，在cloud-openfeign-consumer和cloud-openfeign-provider上进行添加。

修改cloud-openfeign-provider

修改一下方法，便于展示结果

    @PostMapping(value = "/update")
    public String updateOrder(@RequestBody Order order, HttpServletRequest request) {
        String token = request.getHeader("token");
        return "hello," + order.getName() + " " + "haha!I get a token: " + token;
    }

修改cloud-openfeign-consumer

添加拦截器实现feign.RequestInterceptor

@Component
public class FeignTokenInterceptor implements RequestInterceptor {
    @Override
    public void apply(RequestTemplate requestTemplate) {
        if (null == getHttpServletRequest()) {
            //此处可以记录一些日志
            return;
        }
        //将获取Token对应的值往下面传
        requestTemplate.header("token", getHeaders(getHttpServletRequest()).get("token"));
    }
    private HttpServletRequest getHttpServletRequest() {
        try {
            return ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();
        } catch (Exception e) {
            return null;
        }
    }
    /**
     * Feign拦截器拦截请求获取Token对应的值
     *
     * @param request
     * @return
     */
    private Map<String, String> getHeaders(HttpServletRequest request) {
        Map<String, String> map = new LinkedHashMap<>();
        Enumeration<String> enumeration = request.getHeaderNames();
        while (enumeration.hasMoreElements()) {
            String key = enumeration.nextElement();
            String value = request.getHeader(key);
            map.put(key, value);
        }
        return map;
    }
}

最后启动服务就可以开始测试了，测试结果：

总结

本文介绍了一些Feign的用法，后续如果有关于Feign新的东西将会新开文章述说。