ArrayWritable.java
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上传日期:2018-01-08
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文件大小:3k
- /**
- * 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.io;
- import java.io.*;
- import java.lang.reflect.Array;
- /**
- * A Writable for arrays containing instances of a class. The elements of this
- * writable must all be instances of the same class. If this writable will be
- * the input for a Reducer, you will need to create a subclass that sets the
- * value to be of the proper type.
- *
- * For example:
- * <code>
- * public class IntArrayWritable extends ArrayWritable {
- * public IntArrayWritable() {
- * super(IntWritable.class);
- * }
- * }
- * </code>
- */
- public class ArrayWritable implements Writable {
- private Class<? extends Writable> valueClass;
- private Writable[] values;
- public ArrayWritable(Class<? extends Writable> valueClass) {
- if (valueClass == null) {
- throw new IllegalArgumentException("null valueClass");
- }
- this.valueClass = valueClass;
- }
- public ArrayWritable(Class<? extends Writable> valueClass, Writable[] values) {
- this(valueClass);
- this.values = values;
- }
- public ArrayWritable(String[] strings) {
- this(UTF8.class, new Writable[strings.length]);
- for (int i = 0; i < strings.length; i++) {
- values[i] = new UTF8(strings[i]);
- }
- }
- public Class getValueClass() {
- return valueClass;
- }
- public String[] toStrings() {
- String[] strings = new String[values.length];
- for (int i = 0; i < values.length; i++) {
- strings[i] = values[i].toString();
- }
- return strings;
- }
- public Object toArray() {
- Object result = Array.newInstance(valueClass, values.length);
- for (int i = 0; i < values.length; i++) {
- Array.set(result, i, values[i]);
- }
- return result;
- }
- public void set(Writable[] values) { this.values = values; }
- public Writable[] get() { return values; }
- public void readFields(DataInput in) throws IOException {
- values = new Writable[in.readInt()]; // construct values
- for (int i = 0; i < values.length; i++) {
- Writable value = WritableFactories.newInstance(valueClass);
- value.readFields(in); // read a value
- values[i] = value; // store it in values
- }
- }
- public void write(DataOutput out) throws IOException {
- out.writeInt(values.length); // write values
- for (int i = 0; i < values.length; i++) {
- values[i].write(out);
- }
- }
- }