Re: [PR] Add a statements pool to DatasourceResourceLoader t o fix thread safety [velocity-engine]

michael-o commented on code in PR #49:
URL: https://github.com/apache/velocity-engine/pull/49#discussion_r1735145285


##########
velocity-engine-core/src/main/java/org/apache/velocity/runtime/resource/loader/CachingDatabaseObjectsFactory.java:
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@@ -0,0 +1,203 @@
+package org.apache.velocity.runtime. resource.loader;
+
+import org.apache.commons.pool2.BaseKeyedPooledObjectFactory;
+import org.apache.commons.pool2.KeyedObjectPool;
+import org.apache.commons.pool2.PooledObject;
+import org.apache.commons.pool2.impl.DefaultPooledObject;
+import org.apache.commons.pool2.impl.GenericKeyedObjectPool;
+import org.apache.commons.pool2.impl.GenericKeyedObjectPoolConfig;
+import org.apache.velocity.util.ExtProperties;
+import org.slf4j.Logger;
+
+import javax.sql.DataSource;
+import java.sql.Connection;
+import java.sql.PreparedStatement;
+import java.sql.SQLException;
+
+/**
+ * <p>Database objects factory which will keep a single connection to be able to cache statements preparation, by means
+ * of appropriate pools.</p>
+ * <p>This class requires the following optional dependency (maven syntax):</p>
+ * <pre><code>
+ *         &lt;dependency&gt;
+ *             &lt;groupId&gt;org.apache.commons&lt;/groupId&gt;
+ *             &lt;artifactId&gt;commons-pool2&lt;/artifactId&gt;
+ *             &lt;version&gt;2.12.0&lt;/version&gt;
+ *             &lt;scope&gt;runtime&lt;/scope&gt;
+ *          &lt;/dependency&gt;
+ * </code></pre>
+ * <p>To use this class, you must add the following property to the example configuration described in
+ * @link{org.apache.velocity.runtime.resource.loader.DataSourceResourceLoader}
+ * </p>
+ * <pre><code>
+ * resource.loader.ds.database_objects_factory.class = org.apache.velocity.runtime.resource.loader.DataSourceResourceLoader<br>
+ * </code></pre>
+ * <p>The default size of each pool of prepared statements (there is one pool per statement) is 50. You can tune it
+ * with:</p>
+ * <pre><code>
+ * resource.loader.ds.database_objects_factory. = org.apache.velocity.runtime.resource.loader.DataSourceResourceLoader<br>
+ * </code></pre>
+ * @see org.apache.velocity.runtime.resource.loader.DataSourceResourceLoader
+ */
+
+public class CachingDatabaseObjectsFactory implements DatabaseObjectsFactory {
+
+    private static final String STATEMENTS_POOL_MAX_SIZE = "statements_pool_max_size";
+    private static final int STATEMENTS_POOL_MAX_SIZE_DEFAULT = 50;
+
+    private DataSource dataSource;
+    private Connection connection;
+    private int poolsMaxSize;
+    private KeyedObjectPool<String, PreparedStatement> statementsPool;
+    protected Logger log = null;
+
+    private class PreparedStatementFactory  extends BaseKeyedPooledObjectFactory<String, PreparedStatement>
+    {
+        @Override
+        public PreparedStatement create(String sql) throws Exception {
+            checkConnection();
+            return connection.prepareStatement(sql);

Review Comment:
   I am talking about `return connection.prepareStatement(sql);`



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