Tags are supported.

skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/tag/AbstractTag.java

+package com.a.eye.skywalking.trace.tag;
+
+import com.a.eye.skywalking.trace.Span;
+
+/**
+ * This is the abstract tag.
+ * All span's tags inherit from {@link AbstractTag},
+ * which provide an easy way to
+ *      {@link Span#setTag(String, String)} ,
+ *      {@link Span#setTag(String, Number)} ,
+ *      {@link Span#setTag(String, boolean)}
+ *
+ * Created by wusheng on 2017/2/17.
+ */
+public abstract class AbstractTag<T> {
+    /**
+     * The key of this Tag.
+     */
+    protected final String key;
+
+    public AbstractTag(String tagKey) {
+        this.key = tagKey;
+    }
+
+    public String getKey() {
+        return key;
+    }
+
+    protected abstract void set(Span span, T tagValue);
+}

skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/tag/BooleanTag.java

+package com.a.eye.skywalking.trace.tag;
+
+import com.a.eye.skywalking.trace.Span;
+
+/**
+ * Do the same thing as {@link StringTag}, just with a {@link Boolean} value.
+ *
+ * Created by wusheng on 2017/2/17.
+ */
+public class BooleanTag extends AbstractTag<Boolean>{
+    public BooleanTag(String key) {
+        super(key);
+    }
+
+    @Override
+    public void set(Span span, Boolean tagValue) {
+        span.setTag(key, tagValue);
+    }
+}

skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/tag/ShortTag.java

+package com.a.eye.skywalking.trace.tag;
+
+import com.a.eye.skywalking.trace.Span;
+
+/**
+ * Do the same thing as {@link StringTag}, just with a {@link Short} value.
+ *
+ * Created by wusheng on 2017/2/17.
+ */
+public class ShortTag extends AbstractTag<Short> {
+    public ShortTag(String key) {
+        super(key);
+    }
+
+    @Override
+    public void set(Span span, Short tagValue) {
+        span.setTag(super.key, tagValue);
+    }
+}

skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/tag/StringTag.java

+package com.a.eye.skywalking.trace.tag;
+
+import com.a.eye.skywalking.trace.Span;
+
+/**
+ * A subclass of {@link AbstractTag},
+ * represent a tag with a {@link String} value.
+ *
+ * Created by wusheng on 2017/2/17.
+ */
+public class StringTag extends AbstractTag<String> {
+    public StringTag(String tagKey) {
+        super(tagKey);
+    }
+
+    @Override
+    protected void set(Span span, String tagValue) {
+        span.setTag(key, tagValue);
+    }
+}

skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/tag/Tags.java

+package com.a.eye.skywalking.trace.tag;
+
+/**
+ * The span tags are supported by sky-walking engine.
+ * As default, all tags will be stored, but these ones have particular meanings.
+ *
+ * Created by wusheng on 2017/2/17.
+ */
+public final class Tags {
+    private Tags() {
+    }
+
+    /**
+     *  SPAN_KIND hints at the relationship between spans.
+     *  e.g. cl = client; se = server.
+     */
+    public static StringTag SPAN_KIND = new StringTag("span.kind");
+
+    /**
+     *  COMPONENT is a low-cardinality identifier of the module, library, or package that is instrumented.
+     *  Like dubbo/dubbox/motan
+     */
+    public static final StringTag COMPONENT  = new StringTag("component");
+
+    /**
+     * ERROR indicates whether a Span ended in an error state.
+     */
+    public static final BooleanTag ERROR = new BooleanTag("error");
+}