Refactor some theme services

src/main/java/run/halo/app/controller/content/ContentSheetController.java

 package run.halo.app.controller.content;
 
-import cn.hutool.core.util.StrUtil;
 import org.springframework.stereotype.Controller;
 import org.springframework.ui.Model;
 import org.springframework.web.bind.annotation.GetMapping;
@@ -13,6 +12,8 @@ import run.halo.app.service.SheetService;
 import run.halo.app.service.ThemeService;
 
 /**
+ * Content sheet controller.
+ *
  * @author ryanwang
  * @date : 2019-03-21
  */
@@ -68,10 +69,8 @@ public class ContentSheetController {
         model.addAttribute("post", sheetService.convertToDetail(sheet));
         model.addAttribute("is_sheet", true);
 
-        if (StrUtil.isNotEmpty(sheet.getTemplate())) {
-            if (themeService.templateExists(ThemeService.CUSTOM_SHEET_PREFIX + sheet.getTemplate() + HaloConst.SUFFIX_FTL)) {
-                return themeService.render(ThemeService.CUSTOM_SHEET_PREFIX + sheet.getTemplate());
-            }
+        if (themeService.templateExists(ThemeService.CUSTOM_SHEET_PREFIX + sheet.getTemplate() + HaloConst.SUFFIX_FTL)) {
+            return themeService.render(ThemeService.CUSTOM_SHEET_PREFIX + sheet.getTemplate());
         }
         return themeService.render("sheet");
     }

src/main/java/run/halo/app/service/ThemeService.java

 package run.halo.app.service;
 
 import org.springframework.lang.NonNull;
+import org.springframework.lang.Nullable;
 import org.springframework.web.multipart.MultipartFile;
 import run.halo.app.handler.theme.config.support.Group;
 import run.halo.app.handler.theme.config.support.ThemeProperty;
@@ -82,11 +83,11 @@ public interface ThemeService {
     /**
      * Get theme property by theme id.
      *
-     * @param themeId must not be blank
+     * @param themeId theme id
      * @return a optional theme property
      */
     @NonNull
-    Optional<ThemeProperty> getThemeBy(@NonNull String themeId);
+    Optional<ThemeProperty> getThemeBy(@Nullable String themeId);
 
     /**
      * Gets all themes
@@ -126,15 +127,15 @@ public interface ThemeService {
      * @param template template must not be blank
      * @return boolean
      */
-    boolean templateExists(@NonNull String template);
+    boolean templateExists(@Nullable String template);
 
     /**
      * Checks whether theme exists under template path
      *
-     * @param themeId theme name
+     * @param themeId theme id
      * @return boolean
      */
-    boolean themeExists(@NonNull String themeId);
+    boolean themeExists(@Nullable String themeId);
 
     /**
      * Gets theme base path.

src/main/java/run/halo/app/service/impl/ThemeServiceImpl.java

@@ -105,7 +105,9 @@ public class ThemeServiceImpl implements ThemeService {
 
     @Override
     public Optional<ThemeProperty> getThemeBy(String themeId) {
-        Assert.hasText(themeId, "Theme id must not be blank");
+        if (StringUtils.isBlank(themeId)) {
+            return Optional.empty();
+        }
 
         // Get all themes
         Set<ThemeProperty> themes = getThemes();
@@ -181,7 +183,9 @@ public class ThemeServiceImpl implements ThemeService {
 
     @Override
     public boolean templateExists(String template) {
-        Assert.hasText(template, "Template must not be blank");
+        if (StringUtils.isBlank(template)) {
+            return false;
+        }
 
         // Resolve template path
         Path templatePath = Paths.get(getActivatedTheme().getThemePath(), template);
@@ -507,7 +511,7 @@ public class ThemeServiceImpl implements ThemeService {
      */
     private void setActivatedTheme(@Nullable ThemeProperty activatedTheme) {
         this.activatedTheme = activatedTheme;
-        this.activatedThemeId = activatedTheme.getId();
+        this.activatedThemeId = Optional.ofNullable(activatedTheme).map(ThemeProperty::getId).orElse(null);
     }
 
     /**