Add rest-client-test module: @RestClientTest on Boot 4.1, Jackson 3 by default, and the RestClient-vs-RestTemplate root-URI matching trap (post #49)

2026-10-08 16:40:51 +00:00
parent 4370ac7fdf
commit b9388053c4
23 changed files with 704 additions and 0 deletions
@@ -0,0 +1,27 @@
+package com.ankurm.restclienttest;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+/**
+ * Writes a real line of test output to {@code docs/output/<fileName>}, so every number quoted in
+ * the post traces back to a committed transcript rather than a remembered one.
+ */
+final class Capture {
+
+    private Capture() {
+    }
+
+    static void write(String fileName, String heading, String body) {
+        Path dir = Paths.get("docs", "output");
+        try {
+            Files.createDirectories(dir);
+            Files.writeString(dir.resolve(fileName), "== " + heading + " ==\n\n" + body + "\n");
+        } catch (IOException e) {
+            throw new UncheckedIOException(e);
+        }
+    }
+}
@@ -0,0 +1,52 @@
+package com.ankurm.restclienttest;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.restclient.test.autoconfigure.RestClientTest;
+import org.springframework.http.HttpStatus;
+import org.springframework.test.context.bean.override.mockito.MockitoBean;
+import org.springframework.test.web.client.MockRestServiceServer;
+import org.springframework.web.client.HttpClientErrorException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
+import static org.springframework.test.web.client.response.MockRestResponseCreators.withStatus;
+
+/**
+ * A well-rounded client test suite covers failure paths too. {@code MockRestServiceServer} makes
+ * a 404 just as easy to simulate as a 200.
+ */
+@RestClientTest(EmployeeClient.class)
+class ErrorScenarioTest {
+
+    @Autowired
+    private MockRestServiceServer mockServer;
+
+    @Autowired
+    private EmployeeClient employeeClient;
+
+    @MockitoBean
+    private EmployeeAuditLogger auditLogger;
+
+    @Test
+    void whenEmployeeNotFound_thenThrowsException() {
+        mockServer.expect(requestTo("http://hr-api.example.com/employees/99"))
+                .andRespond(withStatus(HttpStatus.NOT_FOUND));
+
+        HttpClientErrorException.NotFound thrown = null;
+        try {
+            employeeClient.getEmployeeById(99);
+        } catch (HttpClientErrorException.NotFound ex) {
+            thrown = ex;
+        }
+
+        assertThat(thrown).isNotNull();
+        mockServer.verify();
+
+        Capture.write("03-404-throws-notfound.txt",
+                "A 404 response from MockRestServiceServer surfaces as HttpClientErrorException.NotFound",
+                "requestTo(\"http://hr-api.example.com/employees/99\") -> 404 Not Found\n"
+                        + "exception class = " + thrown.getClass().getName()
+                        + "\nexception.getStatusCode() = " + thrown.getStatusCode());
+    }
+}
@@ -0,0 +1,54 @@
+package com.ankurm.restclienttest;
+
+import tools.jackson.databind.ObjectMapper;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.restclient.test.autoconfigure.RestClientTest;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.client.MockRestServiceServer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
+import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
+
+/**
+ * {@link EmployeeHttpInterface} has no class {@code @RestClientTest} can point at directly - it
+ * is a bare interface, and the real bean only exists because {@link AppConfig}'s
+ * {@code @Bean} method builds it from an {@code HttpServiceProxyFactory}. Passing the
+ * {@code @Configuration} class itself as the slice's "component" is what gets that bean (and
+ * the underlying {@code RestClient} it is built from) into the test context at all; the mocking
+ * code underneath is otherwise identical to {@link RestClientEmployeeTest}.
+ */
+@RestClientTest(components = AppConfig.class)
+class HttpInterfaceClientTest {
+
+    @Autowired
+    private MockRestServiceServer mockServer;
+
+    @Autowired
+    private EmployeeHttpInterface employeeHttpInterface;
+
+    @Autowired
+    private ObjectMapper objectMapper;
+
+    @Test
+    void whenGetEmployeeById_thenHttpInterfaceReturnsEmployee() throws Exception {
+        Employee mockEmployee = new Employee(3, "Daniel", "O", "[email protected]");
+        String employeeJson = objectMapper.writeValueAsString(mockEmployee);
+
+        mockServer.expect(requestTo("http://hr-api.example.com/employees/3"))
+                .andRespond(withSuccess(employeeJson, MediaType.APPLICATION_JSON));
+
+        Employee result = employeeHttpInterface.getEmployeeById(3);
+
+        assertThat(result).isNotNull();
+        assertThat(result.id()).isEqualTo(3);
+        assertThat(result.firstName()).isEqualTo("Daniel");
+
+        mockServer.verify();
+
+        Capture.write("04-http-interface-client.txt",
+                "A declarative @HttpExchange interface client, mocked the same way as a hand-written one",
+                "requestTo(\"http://hr-api.example.com/employees/3\") -> 200 OK " + employeeJson + "\nresult = " + result);
+    }
+}
@@ -0,0 +1,62 @@
+package com.ankurm.restclienttest;
+
+import tools.jackson.databind.ObjectMapper;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.restclient.test.autoconfigure.RestClientTest;
+import org.springframework.http.MediaType;
+import org.springframework.test.context.bean.override.mockito.MockitoBean;
+import org.springframework.test.web.client.MockRestServiceServer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
+import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
+
+/**
+ * The core example: a {@code RestClient}-based client, tested with {@code @RestClientTest} and
+ * {@code MockRestServiceServer}. {@link EmployeeClient} also depends on
+ * {@link EmployeeAuditLogger}, a plain collaborator the REST-client slice never creates on its
+ * own - replaced here with {@code @MockitoBean} now that {@code @MockBean} no longer exists in
+ * Spring Boot 4.
+ */
+@RestClientTest(EmployeeClient.class)
+class RestClientEmployeeTest {
+
+    @Autowired
+    private MockRestServiceServer mockServer;
+
+    @Autowired
+    private EmployeeClient employeeClient;
+
+    @Autowired
+    private ObjectMapper objectMapper;
+
+    @MockitoBean
+    private EmployeeAuditLogger auditLogger;
+
+    @Test
+    void whenGetEmployeeById_thenReturnsEmployeeAndAudits() throws Exception {
+        Employee mockEmployee = new Employee(1, "Ankur", "M", "[email protected]");
+        String employeeJson = objectMapper.writeValueAsString(mockEmployee);
+
+        mockServer.expect(requestTo("http://hr-api.example.com/employees/1"))
+                .andRespond(withSuccess(employeeJson, MediaType.APPLICATION_JSON));
+
+        Employee result = employeeClient.getEmployeeById(1);
+
+        assertThat(result).isNotNull();
+        assertThat(result.id()).isEqualTo(1);
+        assertThat(result.firstName()).isEqualTo("Ankur");
+
+        mockServer.verify();
+        Mockito.verify(auditLogger).logFetch(1);
+
+        Capture.write("01-restclient-basic-fetch.txt",
+                "RestClient-based EmployeeClient, real deserialized result and audit call",
+                "requestTo(\"http://hr-api.example.com/employees/1\") -> 200 OK " + employeeJson
+                        + "\nresult = " + result
+                        + "\nauditLogger.logFetch(1) called = " + Mockito.mockingDetails(auditLogger)
+                        .getInvocations().stream().anyMatch(i -> i.getMethod().getName().equals("logFetch")));
+    }
+}
@@ -0,0 +1,52 @@
+package com.ankurm.restclienttest;
+
+import tools.jackson.databind.ObjectMapper;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.restclient.test.autoconfigure.RestClientTest;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.client.MockRestServiceServer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
+import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
+
+/**
+ * Same job, built on {@code RestTemplate} instead of {@code RestClient}.
+ * {@code @RestClientTest} auto-configures a {@code RestTemplateBuilder} too, so any
+ * {@code RestTemplate} built from it is wired through the same {@code MockRestServiceServer} -
+ * the mocking code below is identical to {@link RestClientEmployeeTest}'s, line for line.
+ */
+@RestClientTest(EmployeeTemplateClient.class)
+class RestTemplateEmployeeTest {
+
+    @Autowired
+    private MockRestServiceServer mockServer;
+
+    @Autowired
+    private EmployeeTemplateClient employeeTemplateClient;
+
+    @Autowired
+    private ObjectMapper objectMapper;
+
+    @Test
+    void whenGetEmployeeById_thenReturnsEmployee() throws Exception {
+        Employee mockEmployee = new Employee(2, "Priya", "V", "[email protected]");
+        String employeeJson = objectMapper.writeValueAsString(mockEmployee);
+
+        mockServer.expect(requestTo("/employees/2"))
+                .andRespond(withSuccess(employeeJson, MediaType.APPLICATION_JSON));
+
+        Employee result = employeeTemplateClient.getEmployeeById(2);
+
+        assertThat(result).isNotNull();
+        assertThat(result.id()).isEqualTo(2);
+        assertThat(result.firstName()).isEqualTo("Priya");
+
+        mockServer.verify();
+
+        Capture.write("02-resttemplate-same-mocking-code.txt",
+                "RestTemplate-based EmployeeTemplateClient, identical MockRestServiceServer code",
+                "requestTo(\"/employees/2\") -> 200 OK " + employeeJson + "\nresult = " + result);
+    }
+}