[micro service sentinel] @sentinelresource details

We mentioned in the article we wrote before , At the current limit of hot spot parameters , We can only use @SentinelResource Annotation to define resources , To take effect , So what is the use of this annotation ？

Sentinel Provides @SentinelResource Annotations are used to define resources , And provides AspectJ The extension of is used to automatically define resources 、 Handle BlockException etc. .

Introduce

@SentinelResource The annotation contains the following properties ：

• value： Resource name , Required （ Can't be empty ）
• entryType：entry type , optional （ The default is EntryType.OUT）
• blockHandler / blockHandlerClass: blockHandler Deal with BlockException The function name of , optional .blockHandler The function access range needs to be public, Return type needs to match the original method , The parameter type needs to match the original method and add an extra parameter , The type is BlockException.blockHandler Function default needs to be in the same class as the original method . If you want to use functions of other classes , You can specify blockHandlerClass For the corresponding class Class object , Note that the corresponding function must be static function , Otherwise, it cannot be parsed .
• fallback：fallback The name of the function , optional , Used to provide... When an exception is thrown fallback Processing logic .fallback Functions can be used for all types of exceptions （ except exceptionsToIgnore The types of exceptions excluded ） To deal with .fallback Function signature and location requirements ：
  • The return value type must be the same as the return value type of the original function ;
  • Method parameter list should be consistent with the original function , Or maybe one more Throwable The parameter of type is used to receive the corresponding exception .
  • fallback Function default needs to be in the same class as the original method . If you want to use functions of other classes , You can specify fallbackClass For the corresponding class Class object , Note that the corresponding function must be static function , Otherwise, it cannot be parsed .
• defaultFallback（since 1.6.0）： default fallback The name of the function , optional , Usually used for general purpose fallback Logic （ It can be used in many services or methods ）. Default fallback Functions can be used for all types of exceptions （ except exceptionsToIgnore The types of exceptions excluded ） To deal with . If you configure fallback and defaultFallback, only fallback Will take effect .defaultFallback Function signature requirements ：
  • The return value type must be the same as the return value type of the original function ;
  • Method parameter list needs to be empty , Or maybe one more Throwable The parameter of type is used to receive the corresponding exception .
  • defaultFallback Function default needs to be in the same class as the original method . If you want to use functions of other classes , You can specify fallbackClass For the corresponding class Class object , Note that the corresponding function must be static function , Otherwise, it cannot be parsed .
• exceptionsToIgnore（since 1.6.0）： Used to specify which exceptions are excluded , It will not be included in the abnormal statistics , And will not enter fallback In the logic , But will throw out as is .

Specially , if blockHandler and fallback It's all configured , It is degraded by current limiting and thrown BlockException It will only enter blockHandler Processing logic . If not configured blockHandler、fallback and defaultFallback, When it is degraded by current limiting, it will BlockException Direct selling .

Case study

public class TestService {
    

    //  Corresponding  `handleException`  The function needs to be in  `ExceptionUtil`  Class , And must be  static  function .
    @SentinelResource(value = "test", blockHandler = "handleException", blockHandlerClass = {
    ExceptionUtil.class})
    public void test() {
    
        System.out.println("Test");
    }

    //  Primitive function 
    @SentinelResource(value = "hello", blockHandler = "exceptionHandler", fallback = "helloFallback")
    public String hello(long s) {
    
        return String.format("Hello at %d", s);
    }
    
    // Fallback  function , The signature of the function is the same as the original function or add one  Throwable  Parameters of type .
    public String helloFallback(long s) {
    
        return String.format("Halooooo %d", s);
    }

    // Block  Exception handling functions , One more parameter at the end  BlockException, The rest is consistent with the original function .
    public String exceptionHandler(long s, BlockException ex) {
    
        // Do some log here.
        ex.printStackTrace();
        return "Oops, error occurred at " + s;
    }
}