Merge pull request #39 from edu-pi/feature/issue38

[#38]feat: gateway 뒤에 있는 서버가 죽었을 경우 예외 처리

src/main/java/soma/edupigateway/filter/ServerConnectionExceptionFilter.java

@@ -0,0 +1,34 @@
+package soma.edupigateway.filter;
+
+import java.net.ConnectException;
+import java.nio.charset.StandardCharsets;
+import org.springframework.cloud.gateway.filter.GatewayFilterChain;
+import org.springframework.cloud.gateway.filter.GlobalFilter;
+import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.core.io.buffer.DataBufferFactory;
+import org.springframework.http.HttpStatus;
+import org.springframework.stereotype.Component;
+import org.springframework.web.server.ServerWebExchange;
+import reactor.core.publisher.Mono;
+
+@Component
+public class ServerConnectionExceptionFilter implements GlobalFilter {
+
+    @Override
+    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
+        return chain.filter(exchange)
+            .onErrorResume(ConnectException.class, throwable -> handleConnectException(exchange));
+    }
+
+    private Mono<Void> handleConnectException(ServerWebExchange exchange) {
+        // 응답 설정
+        exchange.getResponse().setStatusCode(HttpStatus.SERVICE_UNAVAILABLE);
+
+        String responseBody = "The backend server is unavailable.";
+
+        DataBufferFactory dataBufferFactory = exchange.getResponse().bufferFactory();
+        DataBuffer buffer = dataBufferFactory.wrap(responseBody.getBytes(StandardCharsets.UTF_8));
+
+        return exchange.getResponse().writeWith(Mono.just(buffer));
+    }
+}