Add attr(Attribute attribute) to Tag

Author: kicktipp

src/main/java/j2html/tags/Tag.java

@@ -4,6 +4,7 @@
 import j2html.attributes.Attribute;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Iterator;
 
 public abstract class Tag<T extends Tag<T>> extends DomContent {
     protected String tagName;
@@ -78,6 +79,28 @@ public T attr(String attribute, Object value) {
         setAttribute(attribute, value == null ? null : String.valueOf(value));
         return (T) this;
     }
+    
+    /**
+     * Adds the specified attribute. If the Tag previously contained an attribute with the same name, the old attribute is replaced by the specified attribute.
+     *
+     * @param attribute the attribute
+     * @return itself for easy chaining
+     */
+    public T attr(Attribute attribute) {
+        Iterator<Attribute> iterator = attributes.iterator();
+        String name = attribute.getName();
+        if (name != null) {
+            // name == null is allowed, but those Attributes are not rendered. So we add them anyway.
+            while (iterator.hasNext()) {
+                Attribute existingAttribute = iterator.next();
+                if (existingAttribute.getName().equals(name)) {
+                    iterator.remove();
+                }
+            }
+        }
+        attributes.add(attribute);
+        return (T) this;
+    }
 
     /**
      * Sets a custom attribute without value

src/test/java/j2html/model/DynamicHrefAttribute.java

@@ -0,0 +1,24 @@
+package j2html.model;
+
+import j2html.attributes.Attribute;
+import java.io.IOException;
+
+public class DynamicHrefAttribute extends Attribute {
+
+    public DynamicHrefAttribute() {
+        super("href");
+    }
+
+    @Override
+    public void renderModel(Appendable writer, Object model) throws IOException {
+        writer.append(" ");
+        writer.append(getName());
+        writer.append("=\"");
+        writer.append(getUrl(model));
+        writer.append("\"");
+    }
+
+    public String getUrl(Object model) {
+        return "/";
+    }
+}

src/test/java/j2html/tags/TagTest.java

@@ -1,7 +1,5 @@
 package j2html.tags;
 
-import j2html.Config;
-import org.junit.Test;
 import static j2html.TagCreator.body;
 import static j2html.TagCreator.div;
 import static j2html.TagCreator.footer;
@@ -15,6 +13,9 @@
 import static j2html.TagCreator.tag;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
+import j2html.Config;
+import j2html.model.DynamicHrefAttribute;
+import org.junit.Test;
 
 public class TagTest {
 
@@ -92,5 +93,16 @@ public void testEmptyAttribute() throws Exception {
         assertThat(testTagAttrWithoutAttr.render(), is("<a attribute></a>"));
     }
 
+    @Test
+    public void testDynamicAttribute() throws Exception {
+        ContainerTag testTagWithAttrValueNull = new ContainerTag("a").attr(new DynamicHrefAttribute());
+        assertThat(testTagWithAttrValueNull.render(), is("<a href=\"/\"></a>"));
+    }
+    
+    @Test
+    public void testDynamicAttributeReplacement() throws Exception {
+        ContainerTag testTagWithAttrValueNull = new ContainerTag("a").attr("href", "/link").attr(new DynamicHrefAttribute());
+        assertThat(testTagWithAttrValueNull.render(), is("<a href=\"/\"></a>"));
+    }
 
 }