support to save the uploaded file

src/main/java/io/github/devopsws/demo/service/FileService.java

@@ -1,5 +1,8 @@
 package io.github.devopsws.demo.service;
 
+import java.io.FileOutputStream;
+
+import org.springframework.util.FileCopyUtils;
 import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RequestParam;
@@ -16,8 +19,11 @@ public Message<?> upload(@RequestParam("file") MultipartFile file) {
         System.out.println("Received file uploading request");
         Message<String> message = new Message<String>();
         if (!file.isEmpty()) {
-            try {
-                System.out.println("Uploading file size:" + file.getSize());
+            String filename = file.getOriginalFilename();
+            try (FileOutputStream out = new FileOutputStream(filename)) {
+                System.out.println("Uploading file size: " + file.getSize() + ", name: " + filename);
+
+                FileCopyUtils.copy(file.getInputStream(), out);
 
                 message.setMessage("ok");
             } catch (Exception e) {

src/main/java/io/github/devopsws/demo/service/RootService.java

@@ -0,0 +1,13 @@
+package io.github.devopsws.demo.service;
+
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController("/")
+public class RootService {
+
+    @GetMapping("")
+    public String index() {
+        return "Let's learn spring boot!";
+    }
+}