Simplify Kernel metadata loading approach #83

Author: andrus

RELEASE-NOTES.md

@@ -10,6 +10,7 @@
 - #80 Magics as interfaces
 - #81 Refactoring: JavaKernel must manage JShell
 - #82 Refactoring: Move JavaKernel init logic from constructor to Builder
+- #83 Simplify Kernel metadata loading approach
 
 
 ## 1.0-a5

jjava/pom.xml

@@ -57,12 +57,6 @@
     </dependencies>
 
     <build>
-        <resources>
-            <resource>
-                <directory>src/main/resources</directory>
-                <filtering>true</filtering>
-            </resource>
-        </resources>
         <plugins>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>

jjava/src/main/java/org/dflib/jjava/JJava.java

@@ -1,7 +1,5 @@
 package org.dflib.jjava;
 
-import com.google.gson.JsonObject;
-import com.google.gson.JsonParser;
 import org.dflib.jjava.jupyter.channels.JupyterConnection;
 import org.dflib.jjava.jupyter.channels.JupyterSocket;
 import org.dflib.jjava.jupyter.kernel.KernelConnectionProperties;
@@ -15,19 +13,19 @@
 import org.dflib.jjava.maven.MavenDependencyResolver;
 
 import java.io.IOException;
-import java.io.InputStreamReader;
-import java.io.Reader;
+import java.io.InputStream;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.util.Properties;
 import java.util.logging.Level;
 
 /**
  * The main class launching Jupyter Java kernel.
  */
 public class JJava {
 
-    private static final String KERNEL_METADATA_FILE = "jjava-kernel-metadata.json";
+    private static final String POM_PROPERTIES = "META-INF/maven/org.dflib.jjava/jjava/pom.properties";
 
     private static JJavaKernel kernel;
 
@@ -50,14 +48,11 @@ public static void main(String[] args) throws Exception {
 
         MavenDependencyResolver mavenResolver = new MavenDependencyResolver();
 
-        // TODO: "jjava-kernel-metadata.json" is redundant. We have all this info in pom.properties, and the name of the
-        //  kernel can be hardcoded; also this can be moved to the builder
-        JsonObject meta = loadKernelMetadata();
+        Properties pomProps = loadPOMProps();
 
         kernel = JJavaKernel.builder()
-                .name(meta != null && meta.get("project") != null ? meta.get("project").getAsString() : null)
-                .version(meta != null && meta.get("version") != null ? meta.get("version").getAsString() : null)
-
+                .name("JJava")
+                .version((String) pomProps.getOrDefault("version", ""))
                 .lineMagic("load", new LoadCodeMagic("", ".jsh", ".jshell", ".java", ".jjava"))
                 .lineMagic("classpath", new ClasspathMagic())
                 .lineMagic("maven", new MavenMagic(mavenResolver))
@@ -82,13 +77,25 @@ public static JJavaKernel getKernelInstance() {
         return JJava.kernel;
     }
 
-    private static JsonObject loadKernelMetadata() {
+    private static Properties loadPOMProps() {
+
+        Properties props = new Properties();
+
+        InputStream in = JJava.class.getClassLoader().getResourceAsStream(POM_PROPERTIES);
+        if (in == null) {
+            return props;
+        }
 
-        try (Reader metaReader = new InputStreamReader(JJava.class.getClassLoader().getResourceAsStream(KERNEL_METADATA_FILE))) {
-            return JsonParser.parseReader(metaReader).getAsJsonObject();
+        try {
+            try {
+                props.load(in);
+                return props;
+            } finally {
+                in.close();
+            }
         } catch (IOException e) {
-            e.printStackTrace();
-            return null;
+            // generally, this should be ignorable, but it should also never happen, so still rethrow
+            throw new RuntimeException("Error reading project properties");
         }
     }
 }

jjava/src/main/java/org/dflib/jjava/JJavaKernel.java

@@ -28,12 +28,9 @@
 import org.dflib.jjava.jupyter.kernel.util.CharPredicate;
 import org.dflib.jjava.jupyter.kernel.util.StringStyler;
 
-import java.io.IOException;
-import java.io.InputStream;
 import java.nio.charset.Charset;
 import java.util.ArrayList;
 import java.util.List;
-import java.util.Properties;
 import java.util.Set;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -401,39 +398,6 @@ public JJavaKernel build() {
             );
         }
 
-        protected String buildName() {
-            return name != null ? name : "JJava";
-        }
-
-        protected String buildVersion() {
-
-            if (version != null) {
-                return version;
-            }
-
-            InputStream in = getClass()
-                    .getClassLoader()
-                    .getResourceAsStream("META-INF/maven/org.dflib.jjava/jjava/pom.properties");
-
-            if (in == null) {
-                return "unknown";
-            }
-
-            try {
-                try {
-
-                    Properties props = new Properties();
-                    props.load(in);
-                    return (String) props.getOrDefault("version", "unknown");
-                } finally {
-                    in.close();
-                }
-            } catch (IOException e) {
-                // generally, this should be ignorable, but it should also never happen, so still rethrow
-                throw new RuntimeException("Error reading project properties");
-            }
-        }
-
         protected List<HelpLink> buildHelpLinks() {
             return List.of(
                     new HelpLink("Java tutorials", "https://docs.oracle.com/javase/tutorial/"),

jjava/src/main/resources/jjava-kernel-metadata.json

@@ -1,7 +1,5 @@
 package org.dflib.jjava.jupyter.kernel;
 
-import com.google.gson.Gson;
-import com.google.gson.reflect.TypeToken;
 import org.dflib.jjava.jupyter.ExtensionLoader;
 import org.dflib.jjava.jupyter.channels.JupyterConnection;
 import org.dflib.jjava.jupyter.channels.ShellReplyEnvironment;
@@ -40,47 +38,24 @@
 import org.dflib.jjava.jupyter.messages.request.KernelInfoRequest;
 import org.dflib.jjava.jupyter.messages.request.ShutdownRequest;
 
-import java.io.IOException;
 import java.io.InputStream;
-import java.io.InputStreamReader;
 import java.io.PrintStream;
 import java.io.PrintWriter;
-import java.io.Reader;
 import java.io.StringWriter;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.EnumSet;
 import java.util.List;
-import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicInteger;
 
-
 public abstract class BaseKernel {
 
     public static final String IS_COMPLETE_YES = "complete";
     public static final String IS_COMPLETE_BAD = "invalid";
     public static final String IS_COMPLETE_MAYBE = "unknown";
 
-    // TODO: merge "kernel-metadata.json" values into "kernel.json" and stop using it
-    protected static final Map<String, String> KERNEL_META = createMetadata();
-
-    private static Map<String, String> createMetadata() {
-
-        InputStream metaStream = BaseKernel.class.getClassLoader().getResourceAsStream("kernel-metadata.json");
-        if (metaStream != null) {
-            try (Reader metaReader = new InputStreamReader(metaStream)) {
-                return new Gson().fromJson(metaReader, new TypeToken<Map<String, String>>() {
-                }.getType());
-            } catch (IOException e) {
-                e.printStackTrace();
-            }
-        }
-
-        return Map.of("version", "unknown", "project", "unknown");
-    }
-
     // TODO: create some kind of metadata object to combine these properties?
     protected final String name;
     protected final String version;
@@ -134,6 +109,10 @@ protected BaseKernel(
         Text.registerAll(this.renderer);
     }
 
+    public String getName() {
+        return name;
+    }
+
     public String getVersion() {
         return version;
     }
@@ -491,11 +470,8 @@ private void handleKernelInfoRequest(ShellReplyEnvironment env, Message<KernelIn
         env.setBusyDeferIdle();
         env.reply(new KernelInfoReply(
                         Header.PROTOCOL_VERISON,
-
-                        // TODO: use "name" and "version" properties
-                        KERNEL_META.get("project"),
-                        KERNEL_META.get("version"),
-
+                        name,
+                        version,
                         getLanguageInfo(),
                         getBanner(),
                         getHelpLinks()

jupyter-jvm-basekernel/src/main/java/org/dflib/jjava/jupyter/kernel/BaseKernel.java

@@ -73,6 +73,14 @@ public B magicParser(MagicParser magicParser) {
 
     public abstract K build();
 
+    protected String buildName() {
+        return name != null ? name : "";
+    }
+
+    protected String buildVersion() {
+        return version != null ? version : "";
+    }
+
     protected Charset buildJupyterIOEncoding() {
         return jupyterIOEncoding != null ? jupyterIOEncoding : StandardCharsets.UTF_8;
     }