一起来学SpringCloud之-服务消费者(Feign-上)

文章目录
  1. 1. - Feign简介
  2. 2. - 准备工作
  3. 3. battcn-feign-hello
    1. 3.1. - pom.xml
    2. 3.2. - BattcnFeignHelloApplication.java
    3. 3.3. - HelloController.java
    4. 3.4. - bootstrap.yml
  4. 4. battcn-feign-hi
    1. 4.1. - pom.xml
    2. 4.2. - BattcnFeignHiApplication.java
    3. 4.3. - HelloClient.java
    4. 4.4. - HiController.java
    5. 4.5. - bootstrap.yml
    6. 4.6. - 源码分析
  5. 5. - 说点什么

上一篇文章,讲述了Ribbon去做负载请求的服务消费者,本章讲述声明性REST客户端:Feign的简单使用方式

- Feign简介

Feign是一个声明式的Web服务客户端。这使得Web服务客户端的写入更加方便 。它具有可插拔注释支持,包括Feign注释和JAX-RS注释。Feign还支持可插拔编码器和解码器。Spring Cloud增加了对Spring MVC注释的支持,并HttpMessageConverters在Spring Web中使用了默认使用的相同方式。Spring Cloud集成了Ribbon和Eureka,在使用Feign时提供负载平衡的http客户端。

官方文档:http://cloud.spring.io/spring-cloud-static/Dalston.SR2/#spring-cloud-feign

- 准备工作

1.启动Consul,所有文章都将以Consul作为服务注册中心

2.创建 battcn-feign-hellobattcn-feign-hi

battcn-feign-hello

- pom.xml

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-consul-discovery</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>

- BattcnFeignHelloApplication.java

1
2
3
4
5
6
7
8
@SpringBootApplication
@EnableDiscoveryClient
public class BattcnFeignHelloApplication {

public static void main(String[] args) {
SpringApplication.run(BattcnFeignHelloApplication.class, args);
}
}

创建一个打招呼的的Controller

- HelloController.java

1
2
3
4
5
6
7
8
9
10
11
@RestController
@RequestMapping("/hello")
public class HelloController {

@ResponseStatus(HttpStatus.OK)
@GetMapping
public String findStudentByName(@RequestParam("name") String name) {
// TODO:不做具体代码实现,只打印Log
return "挽歌- My Name's" + name;
}
}

- bootstrap.yml

1
2
3
4
5
6
7
8
9
10
11
12
13
14
server:
port: 8765

spring:
application:
name: battcn-feign-hello
cloud:
consul:
host: localhost
port: 8500
enabled: true
discovery:
enabled: true
prefer-ip-address: true

访问:http://localhost:8765/hello?name=Levin

结果:挽歌- My Name's Levin 表示我们第一个服务运行一切正常

battcn-feign-hi

- pom.xml

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-feign</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-consul-discovery</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>

- BattcnFeignHiApplication.java

1
2
3
4
5
6
7
8
9
@EnableDiscoveryClient
@EnableFeignClients(basePackages = {"com.battcn.client"})
@SpringBootApplication
public class BattcnFeignHiApplication {

public static void main(String[] args) {
SpringApplication.run(BattcnFeignHiApplication.class, args);
}
}

- HelloClient.java

创建一个声明式FeignClient的接口 HelloClient

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
@FeignClient(name = "battcn-feign-hello")
public interface HelloClient {

/**
* 在新版本中,Feign 已经可以解析 RestFul 标准的接口API,比如GET POST DELETE PATCH PUT
* 旧版中
* @RequestMapping(method = RequestMethod.GET, value = "/hello")
* 或者是
* @RequestMapping(method = RequestMethod.POST, value = "/hello")
*
* 早期文章:http://blog.battcn.com/2017/07/07/springcloud-feign-analysis/
* /
@ResponseStatus(HttpStatus.OK)
@GetMapping("/hello")
String findStudentByName(@RequestParam("name") String name);
}

- HiController.java

1
2
3
4
5
6
7
8
9
10
11
12
13
14
@RestController
@RequestMapping("/hi")
public class HiController {

@Autowired
HelloClient helloClient;

@ResponseStatus(HttpStatus.OK)
@GetMapping
public String find(@RequestParam("name") String name) {
// TODO:只是演示Feign调用的方法
return "Hi," + helloClient.findStudentByName(name);
}
}

- bootstrap.yml

1
2
3
4
5
6
7
8
9
10
11
12
13
14
server:
port: 8766

spring:
application:
name: battcn-feign-hi
cloud:
consul:
host: localhost
port: 8500
enabled: true
discovery:
enabled: true
prefer-ip-address: true

访问:http://localhost:8766/hi?name=Levin

结果:Hi,挽歌- My Name'sLevin 表示第二个服务(hi)通过FeignClient调用服务(hello)一切正常

- 源码分析

org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(Object... args),该方法的 args 就是我们传递的请求参数

InvocableHandlerMethod

feign.Target -> HardCodedTarget 解析出 FeignClient中的 name 形成VIP模式 GET http://battcn-feign-hello/hello?name=Levin HTTP/1.1 然后发送请求

HardCodedTarget

feign.SynchronousMethodHandler -> this.client.execute(request, this.options);

第一个就是:feign.Request的一些信息,比如headermethodbodyurl 等一些基本属性,因为这里是feign的Request所以我们servlet中的请求头是无法传递过来的(下篇会讲述这写小技巧)

第二个就是:connectTimeoutMillisreadTimeoutMillis 很多人肯定不陌生

SynchronousMethodHandler

通过三面三个步骤,我们不难看出 Feign 就是解析注解然后发送HTTP(阻断器,OKHTTP模式留到下篇),有兴趣的可以自己Debug(如果该处有错误也希望各位指正)

- 说点什么

本章教程过于简单,因此代码未提交GIT(完整代码都在文章里),自行复制即可,如有问题请及时与我联系

  • 个人QQ:1837307557
  • Spring Cloud中国社区①:415028731
  • Spring For All 社区⑤:157525002