5.2. 创建持续查询
您可以为远程和嵌入式缓存创建持续查询。
流程
-
创建
Query对象。 通过调用适当的方法来获取缓存的
ContinuousQuery对象：-
远程缓存：
org.infinispan.client.hotrod.Search.getContinuousQuery (RemoteCache<K, V> cache) -
嵌入式缓存：
org.infinispan.query.Search.getContinuousQuery (Cache<K, V> cache)
-
远程缓存：
注册查询和
ContinuousQueryListener对象，如下所示：continuousQuery.addContinuousQueryListener(query, listener);
当您不再需要持续查询时，按如下所示删除监听程序：
continuousQuery.removeContinuousQueryListener(listener);
持续查询示例
以下代码示例演示了带有嵌入式缓存的简单持续查询。
在本例中，监听器会在 21 年龄下的任何 Person 实例添加到缓存中时收到通知。这些 Person 实例也添加到"匹配"映射中。当从缓存中删除条目或其年龄大于或等于 21 时，它们会从 "matches" 映射中删除。
注册持续查询
import org.infinispan.query.api.continuous.ContinuousQuery;
import org.infinispan.query.api.continuous.ContinuousQueryListener;
import org.infinispan.query.Search;
import org.infinispan.query.dsl.QueryFactory;
import org.infinispan.query.dsl.Query;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
[...]
// We have a cache of Person objects.
Cache<Integer, Person> cache = ...
// Create a ContinuousQuery instance on the cache.
ContinuousQuery<Integer, Person> continuousQuery = Search.getContinuousQuery(cache);
// Define a query.
// In this example, we search for Person instances under 21 years of age.
QueryFactory queryFactory = Search.getQueryFactory(cache);
Query query = queryFactory.create("FROM Person p WHERE p.age < 21");
final Map<Integer, Person> matches = new ConcurrentHashMap<Integer, Person>();
// Define the ContinuousQueryListener.
ContinuousQueryListener<Integer, Person> listener = new ContinuousQueryListener<Integer, Person>() {
@Override
public void resultJoining(Integer key, Person value) {
matches.put(key, value);
}
@Override
public void resultUpdated(Integer key, Person value) {
// We do not process this event.
}
@Override
public void resultLeaving(Integer key) {
matches.remove(key);
}
};
// Add the listener and the query.
continuousQuery.addContinuousQueryListener(query, listener);
[...]
// Remove the listener to stop receiving notifications.
continuousQuery.removeContinuousQueryListener(listener);
