[ISSUE-alibaba#4258] Fix wrong path when -Dspring.config.location not…

… set (alibaba#4259)

* fix spring.config.location is nullapplication.properties when -Dspring.config.location is not set in env

* fix wrong path when -Dspring.config.location not set

* modify default file resource method name

* fix "/" magic value

* change the way of get file

* not judge pathSplit by self, use Paths.get(a, b);

* when spring.config.location is not set, use {nacos.home}/conf/application.properties to cover it.

* refactor code

* code quality enhance

* just use two level to load conf. {spring.config.location}/application.properties -> classpath:/application.properties

* code clean

sys/src/main/java/com/alibaba/nacos/sys/env/EnvUtil.java

@@ -361,19 +361,31 @@ public static String getMemberList() {
     private static final String FILE_PREFIX = "file:";
 
     public static Resource getApplicationConfFileResource() {
+        Resource customResource = getCustomFileResource();
+        return customResource == null ? getDefaultResource() : customResource;
+    }
+
+    private static Resource getCustomFileResource() {
         String path = getProperty("spring.config.location");
-        InputStream inputStream = null;
         if (StringUtils.isNotBlank(path) && path.contains(FILE_PREFIX)) {
             String[] paths = path.split(",");
             path = paths[paths.length - 1].substring(FILE_PREFIX.length());
+            return getRelativePathResource(path, "application.properties");
         }
+        return null;
+    }
+
+    private static Resource getRelativePathResource(String parentPath, String path) {
         try {
-            inputStream = new FileInputStream(new File(path + "application.properties"));
+            InputStream inputStream = new FileInputStream(Paths.get(parentPath, path).toFile());
+            return new InputStreamResource(inputStream);
         } catch (Exception ignore) {
         }
-        if (inputStream == null) {
-            inputStream = EnvUtil.class.getResourceAsStream("/application.properties");
-        }
+        return null;
+    }
+
+    private static Resource getDefaultResource() {
+        InputStream inputStream = EnvUtil.class.getResourceAsStream("/application.properties");
         return new InputStreamResource(inputStream);
     }