Add convert() to Coder

This addresses Liam's review comment about moving the "translate"
method from the actor Util class into policy-common.
Added a method to Coder to convert from one object type to
another (e.g., from a Map to a POJO, or vice versa).

Issue-ID: POLICY-2363
Signed-off-by: Jim Hahn <jrh3@att.com>
Change-Id: I2a0b5ab4ce4b0eeda216a57cbe23a8bb64f64940

2 files changed, 66 insertions, 1 deletions

diff --git a/utils/src/main/java/org/onap/policy/common/utils/coder/Coder.java b/utils/src/main/java/org/onap/policy/common/utils/coder/Coder.java
index ec0e5e42..3049a5c2 100644
--- a/utils/src/main/java/org/onap/policy/common/utils/coder/Coder.java
+++ b/utils/src/main/java/org/onap/policy/common/utils/coder/Coder.java
@@ -32,6 +32,37 @@ import java.io.Writer;
 public interface Coder {
 
     /**
+     * Converts an object/POJO to an object of the given type.
+     *
+     * @param <T> desired type
+     * @param source source object
+     * @param clazz class of the desired object type
+     * @return the converted object
+     * @throws CoderException if an error occurs
+     */
+    default <S, T> T convert(S source, Class<T> clazz) throws CoderException {
+        if (source == null) {
+            return null;
+
+        } else if (clazz == source.getClass()) {
+            // same class - just cast it
+            return clazz.cast(source);
+
+        } else if (clazz == String.class) {
+            // target is a string - just encode the source
+            return (clazz.cast(encode(source)));
+
+        } else if (source.getClass() == String.class) {
+            // source is a string - just decode it
+            return decode(source.toString(), clazz);
+
+        } else {
+            // do it the long way: encode to a string and then decode the string
+            return decode(encode(source), clazz);
+        }
+    }
+
+    /**
      * Encodes an object into json.
      *
      * @param object object to be encoded
@@ -44,7 +75,8 @@ public interface Coder {
      * Encodes an object into json, optionally making it "pretty".
      *
      * @param object object to be encoded
-     * @param pretty {@code true} if it should be encoded as "pretty" json, {@code false} otherwise
+     * @param pretty {@code true} if it should be encoded as "pretty" json, {@code false}
+     *        otherwise
      * @return a json string representing the object
      * @throws CoderException if an error occurs
      */
diff --git a/utils/src/main/java/org/onap/policy/common/utils/coder/StandardCoder.java b/utils/src/main/java/org/onap/policy/common/utils/coder/StandardCoder.java
index 13973f1c..9d444cae 100644
--- a/utils/src/main/java/org/onap/policy/common/utils/coder/StandardCoder.java
+++ b/utils/src/main/java/org/onap/policy/common/utils/coder/StandardCoder.java
@@ -78,6 +78,39 @@ public class StandardCoder implements Coder {
     }
 
     @Override
+    public <S, T> T convert(S source, Class<T> clazz) throws CoderException {
+        if (source == null) {
+            return null;
+
+        } else if (clazz == source.getClass()) {
+            // same class - just cast it
+            return clazz.cast(source);
+
+        } else if (clazz == String.class) {
+            // target is a string - just encode the source
+            return (clazz.cast(encode(source)));
+
+        } else if (source.getClass() == String.class) {
+            // source is a string - just decode it
+            return decode(source.toString(), clazz);
+
+        } else {
+            /*
+             * Do it the long way: encode to a tree and then decode the tree. This entire
+             * method could have been left out and the default Coder.convert() used
+             * instead, but this should perform slightly better as it only uses a
+             * JsonElement as the intermediate data structure, while Coder.convert() goes
+             * all the way to a String as the intermediate data structure.
+             */
+            try {
+                return fromJson(toJsonTree(source), clazz);
+            } catch (RuntimeException e) {
+                throw new CoderException(e);
+            }
+        }
+    }
+
+    @Override
     public String encode(Object object) throws CoderException {
         return encode(object, false);
     }