wamblee.org Git - utils/blob

   1 package org.wamblee.support.persistence;
   2
   3 import java.util.ArrayList;
   4 import java.util.Arrays;
   5 import java.util.List;
   6 import java.util.ServiceLoader;
   7 import java.util.logging.Logger;
   8
   9 /**
  10  * DatabaseBuilder is used from unit test to obtain a reference to a database
  11  * from unit test. This database is either an inmemory database or represents an
  12  * external database. Purpose of this utility is to make test code independent of the
  13  * particular database used and specifically to be able to run database tests without
  14  * any configuration at all (using an inmemory database).
  15  *
  16  * The type of database to use can be overridden by specifying either a system
  17  * property or an environment variable ({@link #DB_CAPABILITIES_PROP}) that
  18  * contains the comma-separated capabilities of the database. Each database type
  19  * provides its own capabilities (see {@link DatabaseProvider} implementations}.
  20  *
  21  *
  22  * There are currently two database types available:
  23  * <ul>
  24  *   <li> Derby: AN inmemory derby. Provided by {@link DerbyDatabaseProvider}. This is the default.
  25  *   </li>
  26  *   <li> External: An arbitrary external database configured using system properties or environment variables
  27  *     in the usual way using a JDBC URL, username, and password.
  28  *   </li>
  29  * </ul>
  30  *
  31  * The <code>DatabaseBuilder</code> uses the {@link ServiceLoader} mechanism to find implementations
  32  * of {@link DatabaseProvider} on the classpath. In the {@link #getDatabase(String...)} method a number of
  33  * capabilities are passed. The database providers are then searched in (arbitrary) order and the first one that
  34  * has all required capabilities is returned.
  35  *
  36  * {@link #getSupportedDatabases()} gives a list of all available databases.
  37  */
  38 public class DatabaseBuilder {
  39
  40         private static final Logger LOGGER = Logger.getLogger(DatabaseBuilder.class
  41                         .getName());
  42
  43         /**
  44          * Environmment variable by which capabilities of the requested database can
  45          * be defined
  46          */
  47         private static final String DB_CAPABILITIES_PROP = "TEST_DB_CAPABILITIES";
  48
  49         private static ServiceLoader<DatabaseProvider> LOADER = null;
  50
  51         private DatabaseBuilder() {
  52                 // Empty.
  53         }
  54
  55         private static String[] parseCapabilities(String aValue) {
  56                 return aValue.split(",");
  57         }
  58
  59         /**
  60          * Gets the first database that has all required capabilities.
  61          * @param aCapabilities Capabilities.
  62          * @return Database to use.
  63          */
  64         public static Database getDatabase(String... aCapabilities) {
  65                 if (aCapabilities.length == 0) {
  66                         LOGGER.info("Examining database capabilities");
  67                         LOGGER.info("  Checking system property " + DB_CAPABILITIES_PROP);
  68                         String capabilities = System.getProperty(DB_CAPABILITIES_PROP);
  69                         if (capabilities != null) {
  70                                 aCapabilities = parseCapabilities(capabilities);
  71                         } else {
  72                                 LOGGER.info("  Checking environment variable "
  73                                                 + DB_CAPABILITIES_PROP);
  74                                 capabilities = System.getenv(DB_CAPABILITIES_PROP);
  75                                 if (capabilities != null) {
  76                                         aCapabilities = parseCapabilities(capabilities);
  77                                 } else {
  78                                         LOGGER.info("  Using default capabilities");
  79                                         aCapabilities = new String[] { DatabaseProvider.CAPABILITY_IN_MEMORY };
  80                                 }
  81                         }
  82                         LOGGER.info("Using capabilities: " + aCapabilities);
  83                 }
  84                 synchronized (DatabaseBuilder.class) {
  85                         initLoader();
  86                         for (DatabaseProvider db : LOADER) {
  87                                 if (db.supportsCapabilities(aCapabilities)) {
  88                                         return db.create();
  89                                 }
  90                         }
  91                 }
  92                 throw new RuntimeException(
  93                                 "No database found that satisfies capabilities: "
  94                                                 + Arrays.asList(aCapabilities));
  95         }
  96
  97         /**
  98          * Gets a list of available databases.
  99          * @return List of databases.
 100          */
 101         public static List<DatabaseDescription> getSupportedDatabases() {
 102                 initLoader();
 103                 List<DatabaseDescription> descriptions = new ArrayList<DatabaseDescription>();
 104                 for (DatabaseProvider db : LOADER) {
 105                         descriptions.add(db.getDescription());
 106                 }
 107                 return descriptions;
 108         }
 109
 110         private static void initLoader() {
 111                 if (LOADER == null) {
 112                         LOADER = ServiceLoader.load(DatabaseProvider.class);
 113                 }
 114         }
 115
 116 }