Compatible with markdown file from hexo (#1492)

* hexo语法省略开头的---时无法解析元信息，兼容此种情况

* 修复导入markdown文件时固定条件下出现 [该标签已存在] 的异常

* hexo语法的博客在实际使用时可以省略开头的 --- 分隔符 : add unit test

* fix code style

Co-authored-by: zhanglei <zhanglei9588@foxmail.com>

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

@@ -31,7 +31,7 @@ public interface TagService extends CrudService<Tag, Integer> {
      * @param slug slug
      * @return tag
      */
-    @NonNull
+    @Nullable
     Tag getBySlug(@NonNull String slug);
 
     /**

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

@@ -412,10 +412,14 @@ public class PostServiceImpl extends BasePostServiceImpl<Post> implements PostSe
                                 tagName = StringUtils.strip(tagName, "\"");
                                 tagName = StringUtils.strip(tagName, "\'");
                                 tag = tagService.getByName(tagName);
+                                String slug = SlugUtils.slug(tagName);
+                                if (null == tag) {
+                                    tag = tagService.getBySlug(slug);
+                                }
                                 if (null == tag) {
                                     tag = new Tag();
                                     tag.setName(tagName);
-                                    tag.setSlug(SlugUtils.slug(tagName));
+                                    tag.setSlug(slug);
                                     tag = tagService.create(tag);
                                 }
                                 tagIds.add(tag.getId());

src/main/java/run/halo/app/utils/MarkdownUtils.java

@@ -71,7 +71,7 @@ public class MarkdownUtils {
     private static final Parser PARSER = Parser.builder(OPTIONS).build();
 
     private static final HtmlRenderer RENDERER = HtmlRenderer.builder(OPTIONS).build();
-    private static final Pattern FRONT_MATTER = Pattern.compile("^---[\\s\\S]*?---");
+    private static final Pattern FRONT_MATTER = Pattern.compile("^(---)?[\\s\\S]*?---");
 
     //    /**
     //     * Render html document to markdown document.
@@ -136,6 +136,9 @@ public class MarkdownUtils {
                 return row;
             }
         }).collect(Collectors.joining("\n"));
+        if (!markdown.startsWith("---\n")) {
+            markdown = "---\n" + markdown;
+        }
         AbstractYamlFrontMatterVisitor visitor = new AbstractYamlFrontMatterVisitor();
         Node document = PARSER.parse(markdown);
         visitor.visit(document);

src/test/java/run/halo/app/utils/MarkdownUtilsTest.java

@@ -3,6 +3,8 @@ package run.halo.app.utils;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import java.util.List;
+import java.util.Map;
 import lombok.extern.slf4j.Slf4j;
 import org.apache.commons.lang3.StringUtils;
 import org.junit.jupiter.api.Test;
@@ -33,6 +35,15 @@ class MarkdownUtilsTest {
             + "---"
             + "test---";
         assertEquals("test---", MarkdownUtils.removeFrontMatter(markdown));
+
+        markdown = "title: \"test remove\"\n"
+            + "test---";
+        assertEquals("", MarkdownUtils.removeFrontMatter(markdown));
+
+        markdown = "title: \"test remove\"\n"
+            + "---"
+            + "test---";
+        assertEquals("test---", MarkdownUtils.removeFrontMatter(markdown));
     }
 
     @Test
@@ -70,4 +81,18 @@ class MarkdownUtilsTest {
             + "</section>\n";
         assertTrue(StringUtils.equals(s2Expected, s2));
     }
+
+    @Test
+    void getFrontMatter() {
+        String markdown = "---\n"
+            + "title: \"test remove\"\n"
+            + "---";
+        Map<String, List<String>> frontMatter = MarkdownUtils.getFrontMatter(markdown);
+        assertEquals("\"test remove\"", frontMatter.get("title").get(0));
+
+        markdown = "title: \"test remove\"\n"
+            + "---";
+        frontMatter = MarkdownUtils.getFrontMatter(markdown);
+        assertEquals("\"test remove\"", frontMatter.get("title").get(0));
+    }
 }