spring cloud 声明式rest客户端feign调用远程http服务

在Spring Cloud Netflix栈中，各个微服务都是以HTTP接口的形式暴露自身服务的，因此在调用远程服务时就必须使用HTTP客户端。Feign就是Spring Cloud提供的一种声明式REST客户端。可以通过Feign访问调用远端微服务提供的REST接口。现在我们就用Feign来调用SERVICE-HELLOWORLD暴露的REST接口，以获取到“Hello World”信息。在使用Feign时，Spring Cloud集成了Ribbon和Eureka来提供HTTP客户端的负载均衡。

下面我们就采用Feign的方式来调用服务集群。

1. 创建Maven工程，加入spring-cloud-starter-feign依赖

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-feign</artifactId>
        </dependency>

完整的pom.xml

<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>
    <parent>
        <groupId>com.pupeiyuan.springcloud</groupId>
        <artifactId>spring-Cloud</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <artifactId>springcloud-moveServer</artifactId>

    <dependencies>
        <!-- 单元测试 -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <scope>test</scope>
        </dependency>
        <!-- 支持springWEB web支持: 1、web mvc; 2、restful; 3、jackjson支持; 4、aop ........ -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!-- AOP依赖模块 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjrt</artifactId>
            <version>1.8.7</version>
        </dependency>
        <!-- jdbc -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
            <scope>provided</scope>
        </dependency>

        <!-- Mybatis -->
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>1.3.1</version>
        </dependency>
        <!-- 通用Mapper -->
        <dependency>
            <groupId>tk.mybatis</groupId>
            <artifactId>mapper-spring-boot-starter</artifactId>
            <version>RELEASE</version>
        </dependency>
        <!-- 分页助手 -->
        <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper-spring-boot-starter</artifactId>
            <version>1.1.0</version>
        </dependency>
        <dependency>
            <groupId>com.github.jsqlparser</groupId>
            <artifactId>jsqlparser</artifactId>
            <version>0.9.1</version>
        </dependency>

        <!-- mysql 数据库驱动. -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <!-- 连接池 -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.1.9</version>
        </dependency>
        <!-- jstl -->
        <dependency>
            <groupId>jstl</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>
        <dependency>
            <groupId>taglibs</groupId>
            <artifactId>standard</artifactId>
            <version>1.1.2</version>
        </dependency>
        <!-- JSP相关 -->
        <dependency>
            <groupId>com.github.jsqlparser</groupId>
            <artifactId>jsqlparser</artifactId>
            <version>0.9.1</version>
        </dependency>
        <dependency>
            <groupId>org.apache.tomcat.embed</groupId>
            <artifactId>tomcat-embed-jasper</artifactId>
            <scope>provided</scope>
        </dependency>
        <!-- httpclient -->
        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpclient</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <optional>true</optional>
            <scope>true</scope>
        </dependency>

        <!-- spring cloud -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-config</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-eureka</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-bus-amqp</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-feign</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <!-- java编译插件 -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.7</source>
                    <target>1.7</target>
                    <encoding>UTF-8</encoding>
                </configuration>
            </plugin>
            <!-- 这是spring boot devtool plugin -->
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <!--fork : 如果没有该项配置，肯呢个devtools不会起作用，即应用不会restart -->
                    <fork>true</fork>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

2. 创建启动类，需呀加上@EnableFeignClients注解以使用Feign， 使用@EnableDiscoveryClient开启服务自动发现

mainApplication.java

package com.pupeiyuan.config;

import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.web.support.SpringBootServletInitializer;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.context.config.annotation.RefreshScope;
import org.springframework.cloud.netflix.feign.EnableFeignClients;
import org.springframework.cloud.netflix.ribbon.RibbonClient;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.web.client.RestTemplate;

import feign.Logger;

@Configuration
//扫描bean
@ComponentScan(basePackages = "com.pupeiyuan.*")
//不用自动配置数据源
@EnableDiscoveryClient
@SpringBootApplication(exclude=DataSourceAutoConfiguration.class)
@EnableFeignClients(basePackages="com.pupeiyuan.feignClient")
public class MainApplication extends SpringBootServletInitializer {

    @Bean
    Logger.Level feignLoggerLevel() {
        return Logger.Level.FULL;
    }
     //相当于xml中的bean标签 用于调用当前方法获取到指定的对象
    @Bean(name="remoteRestTemplate")
    @LoadBalanced
    public RestTemplate getRestTemplate(){
        return new RestTemplate();
    }
    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
        return builder.sources(MainApplication.class);
    }
}

3. 添加配置文件application-test.properties, 使用端口8085, 名字定义为springcloud-moveServer, 并注册到eureka服务中心

application-test.properties

server.port=8085
server.servlet-path=/

#log4j
#logging.level.org.springframework=DEBUG

#SpringMVC
spring.mvc.view.prefix=/WEB-INF/views/
spring.mvc.view.suffix=.jsp

#mybatis && Mapper
mybatis.configuration.mapUnderscoreToCamelCase=true
mapper.mappers=com.karle.tk.TkMapper
mapper.identity=MYSQL

#banner
banner.charset= UTF-8

#jsp
server.jsp-servlet.init-parameters.development=true

# pagehelper properties
pagehelper.offsetAsPageNum=true
pagehelper.rowBoundsWithCount=true
pagehelper.pageSizeZero=true
pagehelper.reasonable=false
pagehelper.params=pageNum=pageHelperStart;pageSize=pageHelperRows;
pagehelper.supportMethodsArguments=false

#mq
spring.rabbitmq.host=localhost
spring.rabbitmq.port=5672
spring.rabbitmq.username=guest
spring.rabbitmq.password=guest

management.security.enabled=false
logging.level.com.pupeiyuan.feignClient.FeignClient2=DEBUG

bootstrap.properties

spring.application.name=moveServer
spring.cloud.config.discovery.enabled=true
spring.cloud.config.discovery.service-id=pringcloud-configServer
spring.cloud.config.profile=test
spring.cloud.config.label=master

eureka.client.serviceUrl.defaultZone=http://root:123456@peer1:8000/eureka
eureka.instance.prefer-ip-address=true

4. 定义Feign：一个用@FeignClient注解的接口类,UserFeignClient.java

package com.pupeiyuan.feignClient;

import java.util.List;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

import com.pupeiyuan.bean.NhReportStatusHistory;

@FeignClient("MULTIPLE")
public interface UserFeignClient {

      @RequestMapping(value = "/getDate/{id}", method = RequestMethod.GET)
      public List<NhReportStatusHistory> dataList(@PathVariable("id") Long id); // 两个坑：1. @GetMapping不支持   2. @PathVariable得设置value

      /*@RequestMapping(value = "/user", method = RequestMethod.POST)
      public User postUser(@RequestBody User user);

      // 该请求不会成功，只要参数是复杂对象，即使指定了是GET方法，feign依然会以POST方法进行发送请求。可能是我没找到相应的注解或使用方法错误。
      // 如勘误，请@lilizhou2008  eacdy0000@126.com
      @RequestMapping(value = "/get-user", method = RequestMethod.GET)
      public User getUser(User user);*/
        }

Spring Cloud应用在启动时，Feign会扫描标有@FeignClient注解的接口，生成代理，并注册到Spring容器中。生成代理时Feign会为每个接口方法创建一个RequetTemplate对象，该对象封装了HTTP请求需要的全部信息，请求参数名、请求方法等信息都是在这个过程中确定的，Feign的模板化就体现在这里

5. 定义一个WebController。

注入之前通过@FeignClient定义生成的bean,

package com.pupeiyuan.controller;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;
import com.pupeiyuan.bean.NhReportStatusHistory;
import com.pupeiyuan.feignClient.FeignClient2;
import com.pupeiyuan.feignClient.UserFeignClient;

@RestController
public class FeignClientController {

    @Autowired
    private UserFeignClient userFeignClient;

    @GetMapping("/movie/{id}")
      public List<NhReportStatusHistory> list(@PathVariable Long id) {
        return this.userFeignClient.dataList(id);
      }
}

6. 被调用端的WebController--被代理的方法实现

package com.pupeiyuan.controller;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.cloud.context.config.annotation.RefreshScope;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

import com.github.pagehelper.PageHelper;
import com.pupeiyuan.bean.NhReportStatusHistory;
import com.pupeiyuan.core.DataSourceKey;
import com.pupeiyuan.core.DynamicDataSourceContextHolder;
import com.pupeiyuan.services.NhReportService;

@RestController
@RefreshScope
public class ConfigClientController {

    //services层注入
    @Autowired NhReportService nhReportService;

      @GetMapping("/getDate/{id}")
      public List<NhReportStatusHistory> getDate(@PathVariable Long id) {
          //参数容器
            Map<String, Object> params = new HashMap<String, Object>();
            PageHelper.startPage(1, 2);
            DynamicDataSourceContextHolder.set(DataSourceKey.DB_SLAVE1);
            List<NhReportStatusHistory> findList = nhReportService.findList(params);
            return findList;
      }
}

7. 启动Feign应用， 访问http://localhost:8085/movie/1， 多次刷新，可以看到和前一章Ribbon里面的应用一样， 两个Hello World服务的输出交替出现。说明通过Feign访问服务， Spring Cloud已经缺省使用了Ribbon负载均衡。

8. 在Feign中使用Apache HTTP Client

Feign在默认情况下使用的是JDK原生的URLConnection发送HTTP请求，没有连接池，但是对每个地址gwai会保持一个长连接，即利用HTTP的persistence connection 。我们可以用Apache的HTTP Client替换Feign原始的http client, 从而获取连接池、超时时间等与性能息息相关的控制能力。Spring Cloud从Brixtion.SR5版本开始支持这种替换，首先在项目中声明Apache HTTP Client和feign-httpclient依赖：

  <!-- 使用Apache HttpClient替换Feign原生httpclient -->
          <dependency>
              <groupId>org.apache.httpcomponents</groupId>
              <artifactId>httpclient</artifactId>
          </dependency>
          <dependency>
              <groupId>com.netflix.feign</groupId>
              <artifactId>feign-httpclient</artifactId>
              <version>${feign-httpclient}</version>
         </dependency>

然后在application.properties中添加：

feign.httpclient.enabled=true

7. Feign的Encoder、Decoder和ErrorDecoder

Feign将方法签名中方法参数对象序列化为请求参数放到HTTP请求中的过程，是由编码器(Encoder)完成的。同理，将HTTP响应数据反序列化为Java对象是由解码器(Decoder)完成的。默认情况下，Feign会将标有@RequestParam注解的参数转换成字符串添加到URL中，将没有注解的参数通过Jackson转换成json放到请求体中。注意，如果在@RequetMapping中的method将请求方式指定为POST，那么所有未标注解的参数将会被忽略，例如：

@RequestMapping(value = "/group/{groupId}", method = RequestMethod.GET)
void update(@PathVariable("groupId") Integer groupId, @RequestParam("groupName") String groupName, DataObject obj);

此时因为声明的是GET请求没有请求体，所以obj参数就会被忽略。

在Spring Cloud环境下，Feign的Encoder只会用来编码没有添加注解的参数。如果你自定义了Encoder, 那么只有在编码obj参数时才会调用你的Encoder。对于Decoder, 默认会委托给SpringMVC中的MappingJackson2HttpMessageConverter类进行解码。只有当状态码不在200 ~ 300之间时ErrorDecoder才会被调用。ErrorDecoder的作用是可以根据HTTP响应信息返回一个异常，该异常可以在调用Feign接口的地方被捕获到。我们目前就通过ErrorDecoder来使Feign接口抛出业务异常以供调用者处理。