Hystrix is simple in itself and very easy to understand, still some get confused about how it works.
So let me give a simple example of how it works.
I have taken below example from : Hystrix site Getting-Started
public class CommandHelloWorld extends HystrixCommand<String> {
private final String name;
public CommandHelloWorld(String name) {
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 + "!";
}
}
String s = new CommandHelloWorld("Bob").execute();
Let us demystify this code:
First:
You need to extend the HystrixCommand to use Hystrix circuit breaker.HystrixCommand<String> // This statement tells what your Hystrix command is going to return when your execute it. (Return value of run() method)
HystrixCommand<AnyObject>
HystrixCommand<Anything>
Second:
Constructor behave as the entry point of your Hystrix Command. You should define it in such a way that values passed can be used to:
1) defining Hystrix Command name, group name , Cache key etc.
2) help execute the run() method to do the actual task by providing needed element.
1) defining Hystrix Command name, group name , Cache key etc.
2) help execute the run() method to do the actual task by providing needed element.
public CommandHelloWorld(String name) {
}
Example 1:
In above example this parameter is used in run method.
public CommandHelloWorld(String name) {
super(HystrixCommandGroupKey.Factory.asKey("ExampleGroup"));
}
Example 2:
The parameter here are used to define Hystrix Command and are used in run method to make a http call.
public CommandHelloWorld(String groupKeyName,String commandName, HttpClient httpClient, HttpContext httpContext, HttpRequestBase httpRequest) {
super(Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey(groupKeyName)).andCommandKey(HystrixCommandKey.Factory.asKey(commandName)));
}
Example 3:
The parameter here are used to define Hystrix Command and are used in run jdbc call.
public CommandHelloWorld(String groupKeyName,String commandName, JDBCTemplate jdbcTemplate) {
super(Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey(groupKeyName)).andCommandKey(HystrixCommandKey.Factory.asKey(commandName)));
}
Third:
This call is to configure the HystrixCommand.
super(HystrixCommandGroupKey.Factory.asKey("ExampleGroup")); // this define the group name of your Hystrix command.
Hystrix define two constructror for configuration:
protected HystrixCommand(HystrixCommandGroupKey group) { // Example 1
this(new HystrixCommand.Setter(group, null));
}
protected HystrixCommand(HystrixCommand.Setter setter) { // Example 2 or 3
this(setter.groupKey, setter.commandKey, setter.threadPoolKey, (HystrixCircuitBreaker)null, (HystrixThreadPool)null, setter.commandPropertiesDefaults, setter.threadPoolPropertiesDefaults, (HystrixCommandMetrics)null, (HystrixCommand.TryableSemaphore)null, (HystrixCommand.TryableSemaphore)null, (HystrixPropertiesStrategy)null, (HystrixCommandExecutionHook)null);
}
Fourth:
To implement the HystrixComman override the run() method. This is where you will do all the task as per your requirement.
@Override
protected String run() {
// a real example would do work like a network call here
return "Hello " + name + "!";
}
Fifth:
The above created command be used like this :String s = new CommandHelloWorld("Bob").execute(); // this will internally call the run() method
The above created command be used like this :String s = new CommandHelloWorld("Bob").execute(); // this will internally call the run() method