Fix issues #92 and #93: Validation and JMX escaping in metrics exporters

Issue #93: PrometheusMetricsExporter constructor validation
- Add null check for config parameter
- Fail fast with IllegalArgumentException
- Add @throws JavaDoc annotation

Issue #92: JMX special character escaping
- Use ObjectName.quote() to escape JMX special characters (:=,"*?)
- Prevents MalformedObjectNameException for app IDs with special chars
- Update tests to use quoted application IDs for verification

Author: Flossy

jplatform-metrics-jmx/src/main/java/org/flossware/jplatform/metrics/jmx/JmxMetricsExporter.java

@@ -183,8 +183,10 @@ public void registerApplication(String applicationId, ApplicationContext context
 
         try {
             // Create ObjectName with configured domain
+            // Quote applicationId to escape JMX special characters (:=,"*?)
+            String quotedAppId = ObjectName.quote(applicationId);
             String objectNameStr = String.format("%s:type=Application,id=%s",
-                    config.getDomain(), applicationId);
+                    config.getDomain(), quotedAppId);
             ObjectName objectName = new ObjectName(objectNameStr);
 
             // Check if already registered

jplatform-metrics-jmx/src/test/java/org/flossware/jplatform/metrics/jmx/JmxMetricsExporterTest.java

@@ -181,8 +181,9 @@ void testRegisterApplication() throws Exception {
 
         assertEquals(1, exporter.getRegisteredApplicationCount());
 
-        // Verify MBean is registered
-        ObjectName objectName = new ObjectName("org.flossware.jplatform.test:type=Application,id=test-app");
+        // Verify MBean is registered (applicationId is quoted to escape JMX special characters)
+        String quotedAppId = ObjectName.quote("test-app");
+        ObjectName objectName = new ObjectName("org.flossware.jplatform.test:type=Application,id=" + quotedAppId);
         assertTrue(mBeanServer.isRegistered(objectName));
     }
 
@@ -235,8 +236,9 @@ void testRegisterApplicationTwice() throws Exception {
         exporter.registerApplication("test-app", context);
         assertEquals(1, exporter.getRegisteredApplicationCount());
 
-        // MBean should still be registered
-        ObjectName objectName = new ObjectName("org.flossware.jplatform.test:type=Application,id=test-app");
+        // MBean should still be registered (applicationId is quoted to escape JMX special characters)
+        String quotedAppId = ObjectName.quote("test-app");
+        ObjectName objectName = new ObjectName("org.flossware.jplatform.test:type=Application,id=" + quotedAppId);
         assertTrue(mBeanServer.isRegistered(objectName));
     }
 
@@ -352,10 +354,13 @@ void testMultipleApplications() throws Exception {
 
         assertEquals(2, exporter.getRegisteredApplicationCount());
 
-        // Verify correct MBeans remain
-        ObjectName objectName1 = new ObjectName("org.flossware.jplatform.test:type=Application,id=app1");
-        ObjectName objectName2 = new ObjectName("org.flossware.jplatform.test:type=Application,id=app2");
-        ObjectName objectName3 = new ObjectName("org.flossware.jplatform.test:type=Application,id=app3");
+        // Verify correct MBeans remain (applicationId is quoted to escape JMX special characters)
+        String quotedAppId1 = ObjectName.quote("app1");
+        String quotedAppId2 = ObjectName.quote("app2");
+        String quotedAppId3 = ObjectName.quote("app3");
+        ObjectName objectName1 = new ObjectName("org.flossware.jplatform.test:type=Application,id=" + quotedAppId1);
+        ObjectName objectName2 = new ObjectName("org.flossware.jplatform.test:type=Application,id=" + quotedAppId2);
+        ObjectName objectName3 = new ObjectName("org.flossware.jplatform.test:type=Application,id=" + quotedAppId3);
 
         assertTrue(mBeanServer.isRegistered(objectName1));
         assertFalse(mBeanServer.isRegistered(objectName2));

jplatform-metrics-prometheus/src/main/java/org/flossware/jplatform/metrics/prometheus/PrometheusMetricsExporter.java

@@ -64,8 +64,12 @@ public class PrometheusMetricsExporter implements MetricsExporter {
      * Constructs a new Prometheus metrics exporter with the specified configuration.
      *
      * @param config the exporter configuration specifying port and path
+     * @throws IllegalArgumentException if config is null
      */
     public PrometheusMetricsExporter(PrometheusExporterConfig config) {
+        if (config == null) {
+            throw new IllegalArgumentException("PrometheusExporterConfig cannot be null");
+        }
         this.config = config;
         this.applications = new ConcurrentHashMap<>();
         this.running = false;