Github user milleruntime commented on a diff in the pull request:
https://github.com/apache/accumulo/pull/292#discussion_r132999867
--- Diff:
core/src/main/java/org/apache/accumulo/core/client/impl/Table.java ---
@@ -16,24 +16,59 @@
*/
package org.apache.accumulo.core.client.impl;
+import java.lang.ref.WeakReference;
+import java.util.WeakHashMap;
+
import org.apache.accumulo.core.client.Instance;
public class Table {
/**
* Object representing an internal table ID. This class was created to
help with type safety. For help obtaining the value of a table ID from
Zookeeper, see
* {@link Tables#getTableId(Instance, String)}
+ *
+ * Uses an internal WeakHashMap and private constructor for storing a
WeakReference of every Table.ID. Therefore, a Table.ID can't be instantiated
outside
+ * this class and is accessed by calling Table.ID.{@link #of(String)}.
*/
public static class ID extends AbstractId {
private static final long serialVersionUID = 7399913185860577809L;
+ static final WeakHashMap<String,WeakReference<Table.ID>> tableIds =
new WeakHashMap<>();
- public static final ID METADATA = new ID("!0");
- public static final ID REPLICATION = new ID("+rep");
- public static final ID ROOT = new ID("+r");
+ public static final ID METADATA = of("!0");
+ public static final ID REPLICATION = of("+rep");
+ public static final ID ROOT = of("+r");
- public ID(final String canonical) {
+ private ID(final String canonical) {
super(canonical);
}
+
+ /**
+ * Get a Table.ID object for the provided canonical string.
+ *
+ * @param canonical
+ * table ID string
+ * @return Table.ID object
+ */
+ public static Table.ID of(final String canonical) {
+ return dedupeTableId(canonical);
+ }
+
+ private static Table.ID dedupeTableId(String tableIdString) {
--- End diff --
I thought about this but it would require reflection or passing a
pre-constructed instance object as a parameter to the method. I wanted to
avoid reflection since we lose some of the type safety. I also wanted to avoid
created objects every time for parameters since they may not be needed if the
map already contains the id.
Passing in a constructor object as a parameter may be a nice compromise but
this introduces a bunch of potential exceptions:
<pre>
try {
id = constructor.newInstance(idString);
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
idHashMap.put(idString, new WeakReference<>(id));
</pre>
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