Add parameter name reflection

pom.xml

@@ -93,6 +93,9 @@
                     <source>1.8</source>
                     <target>1.8</target>
                     <optimize>true</optimize>
+                    <compilerArgs>
+                        <arg>-parameters</arg>
+                    </compilerArgs>
                 </configuration>
             </plugin>
             <plugin>

src/main/java/j2html/attributes/LambdaAttribute.java

@@ -0,0 +1,24 @@
+package j2html.attributes;
+
+import j2html.reflection.MethodFinder;
+import java.util.function.Function;
+
+public interface LambdaAttribute extends MethodFinder, Function<String, Object> {
+
+    default String name() {
+        checkParametersEnabled();
+        return parameter(0).getName();
+    }
+
+    default String value() {
+        checkParametersEnabled();
+        return String.valueOf(this.apply(name()));
+    }
+
+    default void checkParametersEnabled() {
+        if ("arg0".equals(parameter(0).getName())) {
+            throw new IllegalStateException("You need java 8u60 or newer for parameter reflection to work");
+        }
+    }
+
+}

src/main/java/j2html/reflection/MethodFinder.java

@@ -0,0 +1,48 @@
+package j2html.reflection;
+
+// Written by Benjamin Weber (http://benjiweber.co.uk/blog/author/benji/)
+
+import java.io.Serializable;
+import java.lang.invoke.SerializedLambda;
+import java.lang.reflect.Method;
+import java.lang.reflect.Parameter;
+import java.util.Arrays;
+import java.util.Objects;
+
+public interface MethodFinder extends Serializable {
+
+    default SerializedLambda serialized() {
+        try {
+            Method replaceMethod = getClass().getDeclaredMethod("writeReplace");
+            replaceMethod.setAccessible(true);
+            return (SerializedLambda) replaceMethod.invoke(this);
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    default Class<?> getContainingClass() {
+        try {
+            String className = serialized().getImplClass().replaceAll("/", ".");
+            return Class.forName(className);
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    default Method method() {
+        SerializedLambda lambda = serialized();
+        Class<?> containingClass = getContainingClass();
+        return Arrays.stream(containingClass.getDeclaredMethods())
+            .filter(method -> Objects.equals(method.getName(), lambda.getImplMethodName()))
+            .findFirst()
+            .orElseThrow(UnableToGuessMethodException::new);
+    }
+
+    default Parameter parameter(int n) {
+        return method().getParameters()[n];
+    }
+
+    class UnableToGuessMethodException extends RuntimeException {
+    }
+}

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

@@ -2,6 +2,7 @@
 
 import j2html.attributes.Attr;
 import j2html.attributes.Attribute;
+import j2html.attributes.LambdaAttribute;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Iterator;
@@ -79,7 +80,7 @@ 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.
      *
@@ -134,11 +135,6 @@ public boolean equals(Object obj) {
         return ((Tag) obj).render().equals(this.render());
     }
 
-    /**
-     * Convenience methods that call attr with predefined attributes
-     *
-     * @return itself for easy chaining
-     */
     public T withClasses(String... classes) {
         StringBuilder sb = new StringBuilder();
         for (String s : classes) {
@@ -147,6 +143,19 @@ public T withClasses(String... classes) {
         return attr(Attr.CLASS, sb.toString().trim());
     }
 
+    public T withAttrs(LambdaAttribute... lambdaAttributes) {
+        for (LambdaAttribute attr : lambdaAttributes) {
+            attr(attr.name(), attr.value());
+        }
+        return (T) this;
+    }
+
+    /**
+     * Convenience methods that call attr with predefined attributes
+     *
+     * @return itself for easy chaining
+     */
+
     public T isAutoComplete() {
         return attr(Attr.AUTOCOMPLETE, null);
     }

src/test/java/j2html/reflection/NamedValueTest.java

@@ -0,0 +1,17 @@
+package j2html.reflection;
+
+import j2html.attributes.LambdaAttribute;
+import org.junit.Test;
+import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+public class NamedValueTest {
+
+    @Test
+    public void testNamedValueWorks() {
+        LambdaAttribute pair = five -> 5;
+        assertThat("five", is(pair.name()));
+        assertThat("5", is(pair.value()));
+    }
+
+}

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

@@ -1,8 +1,13 @@
 package j2html.tags;
 
+import j2html.Config;
+import j2html.model.DynamicHrefAttribute;
+import org.junit.Test;
+import static j2html.TagCreator.a;
 import static j2html.TagCreator.body;
 import static j2html.TagCreator.div;
 import static j2html.TagCreator.footer;
+import static j2html.TagCreator.form;
 import static j2html.TagCreator.header;
 import static j2html.TagCreator.html;
 import static j2html.TagCreator.iff;
@@ -13,9 +18,6 @@
 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 {
 
@@ -98,11 +100,24 @@ 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>"));
     }
 
+    @Test
+    public void testParameterNameReflectionAttributes() throws Exception {
+        String expectedAnchor = "<a href=\"http://example.com\">example.com</a>";
+        String actualAnchor = a("example.com").withAttrs(href -> "http://example.com").render();
+        assertThat(actualAnchor, is(expectedAnchor));
+        String expectedForm = "<form method=\"post\" action=\"/form-path\"><input name=\"email\" type=\"email\"><input name=\"password\" type=\"password\"></form>";
+        String actualForm = form().withAttrs(method -> "post", action -> "/form-path").with(
+            input().withAttrs(name -> "email", type -> "email"),
+            input().withAttrs(name -> "password", type -> "password")
+        ).render();
+        assertThat(actualForm, is(expectedForm));
+    }
+
 }