hadoop DataOutputBuffer 源码
haddop DataOutputBuffer 代码
文件路径:/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/DataOutputBuffer.java
/**
* 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 org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.util.Preconditions;
/** A reusable {@link DataOutput} implementation that writes to an in-memory
* buffer.
*
* <p>This saves memory over creating a new DataOutputStream and
* ByteArrayOutputStream each time data is written.
*
* <p>Typical usage is something like the following:<pre>
*
* DataOutputBuffer buffer = new DataOutputBuffer();
* while (... loop condition ...) {
* buffer.reset();
* ... write buffer using DataOutput methods ...
* byte[] data = buffer.getData();
* int dataLength = buffer.getLength();
* ... write data to its ultimate destination ...
* }
* </pre>
*
*/
@InterfaceAudience.LimitedPrivate({"HDFS", "MapReduce"})
@InterfaceStability.Unstable
public class DataOutputBuffer extends DataOutputStream {
private static class Buffer extends ByteArrayOutputStream {
public byte[] getData() { return buf; }
public int getLength() { return count; }
public Buffer() {
super();
}
public Buffer(int size) {
super(size);
}
public void write(DataInput in, int len) throws IOException {
int newcount = count + len;
if (newcount > buf.length) {
byte newbuf[] = new byte[Math.max(buf.length << 1, newcount)];
System.arraycopy(buf, 0, newbuf, 0, count);
buf = newbuf;
}
in.readFully(buf, count, len);
count = newcount;
}
/**
* Set the count for the current buf.
* @param newCount the new count to set
* @return the original count
*/
private int setCount(int newCount) {
Preconditions.checkArgument(newCount >= 0 && newCount <= buf.length);
int oldCount = count;
count = newCount;
return oldCount;
}
}
private Buffer buffer;
/** Constructs a new empty buffer. */
public DataOutputBuffer() {
this(new Buffer());
}
public DataOutputBuffer(int size) {
this(new Buffer(size));
}
private DataOutputBuffer(Buffer buffer) {
super(buffer);
this.buffer = buffer;
}
/**
* Returns the current contents of the buffer.
* Data is only valid to {@link #getLength()}.
*
* @return data byte.
*/
public byte[] getData() { return buffer.getData(); }
/**
* Returns the length of the valid data currently in the buffer.
* @return length.
*/
public int getLength() { return buffer.getLength(); }
/**
* Resets the buffer to empty.
* @return DataOutputBuffer.
*/
public DataOutputBuffer reset() {
this.written = 0;
buffer.reset();
return this;
}
/**
* Writes bytes from a DataInput directly into the buffer.
* @param in data input.
* @param length length.
* @throws IOException raised on errors performing I/O.
*/
public void write(DataInput in, int length) throws IOException {
buffer.write(in, length);
}
/**
* Write to a file stream.
* @param out OutputStream.
* @throws IOException raised on errors performing I/O.
*/
public void writeTo(OutputStream out) throws IOException {
buffer.writeTo(out);
}
/**
* Overwrite an integer into the internal buffer. Note that this call can only
* be used to overwrite existing data in the buffer, i.e., buffer#count cannot
* be increased, and DataOutputStream#written cannot be increased.
*
* @param v v.
* @param offset offset.
* @throws IOException raised on errors performing I/O.
*/
public void writeInt(int v, int offset) throws IOException {
Preconditions.checkState(offset + 4 <= buffer.getLength());
byte[] b = new byte[4];
b[0] = (byte) ((v >>> 24) & 0xFF);
b[1] = (byte) ((v >>> 16) & 0xFF);
b[2] = (byte) ((v >>> 8) & 0xFF);
b[3] = (byte) ((v >>> 0) & 0xFF);
int oldCount = buffer.setCount(offset);
buffer.write(b);
buffer.setCount(oldCount);
}
}
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