Springboot feign的性能优化

1. 更换为okhttp

2. 适量调大http连接池的大小
io线程为CPU核心数×2
work线程 可以适量调大。高并发下建议为io线程数×40

3. 尽量用feign自己的解析器，实在不行使用如下的方式

```
@Configuration
public class FeignClientConfig{
 @Bean
 public Decoder feignDecoder(){
   MessageConverter converter = new MessageConverter();
   HttpMessageConverter httpConverter = new HttpMessageConverter(converter);
   // 如果为new SpringDecoder(() -> new HttpMessageConverter(converter)） 会降低很多并发，在cpu不足是很明显
   return new SpringDecoder(() -> httpConverter);
 }
 
 public static class MessageConverter extends MappingJackson2HttpMessageConverter{
   public MessageConverter(){
     List<MediaType> mediaTypes = new ArrayList<>();
	 mediaTypes.add(MediaType.TEXT_PLAIN);
	 super.setSupportedMediaTypes(mediaTypes);
   }
 }
}
```

4. 大文件读取使用流读取
```
public class Hello {
	@Resource
	private DemoFeign feign;
	
	public streamFile(String fileName) {
		// feign 需要返回 feign.Response 这个对象
		Response response = feign.getFile(fileName);
		Response.Body body = response.body();
		
		try( Reader reader = body.asReader(Charset.defaultCharset())) {
			BufferedReader buff = new BufferedReader(reader);
			String row;
			while( (row = buff.readLine() != null) {
				// TODO 进行处理
			}
		} catch (Exception e) {
			log.error("流式读取异常",e);
		}
	}
}
```

5 修改重试次数
```
@FeignClient(name = "beyondtime-io-kc-client", url = "${btio.keycloakUrl}", path = "/", configuration = KeycloakAdminClient.Configuration.class)
public interface KeycloakAdminClient {
    @PostMapping(value="realms/master/protocol/openid-connect/token", consumes = MediaType.APPLICATION_FROM_URLENCODED_VALUE)
    KeycloakAccessToken getAuthToken(@RequestBody AuthTokenRequest authTokenRequest);
    class Configuration {
        @Bean
        Retryer feignRetry() {
		    // 默认ls的最大等待  5次重试,可自定义
            return new Retryer.Default();
        }
    }
}
```