build(java)!: update to Java 21 (#7)

Author: nyg

library/src/main/java/dev/andstuff/kraken/api/ApiRequest.java

@@ -4,6 +4,8 @@
 import java.io.OutputStreamWriter;
 import java.io.UnsupportedEncodingException;
 import java.net.MalformedURLException;
+import java.net.URI;
+import java.net.URISyntaxException;
 import java.net.URL;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -106,7 +108,9 @@ public JsonNode execute() throws IOException {
             return OBJECT_MAPPER.readTree(connection.getInputStream());
         }
         finally {
-            connection.disconnect();
+            if (connection != null) {
+                connection.disconnect();
+            }
         }
     }
 
@@ -115,18 +119,21 @@ public JsonNode execute() throws IOException {
      *
      * @param method the API method
      * @return the path of the request taking the method into account
-     * @throws MalformedURLException if the request URL could not be created
-     *                               with the method name
      */
-    public String setMethod(KrakenApi.Method method) throws MalformedURLException {
+    public String setMethod(KrakenApi.Method method) {
 
         if (method == null) {
             throw new IllegalArgumentException(ERROR_NULL_METHOD);
         }
 
         isPublic = method.isPublic;
-        url = new URL((isPublic ? PUBLIC_URL : PRIVATE_URL) + method.name);
-        return url.getPath();
+        try {
+            url = new URI((isPublic ? PUBLIC_URL : PRIVATE_URL) + method.name).toURL();
+            return url.getPath();
+        }
+        catch (MalformedURLException | URISyntaxException e) {
+            throw new IllegalStateException("Could not set method URL", e);
+        }
     }
 
     /**

pom.xml

@@ -46,10 +46,8 @@
     </issueManagement>
 
     <properties>
+        <maven.compiler.release>21</maven.compiler.release>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <maven.compiler.source>1.8</maven.compiler.source>
-        <maven.compiler.target>1.8</maven.compiler.target>
-        <maven.compiler.target>8</maven.compiler.target>
 
         <!-- Third-party dependencies -->
         <jackson.version>2.16.1</jackson.version>