BAEL-9085: Introduction to Ambassdor Design Pattern (#18602)

* adding ambassador pattern with retry, timeout, fallback, logging, and caching

* adding tests. fix client class annotations

* change naming

* formatting files

* adding back dependency versions

* renaming test

* switch from system out to slf4j loggers

Author: pedrolopes9-7

patterns-modules/design-patterns-architectural/pom.xml

@@ -72,8 +72,6 @@
         <spring-integration-test.version>5.5.14</spring-integration-test.version>
         <camel-core.version>3.20.4</camel-core.version>
         <camel-test-junit5.version>3.14.0</camel-test-junit5.version>
-        <org.slf4j.version>1.7.32</org.slf4j.version>
-        <logback.version>1.2.7</logback.version>
     </properties>
 
 </project>

patterns-modules/design-patterns-architectural/src/main/java/com/baeldung/ambassadorpattern/AmbassadorPatternApplication.java

@@ -0,0 +1,16 @@
+package com.baeldung.ambassadorpattern;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.cache.annotation.EnableCaching;
+import org.springframework.retry.annotation.EnableRetry;
+
+@EnableRetry
+@EnableCaching
+@SpringBootApplication
+public class AmbassadorPatternApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(AmbassadorPatternApplication.class, args);
+    }
+}

patterns-modules/design-patterns-architectural/src/main/java/com/baeldung/ambassadorpattern/HttpAmbassadorController.java

@@ -0,0 +1,21 @@
+package com.baeldung.ambassadorpattern;
+
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@RequestMapping("/v1/http-ambassador/names")
+public class HttpAmbassadorController {
+
+    private final HttpAmbassadorNamesApiClient httpAmbassadorNamesApiClient;
+
+    public HttpAmbassadorController(HttpAmbassadorNamesApiClient httpAmbassadorNamesApiClient) {
+        this.httpAmbassadorNamesApiClient = httpAmbassadorNamesApiClient;
+    }
+
+    @GetMapping
+    public String get() {
+        return httpAmbassadorNamesApiClient.getResponse();
+    }
+}

patterns-modules/design-patterns-architectural/src/main/java/com/baeldung/ambassadorpattern/HttpAmbassadorNamesApiClient.java

@@ -0,0 +1,46 @@
+package com.baeldung.ambassadorpattern;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.cache.annotation.Cacheable;
+import org.springframework.retry.annotation.Backoff;
+import org.springframework.retry.annotation.Recover;
+import org.springframework.retry.annotation.Retryable;
+import org.springframework.stereotype.Component;
+import org.springframework.web.client.HttpClientErrorException;
+import org.springframework.web.client.HttpServerErrorException;
+import org.springframework.web.client.RestTemplate;
+
+@Component
+public class HttpAmbassadorNamesApiClient {
+
+    private final RestTemplate restTemplate;
+    private final Logger logger = LoggerFactory.getLogger(HttpAmbassadorNamesApiClient.class);
+    public final String apiUrl;
+
+    public HttpAmbassadorNamesApiClient(RestTemplate restTemplate, @Value("${names-api-url}") String apiUrl) {
+        this.restTemplate = restTemplate;
+        this.apiUrl = apiUrl;
+    }
+
+    @Cacheable(value = "httpResponses", key = "#root.target.apiUrl", unless = "#result == null")
+    @Retryable(value = { HttpServerErrorException.class }, maxAttempts = 5, backoff = @Backoff(delay = 1000))
+    public String getResponse() {
+        try {
+            String result = restTemplate.getForObject(apiUrl, String.class);
+            logger.info("HTTP call completed successfully to url={}", apiUrl);
+            return result;
+        } catch (HttpClientErrorException e) {
+            logger.error("HTTP Client Error error_code={} message={}", e.getStatusCode(), e.getMessage());
+            throw e;
+        }
+    }
+
+    @Recover
+    public String recover(Exception e) {
+        final String defaultResponse = "default";
+        logger.error("Too many retry attempts. Falling back to default. error={} default={}", e.getMessage(), defaultResponse);
+        return defaultResponse;
+    }
+}

patterns-modules/design-patterns-architectural/src/main/java/com/baeldung/ambassadorpattern/RestTemplateConfig.java

@@ -0,0 +1,31 @@
+package com.baeldung.ambassadorpattern;
+
+import java.time.Duration;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.boot.web.client.RestTemplateBuilder;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.client.RestTemplate;
+
+@Configuration
+public class RestTemplateConfig {
+
+    private final int connectTimeoutSeconds;
+    private final int readTimeoutSeconds;
+    private final RestTemplateBuilder restTemplateBuilder;
+
+    public RestTemplateConfig(RestTemplateBuilder restTemplateBuilder, @Value("${http.client.read-timeout-seconds}") int readTimeoutSeconds,
+        @Value("${http.client.connect-timeout-seconds}") int connectTimeoutSeconds) {
+        this.restTemplateBuilder = restTemplateBuilder;
+        this.readTimeoutSeconds = readTimeoutSeconds;
+        this.connectTimeoutSeconds = connectTimeoutSeconds;
+    }
+
+    @Bean
+    public RestTemplate restTemplate() {
+        return restTemplateBuilder.setConnectTimeout(Duration.ofMillis(connectTimeoutSeconds))
+            .setReadTimeout(Duration.ofMillis(readTimeoutSeconds))
+            .build();
+    }
+}

patterns-modules/design-patterns-architectural/src/main/resources/application.properties

@@ -0,0 +1,3 @@
+http.client.connect-timeout-seconds=2000
+http.client.read-timeout-seconds=3000
+names-api-url=https://domain.com/names/api

patterns-modules/design-patterns-architectural/src/test/java/com/baeldung/ambassadorpattern/HttpAmbassadorControllerIntegrationTest.java

@@ -0,0 +1,38 @@
+package com.baeldung.ambassadorpattern;
+
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.when;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
+import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
+import org.springframework.boot.test.mock.mockito.MockBean;
+import org.springframework.context.annotation.Import;
+import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.web.client.RestTemplate;
+
+@WebMvcTest(HttpAmbassadorController.class)
+@Import({ HttpAmbassadorNamesApiClient.class, TestConfig.class })
+@AutoConfigureMockMvc(addFilters = false)
+class HttpAmbassadorControllerIntegrationTest {
+
+    @Autowired
+    private MockMvc mockMvc;
+
+    @MockBean
+    private RestTemplate restTemplate;
+
+    @Test
+    void givenExternalCallMock_whenGetNames_thenReturnExpectedName() throws Exception {
+        String expectedResponse = "{'name': 'Baeldung'}";
+        when(restTemplate.getForObject(eq("https://domain.com/names/api"), eq(String.class))).thenReturn(expectedResponse);
+
+        mockMvc.perform(get("/v1/http-ambassador/names"))
+            .andExpect(status().isOk())
+            .andExpect(content().string(expectedResponse));
+    }
+}

patterns-modules/design-patterns-architectural/src/test/java/com/baeldung/ambassadorpattern/TestConfig.java

@@ -0,0 +1,11 @@
+package com.baeldung.ambassadorpattern;
+
+
+import org.springframework.context.annotation.Configuration;
+import org.springframework.retry.annotation.EnableRetry;
+
+@Configuration
+@EnableRetry
+public class TestConfig {
+
+}