hadoop FSInputStream 源码
haddop FSInputStream 代码
文件路径:/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FSInputStream.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.fs;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import org.apache.hadoop.util.Preconditions;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.fs.statistics.IOStatisticsLogging;
import org.apache.hadoop.fs.statistics.IOStatisticsSource;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/****************************************************************
* FSInputStream is a generic old InputStream with a little bit
* of RAF-style seek ability.
*
*****************************************************************/
@InterfaceAudience.Public
@InterfaceStability.Evolving
public abstract class FSInputStream extends InputStream
implements Seekable, PositionedReadable {
private static final Logger LOG =
LoggerFactory.getLogger(FSInputStream.class);
/**
* Seek to the given offset from the start of the file.
* The next read() will be from that location. Can't
* seek past the end of the file.
*/
@Override
public abstract void seek(long pos) throws IOException;
/**
* Return the current offset from the start of the file
*/
@Override
public abstract long getPos() throws IOException;
/**
* Seeks a different copy of the data. Returns true if
* found a new source, false otherwise.
*/
@Override
public abstract boolean seekToNewSource(long targetPos) throws IOException;
@Override
public int read(long position, byte[] buffer, int offset, int length)
throws IOException {
validatePositionedReadArgs(position, buffer, offset, length);
if (length == 0) {
return 0;
}
synchronized (this) {
long oldPos = getPos();
int nread = -1;
try {
seek(position);
nread = read(buffer, offset, length);
} catch (EOFException e) {
// end of file; this can be raised by some filesystems
// (often: object stores); it is swallowed here.
LOG.debug("Downgrading EOFException raised trying to" +
" read {} bytes at offset {}", length, offset, e);
} finally {
seek(oldPos);
}
return nread;
}
}
/**
* Validation code, available for use in subclasses.
* @param position position: if negative an EOF exception is raised
* @param buffer destination buffer
* @param offset offset within the buffer
* @param length length of bytes to read
* @throws EOFException if the position is negative
* @throws IndexOutOfBoundsException if there isn't space for the amount of
* data requested.
* @throws IllegalArgumentException other arguments are invalid.
*/
protected void validatePositionedReadArgs(long position,
byte[] buffer, int offset, int length) throws EOFException {
Preconditions.checkArgument(length >= 0, "length is negative");
if (position < 0) {
throw new EOFException("position is negative");
}
Preconditions.checkArgument(buffer != null, "Null buffer");
if (buffer.length - offset < length) {
throw new IndexOutOfBoundsException(
FSExceptionMessages.TOO_MANY_BYTES_FOR_DEST_BUFFER
+ ": request length=" + length
+ ", with offset ="+ offset
+ "; buffer capacity =" + (buffer.length - offset));
}
}
@Override
public void readFully(long position, byte[] buffer, int offset, int length)
throws IOException {
validatePositionedReadArgs(position, buffer, offset, length);
int nread = 0;
while (nread < length) {
int nbytes = read(position + nread,
buffer,
offset + nread,
length - nread);
if (nbytes < 0) {
throw new EOFException(FSExceptionMessages.EOF_IN_READ_FULLY);
}
nread += nbytes;
}
}
@Override
public void readFully(long position, byte[] buffer)
throws IOException {
readFully(position, buffer, 0, buffer.length);
}
/**
* toString method returns the superclass toString, but if the subclass
* implements {@link IOStatisticsSource} then those statistics are
* extracted and included in the output.
* That is: statistics of subclasses are automatically reported.
* @return a string value.
*/
@Override
public String toString() {
final StringBuilder sb = new StringBuilder(super.toString());
sb.append('{');
if (this instanceof IOStatisticsSource) {
sb.append(IOStatisticsLogging.ioStatisticsSourceToString(
(IOStatisticsSource) this));
}
sb.append('}');
return sb.toString();
}
}
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