Connection error handling in the pool

Author: ZorTik

core/src/main/java/me/zort/sqllib/SQLConnectionPool.java

@@ -71,7 +71,7 @@ public SQLConnectionPool(@NotNull SQLConnectionBuilder from, @NotNull Options po
     public Resource getResource() throws SQLException {
         freeConnections.removeIf(SQLPooledConnection::expired);
         SQLPooledConnection polled = freeConnections.poll();
-        if (polled == null && usedConnections.size() < maxConnections) {
+        if (polled == null && size() < maxConnections) {
             polled = establishObject();
         } else if(polled == null) {
 
@@ -83,7 +83,7 @@ public Resource getResource() throws SQLException {
             while ((polled = freeConnections.poll()) == null) {
                 if (System.currentTimeMillis() - start > borrowObjectTimeout) {
                     throw new SQLException("Timeout while waiting for a connection.");
-                } else if(usedConnections.size() < maxConnections) {
+                } else if(size() < maxConnections) {
                     polled = establishObject();
                     break;
                 }
@@ -99,6 +99,17 @@ private SQLPooledConnection establishObject() throws SQLException {
 
         SQLException error = polled.connection.getLastError();
         if (error != null) throw error;
+
+        if (polled.connection instanceof SQLDatabaseConnectionImpl) {
+            ((SQLDatabaseConnectionImpl) polled.connection).addErrorHandler(code -> {
+                // Remove the connection from the pool and disconnect
+                // on fatal errors.
+                freeConnections.remove(polled);
+                usedConnections.remove(polled);
+                polled.connection.disconnect();
+            });
+        }
+
         return polled;
     }
 

core/src/main/java/me/zort/sqllib/SQLDatabaseConnectionImpl.java

@@ -40,6 +40,8 @@
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.logging.Logger;
 
+import static me.zort.sqllib.util.ExceptionsUtility.runCatching;
+
 /**
  * Main database client object implementation.
  * This class is responsible for handling requests from query
@@ -52,11 +54,11 @@ public class SQLDatabaseConnectionImpl extends SQLDatabaseConnection {
 
     // --***-- Default Constants --***--
 
-    public static boolean DEFAULT_AUTO_RECONNECT = true;
-    public static boolean DEFAULT_DEBUG = false;
-    public static boolean DEFAULT_LOG_SQL_ERRORS = true;
-    public static NamingStrategy DEFAULT_NAMING_STRATEGY = new DefaultNamingStrategy();
-    public static Gson DEFAULT_GSON = Defaults.DEFAULT_GSON;
+    public static final boolean DEFAULT_AUTO_RECONNECT = true;
+    public static final boolean DEFAULT_DEBUG = false;
+    public static final boolean DEFAULT_LOG_SQL_ERRORS = true;
+    public static final NamingStrategy DEFAULT_NAMING_STRATEGY = new DefaultNamingStrategy();
+    public static final Gson DEFAULT_GSON = Defaults.DEFAULT_GSON;
 
     // --***-- Options & Utilities --***--
 
@@ -66,6 +68,7 @@ public class SQLDatabaseConnectionImpl extends SQLDatabaseConnection {
     private final transient StatementMappingFactory mappingFactory;
     @ApiStatus.Experimental
     private final transient StatementMappingResultAdapter mappingResultAdapter;
+    private final transient List<ErrorStateObserver> errorStateHandlers;
     private transient ObjectMapper objectMapper;
     @Setter
     private transient Logger logger;
@@ -101,6 +104,7 @@ public SQLDatabaseConnectionImpl(SQLConnectionFactory connectionFactory, @Nullab
         this.objectMapper = new DefaultObjectMapper(this);
         this.mappingFactory = new DefaultStatementMappingFactory();
         this.mappingResultAdapter = new DefaultResultAdapter();
+        this.errorStateHandlers = new CopyOnWriteArrayList<>();
         this.logger = Logger.getGlobal();
 
         // Default backup value resolvers.
@@ -131,6 +135,16 @@ public void setObjectMapper(@NotNull ObjectMapper objectMapper) {
         this.objectMapper = Objects.requireNonNull(objectMapper, "Object mapper cannot be null!");
     }
 
+    /**
+     * Adds an error state observer to the list of observers to be
+     * notified when a fatal error occurs.
+     *
+     * @param observer Observer to add.
+     */
+    public void addErrorHandler(@NotNull ErrorStateObserver observer) {
+        this.errorStateHandlers.add(observer);
+    }
+
     /**
      * Constructs a mapping repository based on provided interface.
      * The interface should follow rules for creating mapping repositories
@@ -283,6 +297,7 @@ private QueryRowsResult<Row> doQuery(Query query, boolean isRetry) {
             }
 
             logSqlError(e);
+            notifyError(ErrorCode.QUERY_FATAL);
             return new QueryRowsResult<>(false, e.getMessage());
         }
     }
@@ -315,6 +330,7 @@ private QueryResult doExec(Query query, boolean isRetry) {
             }
 
             logSqlError(e);
+            notifyError(ErrorCode.QUERY_FATAL);
             return new QueryResultImpl(false, e.getMessage());
         }
     }
@@ -441,15 +457,19 @@ public void debug(String message) {
     }
 
     @Override
-    public boolean isLogSqlErrors() {
+    public final boolean isLogSqlErrors() {
         return options.isLogSqlErrors();
     }
 
     @Override
-    public boolean isDebug() {
+    public final boolean isDebug() {
         return options.isDebug();
     }
 
+    private void notifyError(int code) {
+        this.errorStateHandlers.forEach(handler -> runCatching(() -> handler.onErrorState(code)));
+    }
+
     public final SQLDatabaseOptions cloneOptions() {
         SQLDatabaseOptions cloned = new SQLDatabaseOptions();
         cloned.setDebug(options.isDebug());
@@ -489,4 +509,12 @@ public static class UnknownValueWrapper {
         private Object object;
     }
 
+    public interface ErrorStateObserver {
+        void onErrorState(int code);
+    }
+
+    public static final class ErrorCode {
+        public static final int QUERY_FATAL = 0;
+    }
+
 }

core/src/main/java/me/zort/sqllib/util/ExceptionsUtility.java

@@ -0,0 +1,16 @@
+package me.zort.sqllib.util;
+
+import lombok.experimental.UtilityClass;
+
+@UtilityClass
+public final class ExceptionsUtility {
+
+    public static void runCatching(Runnable runnable) {
+        try {
+            runnable.run();
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+
+}