refactor: optimize lastmod as much as possible for a fixed time (#26)

### What this PR does?
优化 Sitemap 中关于文章和自定义页面的最后修改时间

how to test it?
生成 sitemap 会有缓存, 每天会重新生成一次,如果修改了文章可以重启插件让其重新生成来**测试 lastmod 的值**

/kind improvement

Fixes #10

```release-note
优化 Sitemap 中关于文章和自定义页面的最后修改时间
```

Author: guqing

src/main/java/run/halo/sitemap/DefaultSitemapEntryLister.java

@@ -36,11 +36,14 @@ public Flux<SitemapEntry> list(SitemapGeneratorOptions options) {
             .map(options::transform);
     }
 
-    private Flux<String> listPostUrls() {
+    private Flux<UrlEntryMeta> listPostUrls() {
         return client.list(Post.class, post -> post.isPublished() && !post.isDeleted()
                     && Post.VisibleEnum.PUBLIC.equals(post.getSpec().getVisible()),
                 defaultComparator())
-            .map(post -> post.getStatusOrDefault().getPermalink());
+            .map(Post::getStatusOrDefault)
+            .map(status -> new UrlEntryMeta(status.getPermalink())
+                .setLastModifiedTime(status.getLastModifyTime())
+            );
     }
 
     Comparator<Post> defaultComparator() {
@@ -49,13 +52,16 @@ Comparator<Post> defaultComparator() {
         return Comparator.comparing(createTime).thenComparing(name);
     }
 
-    private Flux<String> listSinglePageUrls() {
+    private Flux<UrlEntryMeta> listSinglePageUrls() {
         return client.list(SinglePage.class, singlePage -> singlePage.isPublished()
                     && Objects.equals(false, singlePage.getSpec().getDeleted())
                     && ExtensionOperator.isNotDeleted().test(singlePage)
                     && Post.VisibleEnum.PUBLIC.equals(singlePage.getSpec().getVisible()),
                 pageDefaultComparator())
-            .map(post -> post.getStatusOrDefault().getPermalink());
+            .map(SinglePage::getStatusOrDefault)
+            .map(status -> new UrlEntryMeta(status.getPermalink())
+                .setLastModifiedTime(status.getLastModifyTime())
+            );
     }
 
     Comparator<SinglePage> pageDefaultComparator() {
@@ -65,21 +71,23 @@ Comparator<SinglePage> pageDefaultComparator() {
         return Comparator.comparing(createTime).thenComparing(name);
     }
 
-    private Flux<String> listCategoryUrls() {
+    private Flux<UrlEntryMeta> listCategoryUrls() {
         return client.list(Category.class,
                 category -> category.getMetadata().getDeletionTimestamp() == null,
                 Comparator.comparing(tag -> tag.getMetadata().getCreationTimestamp()))
-            .map(category -> category.getStatusOrDefault().getPermalink());
+            .map(Category::getStatusOrDefault)
+            .map(status -> new UrlEntryMeta(status.getPermalink()));
     }
 
-    private Flux<String> listTagUrls() {
+    private Flux<UrlEntryMeta> listTagUrls() {
         return client.list(Tag.class,
                 tag -> tag.getMetadata().getDeletionTimestamp() == null,
                 Comparator.comparing(tag -> tag.getMetadata().getCreationTimestamp()))
-            .map(tag -> tag.getStatusOrDefault().getPermalink());
+            .map(Tag::getStatusOrDefault)
+            .map(status -> new UrlEntryMeta(status.getPermalink()));
     }
 
-    private Flux<String> urlsForListPages() {
+    private Flux<UrlEntryMeta> urlsForListPages() {
         // TODO 优化系统其他路由获取
         return client.fetch(ConfigMap.class, "system")
             .mapNotNull(ConfigMap::getData)
@@ -92,7 +100,8 @@ private Flux<String> urlsForListPages() {
                     StringUtils.prependIfMissing(themeRouteRules.getArchives(), "/")
                 );
             })
-            .flatMapMany(Flux::fromIterable);
+            .flatMapMany(Flux::fromIterable)
+            .map(url -> new UrlEntryMeta(url).setPriority(0.5));
     }
 
     @Data

src/main/java/run/halo/sitemap/SitemapEntry.java

@@ -15,7 +15,6 @@ public class SitemapEntry {
      * <p>Parent tag for each URL entry. The remaining tags are children of this tag.</p>
      * required.
      */
-    @NonNull
     private String loc;
 
     private String lastmod;

src/main/java/run/halo/sitemap/SitemapGeneratorOptions.java

@@ -9,7 +9,6 @@
 import lombok.Builder;
 import lombok.Data;
 import lombok.NonNull;
-import org.apache.commons.lang3.StringUtils;
 import run.halo.app.infra.utils.PathUtils;
 
 /**
@@ -54,14 +53,26 @@ public class SitemapGeneratorOptions {
     @Builder.Default
     private ChangeFreqEnum changefreq = ChangeFreqEnum.DAILY;
 
-    @Builder.Default
-    private double priority = 0.7;
-
     /**
-     * Add <lastmod/> property. Default true
+     * How to assign sitemap priorities:
+     * <pre>
+     * 1.0-0.8
+     * Homepage, product information, landing pages.
+     *
+     * 0.7-0.4
+     * News articles, some weather services, blog posts, category pages, pages that no site would be complete without.
+     *
+     * 0.3-0.0
+     * FAQs, outdated info, old press releases, completely static pages that are still relevant enough to keep from deleting entirely.
+     * </pre>
+     *
+     * @see
+     * <a href="https://www.contentpowered.com/blog/xml-sitemap-priority-changefreq/">xml-sitemap-priority-changefreq</a>
+     * @see
+     * <a href="https://slickplan.com/blog/xml-sitemap-priority-changefreq">xml-sitemap-priority-changefreq</a>
      */
     @Builder.Default
-    private boolean autoLastmod = true;
+    private double priority = 0.7;
 
     /**
      * <p>Array of relative paths (wildcard pattern supported) to exclude from listing on sitemap
@@ -79,28 +90,33 @@ public class SitemapGeneratorOptions {
     @Builder.Default
     private boolean generateIndexSitemap = true;
 
-    public SitemapEntry transform(String url) {
-        if (StringUtils.isBlank(url)) {
-            return null;
-        }
-        String escapedUrl = UrlUtils.escapeSitemapUrl(url);
+    public SitemapEntry transform(UrlEntryMeta context) {
+        String escapedUrl = UrlUtils.escapeSitemapUrl(context.getUrl());
         String loc = UrlUtils.toURI(escapedUrl).normalize().toASCIIString();
         if (!PathUtils.isAbsoluteUri(loc)) {
             loc = getSiteUri().resolve(escapedUrl).normalize().toASCIIString();
         }
 
-        SitemapEntry.SitemapEntryBuilder builder = SitemapEntry.builder()
+        var builder = SitemapEntry.builder()
             .loc(loc)
-            .changefreq(changefreq)
-            .priority(priority);
+            .changefreq(changefreq);
+
+        if (context.getPriority() != null) {
+            builder.priority(context.getPriority());
+        } else {
+            builder.priority(priority);
+        }
 
-        if (dateTimeFormatter != null && autoLastmod) {
+        if (context.getLastModifiedTime() != null) {
+            builder.lastmod(
+                W3cDatetimeFormat.format(context.getLastModifiedTime(), dateTimeFormatter));
+        } else {
             builder.lastmod(W3cDatetimeFormat.format(Instant.now(), dateTimeFormatter));
         }
+
         return builder.build();
     }
 
-
     private URI getSiteUri() {
         try {
             return siteUrl.toURI();

src/main/java/run/halo/sitemap/UrlEntryMeta.java

@@ -0,0 +1,26 @@
+package run.halo.sitemap;
+
+import io.micrometer.common.util.StringUtils;
+import java.time.Instant;
+import lombok.Data;
+import lombok.experimental.Accessors;
+
+@Data
+@Accessors(chain = true)
+public class UrlEntryMeta {
+    private String url;
+
+    /**
+     * see also {@link SitemapGeneratorOptions#getPriority()}.
+     */
+    private Double priority;
+
+    private Instant lastModifiedTime;
+
+    public UrlEntryMeta(String url) {
+        if (StringUtils.isBlank(url)) {
+            throw new IllegalArgumentException("url must not be blank");
+        }
+        this.url = url;
+    }
+}

src/test/java/run/halo/sitemap/SitemapGeneratorOptionsTest.java

@@ -19,23 +19,23 @@ void transform() throws MalformedURLException {
         SitemapGeneratorOptions options = SitemapGeneratorOptions.builder()
             .siteUrl(new URL("https://halo.run"))
             .build();
-        SitemapEntry entry = options.transform("/about");
+        SitemapEntry entry = options.transform(new UrlEntryMeta("/about"));
         assertEquals("https://halo.run/about", entry.getLoc());
         assertEquals(ChangeFreqEnum.DAILY, entry.getChangefreq());
         assertEquals(0.7, entry.getPriority());
 
-        entry = options.transform("/archives");
+        entry = options.transform(new UrlEntryMeta("/archives"));
         assertEquals("https://halo.run/archives", entry.getLoc());
         assertEquals(ChangeFreqEnum.DAILY, entry.getChangefreq());
         assertEquals(0.7, entry.getPriority());
 
-        entry = options.transform("/categories/ümlat/>&>中");
+        entry = options.transform(new UrlEntryMeta("/categories/ümlat/>&>中"));
         assertEquals("https://halo.run/categories/%C3%BCmlat/>&>%E4%B8%AD",
             entry.getLoc());
         assertEquals(ChangeFreqEnum.DAILY, entry.getChangefreq());
         assertEquals(0.7, entry.getPriority());
 
-        entry = options.transform("https://guqing.xyz/hello-中国<>&");
+        entry = options.transform(new UrlEntryMeta("https://guqing.xyz/hello-中国<>&"));
         assertEquals("https://guqing.xyz/hello-%E4%B8%AD%E5%9B%BD&amp;lt;&amp;gt;&amp;amp;",
             entry.getLoc());