BAEL-6162: Code examples from article (#13458)

* Code example from article

* BAEL-6162: Add unit tests

* Rename test class

spring-web-modules/spring-resttemplate-3/README.md

@@ -11,3 +11,4 @@ The "REST With Spring" Classes: http://bit.ly/restwithspring
 - [Download a Large File Through a Spring RestTemplate](https://www.baeldung.com/spring-resttemplate-download-large-file)
 - [Access HTTPS REST Service Using Spring RestTemplate](https://www.baeldung.com/spring-resttemplate-secure-https-service)
 - [Encoding of URI Variables on RestTemplate](https://www.baeldung.com/spring-resttemplate-uri-variables-encode)
+- [Difference Between exchange(), postForEntity() and execute() in RestTemplate](https://www.baeldung.com/difference-between-exchange-postForEntity-and-execute)

spring-web-modules/spring-resttemplate-3/src/main/java/com/baeldung/resttemplate/methods/RestTemplateMethodsApplication.java

@@ -0,0 +1,102 @@
+package com.baeldung.resttemplate.methods;
+
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.ResponseEntity;
+import org.springframework.http.client.ClientHttpRequest;
+import org.springframework.http.client.ClientHttpResponse;
+import org.springframework.web.client.RequestCallback;
+import org.springframework.web.client.ResponseExtractor;
+import org.springframework.web.client.RestTemplate;
+
+import java.io.IOException;
+
+/**
+ * Examples of making the same call with RestTemplate
+ * using postForEntity(), exchange(), and execute().
+ */
+@SpringBootApplication
+public class RestTemplateMethodsApplication {
+    private final static RestTemplate restTemplate = new RestTemplate();
+
+    public static void main(String[] args) {
+
+    }
+
+    private static void postForEntity() {
+        Book book = new Book(
+            "Cruising Along with Java",
+            "Venkat Subramaniam",
+            2023);
+
+        ResponseEntity<Book> response = restTemplate.postForEntity(
+            "https://api.bookstore.com",
+            book,
+            Book.class);
+    }
+
+    private static void exchange() {
+        Book book = new Book(
+            "Effective Java",
+            "Joshua Bloch",
+            2001);
+
+        HttpHeaders headers = new HttpHeaders();
+        headers.setBasicAuth("username", "password");
+
+        ResponseEntity<Book> response = restTemplate.exchange(
+            "https://api.bookstore.com",
+            HttpMethod.POST,
+            new HttpEntity<>(book, headers),
+            Book.class);
+    }
+
+    private static void execute() {
+        ResponseEntity<Book> response = restTemplate.execute(
+            "https://api.bookstore.com",
+             HttpMethod.POST,
+             new RequestCallback() {
+                 @Override
+                 public void doWithRequest(ClientHttpRequest request) throws IOException {
+                        // Create or decorate the request object as needed
+                 }
+             },
+             new ResponseExtractor<ResponseEntity<Book>>() {
+                 @Override
+                 public ResponseEntity<Book> extractData(ClientHttpResponse response) throws IOException {
+                     // extract required data from response
+                     return null;
+                 }
+            }
+        );
+
+        // Could also use some factory methods in RestTemplate for
+        // the request callback and/or response extractor
+
+        Book book = new Book(
+            "Reactive Spring",
+            "Josh Long",
+            2020);
+
+        response = restTemplate.execute(
+            "https://api.bookstore.com",
+            HttpMethod.POST,
+            restTemplate.httpEntityCallback(book),
+            restTemplate.responseEntityExtractor(Book.class)
+        );
+    }
+
+    private static class Book {
+        String title;
+        String author;
+        int yearPublished;
+
+        public Book(String title, String author, int yearPublished) {
+            this.title = title;
+            this.author = author;
+            this.yearPublished = yearPublished;
+        }
+    }
+}

spring-web-modules/spring-resttemplate-3/src/test/java/com/baeldung/resttemplate/methods/RestTemplateMethodsUnitTest.java

@@ -0,0 +1,86 @@
+package com.baeldung.resttemplate.methods;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.http.*;
+import org.springframework.test.web.client.MockRestServiceServer;
+import org.springframework.test.web.client.response.MockRestResponseCreators;
+import org.springframework.web.client.RestTemplate;
+
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.method;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
+
+/**
+ * Unit tests for different ways to send POST with RestTemplate.
+ */
+public class RestTemplateMethodsUnitTest
+{
+
+    private final RestTemplate restTemplate = new RestTemplate();
+
+    private final String URL = "https://localhost:8080";
+
+    private MockRestServiceServer mockServer;
+
+    @BeforeEach
+    public void setup() {
+        mockServer = MockRestServiceServer.createServer(restTemplate);
+    }
+
+    /**
+     * Test that postForEntity sends a POST to the desired URL.
+     */
+    @Test
+    public void testPostForEntity() {
+
+        mockServer.expect(requestTo(URL))
+                .andExpect(method(HttpMethod.POST))
+                .andRespond(MockRestResponseCreators.withStatus(HttpStatus.OK)
+                        .contentType(MediaType.TEXT_PLAIN)
+                        .body("Ok"));
+
+        restTemplate.postForEntity(
+                URL,
+                "Test Body",
+                String.class);
+
+        mockServer.verify();
+    }
+
+    /**
+     * Test that exchange with POST method sends a POST to the desired URL.
+     */
+    @Test
+    public void testPostExchange() {
+        mockServer.expect(requestTo(URL))
+                .andExpect(method(HttpMethod.POST))
+                .andRespond(MockRestResponseCreators.withStatus(HttpStatus.OK)
+                        .contentType(MediaType.TEXT_PLAIN)
+                        .body("Ok"));
+
+        restTemplate.exchange(
+                URL,
+                HttpMethod.POST,
+                new HttpEntity<>("Test Body"),
+                String.class);
+
+        mockServer.verify();
+    }
+
+    @Test
+    public void testPostExecute() {
+        mockServer.expect(requestTo(URL))
+                .andExpect(method(HttpMethod.POST))
+                .andRespond(MockRestResponseCreators.withStatus(HttpStatus.OK)
+                        .contentType(MediaType.TEXT_PLAIN)
+                        .body("Ok"));
+
+        restTemplate.execute(
+                URL,
+                HttpMethod.POST,
+                restTemplate.httpEntityCallback("Test body"),
+                restTemplate.responseEntityExtractor(String.class));
+
+        mockServer.verify();
+    }
+}