Add spring property binding example

src/main/java/com/wilkins/showcase/DefaultProperties.java

@@ -0,0 +1,9 @@
+package com.wilkins.showcase;
+
+import com.wilkins.showcase.domain.Greeting;
+import org.springframework.boot.context.properties.ConfigurationProperties;
+
+@ConfigurationProperties(prefix = "app.default")
+public record DefaultProperties(Greeting greeting) {
+
+}

src/main/java/com/wilkins/showcase/KebabProperties.java

@@ -0,0 +1,35 @@
+package com.wilkins.showcase;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+
+import java.util.Map;
+
+import static java.lang.Character.toUpperCase;
+import static java.util.stream.Collectors.joining;
+import static java.util.stream.Collectors.toMap;
+import static java.util.stream.IntStream.range;
+
+@ConfigurationProperties(prefix = "kebab")
+public record KebabProperties(Map<String, Object> config) {
+    public KebabProperties(Map<String, Object> config) {
+        this.config = config.entrySet().stream()
+                .collect(toMap(e -> fromKebabToCamel(e.getKey()), Map.Entry::getValue));
+    }
+
+    private static String fromKebabToCamel(String key) {
+        var words = key.split("-");
+        return range(0, words.length)
+                .mapToObj(
+                        i -> {
+                            String word = words[i];
+                            if (i == 0) {
+                                return word.isEmpty() ? word : word.toLowerCase();
+                            } else {
+                                return word.isEmpty()
+                                        ? word
+                                        : toUpperCase(word.charAt(0)) + word.substring(1).toLowerCase();
+                            }
+                        })
+                .collect(joining());
+    }
+}

src/main/java/com/wilkins/showcase/ShowcaseApplication.java

@@ -2,7 +2,9 @@
 
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
 
+@EnableConfigurationProperties(value = {KebabProperties.class, DefaultProperties.class})
 @SpringBootApplication
 public class ShowcaseApplication {
 

src/main/java/com/wilkins/showcase/controller/GreetingController.java

@@ -1,25 +1,35 @@
 package com.wilkins.showcase.controller;
 
+import com.wilkins.showcase.DefaultProperties;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RequestParam;
 import org.springframework.web.bind.annotation.RestController;
 
+import static java.util.Optional.ofNullable;
+
 @RestController
 @RequestMapping("/greetings")
 public class GreetingController {
 
     private static final Logger log = LoggerFactory.getLogger(GreetingController.class);
+    private final DefaultProperties defaultProperties;
+
+    public GreetingController(DefaultProperties defaultProperties) {
+        this.defaultProperties = defaultProperties;
+    }
 
     @GetMapping
-    public JsonGreeting getGreeting(@RequestParam(name = "salutation", required = false, defaultValue = "hello") String salutationParam,
-                                    @RequestParam(name = "name", required = false, defaultValue = "world") String nameParam) {
+    public JsonGreeting getGreeting(@RequestParam(name = "salutation", required = false) String salutationParam,
+                                    @RequestParam(name = "name", required = false) String nameParam) {
 
         log.info("A greeting was requested");
 
-        var greeting = JsonGreeting.of(salutationParam, nameParam);
+        var greeting = JsonGreeting.of(
+                ofNullable(salutationParam).orElse(defaultProperties.greeting().salutation()),
+                ofNullable(nameParam).orElse(defaultProperties.greeting().name()));
 
         log.info("Greeting returned: {}", greeting);
 

src/main/java/com/wilkins/showcase/domain/Greeting.java

@@ -0,0 +1,7 @@
+package com.wilkins.showcase.domain;
+
+public record Greeting(String salutation, String name) {
+    public static Greeting of(String salutation, String name) {
+        return new Greeting(salutation, name);
+    }
+}

src/main/resources/application.yml

@@ -0,0 +1,9 @@
+kebab:
+  config:
+    key-one: a
+    key-two: b
+app:
+  default:
+    greeting:
+      salutation: hello
+      name: world

src/test/java/com/wilkins/showcase/controller/GreetingControllerTest.java

@@ -1,10 +1,16 @@
 package com.wilkins.showcase.controller;
 
+import com.wilkins.showcase.DefaultProperties;
+import com.wilkins.showcase.KebabProperties;
+import com.wilkins.showcase.domain.Greeting;
 import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
+import org.springframework.test.context.DynamicPropertyRegistry;
+import org.springframework.test.context.DynamicPropertySource;
 import org.springframework.test.web.servlet.MockMvc;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.hamcrest.CoreMatchers.is;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
@@ -16,12 +22,29 @@ public class GreetingControllerTest {
     @Autowired
     MockMvc mockMvc;
 
+    @Autowired
+    KebabProperties kebabProperties;
+
+    @Autowired
+    DefaultProperties defaultProperties;
+
     @Test
     void returnsGreeting() throws Exception {
         mockMvc.perform(get("/greetings"))
                 .andExpect(status().isOk())
-                .andExpect(jsonPath("$.salutation", is("hello")))
-                .andExpect(jsonPath("$.name", is("world")));
+                .andExpect(jsonPath("$.salutation", is("good morning")))
+                .andExpect(jsonPath("$.name", is("Vietnam!")));
     }
 
+    @Test
+    void propertiesAreLoaded() {
+        assertThat(kebabProperties.config()).containsEntry("keyOne", "a");
+        assertThat(defaultProperties.greeting()).isEqualTo(Greeting.of("good morning", "Vietnam!"));
+    }
+
+    @DynamicPropertySource
+    static void dynamicPropertySource(DynamicPropertyRegistry registry) {
+        registry.add("app.default.greeting.salutation", () -> "good morning");
+        registry.add("app.default.greeting.name", () -> "Vietnam!");
+    }
 }