Implement ExpressionValue as a sealed class and support (de)serializing it. It is now part of the API as kernels may need to use it.

Author: SpencerPark

src/main/java/io/github/spencerpark/jupyter/channels/JupyterSocket.java

@@ -5,6 +5,7 @@
 import com.google.gson.JsonElement;
 import com.google.gson.JsonParser;
 import com.google.gson.reflect.TypeToken;
+import io.github.spencerpark.jupyter.kernel.ExpressionValue;
 import io.github.spencerpark.jupyter.kernel.KernelConnectionProperties;
 import io.github.spencerpark.jupyter.kernel.history.HistoryEntry;
 import io.github.spencerpark.jupyter.messages.*;
@@ -30,6 +31,7 @@ protected static String formatAddress(String transport, String ip, int port) {
     private static final byte[] IDENTITY_BLOB_DELIMITER = "<IDS|MSG>".getBytes(ASCII); // Comes from a python bytestring
     private static final Gson replyGson = new GsonBuilder()
             .registerTypeAdapter(HistoryEntry.class, HistoryEntryAdapter.INSTANCE)
+            .registerTypeAdapter(ExpressionValue.class, ExpressionValueAdapter.INSTANCE)
             .create();
     private static final Gson gson = new GsonBuilder()
             .registerTypeAdapter(KernelTimestamp.class, KernelTimestampAdapter.INSTANCE)

src/main/java/io/github/spencerpark/jupyter/kernel/ExpressionValue.java

@@ -0,0 +1,62 @@
+package io.github.spencerpark.jupyter.kernel;
+
+import com.google.gson.annotations.SerializedName;
+import io.github.spencerpark.jupyter.kernel.display.DisplayData;
+
+import java.util.List;
+
+public abstract class ExpressionValue {
+
+    private ExpressionValue() { } // Seal the class
+
+    public abstract boolean isSuccess();
+
+    public static class Error extends ExpressionValue {
+        @SerializedName("ename")
+        protected final String errName;
+        @SerializedName("evalue")
+        protected final String errMsg;
+        @SerializedName("traceback")
+        protected final List<String> stacktrace;
+
+        public Error(String errName, String errMsg, List<String> stacktrace) {
+            this.errName = errName;
+            this.errMsg = errMsg;
+            this.stacktrace = stacktrace;
+        }
+
+        @Override
+        public boolean isSuccess() {
+            return false;
+        }
+
+        public String getErrName() {
+            return this.errName;
+        }
+
+        public String getErrMsg() {
+            return this.errMsg;
+        }
+
+        public List<String> getStacktrace() {
+            return this.stacktrace;
+        }
+    }
+
+    public static class Success extends ExpressionValue {
+        protected final DisplayData data;
+
+        public Success(DisplayData data) {
+            this.data = data;
+        }
+
+        @Override
+        public boolean isSuccess() {
+            return true;
+        }
+
+        public DisplayData getData() {
+            return this.data;
+        }
+    }
+}

src/main/java/io/github/spencerpark/jupyter/messages/ExpressionValue.java

@@ -0,0 +1,38 @@
+package io.github.spencerpark.jupyter.messages.adapters;
+
+import com.google.gson.*;
+import io.github.spencerpark.jupyter.kernel.display.DisplayData;
+import io.github.spencerpark.jupyter.kernel.ExpressionValue;
+
+import java.lang.reflect.Type;
+
+/**
+ * Decode/encode an {@link ExpressionValue} as either a {@link ExpressionValue.Error} or {@link ExpressionValue.Success}
+ * based on the {@code "status"} field.
+ */
+public class ExpressionValueAdapter implements JsonSerializer<ExpressionValue>, JsonDeserializer<ExpressionValue> {
+    public static final ExpressionValueAdapter INSTANCE = new ExpressionValueAdapter();
+
+    private ExpressionValueAdapter() { }
+
+    @Override
+    public ExpressionValue deserialize(JsonElement jsonElement, Type type, JsonDeserializationContext ctx) throws JsonParseException {
+        if (jsonElement.isJsonObject()) {
+            JsonElement status = jsonElement.getAsJsonObject().get("status");
+            if (status != null && status.isJsonPrimitive()
+                    && status.getAsString().equalsIgnoreCase("error"))
+                return ctx.deserialize(jsonElement, ExpressionValue.Error.class);
+        }
+
+        DisplayData data = ctx.deserialize(jsonElement, DisplayData.class);
+        return new ExpressionValue.Success(data);
+    }
+
+    @Override
+    public JsonElement serialize(ExpressionValue exprVal, Type type, JsonSerializationContext ctx) {
+        if (exprVal.isSuccess())
+            return ctx.serialize(exprVal, ExpressionValue.Success.class);
+        else
+            return ctx.serialize(exprVal, ExpressionValue.Error.class);
+    }
+}

src/main/java/io/github/spencerpark/jupyter/messages/adapters/ExpressionValueAdapter.java

@@ -1,11 +1,10 @@
 package io.github.spencerpark.jupyter.messages.publish;
 
-import io.github.spencerpark.jupyter.messages.ContentType;
 import io.github.spencerpark.jupyter.kernel.display.DisplayData;
-import io.github.spencerpark.jupyter.messages.ExpressionValue;
+import io.github.spencerpark.jupyter.messages.ContentType;
 import io.github.spencerpark.jupyter.messages.MessageType;
 
-public class PublishDisplayData extends DisplayData implements ExpressionValue, ContentType<PublishDisplayData> {
+public class PublishDisplayData extends DisplayData implements ContentType<PublishDisplayData> {
     public static final MessageType<PublishDisplayData> MESSAGE_TYPE = MessageType.PUBLISH_DISPLAY_DATA;
 
     @Override

src/main/java/io/github/spencerpark/jupyter/messages/publish/PublishDisplayData.java

@@ -1,15 +1,19 @@
 package io.github.spencerpark.jupyter.messages.reply;
 
 import com.google.gson.annotations.SerializedName;
-import io.github.spencerpark.jupyter.messages.ExpressionValue;
 import io.github.spencerpark.jupyter.messages.MessageType;
 import io.github.spencerpark.jupyter.messages.ReplyType;
 
 import java.util.Arrays;
 import java.util.List;
 import java.util.stream.Collectors;
 
-public class ErrorReply implements ExpressionValue, ReplyType<Object> {
+public class ErrorReply implements ReplyType<Object> {
+    @Override
+    public MessageType<Object> getRequestType() {
+        return MessageType.UNKNOWN;
+    }
+
     public static ErrorReply of(Exception exception) {
         String name = exception.getClass().getSimpleName();
         String msg = exception.getLocalizedMessage();
@@ -57,9 +61,4 @@ public String getErrorMessage() {
     public List<String> getStacktrace() {
         return stacktrace;
     }
-
-    @Override
-    public MessageType<Object> getRequestType() {
-        return MessageType.UNKNOWN;
-    }
 }

src/main/java/io/github/spencerpark/jupyter/messages/reply/ErrorReply.java

@@ -1,7 +1,7 @@
 package io.github.spencerpark.jupyter.messages.reply;
 
 import com.google.gson.annotations.SerializedName;
-import io.github.spencerpark.jupyter.messages.ExpressionValue;
+import io.github.spencerpark.jupyter.kernel.ExpressionValue;
 import io.github.spencerpark.jupyter.messages.MessageType;
 import io.github.spencerpark.jupyter.messages.ReplyType;
 import io.github.spencerpark.jupyter.messages.publish.PublishDisplayData;