Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.hadoop.hdfs.protocol; import java.io.IOException; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.classification.InterfaceStability; import org.apache.hadoop.fs.BatchedRemoteIterator; import org.apache.htrace.core.TraceScope; import org.apache.htrace.core.Tracer; /** * EncryptionZoneIterator is a remote iterator that iterates over encryption * zones. It supports retrying in case of namenode failover. */ @InterfaceAudience.Private @InterfaceStability.Evolving public class EncryptionZoneIterator extends BatchedRemoteIterator<Long, EncryptionZone> { private final ClientProtocol namenode; private final Tracer tracer; public EncryptionZoneIterator(ClientProtocol namenode, Tracer tracer) { super((long) 0); this.namenode = namenode; this.tracer = tracer; } @Override public BatchedEntries<EncryptionZone> makeRequest(Long prevId) throws IOException { try (TraceScope ignored = tracer.newScope("listEncryptionZones")) { return namenode.listEncryptionZones(prevId); } } @Override public Long elementToPrevKey(EncryptionZone entry) { return entry.getId(); } }