diff -r 822b7e3d064d -r b3f14cd4f3ab src/main/kotlin/de/uapcore/lightpit/DataSourceProvider.kt
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/main/kotlin/de/uapcore/lightpit/DataSourceProvider.kt	Sat Oct 24 12:09:08 2020 +0200
@@ -0,0 +1,165 @@
+/*
+ * Copyright 2020 Mike Becker. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package de.uapcore.lightpit
+
+import java.sql.SQLException
+import javax.naming.Context
+import javax.naming.InitialContext
+import javax.naming.NamingException
+import javax.servlet.ServletContextEvent
+import javax.servlet.ServletContextListener
+import javax.servlet.annotation.WebListener
+import javax.sql.DataSource
+
+enum class DatabaseDialect {
+    Postgres
+}
+
+/**
+ * Provides access to the database.
+ */
+@WebListener
+class DataSourceProvider : ServletContextListener, LoggingTrait {
+
+    /**
+     * The database dialect to use.
+     * May be overridden by context parameter.
+     *
+     * @see Constants.CTX_ATTR_DB_DIALECT
+     */
+    var dialect = DatabaseDialect.Postgres; private set
+
+    /**
+     * The data source, if available.
+     */
+    var dataSource: DataSource? = null
+
+    companion object {
+        /**
+         * The attribute name in the Servlet context under which an instance of this class can be found.
+         */
+        val SC_ATTR_NAME = "lightpit.service.DataSourceProvider"
+
+        /**
+         * Timeout in seconds for the validation test.
+         */
+        private val DB_TEST_TIMEOUT = 10
+
+        /**
+         * The default schema to test against when validating the connection.
+         * May be overridden by context parameter.
+         *
+         * @see Constants.CTX_ATTR_DB_SCHEMA
+         */
+        private val DB_DEFAULT_SCHEMA = "lightpit"
+
+        /**
+         * The JNDI resource name for the data source.
+         */
+        private val DS_JNDI_NAME = "jdbc/lightpit/app"
+    }
+
+    private fun checkConnection(ds: DataSource, testSchema: String) {
+        try {
+            ds.connection.use { conn ->
+                if (!conn.isValid(DB_TEST_TIMEOUT)) {
+                    throw SQLException("Validation check failed.")
+                }
+                if (conn.isReadOnly) {
+                    throw SQLException("Connection is read-only and thus unusable.")
+                }
+                if (conn.schema != testSchema) {
+                    throw SQLException(
+                        String.format(
+                            "Connection is not configured to use the schema %s.",
+                            testSchema
+                        )
+                    )
+                }
+                val metaData = conn.metaData
+                logger().info(
+                    "Connections as {} to {}/{} ready to go.",
+                    metaData.userName,
+                    metaData.url,
+                    conn.schema
+                )
+            }
+        } catch (ex: SQLException) {
+            logger().error("Checking database connection failed", ex)
+        }
+    }
+
+    private fun retrieveDataSource(ctx: Context): DataSource? {
+        return try {
+            val ret = ctx.lookup(DS_JNDI_NAME) as DataSource
+            logger().info("Data source retrieved.")
+            ret
+        } catch (ex: NamingException) {
+            logger().error("Data source {} not available.", DS_JNDI_NAME)
+            logger().error("Reason for the missing data source: ", ex)
+            null
+        }
+    }
+
+    override fun contextInitialized(sce: ServletContextEvent?) {
+        val sc = sce!!.servletContext
+
+        val dbSchema = sc.getInitParameter(Constants.CTX_ATTR_DB_SCHEMA) ?: DB_DEFAULT_SCHEMA
+        sc.getInitParameter(Constants.CTX_ATTR_DB_DIALECT)?.let {dbDialect ->
+            try {
+                dialect = DatabaseDialect.valueOf(dbDialect)
+            } catch (ex: IllegalArgumentException) {
+                logger().error(
+                    "Unknown or unsupported database dialect {}. Defaulting to {}.",
+                    dbDialect,
+                    dialect
+                )
+            }
+        }
+
+        dataSource = try {
+            logger().debug("Trying to access JNDI context ...")
+            val initialCtx: Context = InitialContext()
+            val ctx = initialCtx.lookup("java:comp/env") as Context
+            retrieveDataSource(ctx)
+        } catch (ex: NamingException) {
+            logger().error("Cannot access JNDI resources.", ex)
+            null
+        } catch (ex: ClassCastException) {
+            logger().error("Cannot access JNDI resources.", ex)
+            null
+        }
+
+        dataSource?.let { checkConnection(it, dbSchema) }
+
+        sc.setAttribute(SC_ATTR_NAME, this)
+        logger().info("Database facade injected into ServletContext.")
+    }
+
+    override fun contextDestroyed(sce: ServletContextEvent?) {
+        dataSource = null
+    }
+}
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