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java/org/apache/catalina/loader/JdbcLeakPrevention.java

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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+
+package org.apache.catalina.loader;
+
+import java.sql.Driver;
+import java.sql.DriverManager;
+import java.sql.SQLException;
+import java.util.ArrayList;
+import java.util.Enumeration;
+import java.util.HashSet;
+import java.util.List;
+
+/**
+ * This class is loaded by {@link WebappClassLoaderBase} to enable it to
+ * deregister JDBC drivers forgotten by the web application. There are some
+ * classloading hacks involved - see
+ * {@link WebappClassLoaderBase#clearReferences()} for details - but the short
+ * version is do not just create a new instance of this class with the new
+ * keyword.
+ *
+ * Since this class is loaded by {@link WebappClassLoaderBase}, it cannot refer
+ * to any internal Tomcat classes as that will cause the security manager to
+ * complain.
+ */
+public class JdbcLeakPrevention {
+
+    public List<String> clearJdbcDriverRegistrations() throws SQLException {
+        List<String> driverNames = new ArrayList<>();
+
+        /*
+         * DriverManager.getDrivers() has a nasty side-effect of registering
+         * drivers that are visible to this class loader but haven't yet been
+         * loaded. Therefore, the first call to this method a) gets the list
+         * of originally loaded drivers and b) triggers the unwanted
+         * side-effect. The second call gets the complete list of drivers
+         * ensuring that both original drivers and any loaded as a result of the
+         * side-effects are all de-registered.
+         */
+        HashSet<Driver> originalDrivers = new HashSet<>();
+        Enumeration<Driver> drivers = DriverManager.getDrivers();
+        while (drivers.hasMoreElements()) {
+            originalDrivers.add(drivers.nextElement());
+        }
+        drivers = DriverManager.getDrivers();
+        while (drivers.hasMoreElements()) {
+            Driver driver = drivers.nextElement();
+            // Only unload the drivers this web app loaded
+            if (driver.getClass().getClassLoader() !=
+                this.getClass().getClassLoader()) {
+                continue;
+            }
+            // Only report drivers that were originally registered. Skip any
+            // that were registered as a side-effect of this code.
+            if (originalDrivers.contains(driver)) {
+                driverNames.add(driver.getClass().getCanonicalName());
+            }
+            DriverManager.deregisterDriver(driver);
+        }
+        return driverNames;
+    }
+}