Request Events Streaming

/**
 * Servlet that writes SSE JSON every time a request is made
 * Provides detailed request execution information including events and latencies
 */
public class HystrixRequestEventsSseServlet extends HystrixSampleSseServlet {
    
    /**
     * Default constructor using HystrixRequestEventsStream and default delay
     */
    public HystrixRequestEventsSseServlet();
    
    /**
     * Package-private constructor for testing with custom stream and delay
     * @param sampleStream Observable stream of request events
     * @param pausePollerThreadDelayInMs Delay between polling cycles in milliseconds
     */
    HystrixRequestEventsSseServlet(Observable<HystrixRequestEvents> sampleStream, int pausePollerThreadDelayInMs);
    
    /**
     * Returns maximum number of concurrent connections allowed
     * @return Maximum concurrent connections (default: 5)
     */
    protected int getMaxNumberConcurrentConnectionsAllowed();
    
    /**
     * Returns current number of active connections
     * @return Current connection count
     */
    protected int getNumberCurrentConnections();
    
    /**
     * Atomically increments and returns current concurrent connection count
     * @return New connection count after increment
     */
    protected int incrementAndGetCurrentConcurrentConnections();
    
    /**
     * Atomically decrements current concurrent connection count
     */
    protected void decrementCurrentConcurrentConnections();
}

/**
 * Stream that converts HystrixRequestEvents into JSON
 * @deprecated Since 1.5.4 - prefer mapping serialization on HystrixRequestEventsStream.observe()
 */
@Deprecated
public class HystrixRequestEventsJsonStream {
    
    /**
     * Get the underlying request events stream
     * @return Observable stream of request events
     */
    public Observable<HystrixRequestEvents> getStream();
    
    /**
     * Convert collection of request events to JSON string
     * @param requests Collection of request events to convert
     * @return JSON string representation
     * @throws IOException if JSON generation fails
     */
    public static String convertRequestsToJson(Collection<HystrixRequestEvents> requests) throws IOException;
    
    /**
     * Convert single request event to JSON string
     * @param request Request event to convert
     * @return JSON string representation
     * @throws IOException if JSON generation fails
     */
    public static String convertRequestToJson(HystrixRequestEvents request) throws IOException;
    
    /**
     * Write request as JSON to a JsonGenerator
     * @param json JsonGenerator to write to
     * @param request Request event to write
     * @throws IOException if JSON writing fails
     */
    private static void writeRequestAsJson(JsonGenerator json, HystrixRequestEvents request) throws IOException;
    
    /**
     * Convert execution signature to JSON
     * @param json JsonGenerator to write to
     * @param executionSignature Execution signature containing command details
     * @param latencies List of execution latencies in milliseconds
     * @throws IOException if JSON writing fails
     */
    private static void convertExecutionToJson(JsonGenerator json, HystrixRequestEvents.ExecutionSignature executionSignature, List<Integer> latencies) throws IOException;
}

/**
 * Request events types for detailed request information
 */
public interface HystrixRequestEvents.ExecutionSignature {
    String getCommandName();
    ExecutionResult.EventCounts getEventCounts();
    int getCachedCount();
    HystrixCollapserKey getCollapserKey();
    int getCollapserBatchSize();
}

<servlet>
  <servlet-name>HystrixRequestEventsSseServlet</servlet-name>
  <servlet-class>com.netflix.hystrix.contrib.requests.stream.HystrixRequestEventsSseServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>HystrixRequestEventsSseServlet</servlet-name>
  <url-pattern>/hystrix/requests.stream</url-pattern>
</servlet-mapping>

// Deploy servlet via web.xml configuration
// Access stream endpoint
curl http://localhost:8080/app/hystrix/requests.stream

// Custom request events processing (using deprecated API)
HystrixRequestEventsJsonStream stream = new HystrixRequestEventsJsonStream();
stream.getStream().subscribe(requestEvents -> {
    String json = HystrixRequestEventsJsonStream.convertRequestToJson(requestEvents);
    System.out.println("Request event: " + json);
});

data: [
  {
    "name": "GetUser",
    "events": [
      "SUCCESS"
    ],
    "latencies": [45],
    "cached": 0
  },
  {
    "name": "GetUserPreferences", 
    "events": [
      "TIMEOUT",
      "FALLBACK_SUCCESS"
    ],
    "latencies": [800],
    "cached": 0
  },
  {
    "name": "GetUserProfile",
    "events": [
      {
        "name": "FAILURE",
        "count": 3
      },
      "FALLBACK_SUCCESS"
    ],
    "latencies": [23, 45, 67],
    "cached": 2,
    "collapsed": {
      "name": "UserDataCollapser",
      "count": 5
    }
  }
]

// Configuration property for max concurrent connections
public static final String MAX_CONCURRENT_CONNECTIONS_PROPERTY = "hystrix.config.stream.maxConcurrentConnections";
public static final int DEFAULT_MAX_CONCURRENT_CONNECTIONS = 5;

// Old approach (deprecated)
HystrixRequestEventsJsonStream jsonStream = new HystrixRequestEventsJsonStream();
jsonStream.getStream().subscribe(events -> {
    String json = HystrixRequestEventsJsonStream.convertRequestToJson(events);
    // process json
});

// New approach (recommended)
HystrixRequestEventsStream.getInstance()
    .observe()
    .map(SerialHystrixRequestEvents::toJsonString)
    .subscribe(json -> {
        // process json
    });