1.压缩从标准输入读取的数据,然后将其写到标准输出
通过GzipCodec的StreamCompressor对象对字符串“Text”进行压缩,再使用gunzip从标准输出中对它进行读取并解压缩
public class StreamCompressor {
public static void main(String[] args) throws Exception {
String codecClassname = args[0];
Class<?> codecClass = Class.forName(codecClassname);
Configuration conf = new Configuration();
CompressionCodec codec = (CompressionCodec)
ReflectionUtils.newInstance(codecClass, conf);
CompressionOutputStream out = codec.createOutputStream(System.out);
IOUtils.copyBytes(System.in, out, 4096, false);
out.finish();
}
}
2.根据文件扩展名选取codec解压缩文件
public class FileDecompressor {
public static void main(String[] args) throws Exception {
String uri = args[0];
Configuration conf = new Configuration();
FileSystem fs = FileSystem.get(URI.create(uri), conf);
Path inputPath = new Path(uri);
CompressionCodecFactory factory = new CompressionCodecFactory(conf);
CompressionCodec codec = factory.getCodec(inputPath);
if (codec == null) {
System.err.println("No codec found for " + uri);
System.exit(1);
}
String outputUri =
CompressionCodecFactory.removeSuffix(uri, codec.getDefaultExtension());
InputStream in = null;
OutputStream out = null;
try {
in = codec.createInputStream(fs.open(inputPath));
out = fs.create(new Path(outputUri));
IOUtils.copyBytes(in, out, conf);
} finally {
IOUtils.closeStream(in);
IOUtils.closeStream(out);
}
}
}
3. 使用压缩池对读取自标准输入数据进行压缩,然后将其写在标准输出里
public class PooledStreamCompressor {
public static void main(String[] args) throws Exception {
String codecClassname = args[0];
Class<?> codecClass = Class.forName(codecClassname);
Configuration conf = new Configuration();
CompressionCodec codec = (CompressionCodec)
ReflectionUtils.newInstance(codecClass, conf);
Compressor compressor = null;
try {
compressor = CodecPool.getCompressor(codec);
CompressionOutputStream out =
codec.createOutputStream(System.out, compressor);
IOUtils.copyBytes(System.in, out, 4096, false);
out.finish();
} finally {
CodecPool.returnCompressor(compressor);
}
}
}
4.在MapReduce中使用压缩
对输出进行压缩
./hadoop jar /tmp/hadoop-1.0-SNAPSHOT.jar HotSearch /input/IAMSinger.txt /output/
5.使用SequenceFile对小文件进行读取
public class SequenceFileWriteDemo {
private static final String[] DATA = {
"One, two, buckle my shoe",
"Three, four, shut the door",
"Five, six, pick up sticks",
"Seven, eight, lay them straight",
"Nine, ten, a big fat hen"
};
public static void main(String[] args) throws IOException {
String uri = args[0];
Configuration conf = new Configuration();
FileSystem fs = FileSystem.get(URI.create(uri), conf);
Path path = new Path(uri);
IntWritable key = new IntWritable();
Text value = new Text();
SequenceFile.Writer writer = null;
try {
writer = SequenceFile.createWriter(fs, conf, path,
key.getClass(), value.getClass());
for (int i = 0; i < 100; i++) {
key.set(100 - i);
value.set(DATA[i % DATA.length]);
System.out.printf("[%s]\t%s\t%s\n", writer.getLength(), key, value);
writer.append(key, value);
}
} finally {
IOUtils.closeStream(writer);
}
}
}
public class SequenceFileReadDemo {
public static void main(String[] args) throws IOException {
String uri = args[0];
Configuration conf = new Configuration();
FileSystem fs = FileSystem.get(URI.create(uri), conf);
Path path = new Path(uri);
SequenceFile.Reader reader = null;
try {
reader = new SequenceFile.Reader(fs, path, conf);
Writable key = (Writable)
ReflectionUtils.newInstance(reader.getKeyClass(), conf);
Writable value = (Writable)
ReflectionUtils.newInstance(reader.getValueClass(), conf);
long position = reader.getPosition();
while (reader.next(key, value)) {
String syncSeen = reader.syncSeen() ? "*" : "";
System.out.printf("[%s%s]\t%s\t%s\n", position, syncSeen, key, value);
position = reader.getPosition(); // beginning of next record
}
} finally {
IOUtils.closeStream(reader);
}
}
}