Enhance Azure Managed Identity configuration with environment variable support and improved error handling

.gitignore

@@ -58,3 +58,6 @@ build/
 .vscode/
 
 /logs/
+
+# Maven shade plugin generated files
+dependency-reduced-pom.xml

mi-sql-public-demo/src/main/java/com/example/MainSQL.java

@@ -4,13 +4,42 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.Properties;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 import java.sql.*;
 
 import com.microsoft.sqlserver.jdbc.SQLServerDataSource;
 
 public class MainSQL {
 
+    /**
+     * Simple placeholder resolver for ${VAR_NAME} and ${VAR_NAME:default} patterns
+     */
+    private static String resolvePlaceholders(String input) {
+        if (input == null) return null;
+
+        Pattern pattern = Pattern.compile("\\$\\{([^}:]+)(?::([^}]*))?\\}");
+        Matcher matcher = pattern.matcher(input);
+        StringBuffer result = new StringBuffer();
+
+        while (matcher.find()) {
+            String varName = matcher.group(1);
+            String defaultValue = matcher.group(2);
+            String envValue = System.getenv(varName);
+
+            if (envValue != null) {
+                matcher.appendReplacement(result, Matcher.quoteReplacement(envValue));
+            } else if (defaultValue != null) {
+                matcher.appendReplacement(result, Matcher.quoteReplacement(defaultValue));
+            } else {
+                // Leave placeholder unresolved
+                matcher.appendReplacement(result, Matcher.quoteReplacement(matcher.group(0)));
+            }
+        }
+        matcher.appendTail(result);
+        return result.toString();
+    }
 
     public static void main(String[] args) {
 
@@ -30,10 +59,29 @@ public static void main(String[] args) {
         String connString = properties.getProperty("spring.datasource.url");
 
         if (connString == null) {
-            System.out.println("spring.datasource.url property not found in application.properties");
+            System.out.println("ERROR: spring.datasource.url property not found in application.properties");
+            return;
+        }
+
+        // Resolve environment variable placeholders
+        connString = resolvePlaceholders(connString);
+
+        // Check for unresolved placeholders
+        if (connString.contains("${AZ_DATABASE_SERVER_NAME}")) {
+            System.out.println("ERROR: AZ_DATABASE_SERVER_NAME environment variable is not set");
+            System.out.println("Please set the AZ_DATABASE_SERVER_NAME environment variable to your Azure SQL server name");
             return;
         }
 
+        String clientId = properties.getProperty("spring.cloud.azure.credential.client-id");
+        if (clientId != null) {
+            clientId = resolvePlaceholders(clientId);
+            if (clientId.contains("${AZURE_CLIENT_ID}")) {
+                System.out.println("WARNING: AZURE_CLIENT_ID environment variable is not set");
+                System.out.println("This is required for user-assigned managed identity, but optional for system-assigned managed identity");
+            }
+        }
+
         System.out.println("Connection string: " + connString);
 
         SQLServerDataSource ds = new SQLServerDataSource();

mi-sql-public-demo/src/main/resources/application.properties

@@ -1,6 +1,6 @@
 # Azure SQL Database configuration with Managed Identity
-spring.datasource.url=jdbc:sqlserver://${AZ_DATABASE_SERVER_NAME}.database.windows.net:1433;database=demo;encrypt=true;trustServerCertificate=false;hostNameInCertificate=*.database.windows.net;loginTimeout=30;authentication=ActiveDirectoryMSI
+spring.datasource.url=jdbc:sqlserver://${AZ_DATABASE_SERVER_NAME}.database.windows.net:1433;database=${AZ_DATABASE_NAME:demo};encrypt=true;trustServerCertificate=false;hostNameInCertificate=*.database.windows.net;loginTimeout=30;authentication=ActiveDirectoryMSI
 
 # Azure Managed Identity configuration
 spring.cloud.azure.credential.managed-identity-enabled=true
-spring.cloud.azure.credential.client-id=<your_managed_identity_client_id>
+spring.cloud.azure.credential.client-id=${AZURE_CLIENT_ID}