BAEL-5775 | Add classes and tests relevant to BAEL-5775 article. (#18674)

* BAEL-5775 | Add classes and tests relevant to BAEL-5775 article.

* BAEL-5775 | Updates according to editor feedback

* BAEL-5775 | Removed some not needed code.

* BAEL-5775 | Update spring-webflux and reactor versions in pom.xml

* BAEL-5775 | Refactor code for improved readability and consistency

* Add method to fetch users list using existing ParameterizedTypeReference

* BAEL-5775 | Update Java version in pom.xml to 17

---------

Co-authored-by: Andrei Branza <[email protected]>

Author: AndreiBranza

spring-core-4/pom.xml

@@ -5,6 +5,18 @@
     <modelVersion>4.0.0</modelVersion>
     <artifactId>spring-core-4</artifactId>
     <name>spring-core-4</name>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>17</source>
+                    <target>17</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
 
     <parent>
         <groupId>com.baeldung</groupId>
@@ -70,13 +82,56 @@
             <artifactId>commons-text</artifactId>
             <version>${commons-text.version}</version>
         </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-webflux</artifactId>
+            <version>${spring-webflux.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-junit-jupiter</artifactId>
+            <version>${mockito.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>io.projectreactor</groupId>
+            <artifactId>reactor-test</artifactId>
+            <version>${reactor.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.github.tomakehurst</groupId>
+            <artifactId>wiremock-jre8-standalone</artifactId>
+            <version>${wiremock.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>${jackson.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-core</artifactId>
+            <version>${jackson.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-annotations</artifactId>
+            <version>${jackson.version}</version>
+        </dependency>
     </dependencies>
 
     <properties>
         <awaitility.version>4.0.2</awaitility.version>
         <jakarta-servlet.version>6.1.0</jakarta-servlet.version>
         <jakarta-annotation.version>3.0.0</jakarta-annotation.version>
         <commons-text.version>1.10.0</commons-text.version>
+        <spring-webflux.version>6.2.9</spring-webflux.version>
+        <mockito.version>5.18.0</mockito.version>
+        <reactor.version>3.7.8</reactor.version>
+        <wiremock.version>2.35.0</wiremock.version>
+        <jackson.version>2.19.1</jackson.version>
     </properties>
 
 </project>

spring-core-4/src/main/java/com/baeldung/parametrizedtypereference/ApiException.java

@@ -0,0 +1,12 @@
+package com.baeldung.parametrizedtypereference;
+
+public class ApiException extends RuntimeException {
+
+    public ApiException(String message) {
+        super(message);
+    }
+
+    public ApiException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}

spring-core-4/src/main/java/com/baeldung/parametrizedtypereference/ApiResponse.java

@@ -0,0 +1,5 @@
+package com.baeldung.parametrizedtypereference;
+
+public record ApiResponse<T>(boolean success, String message, T data) {
+
+}

spring-core-4/src/main/java/com/baeldung/parametrizedtypereference/ApiService.java

@@ -0,0 +1,70 @@
+package com.baeldung.parametrizedtypereference;
+
+import static com.baeldung.parametrizedtypereference.TypeReferences.USER_LIST;
+
+import java.util.List;
+
+import org.springframework.core.ParameterizedTypeReference;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.ResponseEntity;
+import org.springframework.stereotype.Service;
+import org.springframework.web.client.RestTemplate;
+
+@Service
+public class ApiService {
+
+    private final RestTemplate restTemplate;
+    private final String baseUrl;
+
+    public ApiService(RestTemplate restTemplate, String baseUrl) {
+        this.restTemplate = restTemplate;
+        this.baseUrl = baseUrl;
+    }
+
+    public List<User> fetchUserList() {
+        ParameterizedTypeReference<List<User>> typeRef = new ParameterizedTypeReference<List<User>>() {
+        };
+
+        ResponseEntity<List<User>> response = restTemplate.exchange(baseUrl + "/api/users", HttpMethod.GET, null, typeRef);
+
+        return response.getBody();
+    }
+
+    public List<User> fetchUsersWrongApproach() {
+        ResponseEntity<List> response = restTemplate.getForEntity(baseUrl + "/api/users", List.class);
+
+        return (List<User>) response.getBody();
+    }
+
+    public List<User> fetchUsersCorrectApproach() {
+        ParameterizedTypeReference<List<User>> typeRef = new ParameterizedTypeReference<List<User>>() {
+        };
+
+        ResponseEntity<List<User>> response = restTemplate.exchange(baseUrl + "/api/users", HttpMethod.GET, null, typeRef);
+
+        return response.getBody();
+    }
+
+    public User fetchUser(Long id) {
+        return restTemplate.getForObject(baseUrl + "/api/users/" + id, User.class);
+    }
+
+    public User[] fetchUsersArray() {
+        return restTemplate.getForObject(baseUrl + "/api/users", User[].class);
+    }
+
+    public List<User> fetchUsersList() {
+        ParameterizedTypeReference<List<User>> typeRef = new ParameterizedTypeReference<List<User>>() {
+        };
+
+        ResponseEntity<List<User>> response = restTemplate.exchange(baseUrl + "/api/users", HttpMethod.GET, null, typeRef);
+
+        return response.getBody();
+    }
+
+    public List<User> fetchUsersListWithExistingReference() {
+        ResponseEntity<List<User>> response = restTemplate.exchange(baseUrl + "/api/users", HttpMethod.GET, null, USER_LIST);
+
+        return response.getBody();
+    }
+}

spring-core-4/src/main/java/com/baeldung/parametrizedtypereference/ReactiveApiService.java

@@ -0,0 +1,43 @@
+package com.baeldung.parametrizedtypereference;
+
+import java.util.List;
+import java.util.Map;
+
+import org.springframework.core.ParameterizedTypeReference;
+import org.springframework.stereotype.Service;
+import org.springframework.web.reactive.function.client.WebClient;
+
+import reactor.core.publisher.Mono;
+
+@Service
+public class ReactiveApiService {
+
+    private final WebClient webClient;
+
+    public ReactiveApiService(String baseUrl) {
+        this.webClient = WebClient.builder()
+            .baseUrl(baseUrl)
+            .build();
+    }
+
+    public Mono<Map<String, List<User>>> fetchUsersByDepartment() {
+        ParameterizedTypeReference<Map<String, List<User>>> typeRef = new ParameterizedTypeReference<Map<String, List<User>>>() {
+        };
+
+        return webClient.get()
+            .uri("/users/by-department")
+            .retrieve()
+            .bodyToMono(typeRef);
+    }
+
+    public Mono<ApiResponse<List<User>>> fetchUsersWithWrapper() {
+        ParameterizedTypeReference<ApiResponse<List<User>>> typeRef = new ParameterizedTypeReference<ApiResponse<List<User>>>() {
+        };
+
+        return webClient.get()
+            .uri("/users/wrapped")
+            .retrieve()
+            .bodyToMono(typeRef);
+    }
+
+}

spring-core-4/src/main/java/com/baeldung/parametrizedtypereference/TypeReferences.java

@@ -0,0 +1,16 @@
+package com.baeldung.parametrizedtypereference;
+
+import java.util.List;
+import java.util.Map;
+
+import org.springframework.core.ParameterizedTypeReference;
+
+public class TypeReferences {
+
+    public static final ParameterizedTypeReference<List<User>> USER_LIST = new ParameterizedTypeReference<List<User>>() {
+    };
+
+    public static final ParameterizedTypeReference<Map<String, List<User>>> USER_MAP = new ParameterizedTypeReference<Map<String, List<User>>>() {
+    };
+
+}

spring-core-4/src/main/java/com/baeldung/parametrizedtypereference/User.java

@@ -0,0 +1,52 @@
+package com.baeldung.parametrizedtypereference;
+
+public class User {
+
+    private Long id;
+    private String name;
+    private String email;
+    private String department;
+
+    public User() {
+    }
+
+    public User(Long id, String name, String email, String department) {
+        this.id = id;
+        this.name = name;
+        this.email = email;
+        this.department = department;
+    }
+
+    // Getters and setters
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email = email;
+    }
+
+    public String getDepartment() {
+        return department;
+    }
+
+    public void setDepartment(String department) {
+        this.department = department;
+    }
+}