Custom ConfigStores

The `ConfigStore` API has been written to allow easy development of custom configuration storage classes.

The example below shows a starting point for an implementation based on polling a relational database.
Completing it is left as an exercise:

##### Example Store Class:

public class ConfigSqlStore extends ConfigStore { // Configurable properties static final String CONFIGSQLSTORE_jdbcUrl = "ConfigSqlStore.jdbcUrl.s", CONFIGSQLSTORE_tableName = "ConfigSqlStore.tableName.s", CONFIGSQLSTORE_nameColumn = "ConfigSqlStore.nameColumn.s", CONFIGSQLSTORE_valueColumn = "ConfigSqlStore.valueColumn.s", CONFIGSQLSTORE_pollInterval = "ConfigSqlStore.pollInterval.i"; // Instance fields private final String jdbcUrl; private final String tableName, nameColumn, valueColumn; private final Timer watcher; private final ConcurrentHashMap<String,String> cache = new ConcurrentHashMap<>(); // Constructor called from builder. protected ConfigSqlStore(PropertyStore ps) { super(ps); this.jdbcUrl = getStringProperty(CONFIGSQLSTORE_jdbcUrl, "jdbc:derby:mydb"); this.tableName = getStringProperty(CONFIGSQLSTORE_tableName); this.nameColumn = getStringProperty(CONFIGSQLSTORE_nameColumn); this.valueColumn = getStringProperty(CONFIGSQLSTORE_valueColumn); int pollInterval = getStringProperty(CONFIGSQLSTORE_pollInterval, 600); TimerTask timerTask = new TimerTask() { @Override public void run() { ConfigSqlStore.this.poll(); } }; this.watcher = new Timer("MyTimer"); watcher.scheduleAtFixedRate(timerTask, 0, pollInterval * 10000); } private synchronized void poll() { // Loop through all our entries and find the latest values. for (Map.Entry<String,String> e : cache.entrySet()) { String name = e.getKey(); String cacheContents = e.getValue(); String newContents = getDatabaseValue(name); // Change detected! if (! cacheContents.equals(newContents)) update(name, newContents); } } // Reads the value from the database. protected String getDatabaseValue(String name) { // Implement me! } @Override /* ConfigStore */ public synchronized String read(String name) { String contents = cache.get(name); if (contents == null) { contents = getDatabaseValue(name); update(name, contents); } return contents; } @Override /* ConfigStore */ public synchronized String write(String name, String expectedContents, String newContents) { // This is a no-op. if (isEquals(expectedContents, newContents)) return null; String currentContents = read(name); if (expectedContents != null && ! isEquals(currentContents, expectedContents)) return currentContents; update(name, newContents); // Success! return null; } @Override /* ConfigStore */ public synchronized ConfigSqlStore update(String name, String newContents) { cache.put(name, newContents); super.update(name, newContents); // Trigger any listeners. return this; } @Override /* Closeable */ public synchronized void close() { if (watcher != null) watcher.cancel(); } }

The purpose of the builder class is to simply set values in the {@link oaj.PropertyStore} that's passed to the `ConfigStore`:

##### Example Builder Class:

public class ConfigSqlStoreBuilder extends ConfigStoreBuilder { public ConfigSqlStoreBuilder() { super(); } public ConfigSqlStoreBuilder(PropertyStore ps) { super(ps); } public ConfigSqlStoreBuilder jdbcUrl(String value) { super.set(CONFIGSQLSTORE_jdbcUrl, value); return this; } public ConfigSqlStoreBuilder tableName(String value) { super.set(CONFIGSQLSTORE_tableName, value); return this; } public ConfigSqlStoreBuilder nameColumn(String value) { super.set(CONFIGSQLSTORE_nameColumn, value); return this; } public ConfigSqlStoreBuilder valueColumn(String value) { super.set(CONFIGSQLSTORE_valueColumn, value); return this; } public ConfigSqlStoreBuilder pollInterval(int value) { super.set(CONFIGSQLSTORE_pollInterval, value); return this; } @Override /* ContextBuilder */ public ConfigFileStore build() { return new ConfigFileStore(getPropertyStore()); } }