Create GreetingsController.java (#11057)

* Create GreetingsController.java

add controller to test the content type being set properly or not

* add unit tests for greetings controller

* update to avoid PMD violation

* correct the file type

* Update GreetingsControllerUnitTest.java

fix some imports & correct the names

* Update GreetingsControllerUnitTest.java

update the unit case to avoid internal server error for junit

spring-web-modules/spring-mvc-basics-4/src/main/java/com/baeldung/controller/controller/GreetingsController.java

@@ -0,0 +1,49 @@
+package com.baeldung.controller.controller;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
+import org.springframework.stereotype.Controller;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestMethod;
+import org.springframework.web.bind.annotation.ResponseBody;
+
+@Controller
+public class GreetingsController {
+    
+    @RequestMapping(
+        value = "/greetings-with-response-body", 
+        method = RequestMethod.GET, 
+        produces="application/json"
+    ) 
+    @ResponseBody
+    public String getGreetingWhileReturnTypeIsString() { 
+        return "{\"test\": \"Hello using @ResponseBody\"}";
+    }
+        
+    @RequestMapping(
+        value = "/greetings-with-response-entity",
+        method = RequestMethod.GET, 
+        produces = "application/json"
+    )
+    public ResponseEntity<String> getGreetingWithResponseEntity() {
+        final HttpHeaders httpHeaders= new HttpHeaders();
+        httpHeaders.setContentType(MediaType.APPLICATION_JSON);
+        return new ResponseEntity<String>("{\"test\": \"Hello with ResponseEntity\"}", httpHeaders, HttpStatus.OK);
+    }
+    @RequestMapping(
+        value = "/greetings-with-map-return-type", 
+        method = RequestMethod.GET, 
+        produces = "application/json"
+    )
+    @ResponseBody
+    public Map<String, Object> getGreetingWhileReturnTypeIsMap() {
+        HashMap<String, Object> map = new HashMap<String, Object>();
+        map.put("test", "Hello from map");
+        return map;
+    }
+}

spring-web-modules/spring-mvc-basics-4/src/test/java/com/baeldung/controller/GreetingsControllerUnitTest.java

@@ -0,0 +1,58 @@
+package com.baeldung.controller;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.baeldung.controller.controller.GreetingsController;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+import org.springframework.test.context.web.AnnotationConfigWebContextLoader;
+import org.springframework.test.context.web.WebAppConfiguration;
+import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;
+import org.springframework.test.web.servlet.setup.MockMvcBuilders;
+import org.springframework.web.context.WebApplicationContext;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@WebAppConfiguration
+@ContextConfiguration(classes = { GreetingsController.class }, loader = AnnotationConfigWebContextLoader.class)
+public class GreetingsControllerUnitTest {
+    
+    private MockMvc mockMvc;
+
+    @Autowired
+    private WebApplicationContext wac;
+
+    @Before
+    public void setUp() {
+        this.mockMvc = MockMvcBuilders.webAppContextSetup(this.wac).build();
+    }
+	
+	@Test
+    public void givenReturnTypeIsString_whenJacksonOnClasspath_thenDefaultContentTypeIsJSON() throws Exception {
+        
+        // Given
+        String expectedMimeType = "application/json";
+        
+        // Then
+        String actualMimeType = this.mockMvc.perform(MockMvcRequestBuilders.get("/greetings-with-response-body", 1)).andReturn().getResponse().getContentType();
+
+        Assert.assertEquals(expectedMimeType, actualMimeType);
+        
+    }
+    
+    @Test
+    public void givenReturnTypeIsResponseEntity_thenDefaultContentTypeIsJSON() throws Exception {
+        
+        // Given
+        String expectedMimeType = "application/json";
+        
+        // Then
+        String actualMimeType = this.mockMvc.perform(MockMvcRequestBuilders.get("/greetings-with-response-entity", 1)).andReturn().getResponse().getContentType();
+
+        Assert.assertEquals(expectedMimeType, actualMimeType);
+    }
+}