Uncomment stream block in Element (#1988)

* Uncomment stream block in Element

* Add custom StringJoiner collector

---------

Co-authored-by: Jonathan Hedley <jonathan@hedley.net>

pom.xml

@@ -95,6 +95,7 @@
                 <ignore>java.util.List</ignore> <!-- List#stream() -->
                 <ignore>java.util.Objects</ignore>
                 <ignore>java.util.Optional</ignore>
+                <ignore>java.util.Set</ignore> <!-- Set#stream() -->
                 <ignore>java.util.Spliterator</ignore>
                 <ignore>java.util.Spliterators</ignore>
 

src/main/java/org/jsoup/internal/StringUtil.java

@@ -10,6 +10,8 @@
 import java.util.Iterator;
 import java.util.Stack;
 import java.util.regex.Pattern;
+import java.util.stream.Collector;
+import java.util.stream.Collectors;
 
 /**
  A minimal String utility class. Designed for <b>internal</b> jsoup use only - the API and outcome may change without
@@ -375,6 +377,23 @@ public static String releaseBuilder(StringBuilder sb) {
         return string;
     }
 
+    /**
+     * Return a {@link Collector} similar to the one returned by {@link Collectors#joining(CharSequence)},
+     * but backed by jsoup's {@link StringJoiner}, which allows for more efficient garbage collection.
+     *
+     * @param delimiter The delimiter for separating the strings.
+     * @return A {@code Collector} which concatenates CharSequence elements, separated by the specified delimiter
+     */
+    public static Collector<CharSequence, ?, String> joining(String delimiter) {
+        return Collector.of(() -> new StringJoiner(delimiter),
+            StringJoiner::add,
+            (j1, j2) -> {
+                j1.append(j2.complete());
+                return j1;
+            },
+            StringJoiner::complete);
+    }
+
     private static final int MaxCachedBuilderSize = 8 * 1024;
     private static final int MaxIdleBuilders = 8;
 }

src/main/java/org/jsoup/nodes/Element.java

@@ -6,6 +6,7 @@
 import org.jsoup.parser.ParseSettings;
 import org.jsoup.parser.Parser;
 import org.jsoup.parser.Tag;
+import org.jsoup.parser.TokenQueue;
 import org.jsoup.select.Collector;
 import org.jsoup.select.Elements;
 import org.jsoup.select.Evaluator;
@@ -935,12 +936,9 @@ private String cssSelectorComponent() {
         // Escape tagname, and translate HTML namespace ns:tag to CSS namespace syntax ns|tag
         String tagName = escapeCssIdentifier(tagName()).replace("\\:", "|");
         StringBuilder selector = StringUtil.borrowBuilder().append(tagName);
-        // String classes = StringUtil.join(classNames().stream().map(TokenQueue::escapeCssIdentifier).iterator(), ".");
-        // todo - replace with ^^ in 1.16.1 when we enable Android support for stream etc
-        StringUtil.StringJoiner escapedClasses = new StringUtil.StringJoiner(".");
-        for (String name : classNames()) escapedClasses.add(escapeCssIdentifier(name));
-        String classes = escapedClasses.complete();
-        if (classes.length() > 0)
+        String classes = classNames().stream().map(TokenQueue::escapeCssIdentifier)
+                .collect(StringUtil.joining("."));
+        if (!classes.isEmpty())
             selector.append('.').append(classes);
 
         if (parent() == null || parent() instanceof Document) // don't add Document to selector, as will always have a html node