X-Git-Url: http://wamblee.org/gitweb/?a=blobdiff_plain;ds=inline;f=support%2Ftest%2Fsrc%2Fmain%2Fjava%2Forg%2Fwamblee%2Fsupport%2Fpersistence%2FDatabaseBuilder.java;fp=support%2Ftest%2Fsrc%2Fmain%2Fjava%2Forg%2Fwamblee%2Fsupport%2Fpersistence%2FDatabaseBuilder.java;h=9c599a0a75cddf8f81203b217aeb76885827a5e4;hb=e8b7f484cbd8168c4341eee5cb020cdd080ce944;hp=0000000000000000000000000000000000000000;hpb=c6dd7d29643a8e4a6ec11088ecb5ab9f58845e0b;p=utils

diff --git a/support/test/src/main/java/org/wamblee/support/persistence/DatabaseBuilder.java b/support/test/src/main/java/org/wamblee/support/persistence/DatabaseBuilder.java
new file mode 100644
index 00000000..9c599a0a
--- /dev/null
+++ b/support/test/src/main/java/org/wamblee/support/persistence/DatabaseBuilder.java
@@ -0,0 +1,116 @@
+package org.wamblee.support.persistence;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.ServiceLoader;
+import java.util.logging.Logger;
+
+/**
+ * DatabaseBuilder is used from unit test to obtain a reference to a database
+ * from unit test. This database is either an inmemory database or represents an
+ * external database. Purpose of this utility is to make test code independent of the 
+ * particular database used and specifically to be able to run database tests without 
+ * any configuration at all (using an inmemory database).  
+ * 
+ * The type of database to use can be overridden by specifying either a system
+ * property or an environment variable ({@link #DB_CAPABILITIES_PROP}) that
+ * contains the comma-separated capabilities of the database. Each database type
+ * provides its own capabilities (see {@link DatabaseProvider} implementations}.
+ * 
+ * 
+ * There are currently two database types available: 
+ * <ul>
+ *   <li> Derby: AN inmemory derby. Provided by {@link DerbyDatabaseProvider}. This is the default. 
+ *   </li>
+ *   <li> External: An arbitrary external database configured using system properties or environment variables
+ *     in the usual way using a JDBC URL, username, and password. 
+ *   </li>
+ * </ul>
+ * 
+ * The <code>DatabaseBuilder</code> uses the {@link ServiceLoader} mechanism to find implementations
+ * of {@link DatabaseProvider} on the classpath. In the {@link #getDatabase(String...)} method a number of 
+ * capabilities are passed. The database providers are then searched in (arbitrary) order and the first one that
+ * has all required capabilities is returned. 
+ * 
+ * {@link #getSupportedDatabases()} gives a list of all available databases. 
+ */
+public class DatabaseBuilder {
+
+	private static final Logger LOGGER = Logger.getLogger(DatabaseBuilder.class
+			.getName());
+
+	/**
+	 * Environmment variable by which capabilities of the requested database can
+	 * be defined
+	 */
+	private static final String DB_CAPABILITIES_PROP = "TEST_DB_CAPABILITIES";
+
+	private static ServiceLoader<DatabaseProvider> LOADER = null;
+
+	private DatabaseBuilder() {
+		// Empty.
+	}
+
+	private static String[] parseCapabilities(String aValue) {
+		return aValue.split(",");
+	}
+
+	/**
+	 * Gets the first database that has all required capabilities. 
+	 * @param aCapabilities Capabilities. 
+	 * @return Database to use. 
+	 */
+	public static Database getDatabase(String... aCapabilities) {
+		if (aCapabilities.length == 0) {
+			LOGGER.info("Examining database capabilities");
+			LOGGER.info("  Checking system property " + DB_CAPABILITIES_PROP);
+			String capabilities = System.getProperty(DB_CAPABILITIES_PROP);
+			if (capabilities != null) {
+				aCapabilities = parseCapabilities(capabilities);
+			} else {
+				LOGGER.info("  Checking environment variable "
+						+ DB_CAPABILITIES_PROP);
+				capabilities = System.getenv(DB_CAPABILITIES_PROP);
+				if (capabilities != null) {
+					aCapabilities = parseCapabilities(capabilities);
+				} else {
+					LOGGER.info("  Using default capabilities");
+					aCapabilities = new String[] { DatabaseProvider.CAPABILITY_IN_MEMORY };
+				}
+			}
+			LOGGER.info("Using capabilities: " + aCapabilities);
+		}
+		synchronized (DatabaseBuilder.class) {
+			initLoader();
+			for (DatabaseProvider db : LOADER) {
+				if (db.supportsCapabilities(aCapabilities)) {
+					return db.create();
+				}
+			}
+		}
+		throw new RuntimeException(
+				"No database found that satisfies capabilities: "
+						+ Arrays.asList(aCapabilities));
+	}
+
+	/**
+	 * Gets a list of available databases. 
+	 * @return List of databases. 
+	 */
+	public static List<DatabaseDescription> getSupportedDatabases() {
+		initLoader();
+		List<DatabaseDescription> descriptions = new ArrayList<DatabaseDescription>();
+		for (DatabaseProvider db : LOADER) {
+			descriptions.add(db.getDescription());
+		}
+		return descriptions;
+	}
+
+	private static void initLoader() {
+		if (LOADER == null) {
+			LOADER = ServiceLoader.load(DatabaseProvider.class);
+		}
+	}
+
+}