:-: 
* [ ] 服务降级
* [ ] 服务熔断
* [ ] 依赖隔离
* [ ] 监控
## 服务降级
1. 引入依赖
```
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-hystrix</artifactId>
</dependency>
```
2. 启动类加上注解
``` @SpringBootApplication
@EnableCircuitBreaker
@EnableDiscoveryClient
@EnableFeignClients(basePackages = "com.eclab.product.iclient")
public class OrderApplication {
public static void main(String[] args) {
SpringApplication.run(OrderApplication.class, args);
}
}
```
随着业务的不断增加，注解也越来越多，此时有些注解可以使用另外的注解代替：
```
/*@SpringBootApplication
@EnableDiscoveryClient
@EnableCircuitBreaker*/
@SpringCloudApplication
@EnableFeignClients(basePackages = "com.eclab.product.iclient")
@EnableHystrixDashboard
public class OrderApplication {
public static void main(String[] args) {
SpringApplication.run(OrderApplication.class, args);
}
}
```
服务降级实例：
```
@HystrixCommand(fallbackMethod = "fallback"）
@GetMapping("/getProductInfoList")
public String getProductInfoList(@RequestParam("i") Integer i){
if (i % 2 == 0){
return "Sucess";
}
RestTemplate restTemplate = new RestTemplate();
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
return restTemplate.postForObject("http://localhost:8081/product/listForOrder",
Arrays.asList("157875152258154"),
String.class);
}
private String fallback(){
return "太拥挤了，请稍后再试~";
}
```
在服务降级中，除了调用的目标服务不可用导致的错误引起降级之外，自身的异常也可以进行降级
降级的方法除了自定外，还可以有个全局的通用方法，将注解加在类上：
```
@RestController
@DefaultProperties(defaultFallback = "defaultFallback")
public class HystrixController {
//超时配置
/* @HystrixCommand(fallbackMethod = "fallback",
commandProperties = {
@HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds" , value = "3000")
}
)*/
@HystrixCommand(commandProperties = {
@HystrixProperty(name = "circuitBreaker.enabled" , value = "true"), //设置熔断
@HystrixProperty(name = "circuitBreaker.requestVolumeThreshold" , value = "10"),
@HystrixProperty(name = "circuitBreaker.sleepWindowInMilliseconds" , value = "1000"),
@HystrixProperty(name = "circuitBreaker.errorThresholdPercentage" , value = "60")
})
@GetMapping("/getProductInfoList")
public String getProductInfoList(@RequestParam("i") Integer i){
if (i % 2 == 0){
return "Sucess";
}
RestTemplate restTemplate = new RestTemplate();
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
return restTemplate.postForObject("http://localhost:8081/product/listForOrder",
Arrays.asList("157875152258154"),
String.class);
}
private String fallback(){
return "太拥挤了，请稍后再试~";
}
private String defaultFallback(){
return "默认提示：太拥挤了，请稍后再试~";
}
}
```
上面的代码中的超时设置，可以用来配置是否降级
