StubbornJava · billoneil · Jan 29, 2018 · Jan 29, 2018 · Jan 29, 2018
diff --git a/...common/src/main/java/com/stubbornjava/common/undertow/handlers/CircuitBreakerHandler.java b/...common/src/main/java/com/stubbornjava/common/undertow/handlers/CircuitBreakerHandler.java
@@ -0,0 +1,39 @@
+package com.stubbornjava.common.undertow.handlers;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import io.undertow.server.HttpHandler;
+import io.undertow.server.HttpServerExchange;
+import net.jodah.failsafe.CircuitBreaker;
+import net.jodah.failsafe.Failsafe;
+
+// {{start:handler}}
+public class CircuitBreakerHandler implements HttpHandler {
+    private static final Logger log = LoggerFactory.getLogger(CircuitBreakerHandler.class);
+
+    private final CircuitBreaker circuitBreaker;
+    private final HttpHandler delegate;
+    private final HttpHandler failureHandler;
+
+    public CircuitBreakerHandler(CircuitBreaker circuitBreaker, HttpHandler delegate, HttpHandler failureHandler) {
+        super();
+        this.circuitBreaker = circuitBreaker;
+        this.delegate = delegate;
+        this.failureHandler = failureHandler;
+    }
+
+    @Override
+    public void handleRequest(HttpServerExchange exchange) throws Exception {
+        Failsafe.with(circuitBreaker)
+                .withFallback(() -> failureHandler.handleRequest(exchange))
+                // We need to call get here instead of execute so we can return the
+                // mutated exchange to run checks on it
+                .get(() -> {
+                    delegate.handleRequest(exchange);
+                    return exchange;
+                });
+    }
+}
+// {{end:handler}}
+
diff --git a/...bornjava-examples/src/main/java/com/stubbornjava/examples/failsafe/FailsafeWebserver.java b/...bornjava-examples/src/main/java/com/stubbornjava/examples/failsafe/FailsafeWebserver.java
@@ -0,0 +1,128 @@
+package com.stubbornjava.examples.failsafe;
+
+import java.io.IOException;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import com.stubbornjava.common.HttpClient;
+import com.stubbornjava.common.undertow.Exchange;
+import com.stubbornjava.common.undertow.SimpleServer;
+import com.stubbornjava.common.undertow.handlers.CircuitBreakerHandler;
+import com.stubbornjava.common.undertow.handlers.CustomHandlers;
+
+import io.undertow.server.HttpHandler;
+import io.undertow.server.HttpServerExchange;
+import io.undertow.util.StatusCodes;
+import net.jodah.failsafe.CircuitBreaker;
+import okhttp3.HttpUrl;
+import okhttp3.Request;
+
+public class FailsafeWebserver {
+    private static final Logger log = LoggerFactory.getLogger(FailsafeWebserver.class);
+
+    // {{start:handlers}}
+    private static final void serverError(HttpServerExchange exchange) {
+        exchange.setStatusCode(StatusCodes.INTERNAL_SERVER_ERROR);
+        Exchange.body().sendText(exchange, "500 - Internal Server Error");
+    }
+
+    // This handler helps simulate errors, bad requests, and successful requests.
+    private static final void circuitClosed(HttpServerExchange exchange) {
+        boolean error = Exchange.queryParams().queryParamAsBoolean(exchange, "error").orElse(false);
+        boolean exception = Exchange.queryParams().queryParamAsBoolean(exchange, "exception").orElse(false);
+        if (error) {
+            exchange.setStatusCode(StatusCodes.BAD_REQUEST);
+            Exchange.body().sendText(exchange, "Bad Request");
+        } else if (exception) {
+            throw new RuntimeException("boom");
+        } else {
+            Exchange.body().sendText(exchange, "Circuit is open everything is functioning properly.");
+        }
+    }
+
+    private static final HttpHandler CIRCUIT_BREAKER_HANDLER;
+    static {
+        CircuitBreaker breaker = new CircuitBreaker()
+             // Trigger circuit breaker failure on exceptions or bad requests
+            .failIf((HttpServerExchange exchange, Throwable ex) -> {
+                return (exchange != null && StatusCodes.BAD_REQUEST == exchange.getStatusCode())
+                        || ex != null;
+            })
+            // If 7 out of 10 requests fail Open the circuit
+            .withFailureThreshold(7, 10)
+            // When half open if 3 out of 5 requests succeed close the circuit
+            .withSuccessThreshold(3, 5)
+            // Delay this long before half opening the circuit
+            .withDelay(2, TimeUnit.SECONDS)
+            .onClose(() -> log.info("Circuit Closed"))
+            .onOpen(() -> log.info("Circuit Opened"))
+            .onHalfOpen(() -> log.info("Circuit Half-Open"));
+
+        CIRCUIT_BREAKER_HANDLER = new CircuitBreakerHandler(breaker,
+                                                            FailsafeWebserver::circuitClosed,
+                                                            FailsafeWebserver::serverError);
+    }
+    // {{end:handlers}}
+
+    // {{start:request}}
+    private static void request(boolean error, boolean exception) {
+        HttpUrl url = HttpUrl.parse("http://localhost:8080")
+                             .newBuilder()
+                             .addQueryParameter("error", String.valueOf(error))
+                             .addQueryParameter("exception", String.valueOf(exception))
+                             .build();
+
+        Request request = new Request.Builder().get().url(url).build();
+        try {
+            log.info(HttpClient.globalClient().newCall(request).execute().body().string());
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+    // {{end:request}}
+
+    // {{start:main}}
+    public static void main(String[] args) {
+
+        HttpHandler exceptionHandler =
+                CustomHandlers.exception(CIRCUIT_BREAKER_HANDLER)
+                              .addExceptionHandler(Throwable.class, FailsafeWebserver::serverError);
+
+        SimpleServer server = SimpleServer.simpleServer(exceptionHandler);
+        server.start();
+
+
+        // Warm-up the circuit breaker it needs to hit at least max executions
+        // Before it will reject anything. This will make that easier.
+        for (int i = 0; i < 10; i++) {
+            request(false, false);
+        }
+        ScheduledExecutorService schedExec = Executors.newScheduledThreadPool(1);
+
+        // A simple request that should always succeed
+        schedExec.scheduleAtFixedRate(() -> request(false, false), 0, 500, TimeUnit.MILLISECONDS);
+
+        // Send a batch of 15 bad requests to trigger the circuit breaker
+        Runnable errors = () -> {
+            log.info("Executing bad requests!");
+            for (int i = 0; i < 15; i++) {
+                request(true, false);
+            }
+        };
+        schedExec.schedule(errors, 1, TimeUnit.SECONDS);
+
+        // Send a batch of 15 requests that throw exceptions
+        Runnable exceptions = () -> {
+            log.info("Executing requests that throw exceptions!");
+            for (int i = 0; i < 15; i++) {
+                request(false, true);
+            }
+        };
+        schedExec.schedule(exceptions, 5, TimeUnit.SECONDS);
+    }
+    // {{end:main}}
+}