From bfeebfeb693f1f2ef0d2f6abb34bdf0aeffa3af4 Mon Sep 17 00:00:00 2001
From: Thomas <>
Date: Mon, 15 May 2023 08:34:22 +0200
Subject: feat(utils): add custom Jackson (de)serialization for polymorph class
 structures

---
 .../core/impl/json/EscapedJsonDeserializer.java    | 97 ++++++++++++++++++++++
 .../eaaf/core/impl/json/EscapedJsonSerializer.java | 73 ++++++++++++++++
 2 files changed, 170 insertions(+)
 create mode 100644 eaaf_core_utils/src/main/java/at/gv/egiz/eaaf/core/impl/json/EscapedJsonDeserializer.java
 create mode 100644 eaaf_core_utils/src/main/java/at/gv/egiz/eaaf/core/impl/json/EscapedJsonSerializer.java

diff --git a/eaaf_core_utils/src/main/java/at/gv/egiz/eaaf/core/impl/json/EscapedJsonDeserializer.java b/eaaf_core_utils/src/main/java/at/gv/egiz/eaaf/core/impl/json/EscapedJsonDeserializer.java
new file mode 100644
index 00000000..5a081ec5
--- /dev/null
+++ b/eaaf_core_utils/src/main/java/at/gv/egiz/eaaf/core/impl/json/EscapedJsonDeserializer.java
@@ -0,0 +1,97 @@
+package at.gv.egiz.eaaf.core.impl.json;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
+
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.core.TreeNode;
+import com.fasterxml.jackson.databind.BeanProperty;
+import com.fasterxml.jackson.databind.DeserializationContext;
+import com.fasterxml.jackson.databind.JavaType;
+import com.fasterxml.jackson.databind.JsonDeserializer;
+import com.fasterxml.jackson.databind.JsonMappingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.deser.ContextualDeserializer;
+import com.fasterxml.jackson.databind.jsontype.TypeDeserializer;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import com.fasterxml.jackson.databind.node.TextNode;
+
+/**
+ * Custom Jackson Deserializer to support generic types serialized as escaped
+ * Strings.
+ * 
+ * <p>
+ * Code was an example from stack-overflow. <br>
+ * <br>
+ * This implementation checks if the generic class type is compatible to
+ * original interface, by using <code>Class.isAssignableFrom(...).</code>
+ * </p>
+ * 
+ * @author tlenz
+ *
+ */
+public class EscapedJsonDeserializer extends JsonDeserializer<Object> implements ContextualDeserializer {
+  private final Map<JavaType, JsonDeserializer<Object>> cachedDeserializers = new HashMap<>();
+
+  @Override
+  public Object deserialize(JsonParser p, DeserializationContext ctxt) throws IOException,
+      JsonProcessingException {
+    throw new IllegalArgumentException(
+        "EscapedJsonDeserializer should delegate deserialization for concrete class");
+
+  }
+
+  @Override
+  public JsonDeserializer<?> createContextual(DeserializationContext ctxt, BeanProperty property)
+      throws JsonMappingException {
+    JavaType type = (ctxt.getContextualType() != null) ? ctxt.getContextualType()
+        : property.getMember().getType();
+    return cachedDeserializers.computeIfAbsent(type, (a) -> new InnerDeserializer(type));
+  }
+
+  private static class InnerDeserializer extends JsonDeserializer<Object> {
+    private final JavaType javaType;
+
+    private InnerDeserializer(JavaType javaType) {
+      this.javaType = javaType;
+    }
+
+    @Override
+    public Object deserialize(JsonParser p, DeserializationContext ctxt) throws IOException,
+        JsonProcessingException {
+      String string = p.readValueAs(String.class);
+      return ((ObjectMapper) p.getCodec()).readValue(string, javaType);
+    }
+
+    @Override
+    public Object deserializeWithType(JsonParser p, DeserializationContext ctxt,
+        TypeDeserializer typeDeserializer)
+        throws IOException {
+      String str = p.readValueAs(String.class);
+      TreeNode root = ((ObjectMapper) p.getCodec()).readTree(str);
+      try {
+        Class clz = Class.forName(((TextNode) root.get("@class")).asText());
+
+        if (this.javaType.getRawClass().isAssignableFrom(clz)) {
+          // remove '@class' before deserialization because it's unknown in target class
+          if (root.isObject()) {
+            ((ObjectNode) root).remove("@class");
+          }
+
+          Object newJsonNode = p.getCodec().treeToValue(root, clz);
+          return newJsonNode;
+
+        } else {
+          throw new RuntimeException("Class looks supect because it does not match to interface.");
+
+        }
+
+      } catch (ClassNotFoundException e) {
+        throw new RuntimeException(e);
+
+      }
+    }
+  }
+}
diff --git a/eaaf_core_utils/src/main/java/at/gv/egiz/eaaf/core/impl/json/EscapedJsonSerializer.java b/eaaf_core_utils/src/main/java/at/gv/egiz/eaaf/core/impl/json/EscapedJsonSerializer.java
new file mode 100644
index 00000000..a79f4d90
--- /dev/null
+++ b/eaaf_core_utils/src/main/java/at/gv/egiz/eaaf/core/impl/json/EscapedJsonSerializer.java
@@ -0,0 +1,73 @@
+package at.gv.egiz.eaaf.core.impl.json;
+
+import java.io.IOException;
+import java.io.StringWriter;
+import java.util.Collection;
+
+import com.fasterxml.jackson.core.JsonFactory;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.jsontype.TypeSerializer;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import com.fasterxml.jackson.databind.node.TextNode;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
+
+
+/**
+ * Custom Jackson Serializer to support generic types and serialize them as
+ * escaped Strings.
+ * 
+ * <p>
+ * Code was an example from stack-overflow.
+ * </p>
+ * 
+ * @author tlenz
+ *
+ */
+public class EscapedJsonSerializer extends StdSerializer<Object> {
+  private static final long serialVersionUID = 7334472154148003249L;
+
+  public EscapedJsonSerializer() {
+    super((Class<Object>) null);
+  }
+
+  @Override
+  public void serialize(Object value, JsonGenerator gen, SerializerProvider provider) throws IOException {
+    StringWriter str = new StringWriter();
+    JsonGenerator tempGen = new JsonFactory().setCodec(gen.getCodec()).createGenerator(str);
+    if (value instanceof Collection || value.getClass().isArray()) {
+      tempGen.writeStartArray();
+      if (value instanceof Collection) {
+        for (Object it : (Collection) value) {
+          writeTree(gen, it, tempGen);
+        }
+      } else if (value.getClass().isArray()) {
+        for (Object it : (Object[]) value) {
+          writeTree(gen, it, tempGen);
+        }
+      }
+      tempGen.writeEndArray();
+    } else {
+      provider.defaultSerializeValue(value, tempGen);
+    }
+    tempGen.flush();
+    gen.writeString(str.toString());
+  }
+
+  @Override
+  public void serializeWithType(Object value, JsonGenerator gen, SerializerProvider serializers,
+      TypeSerializer typeSer) throws IOException {
+    StringWriter str = new StringWriter();
+    JsonGenerator tempGen = new JsonFactory().setCodec(gen.getCodec()).createGenerator(str);
+    writeTree(gen, value, tempGen);
+    tempGen.flush();
+    gen.writeString(str.toString());
+  }
+
+  private void writeTree(JsonGenerator gen, Object it, JsonGenerator tempGen) throws IOException {
+    ObjectNode tree = ((ObjectMapper) gen.getCodec()).valueToTree(it);
+    tree.set("@class", new TextNode(it.getClass().getName()));
+    tempGen.writeTree(tree);
+  }
+}
-- 
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