扩展实现

1. MapFile  一个key-value 对应的查找数据结构，由数据文件/data 和索引文件 /index 组成，数据文件中包含所有需要存储的key-value对，按key的顺序排列。索引文件包含一部分key值，用以指向数据文件的关键位置
2. SetFile – 基于 MapFile 实现的，他只有key，value为不可变的数据。
3. ArrayFile – 也是基于 MapFile 实现，他就像我们使用的数组一样，key值为序列化的数字。      
4. BloomMapFile – 他在 MapFile 的基础上增加了一个 /bloom 文件，包含的是二进制的过滤表，在每一次写操作完成时，会更新这个过滤表。

package com.eric.hadoop.io.sequencefile;
import java.io.IOException;
import java.net.URI;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Text;
/**
 * @author Eric.sunah 2014年12月10日
 *
 */
public class SequenceFileDemo {
 
 private static final String OPERA_FILE = "./output.seq";
 /**
  * 随便从网上截取的一段文本
  */
 private static String[]    testArray = { "<plugin>                                                                     ",
         "  <groupId>org.apache.avro</groupId>                                         ",
         "  <artifactId>avro-maven-plugin</artifactId>                                 ",
         "  <version>1.7.7</version>                                                   ",
         "  <executions>                                                               ",
         "    <execution>                                                              ",
         "      <phase>generate-sources</phase>                                        ",
         "      <goals>                                                                ",
         "        <goal>schema</goal>                                                  ",
         "      </goals>                                                               ",
         "      <configuration>                                                        ",
         "        <sourceDirectory>${project.basedir}/src/main/avro/</sourceDirectory> ",
         "        <outputDirectory>${project.basedir}/src/main/java/</outputDirectory> ",
         "      </configuration>                                                       ",
         "    </execution>                                                             ",
         "  </executions>                                                              ",
         "</plugin>                                                                    ",
         "<plugin>                                                                     ",
         "  <groupId>org.apache.maven.plugins</groupId>                                ",
         "  <artifactId>maven-compiler-plugin</artifactId>                             ",
         "  <configuration>                                                            ",
         "    <source>1.6</source>                                                     ",
         "    <target>1.6</target>                                                     ",
         "  </configuration>                                                           ", "</plugin>"};
 
 public static void main(String[] args) throws IOException {
  writeSequenceFile(OPERA_FILE);
  readSequenceFile(OPERA_FILE);
 }
 
 private static void readSequenceFile(String inputFile) throws IOException {
  Configuration config = new Configuration();
  Path path = new Path(inputFile);
  SequenceFile.Reader reader = null;
  try {
   
   FileSystem fs = FileSystem.get(URI.create(inputFile), config);
   reader = new SequenceFile.Reader(fs, path, config);
   IntWritable key = new IntWritable();
   Text value = new Text();
   long posion = reader.getPosition();
   // reader.next()返回非空的话表示正在读，如果返回null表示已经读到文件结尾的地方
   while (reader.next(key, value)) {
    //打印同步点的位置信息
    String syncMark = reader.syncSeen() ? "*" : "";
    System.out.printf("[%s\t%s]\t%s\t%s\n", posion, syncMark, key, value);
    posion = reader.getPosition();
   }
  } finally {
   IOUtils.closeStream(reader);
  }
 
 }
 
 /**
  * 写Sequence File 文件
  *
  * @param outputFile
  * @throws IOException
  */
 private static void writeSequenceFile(String outputFile) throws IOException {
  Configuration config = new Configuration();
  Path path = new Path(outputFile);
  IntWritable key = new IntWritable();
  Text value = new Text();
  SequenceFile.Writer writer = null;
  try {
   
   FileSystem fs = FileSystem.get(URI.create(outputFile), config);
   writer = SequenceFile.createWriter(fs, config, path, key.getClass(), value.getClass());
   for (int i = 1; i < 2000; i++) {
    key.set(2000 - i);
    value.set(testArray[i % testArray.length]);
    System.out.printf("[%s]\t%s\t%s\n", writer.getLength() + "", key, value);
    // 通过Append方法进行写操作
    writer.append(key, value);
   }
  } finally {
   IOUtils.closeStream(writer);
  }
 
 }
}