【SpringCloud技术专题】「Hystrix」（1）基本使用以及参数动态配置更新实现
### 概述
> 只介绍同步模式下简单的使用, 有助于快速接入, 会有一些官方文档中没有涉及的细节.
### 默认方式
```java
public class CommandHelloWorld extends HystrixCommand {
private final String name;
// 构造方法中传入需要用到的数据, run 方法处理逻辑.
public CommandHelloWorld(String name) {
// 构造 Setter 比较麻烦, 后面会进一步介绍
super(HystrixCommandGroupKey.Factory.asKey("ExampleGroup"));
this.name = name;
}
@Override
protected String run() {
// a real example would do work like a network call here
return "Hello " + name + "!";
}
// fallback 方法可选, 如果没有, 默认抛异常.
@Override
protected String getFallback() {
return "fallback";
}
}
```
### 构造Setter
Hystrix 讲求的大而全, 设计的比较模式, 用起来不是很方便. 下面是一个构造 Setter 的实例:
```java
Setter setter = Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey(site)) // groupKey 对command进行分组, 用于 reporting, alerting, dashboards, or team/library ownership, 也是 ThreadPool 的默认 key
.andCommandKey(HystrixCommandKey.Factory.asKey(site)) // 可以根据 commandKey 具体的运行时参数
.andThreadPoolKey(HystrixThreadPoolKey.Factory.asKey(site)) // 指定 ThreadPool key, 这样就不会默认使用 GroupKey
.andCommandPropertiesDefaults(HystrixCommandProperties.Setter() // 初始化 Command 相关属性
.withMetricsRollingStatisticalWindowInMilliseconds(
100 * 1000) // 设置统计窗口为100秒
.withCircuitBreakerSleepWindowInMilliseconds(
10 * 1000) // 设置熔断以后, 试探间隔为10秒
.withCircuitBreakerRequestVolumeThreshold(
10) // 设置判断熔断请求阈值为10
.withCircuitBreakerErrorThresholdPercentage(
80) // 设置判断熔断失败率为80%
.withExecutionTimeoutInMilliseconds(3 * 1000)) // 设置每个请求超时时间为3秒
.andThreadPoolPropertiesDefaults( // 设置和threadPool相关
HystrixThreadPoolProperties.Setter().withCoreSize(20)); // 设置 threadPool 大小为20(最大20个并发)
```
- **另外threadPool还有个设置统计窗口的选项, 因为Hystrix统计维度会从主线程和线程池两个维度来统计.**
- 还有好多配置信息可以配置, 这里只提供了几个重要的，其他配置参考：[hystrix-configuration](https://github.com/Netflix/Hystrix/wiki/Configuration)
### Spring cloud 注解方式
需要用到两个注解: **@EnableCircuitBreaker, @HystrixCommand(fallbackMethod = "reliable")**
启动类:
```java
package hello;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.web.client.RestTemplate;
@EnableCircuitBreaker
@RestController
@SpringBootApplication
public class ReadingApplication {
@Autowired
private BookService bookService;
@Bean
public RestTemplate rest(RestTemplateBuilder builder) {
return builder.build();
}
@RequestMapping("/to-read")
public String toRead() {
return bookService.readingList();
}
public static void main(String[] args) {
SpringApplication.run(ReadingApplication.class, args);
}
}
```
服务类:
```java
package hello;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;
import java.net.URI;
@Service
public class BookService {
private final RestTemplate restTemplate;
public BookService(RestTemplate rest) {
this.restTemplate = rest;
}
@HystrixCommand(fallbackMethod = "reliable")
public String readingList() {
URI uri = URI.create("http://localhost:8090/recommended");
return this.restTemplate.getForObject(uri, String.class);
}
public String reliable() {
return "Cloud Native Java (O'Reilly)";
}
}
```
### 动态更新配置
Hystrix 使用 Archaius 来实现动态配置. 使用 Spring 配置方式:
#### 创建配置获取源
> 实现接口 PolledConfigurationSource, 并返回一个 Map. 注意 Key 为 hystrix 配置key, 可以参考：[hystrix-configuration](https://github.com/Netflix/Hystrix/wiki/Configuration)
```java
package com.rh.config.hystrix;
import com.netflix.config.PollResult;
import com.netflix.config.PolledConfigurationSource;
import org.springframework.core.env.*;
import org.springframework.core.io.ResourceLoader;
import org.springframework.stereotype.Component;
import javax.annotation.Resource;
import java.util.*;
/**
* @Auther: wangyunfei
* @Date: 2019/12/10 14:12
* @Description:
*/
@Component
/**
* @Author wangyunfei
* @Description 定期读取配置文件中的hystrix配置
* @Date 2019/12/10 14:13
* @Param
* @return
**/
public class DegradeConfigSource implements PolledConfigurationSource {
public final String HystrixPrefix = "hystrix";
//spring的Environment
private ConfigurableEnvironment environment;
private PropertySourcesPropertyResolver resolver;
DegradeConfigSource(ConfigurableEnvironment environment) {
this.environment = environment;
this.resolver = new PropertySourcesPropertyResolver(this.environment.getPropertySources());
this.resolver.setIgnoreUnresolvableNestedPlaceholders(true);
}
@Override
public PollResult poll(boolean initial, Object checkPoint) throws Exception {
//Map<String, Object> complete = getHystrixConfig();
Map<String, Object> complete = getProperties();
return PollResult.createFull(complete);
}
@Resource
private ResourceLoader resourceLoader;
/**
* @Author wangyunfei
* @Description 获取配置文件中的指定hystrix前缀信息
* 缺点：1）不支持yml格式 只支持properties
* 2）只能读取某一个配置文件中的信息 如果配置是写在不同配置文件则不支持
* @Date 2019/12/20 14:58
* @Param []
* @return java.util.HashMap<java.lang.String,java.lang.String>
**/
public HashMap<String,Object> getHystrixConfig() throws Exception
{
HashMap<String,Object> hystrixMap = new HashMap<String,Object>();
org.springframework.core.io.Resource resource = resourceLoader.getResource("classpath:application-mod.properties");
Properties props = new Properties();
props.load(resource.getInputStream());
Enumeration keys = props.propertyNames();
while (keys.hasMoreElements()) {
String key = (String) keys.nextElement();
System.out.println(key + "=" + props.getProperty(key));
if(key.contains(HystrixPrefix))
{
hystrixMap.put(key, props.getProperty(key));
}
}
return hystrixMap;
}
/**
* @Author wangyunfei
* @Description 获取所有配置信息
* @Date 2019/12/20 15:06
* @Param []
* @return java.util.Map<java.lang.String,java.lang.Object>
**/
public Map<String, Object> getProperties() {
Map<String, Object> properties = new LinkedHashMap<>();
//spring env 里面也是多个source组合的
for (Map.Entry<String, PropertySource<? >> entry : getPropertySources().entrySet()) {
PropertySource<? > source = entry.getValue();
if (source instanceof EnumerablePropertySource) {
EnumerablePropertySource<? > enumerable = (EnumerablePropertySource<? >) source;
for (String name : enumerable.getPropertyNames()) {
if (!properties.containsKey(name) && name.contains(HystrixPrefix)) {
properties.put(name, resolver.getProperty(name));
}
}
}
}
return properties;
}
//PropertySource也可能是组合的，通过递归获取
private Map<String, PropertySource<? >> getPropertySources() {
Map<String, PropertySource<? >> map = new LinkedHashMap<String, PropertySource<? >>();
MutablePropertySources sources = null;
if (environment != null) {
sources = environment.getPropertySources();
} else {
sources = new StandardEnvironment().getPropertySources();
}
for (PropertySource<? > source : sources) {
extract("", map, source);
}
return map;
}
private void extract(String root, Map<String, PropertySource<? >> map,
PropertySource<? > source) {
if (source instanceof CompositePropertySource) {
for (PropertySource<? > nest : ((CompositePropertySource) source)
.getPropertySources()) {
extract(source.getName() + ":", map, nest);
}
} else {
map.put(root + source.getName(), source);
}
}
}
```
#### 配置并初始化自动配置
创建一个 DynamicConfiguration, 并注册一下就可以了. 注意, 我们使用了 FixedDelayPollingScheduler 来定期加载新的配置. 默认60秒加载一次.
```java
@Configuration
public class DegradeDynamicConfig {
@Bean
public DynamicConfiguration dynamicConfiguration(@Autowired DegradeConfigSource degradeConfigSource) {
AbstractPollingScheduler scheduler = new FixedDelayPollingScheduler(30 * 1000,
60 * 1000, false);
DynamicConfiguration configuration = new DynamicConfiguration(degradeConfigSource,
scheduler);
ConfigurationManager.install(configuration); // must install to enable configuration
return configuration;
}
}
```
其中从配置文件获取hystrix配置信息等参考如下代码 http://techblog.ppdai.com/2018/05/08/20180508/
### 参考
https://github.com/Netflix/Hystrix/wiki/How-To-Use
https://github.com/Netflix/Hystrix/wiki/Configuration
https://github.com/Netflix/Hystrix/issues/1717
https://github.com/Netflix/archaius/wiki/Users-Guide
https://spring.io/guides/gs/circuit-breaker/