Revert "Remove the “get” method of String/Boolean/Integer Tags."

This reverts commit 04041ebd7e.

apm-commons/apm-trace/src/main/java/org/skywalking/apm/trace/tag/AbstractTag.java

@@ -30,4 +30,6 @@ public abstract class AbstractTag<T> {
     public String key() {
         return this.key;
     }
+
+    public abstract T get(Span span);
 }

apm-commons/apm-trace/src/main/java/org/skywalking/apm/trace/tag/BooleanTag.java

@@ -21,7 +21,20 @@ public class BooleanTag extends AbstractTag<Boolean> {
         span.setTag(key, tagValue);
     }
 
-    public boolean defaultValue() {
-        return this.defaultValue;
+    /**
+     * Get a tag value, type of {@link Boolean}. After akka-message/serialize, all tags values are type of {@link
+     * String}, convert to {@link Boolean}, if necessary.
+     *
+     * @param span
+     * @return tag value
+     */
+    @Override
+    public Boolean get(Span span) {
+        Boolean tagValue = span.getBoolTag(super.key);
+        if (tagValue == null) {
+            return defaultValue;
+        } else {
+            return tagValue;
+        }
     }
 }

apm-commons/apm-trace/src/main/java/org/skywalking/apm/trace/tag/IntTag.java

@@ -16,4 +16,21 @@ public class IntTag extends AbstractTag<Integer> {
     public void set(Span span, Integer tagValue) {
         span.setTag(super.key, tagValue);
     }
+
+    /**
+     * Get a tag value, type of {@link Integer}. After akka-message/serialize, all tags values are type of {@link
+     * String}, convert to {@link Integer}, if necessary.
+     *
+     * @param span
+     * @return tag value
+     */
+    @Override
+    public Integer get(Span span) {
+        Integer tagValue = span.getIntTag(super.key);
+        if (tagValue == null) {
+            return null;
+        } else {
+            return tagValue;
+        }
+    }
 }

apm-commons/apm-trace/src/main/java/org/skywalking/apm/trace/tag/StringTag.java

@@ -17,4 +17,9 @@ public class StringTag extends AbstractTag<String> {
     public void set(Span span, String tagValue) {
         span.setTag(key, tagValue);
     }
+
+    @Override
+    public String get(Span span) {
+        return span.getStrTag(super.key);
+    }
 }

apm-sniffer/apm-sniffer-mock/src/main/java/org/skywalking/apm/sniffer/mock/trace/tag/BooleanTagGetter.java

@@ -10,11 +10,6 @@ import org.skywalking.apm.trace.tag.BooleanTag;
  */
 public class BooleanTagGetter {
     public static Boolean get(Span span, BooleanTag tag) {
-        Boolean tagValue = span.getBoolTag(tag.key());
-        if (tagValue == null) {
-            return tag.defaultValue();
-        } else {
-            return tagValue;
-        }
+        return span.getBoolTag(tag.key());
     }
 }

apm-sniffer/apm-sniffer-mock/src/main/java/org/skywalking/apm/sniffer/mock/trace/tag/IntTagGetter.java

@@ -10,11 +10,6 @@ import org.skywalking.apm.trace.tag.IntTag;
  */
 public class IntTagGetter {
     public static Integer get(Span span, IntTag tag) {
-        Integer tagValue = span.getIntTag(tag.key());
-        if (tagValue == null) {
-            return null;
-        } else {
-            return tagValue;
-        }
+        return span.getIntTag(tag.key());
     }
 }