Feign--基础

忘是亡心i 2023-02-24 08:11 7阅读 0赞

原文网址：[Feign--基础\_IT利刃出鞘的博客-CSDN博客][Feign--_IT_-CSDN]

# Controller #

**必须用@RestController不能用@Controller**

> SpringCloud的RPC是基于json（用的RestTemplate）的，所有用到RPC（ribbon或feign）的Controller，必须用@RestControlelr，不能用@Controller，否则调用方会报错，例如：
> 
>     feign.FeignException$NotFound: status 404 reading UserFeignService#getUser(Long)

> 继而产生的影响：默认情况下：feign接口及feign服务提供者都是@RequestBody，只能有一个参数。若想改变，则必须在每一个参数前边加@RequestParam

# Feign接口 #

**版本问题**

> 有的老版本不支持@GetMapping等组合注解，需要@RequestMapping(method = RequestMethod.GET)

**@PathVariable**

> 使用@PathVariable时，需要指定其value。否则会报错：Caused by: java.lang.IllegalStateException: PathVariable annotation was empty on param 0
> 
>     public String findServiceName(@PathVariable("Name") String Name);

**@RequestParam**

> **请求方法**
> 
> 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(无论是指定了get还是post）。
> 
> 如果请求方式指定为POST，那么所有未标注解的参数将会被忽略，所以这里的@RequestMapping必须指定。必须指定value的值，否则将报QueryMap parameter must be a Map错误。
> 
> 如果请求方式指定为GET，则必须添加@RequestParam，否则，将报错：Request parameter of Get can't be a body。
> 
> **指定名称**
> 
> 若不指定名称有时会报错：
> 
>     @RequestMapping("/greeting")
>     String greeting(@RequestParam String name);
> 
> 报错信息
> 
>     Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.example.UserFeignClient': FactoryBean threw exception on object creation; nested exception is java.lang.IllegalStateException: RequestParam.value() was empty on parameter 0
> 
> 解决方法：
> 
>     @RequestMapping("/greeting")
>     String greeting(@RequestParam("name") String name);

**调用同一个服务的接口要放到一个feign接口中**

> 错误写法
> 
>     @FeignClient("user")
>     public interface TestLongFeignService {
>         @PostMapping("/user/long")
>         public ResultWrapper testLong(String param1);
>     }
> 
>     @FeignClient("user")
>     public interface UserFeignService {
>         @GetMapping("/user/{id}")
>         public User getUser(@PathVariable("id") Long id);
>     }
> 
> 错误日志：
> 
>     The bean 'user.FeignClientSpecification' could not be registered. A bean with that name has already been defined and overriding is disabled.
> 
> 应该这样写
> 
>     @FeignClient("user")
>     public interface UserFeignService {
>         @GetMapping("/user/{id}")
>         public User getUser(@PathVariable("id") Long id);
>     
>         @PostMapping("/user/long")
>         public ResultWrapper testLong(String param1);
>     }

# 参数长度问题 #

**描述**

> 如果参数过长，会报错：  
> 调用端报错： feign.FeignException: status 400 reading xxx\#xxxx(  
> 被调用端报错： java.lang.IllegalArgumentException: Request header is too large

**复现**

> 浏览器访问：[http://localhost:9001/product/long][http_localhost_9001_product_long]
> 
> 调用者
> 
>     @RestController
>     @RequestMapping("/product")
>     public class ProductController {
>         @Autowired
>         UserFeignService userFeignService;
>     
>         @GetMapping("/long")
>         public ResultWrapper testLong(){
>             StringBuffer stringBuffer = new StringBuffer();
>             for (int i = 0; i < 10000; i++) {
>                 stringBuffer.append(i % 10);
>             }
>             StringBuffer stringBuffer2 = new StringBuffer();
>             for (int i = 0; i < 10000; i++) {
>                 stringBuffer2.append(i % 5);
>             }
>             ResultWrapper resultWrapper = userFeignService.testLong(stringBuffer.toString(),
>                     stringBuffer2.toString());
>             return resultWrapper;
>         }
>     }
> 
>     @FeignClient("user")
>     public interface UserFeignService {
>         @PostMapping("/user/long")
>         public ResultWrapper testLong(@RequestParam String param1, @RequestParam String param2);
>     }
> 
> 被调用者
> 
>     @RestController
>     @RequestMapping("/user")
>     public class UserController {
>         private Logger logger = Logger.getLogger(String.valueOf(getClass()));
>     
>         @Autowired
>         private DiscoveryClient discoveryClient;
>     
>         @PostMapping("/long")
>         public ResultWrapper testLong(@RequestParam String param1, @RequestParam String param2) {
>             System.out.println(param1);
>             System.out.println(param2);
>             List<String> stringList = new ArrayList<>();
>             stringList.add(param1);
>             stringList.add(param2);
>             return new ResultWrapper().success(true).message("成功").object(stringList);
>         }
>     }

**解决方法**

> 法1（不推荐）：修改Tomcat配置，把header的值改大  
> 法2（推荐）：将其放到一个类中。  
> 法3（最推荐）：自定义HttpMessageConverter。使用Map<String, Object>来传输。

# HttpMessageConverter #

**其他网址**

> [Feign源码分析:记初次使用Feign踩的一些坑 - 掘金][Feign_Feign_ -]
> 
> 示例代码对应网址：[https://gitee.com/shapeless/demo\_SpringCloud][https_gitee.com_shapeless_demo_SpringCloud]

如果传输数据很大，最好放到一个类中，直接使用JSON传输，但这样做有个缺点：每次都要将参数封装到一个类中，很麻烦。解决方法：自定义HttpMessageConverter，若有多个参数，可用Map<String, Object>。

![SouthEast][]

**调用端**

配置（只在调用端配置即可）

package com.example.product.config;
    
    import feign.Logger;
    import feign.form.spring.SpringFormEncoder;
    import org.springframework.beans.factory.ObjectFactory;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.boot.autoconfigure.http.HttpMessageConverters;
    import org.springframework.cloud.openfeign.support.SpringEncoder;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Configuration;
    
    @Configuration
    public class FeignConfiguration {
        @Autowired
        private ObjectFactory<HttpMessageConverters> messageConverters;
    
        @Bean
        public SpringFormEncoder feignFormEncoder() {
            return new SpringFormEncoder(new SpringEncoder(messageConverters));
        }
    
        @Bean
        public Logger.Level logger() {
            // 为了方便问题排查，把http的请求和响应全部打印出来
            return Logger.Level.FULL;
        }
    }

package com.example.product.feign;
    
    import com.example.product.entity.LongDTO;
    import com.example.product.entity.ResultWrapper;
    import com.example.product.entity.User;
    import org.springframework.cloud.openfeign.FeignClient;
    import org.springframework.util.MultiValueMap;
    import org.springframework.web.bind.annotation.GetMapping;
    import org.springframework.web.bind.annotation.PathVariable;
    import org.springframework.web.bind.annotation.PostMapping;
    
    import java.util.Map;
    //如果这样写，则FeignConfiguration.java就不用@Configuration了
    //@FeignClient(name = "user", configuration = FeignConfiguration.class)
    @FeignClient(name = "user")
    public interface UserFeignService {
        @GetMapping("/user/{id}")
        public User getUser(@PathVariable("id") Long id);
    
        @PostMapping(value = "/user/long1")
        public ResultWrapper testLong(LongDTO longDTO);
    
        //下边这两种都可以
        // @PostMapping(value = "/user/long3", headers = "content-type=application/x-www-form-urlencoded")
        @PostMapping(value = "/user/long2", consumes = {"application/x-www-form-urlencoded"})
        public ResultWrapper testLong(Map<String, ?> map);
    
        // @PostMapping(value = "/user/long2", consumes = MediaType.APPLICATION_FORM_URLENCODED_VALUE)
        @PostMapping(value = "/user/long3")
        public ResultWrapper testLong(MultiValueMap<String, Object> map);
    }

package com.example.product.controller;
    
    import com.example.product.entity.LongDTO;
    import com.example.product.entity.ResultWrapper;
    import com.example.product.entity.User;
    import com.example.product.feign.UserFeignService;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.util.LinkedMultiValueMap;
    import org.springframework.util.MultiValueMap;
    import org.springframework.web.bind.annotation.GetMapping;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.RestController;
    
    import java.util.HashMap;
    import java.util.Map;
    
    @RestController
    @RequestMapping("/product")
    public class ProductController {
        @Autowired
        UserFeignService userFeignService;
    
        @GetMapping("/long2")
        public ResultWrapper testLong2(){
            StringBuffer stringBuffer = new StringBuffer();
            stringBuffer.append("abc").append(",").append("defg");
    
            StringBuffer stringBuffer2 = new StringBuffer();
            for (int i = 0; i < 10000; i++) {
                stringBuffer2.append(String.valueOf(i % 10));
            }
            Map<String, Object> map = new HashMap<>();
            map.put("param1", stringBuffer.toString());
            map.put("param2", stringBuffer2.toString());
    
            System.out.println(map);
    
            ResultWrapper resultWrapper = userFeignService.testLong(map);
            return resultWrapper;
        }
    }

**被调用端**

package com.example.user.controller;
    
    import com.example.user.entity.LongDTO;
    import com.example.user.entity.ResultWrapper;
    import com.example.user.entity.User;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.cloud.client.ServiceInstance;
    import org.springframework.cloud.client.discovery.DiscoveryClient;
    import org.springframework.util.MultiValueMap;
    import org.springframework.web.bind.annotation.*;
    
    import java.util.ArrayList;
    import java.util.List;
    import java.util.logging.Logger;
    
    //必须用这个，不能用@Controller。
    @RestController
    @RequestMapping("/user")
    public class UserController {
        private Logger logger = Logger.getLogger(String.valueOf(getClass()));
    
        @Autowired
        private DiscoveryClient discoveryClient;
    
        @PostMapping("/long2")
        public ResultWrapper testLong2(String[] param1, String param2) {
            System.out.println("param1: ");
            for (String string : param1) {
                System.out.println(string);
            }
            System.out.println();
            System.out.println("param2: " + param2);
    
            return new ResultWrapper().success(true).message("成功");
        }
    }

postman访问 [http://localhost:9001/product/long2][http_localhost_9001_product_long2]

结果：

user端（被调用端）打印结果

param1: 
    abc
    defg
    
    param2: 01234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789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

**注意：****通过Map传数据时，value不能为null**

@FallbackReturn(impl = CommonFeignFallback.class)
    @FeignClient(value = "common", fallbackFactory = CommonFeignFallbackFactory.class)
    public interface CommonFeignService {
        @PostMapping(value = "/abc/def", headers = "content-type=application/x-www-form-urlencoded")
        ResultWrapper sendQRCode(Map<String, ?> params);
    }

Map<String, Object> map = new HashMap<>();
    map.put("title", "This is Title");
    map.put("content", null);

日志

Caused by: java.lang.NullPointerException: message
    	at feign.Util.checkNotNull(Util.java:114)
    	at feign.codec.EncodeException.<init>(EncodeException.java:32)
    	at feign.form.FormEncoder.encode(FormEncoder.java:96)
    	at feign.form.spring.SpringFormEncoder.encode(SpringFormEncoder.java:64)
    	at feign.ReflectiveFeign$BuildEncodedTemplateFromArgs.resolve(ReflectiveFeign.java:372)
    	... 42 common frames omitted

解决方法

> 将值为null的项删掉。
> 
>     Map<String, Object> map = new HashMap<>();
>             map.put("title", "This is Title");

# feign与zuul #

一般情况下，@FeignClient的name属性指定为特定服务的微服务名，这样在调用时不会通过zuul，此时可以将name直接指定为网关微服务名，这样就可以经过zuul，从而可以使用zuul的鉴权、过滤等功能。

**指定为特定微服务**

package com.example.product.feign;
    
    import java.util.Map;
    
    @FeignClient(name = "user")
    public interface UserFeignService {
        @GetMapping("/user/{id}")
        public User getUser(@PathVariable("id") Long id);
    }

**指定为zuul微服务**

package com.example.product.feign;
    
    import java.util.Map;
    
    @FeignClient(name = "zuul")
    public interface UserFeignService {
        @GetMapping("/user/{id}")
        public User getUser(@PathVariable("id") Long id);
    }

[Feign--_IT_-CSDN]: https://knife.blog.csdn.net/article/details/107211299
[http_localhost_9001_product_long]: http://localhost:9001/product/long
[Feign_Feign_ -]: https://juejin.im/post/5df19a4751882512816014e2
[https_gitee.com_shapeless_demo_SpringCloud]: https://gitee.com/shapeless/demo_SpringCloud
[SouthEast]: /images/20230209/04475ff1923d411d809f4485bb778d01.png
[http_localhost_9001_product_long2]: http://localhost:9001/product/long2