Interview Questions

Hystrix - Example

package com.test.hystrix;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.Socket;

import com.netflix.hystrix.HystrixCommand;
import com.netflix.hystrix.HystrixCommandGroupKey;

public class Example {

        public static void main(String[] args){
               
        }
       
}

 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
        try{
        Socket socket = new Socket("localhost", 19065);
            System.out.println("Started client  socket at "
                + socket.getLocalSocketAddress());
            BufferedReader socketReader = new BufferedReader(new InputStreamReader(
                socket.getInputStream()));
            BufferedWriter socketWriter = new BufferedWriter(new OutputStreamWriter(
                socket.getOutputStream()));
            BufferedReader consoleReader = new BufferedReader(
                new InputStreamReader(System.in));

            String promptMsg = "Please enter a  message  (Bye  to quit):";
            String outMsg = "hello";

            System.out.print(promptMsg);
           // while ((outMsg = consoleReader.readLine()) != null) {
             /* if (outMsg.equalsIgnoreCase("bye")) {
                break;
              }*/

              // Add a new line to the message to the server,
              // because the server reads one line at a time.
              socketWriter.write(outMsg);
              socketWriter.write("\n");
              socketWriter.flush();

              // Read and display the message from the server
              String inMsg = socketReader.readLine();
              System.out.println("Server: " + inMsg);
              System.out.println(); // Print a blank line
              System.out.print(promptMsg);
          //  }
            socket.close();
        }catch(Exception e)
        {
                e.printStackTrace();
        }
       
        return "Hello " + name + "!";
    }
}

______________________________________________________________________________________________

package com.test.hystrix;

import static org.junit.Assert.*;


import java.util.concurrent.Future;

import org.junit.Test;

import com.netflix.config.ConfigurationManager;
import com.netflix.hystrix.HystrixCommandKey;
import com.netflix.hystrix.HystrixCommandMetrics;
import com.netflix.hystrix.HystrixRequestLog;
import com.netflix.hystrix.strategy.concurrency.HystrixRequestContext;

import rx.Observable;
import rx.Observer;
import rx.functions.Action1;

public class ExampleTest {

    @Test
    public void testSynchronous() {
        assertEquals("Hello World!", new CommandHelloWorld("World").execute());
        assertEquals("Hello Bob!", new CommandHelloWorld("Bob").execute());
    }

    @Test
    public void testAsynchronous1() throws Exception {
        assertEquals("Hello World!", new CommandHelloWorld("World").queue().get());
        assertEquals("Hello Bob!", new CommandHelloWorld("Bob").queue().get());
    }

    @Test
    public void testAsynchronous2() throws Exception {

        Future<String> fWorld = new CommandHelloWorld("World").queue();
        Future<String> fBob = new CommandHelloWorld("Bob").queue();

        assertEquals("Hello World!", fWorld.get());
        assertEquals("Hello Bob!", fBob.get());
    }

    @Test
    public void testObservable() throws Exception {

        Observable<String> fWorld = new CommandHelloWorld("World").observe();
        Observable<String> fBob = new CommandHelloWorld("Bob").observe();

        // blocking
        assertEquals("Hello World!", fWorld.toBlocking().single());
        assertEquals("Hello Bob!", fBob.toBlocking().single());

        // non-blocking
        // - this is a verbose anonymous inner-class approach and doesn't do assertions
        fWorld.subscribe(new Observer<String>() {

            @Override
            public void onCompleted() {
                // nothing needed here
                System.out.println("Completed");
            }

            @Override
            public void onError(Throwable e) {
                e.printStackTrace();
            }

            @Override
            public void onNext(String v) {
                System.out.println("onNext: " + v);
            }

        });

     
        fBob.subscribe(new Action1<String>() {

            @Override
            public void call(String v) {
                System.out.println("onNext: " + v);
            }

        });

     
       
     

    }
   
    @Test
    public void should_execute_fallback_method_when_circuit_is_open() {
     
      //Initialize HystrixRequestContext to be able to get some metrics
      HystrixRequestContext context = HystrixRequestContext.initializeContext();
      HystrixCommandMetrics creditCardMetrics = HystrixCommandMetrics.getInstance(HystrixCommandKey.Factory.asKey(CommandHelloWorld.class.getSimpleName()));
     
      //We use Archaius to set the circuit as closed.
      ConfigurationManager.getConfigInstance().setProperty("hystrix.command.default.circuitBreaker.forceOpen", false);
     
      String successMessage = new CommandHelloWorld("Heaven").execute();
      assertThat(successMessage, is("Hello World"));
     
      //We use Archaius to open the circuit
      ConfigurationManager.getConfigInstance().setProperty("hystrix.command.default.circuitBreaker.forceOpen", true);
     
      String failMessage = new CommandHelloWorld("Magnanimous").execute();
      assertThat(failMessage, is("Good Bye"));
     
      //Prints Request => HelloWorldRestCommand[SUCCESS][19ms], HelloWorldRestCommand[SHORT_CIRCUITED, FALLBACK_SUCCESS][0ms]
      System.out.println("Request => " + HystrixRequestLog.getCurrentRequest().getExecutedCommandsAsString());
     
      assertThat(creditCardMetrics.getHealthCounts().getTotalRequests(), is(2));
      assertThat(creditCardMetrics.getHealthCounts().getErrorCount(), is(1));

    }
}